Review Article Graphene and g-C3N4-Based Gas Sensors

Review ArticleGraphene and g-C3N4-Based Gas Sensors

AhmedKotbi12MohammedImran3KhaledKaja4ArifulRahaman3ElMostafaRessami2

Michael Lejeune1 Brahim Lakssir2 and Mustapha Jouiad 1

1Laboratory of Physics of Condensed Matter University of Picardie Jules Verne Amiens 80039 France2Moroccan Foundation for Advanced Science Innovation and ResearchMadinat Al Irfane Rabat 10100 Morocco3School of Mechanical Engineering Vellore Institute of Technology Vellore Tamil Nadu 632014 India4Laboratoire National de Metrologie et Drsquoessais (LNE) 29 Av Roger Hannequin Trappes 78197 France

Correspondence should be addressed to Mustapha Jouiad mustaphajouiadu-picardiefr

Received 31 October 2021 Accepted 29 January 2022 Published 27 February 2022

Academic Editor Eduard Llobet

Copyright copy 2022 Ahmed Kotbi et al is is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

e efficient monitoring of the environment is currently gaining a continuous growing interest in view of finding solutions for theglobal pollution issues and their associated climate change In this sense two-dimensional (2D) materials appear as one of highlyattractive routes for the development of efficient sensing devices due in particular to the interesting blend of their superlativeproperties For instance graphene (Gr) and graphitic carbon nitride g-C3N4 (g-CN) have specifically attracted great attention inseveral domains of sensing applications owing to their excellent electronic and physical-chemical properties Despite the highpotential they offer in the development and fabrication of high-performance gas-sensing devices an exhaustive comparisonbetween Gr and g-CN is not well established yet regarding their electronic properties and their sensing performances such assensitivity and selectivity Hence this work aims at providing a state-of-the-art overview of the latest experimental advances in thefabrication characterization development and implementation of these 2D materials in gas-sensing applications en thereported results are compared to our numerical simulations using density functional theory carried out on the interactions of Grand g-CN with some selected hazardous gasesrsquo molecules such as NO2 CO2 and HF Our findings conform with the superiorperformances of the g-CN regarding HF detection while both g-CN and Gr show comparable detection performances for theremaining considered gasesis allows suggesting an outlook regarding the future use of these 2Dmaterials as high-performancegas sensors

1 Introduction

A fast-paced race for devicesrsquo miniaturization based on 2Dmaterials is marking the particularly rapid evolvement in theresearch and development of carbon nanomaterials (CNM)in biomedical systems electronic appliances computingdevices and sensor manufacturing industries [1ndash5] Ad-vancements in these application fields depend on the abilityto grow CNM on various substrates with controlled mor-phologies and quality while increasing their efficiency ofgetting assembled in complex architectures [6] Since its firstisolation in 2004 graphene (Gr) has constantly been thehighlight superlative star of 2D materials Formed by sp2-hybridized carbon atoms bonded covalently and packeddensely to form honeycomb crystal lattice [7 8] graphene is

a single-atom-thick sheet semimetal with commendableelectron transport properties and superior thermal andelectrical conductivities in addition to superior mechanicalproperties [9ndash13] In contrast to graphene graphitic carbonnitride g-C3N4 (g-CN) is a semiconducting nanomaterialwith a crystal structure analogous to graphite constructedfrom Van der Waals sheets of sp2 hybrid carbon and ni-trogen atoms g-CN is an abundant inexpensive and easy tomanufacture nanomaterial at large scale [14] is added toits high electrical properties and good thermal and chemicalstabilities has recently created an increasing interest aroundit With an appropriate bandgap and high electron mobilityg-CN also constitutes a potentially good candidate forvarious applications in energy storage solar cells gassensing and catalysis [15ndash18]

HindawiJournal of NanotechnologyVolume 2022 Article ID 9671619 20 pageshttpsdoiorg10115520229671619

Gas sensing is one of the important applications of Grand associated 2D nanomaterials owing mainly to severalinteresting properties such as (i) large surface area (for Gr2630m2g) (ii) good conductivity (iii) high gas sensitivity(iv) and the possibility of tailored surface functionalizationfor a specific gas absorption In Gr the gas absorption is aresult of a pull electron effect [19 20] In fact the adsorbedmolecules change the Fermi level of Gr and hence itsconductivity due to hybridization and coupling on itssurface ey act as electron donors in case their valenceband energy is higher than the Fermi level of Gr and aselectron acceptors in the opposite case when the valenceband energy is lower than Fermi level of Gr [21 22]

Nowadays highly performing portable sensors havebecome a key necessity for all technological advances Whilemetal-oxide-semiconductor based gas sensors are farcommonly used their performances remain very limited dueto their short life poor selectivity temperature instabilitiesand high sensitivity to environmentrsquos perturbations e useof nanostructured materials with higher gas-sensing capa-bilities has therefore become inevitable [5]

Besides the development of g-CN based gas sensorscompared to those based on Gr or transition metal disulfidenanosheets is becoming more attractive [23] Many ap-proaches have been adopted so far for the development ofthis material in view of its incorporation in gas-sensingapplications In this sense researchers attempted to combineg-CN with other materials to improve its performances [24]For instance the use of porous g-CN in nanostructuredesigns as gas sensors appeared to greatly improve theirselectivity and their sensitivity in ambient conditionsSimilarly hybridization of g-CN with other materials wasfound as a promising route for further enhancement indetection performances [23] e resulting heterostructuresmade of metal oxide nanoparticles attached to the surface of2D materials were found to exhibit higher detectionproperties [14] For instance g-CNMOX heterostructuresrevealed much superior detection performances comparedto a pure MOX sensor (MnO2 ZnO and TiO2) Howeversome drawbacks remain which prevent the direct appli-cation of these sensors such as the high working temper-ature and the slow sensing response [25] eseachievements are attributed on one hand to the increasedsurface area obtained by the combination of 2D g-CN withthe MOx leading to an increased number of gas-materialinteraction sites [20] and to the low operating temperaturewhile improving the gas sensitivity and selectivity on theother hand [23] Despite these interesting gas-sensingperformances g-CN presents some limitations when com-pared to Gr such as its moderate band gap that requires ahigh excitation voltage and its fast electron-hole pairs re-combination leading to low responsivity In addition g-CNadsorbs most of gases and liquids while Gr is known to beimpermeable to most of fluids which reduces the operatingtemperature of graphene compared to g-CN

In the following we intend to provide a detailed over-view of both CNM in terms of fabrication and character-ization with special emphasis on their gas-sensingperformances en theoretical calculations using density

functional theory (DFT) will be carried out to determine theadsorption mechanisms of selected gas molecules namelyCO2 NO2 and HF and to examine the g-CN sensingperformances to be compared to other graphitic nano-materials such as Gr or reduced graphene oxide (r-GrO)

2 Synthesis of Graphene

Several methods are most commonly used for the fabricationof Gr layers including (i) micromechanical exfoliation (ii)reduction of graphene oxide (iii) chemical vapor deposition(CVD) [5 26] or plasma-enhanced chemical vapor depo-sition (PECVD) and (iv) epitaxial growth on insulatingmaterials e choice of a fabrication route is mainly de-pendent upon the material quality and overall productioncost required for given application

e structural and vibrational properties of Gr areusually examined by Fourier-transform infrared spectros-copy (FTIR) X-ray diffraction (XRD) and Raman spec-troscopy respectively and given in Figure 1 [27]

Transmission spectra (Figure 1(a)) show an obvioussimilarity for all three materials mainly due to the C-C bondpeaks present in the 2325ndash1981 cmminus1 range e XRD dia-gram (Figure 1(b)) shows a narrow diffraction peak at 265deg(2θ) corresponding to the characteristic (002) plane ofgraphite is peak is broadened and downshifted in gra-phene towards 239deg representing an increased spacing ofC-C layer in sp2 bonding e Raman spectra (Figure 1(c))show a characteristic vibration peak at 1601 cmminus1 (G-band)related to the original graphitic structure for all three ma-terials However a wider peak at 1352 cmminus1 (D-band) ap-pears for graphite oxide and Gr sheets related to the presenceof defects in these structures e ratio of these bandsrsquo in-tensities (IDIG) is a good indicator of the graphitizationrsquosquality in these layers

21 Mechanical Exfoliation Mechanical exfoliation is thefirst process through which Gr was isolated by Novoselovet al [28] It is a top-down approach in which Gr layers areexfoliated from bulk graphite using adhesive tape eprocedure involves repeated pealing of Gr from flakes ofgraphite e tape containing Gr is finally placed on an SiSiO2 surface and gently pressed to get Gr attached to the Sisubstrate is method allows investigating the basicproperties of Gr For in-depth investigations of Gr prop-erties for technical applications scalable methods are beingdeveloped [29]

22 Chemical Vapor Deposition Chemical vapor deposition(CVD) is the most commonmethod used to produce Gr on asubstrate with commendable quality and tailored dimen-sions Growth mechanism and number of layers grown onthe substrate depend on the catalyst metal substrate usedsuch as Cu [26] Ni [30 31] Cu-Ni alloy [1] and Co Figure 2shows a schematic of CVD setup used to grow carbonnanomaterials

For Gr grown on Ni substrate the Ni foil is annealed inhydrogen atmosphere and then carbon source gas such as

2 Journal of Nanotechnology

methane or acetylene is admitted into the chamber Argongas is used during the process to maintain an inert atmo-sphere A controlled cooling rate is necessary to produce

desired thicknesses of the Gr layers Faster cooling rates yieldthick graphite and slower cooling rates avoid segregation ofcarbon deposited on Ni foil [33] If Ni foil grain growth is

Wavenumber (cm-1)

T

rans

mitt

ance

4000 3500 3000 2500 2000 1500 1000

Graphite Oxide

Graphene Sheets

Graphite

(a)

2θ (degree)

Inte

nsity

(au

)

10 20 30 40 50 60 70 805 15 25 35 45 55 65 75

Graphite Oxide

Graphene Sheets

Graphite

(002)

(001)

(002)

(b)

Wavenumber (cm-1)

Inte

nsity

(au

)

1000 1250 1500 1750 2000

Graphite Oxide

Graphene Sheets

Graphite

D band G band

(c)

Figure 1 (a) FTIR (b) XRD and (c) Raman spectroscopy of graphite graphite oxide and graphene [27]

Heating Coil

Heating Coil

Gas outletQuartz tube

Sample

NitrogenAccetylene

Alumina Crucible

Figure 2 Schematic of CVD setup for graphene preparation [32]

Journal of Nanotechnology 3

small (few minutes of preannealing time) and chamberpressure is maintained high during growth step nanosizedgraphite films are formed [30 34] rather than few-layer Gr[5 35] Processing Gr on Cu substrate is most usually used toproduce large-scale monolayer Gr films e Cu foil isheated up to 1000degC in the presence of hydrogen atmosphereat low pressure and then carbon-containing gases such asmethane or acetylene are admitted into the CVD chamberfor 20ndash30 minutes and then gradually cooled Table 1 showscomparison of Gr obtained using several fabricationmethods [35]

Table 1 shows comparison of various properties of Grsynthesized through various methods Gr synthesizedthrough CVD shows a good mobility compared to Grfabricated by other methods Processing costs are also re-duced with high volume of production by CVD technique

Moreover plasma-enhanced chemical vapor deposition(PECVD) was used as a potentially industrially scalableroute for Gr synthesis Kaindl et al [42] have synthesized Gron Si (100) SiSiO2 Ni Cu MgO (100) and NaCl and onstandard glass substrates using a mixture of C2H2 and C2H2-Ar irradiated with Ar+ At a deposition temperature of 400degCand postdeposition annealing up to 800degC under Ar flowcrystal growth and graphitization are obtained on Cu and Nifoils and interestingly on NaCl Recently the growth of Grgrains on Cu substrate using the radio frequency PECVD(RF-PECVD) at different temperatures has been reported[43] ese authors demonstrated the fabrication of largepolycrystalline Gr grains at high temperatures and a rela-tively long dwell time Large area Gr sheets of several mm2

were synthesized on Cu substrates by this technique using aH2CH4 gas mixture [44] Using PECVD Yang et al [45]demonstrated the direct growth of Gr walls on dielectricsubstrates and Hussain et al [46] fabricated verticallyaligned Gr at lower temperature and low power whileChugh et al [47] compared the growth of Gr on arbitrarynoncatalytic substrates at low temperature To summarizethe various conditions of the Gr growth using PECVDtechnique we have drawn up Table 2

23 Chemical and Green Synthesis Oxidative exfoliation ofgraphite was also used to synthesize GrO which in turn wasreduced to obtain Gr sheets Brodie Staudenmaier andHummers are the major methods to obtain Gr from theoxidative exfoliation-reduction (Figure 3)

Oxidation of graphite in the presence of graphite in-tercalation compounds increases the distance betweengraphite layers is weakens the interlayer Van der Waalsforces which allows their exfoliation by sonication in thepresence of suitable solvents Single-layer GrO dual-layerGrO and few-layer GrO are thus obtained is is followedby the reduction of GrO into Gr using hydrazine (N2H4)However due to its toxicity and high cost alternate methodswere developed to replace the use of hydrazine Among thosemethods we cite thermal reduction hydrothermal reduc-tion and electrochemical reduction Besides Gurunlu et alreported on a green synthesis method of Gr at the tem-perature range of 500ndash800degC in which Gr powder was mixed

with LiClKCl and subsequently heated under Ar or N2atmosphere in a steel reactor e thickness of the syn-thesized Gr films was found to be in the range of 5 to 9 nmwhich was attributed to the presence of few layers of Gr [48]

3 Synthesis of g-CN

Various elaboration techniques have been reported in theliterature for the fabrication of g-CN Methods such asCVD physical vapor deposition (PVD) Radio FrequencyMagnetron- (RFM-) based sputtering method and sol-gel-based spin-coating deposition have been used most oftene various characteristics are listed and compared inTable 3

e spin-coating method is a simple and efficienttechnique e stability of the dispersion depends on manyparameters such as the type of solvent the viscosity of thesolvent and the size of the particles To increase the per-formance and quality of the thin film it is necessary to avoidthe agglomeration of the powder and to ensure that it isdeposited evenly on the substrate to prevent the formation ofholes [54] PVD is one of the effective techniques for fab-ricating thin films and nanostructures with high optical andelectronic properties In the PVD process the crucial step isto produce the vapor phase of the solid precursor PVD hasbeen successfully applied in the elaboration of many ma-terials including carbon nitride for nanotubes [55] CVDmethod can synthesize ultrathin films and can be used in thefabrication of heterojunctions [56] Reactive RFM-basedsputtering technique is a technique capable of making largearea films However this is a multiparameter process ereactive sputtering process involves the use of a high puritytarget and plasma medium [52]

31 ermal Condensation Synthesis g-CN bulk crystal iseasily prepared at large scale by thermal condensation ofprecursors rich in carbon and nitrogen such as thiourea(CH4N2S) [57] melamine (C3H6N6) [58] dicyandiamide(C2H4N4) [23] and urea (CH₄N₂O) [59] as schematicallydepicted in Figure 4

Single-layered or multilayered g-CN nanosheets (NSs)are subsequently obtained through exfoliation of the bulkg-CN resulting in large active surfaces [58] e bulk g-CNpresents dense and thick layers due to the agglomeration offlat sheets of g-CN to build a massive layered structureTable 4 summarizes the various conditions formanufacturing g-CN under atmosphere

Ismael et al synthesized bulk g-CN from melaminethiourea and urea [61] and reported that bulk g-CN elab-orated by melamine and thiourea contains smooth thin andlarge sheets Meanwhile the sample elaborated by ureaconsists of smaller sheets and porous sheets e exfoliationof bulk g-CN results in the formation of large irregular-shaped porous thin sheets with a variable degree of flexi-bility [56 62ndash64] Iqbal et al [65] synthesized mesoporousg-CN NSs by a simple one-step approach using glucose andNH4I together with the chosen precursor for exfoliation ofbulk g-CN


Table 1 Comparison of various Gr preparation methods

Method Exfoliation SiC epitaxy CVD on Ni CVD on CuLayers 1ndash10 [36] 1ndash4 [37] 1ndash4 [38] Single [39]Size 1mm [36] 50 microm [37] 1 cm [38] 65 cm [40]Mobility(cm2Vminus1sminus1) 1500ndash106 [41] 2000ndash11000 [37] 3700 [38] 16000ndash65000 [40]

Synthesistemperature (degC) Room temperature 1000ndash1500 1000 1000

Cost High High Low LowScalability Not possible Good Good Good

Advantages

(i) Easy and low cost(ii) No special equipment is needed(iii) SiO2 thickness is tuned forbetter optical contrast used forvisual localization(iv) Large-scale area

(i) Graphene sheetsof even thickness(ii) Large-scale area

(i) Morphology can becontrolled by maintainingprocess parameters(ii) Large-scale production iseasy

(i) Morphology can becontrolled bymaintaining processparameters(ii) Large-scaleproduction is easy

Disadvantages(i) Serendipitous(ii) Uneven films(iii) Nonscalable

(i) Difficult controlof morphology(ii) High processingtemperatures

(i) Uniform thickness isdifficult(ii) Low deposition rates


Table 2 Parameters for the production of Gr by the PECVD technique

Carbon sourceflowrate (sccm)

Gas carrierflowrate (sccm) Substrate Substrateannealed

temperature (degC)Time(s)

Power(KW)

RF power(MHz) Ref

C2H215 Ar5 Si SiSiO2 Ni Cu MgONaCl glass Ambient to 400800 mdash mdash mdash [42]

CH48 Ar30 and H210 Cu 670ndash850 10ndash90 0050 mdash [43]CH425 H2200 Cu 900 600 1 mdash [44]CH45 H220 SiO2 900 3600 0300 1356 [45]C2H420 H240 SiAl 450(450 to 620) 900 0030 1356 [46]CH46 Ar5 SiO2 quartz 650 900 - 1356 [47]

Brodie

Graphite + KClO3Oxidation

Temp 60degCDuration 3-4 days

Graphite oxide + H2OOxidation

4 cycles

Graphite oxide(purified)

Dried in vaccumTemp 100degC

Graphene oxide

Staudenmaier

Graphite + H2SO4HNO3(Fuming)Temp 0degC

Graphite oxide + H2O + HCl



Graphene oxide

Suspension + KClO3Oxidationfor 3-4 days

Hummer

Graphite + NaNO3

Suspension + KMnO4Temp 20degC



Graphene oxide

Cooled to 0degCSuspension + H2SO4

Graphite oxide + H2OTemp 98degC

Graphite oxide + H2O2

Figure 3 Schematic of various methods of exfoliation by oxidation


32 Chemical Vapor Deposition For the synthesis of g-CNfilms by the CVD method generally a precursor rich in Cand N is placed at the inlet of an Ar gas stream in a quartztube that is maintained at low pressure e powder

vapors penetrate inside the hot zone of the furnace(600degC) due to the flow of Ar gas with the low vacuuminside the quartz tube Condensation of the precursor athigh temperature produces the g-CN structure Afterdeposition the furnace should be allowed to cool to roomtemperature automatically in Ar environment [66] Ta-ble 5 summarizes the conditions for depositing g-CNusing the CVD technique

Similarly plasma-enhanced chemical vapor deposition(PECVD) allows the deposition of thin layers of material ondifferent types of substrates (glass Si etc) after decom-position of the molecules of the reactive gases in a plasmaTable 6 shows the conditions for depositing g-CN using thePECVD technique

Table 3 Advantages and disadvantages of different techniques employed for the fabrication of g-CN films

Techniques Advantages Disadvantages Ref

Spin-coating

(i) Large surface area(ii) Highly adhesive(iii) Easiest homogeneity(iv) Appropriate for deposition on any substrate

(i) High cost for the fabrication(ii) High cost of precursors(iii) Needed controlled atmosphere

[49 50]

CVD (i) High deposition rate(ii) Uniform film (i) Low deposition rates [49 51]

RFM-based sputteringdeposition

(i) High quality and uniform films simply controlledsputtering speed good adhesion(ii) Useful manipulation offers large area coatings(iii) Uniform coating thickness Compact pore-free coatingCapability to coat on heat-sensitive substrates

(i) Plasma damage(ii) Plasma contamination(iii) Probability of substrate damage dueto ionic bombardment

[49 52]

PVD (i) Low hydrogen content (i) Low deposition rate(ii) Difficult to control film thickness [51 53]

Melamine(C3H6N6)

Graphitic carbon nitride(g-C3N4)

iourea(CH4N2S)

Cyanamide (CH2N2)

Dicyandiamide(C2H4N4)

Urea(CH4N2O)

500-

580deg

C

520-

550deg

C

460-

650deg

C

550deg

C

550deg

C

Figure 4 Synthesis processes of g-CN by thermal condensation of different precursors (reproduced and adapted from [60])

Table 4 Various conditions for manufacturing g-CN under airatmosphere with thermal condensation

Precursors T (degC) t (h) Heating rate (Kmin) RefUrea 520 05 mdash [54]Dicyandiamide 550 4 20 [52]Dicyandiamide 550 4 22 [23]Melamine 520 5 5 [58]Melamine 530 2 5 [25]


4 Characterization of g-CN

e characterization of g-CN by molecular vibrationalspectroscopy (FTIR) basically reveals specificities of g-CNe transmission spectrum of bulk g-CN in the wavelengthrange of 500ndash4000 cmminus1 is shown in Figure 5

e peaks at 802 cmminus1 and 889 cmminus1 correspond to thepresence of s-triazine units in g-CN caused by the bendingvibration of the triazine ring e peaks in the range of 1200to 1700 cmminus1 are attributed to the stretching vibration of thearomatic heterocyclic units of heptazine (C6N7) e smallerpeaks observed at 1250 1320 1419 and 1457 cmminus1 are re-lated to the stretching vibrations of the C-N bonds while thepeak appearing at 1612 cmminus1 relates to the stretching vi-bration of the CN bond in heptazine units e largeabsorption band centered at 3124 cmminus1 corresponds to thestretching vibration of the NndashH bond to NH and NH2groups present at the end of g-CN indicating that g-CN wasundergoing incomplete polycondensation [65 71] Guigozet al [72] reported that the FTIR spectrum of g-CN NSsexhibits the same distinctive main bands signature of theg-CN bulk

X-ray photoelectron spectroscopy (XPS) indicates thepresence of two main elements (carbon C and nitrogen N)with two predominant peaks of C1s and N1s (Figure 6)

At high-resolution XPS spectrum of C1s the peak isdeconvoluted into three different components with bindingenergies at 2846 2860 and 2881 eV corresponding tofunctional groups of graphitic carbon [74] e first com-ponent is assigned to C-C or CC bonds and the second isidentified as a carbon bonded to nitrogen atoms in aromaticrings [C- (N)3] while that at 2881 eV is assigned to the (N-CN) bonds e high resolution of N1s spectrum exhibitsthree components around 3983 eV 3999 eV and 4006 eVe peak at 3983 eV is attributed to N binding to carbonatoms involved in triazine units (C-NC) while the peak at3999 eV is assigned to tertiary nitrogen groups Nndashcopy3 eselast two peaks constitute the heterocyclic ring units of tri-s-triazine constructing g-CN e third peak at 4006 eVindicates the presence of amino functions (C-N-H)resulting from the incomplete condensation of the structuresof the melon [57]

e elemental composition their atomic percentagesand the carbonnitrogen atomic ratio (CN) in g-CN are

shown in Table 7 [75] A smaller percentage of oxygenformed at the samplesrsquo surfaces is found with the ratio of CN often at 073 [75]

emolecular vibration properties of g-CN examined byRaman spectroscopy under UV illumination reveal severalcharacteristic peaks corresponding to the vibrational modesof CN heterocycles (Figure 7(a)) Similar trends are obtainedusing the Cambridge Sequential Total Energy Package(CASTEP) code implemented using density functionaltheory (DFT) (Figure 7(b)) [76]

is confirms the results of experimental Raman spec-troscopy Interestingly the comparison of the bulk andsingle layer of g-CN theoretical Raman spectra shows thatthe characteristic bands remain visible in both cases indi-cating that the exfoliation treatment does not cause anydamage to the g-tri-s-triazine-CN Only a decrease in in-tensity for the nanosheets is observed which is attributed tothe low-dimensional character Nonetheless a small shift isobserved for the N-C (sp2) bending vibration peak at1224 cmminus1 for the bulk sample which is displaced to1232 cmminus1 in g-CN NSs is originates from phononconfinement and strong quantum confinement effects [76]e second characteristic is related to the peak height ratiosof 583ndash478 cmminus1 (I583I478) and 761ndash704 cmminus1 (I761I704)equivalent to the layer-layer strain vibrations or the cor-relating vibrations induced by the layer-layer vibrations It isfound that these ratios tend to increase with the decreasingnumber of g-CN layers

e XRD diagrams depicted in Figure 8 show two dif-fraction peaks at 130deg and 272deg e large peak (002) at2θ 272deg is the peak characteristic of the interlayer stackingof an aromatic cyclic system of graphitic type e muchsmaller peak (100) at 2θ 130deg is characteristic of tri-s-triazine repeating units in melon-like materials [71 77] Itsunchanged position in the g-CN NSs revealed that thechemical exfoliation has no impact on the aromatic cyclicstructure of g-CN

e intensity reduction of (002) peak observed innanosheets is a signature of successful exfoliation of g-CN Itis worth noting that the diffraction peak at 130deg is alsodecreased compared to the g-CN bulk which is likely due tothe reduced planar size after exfoliation step e calculatedinterplanar distance of the aromatic series is d 033 nmindicating a layered-like structure similar to crystalline

Table 5 e deposition conditions of carbon nitride by CVD technique

Precursors Atmosphere T (degC) t (h) Heating rate (Kmin) Shape RefMelamine and thiourea Air 550 4 2 mdash [51]Melamine mdash 550 3 mdash Flakes [67]Dicyandiamide Ar 600 mdash mdash Films [66]

Table 6 e deposition conditions of carbon nitride by PECVD technique

Carbon sourceflow rate

Nitrogen sourceflow rate

Carrier gasesflowrate

Substrate temperature(degC)

Depositiontime

Power(W)

RF power(MHz) Ref

C2H405 Lmin N23 Lmin H24 sccm 400 6 h 840 mdash [68]C6H6mdash N210 sccm H25 sccm RT to 200 mdash 60 1356 [69]


Wavenumber (cm-1)

Tran

smitt

ance

500 1000 1500 2000 2500 3000 3500 4000

3124

161214

57

1250

1320

1419

889

802

(a)

Wavenumber (cm-1)

Tran

smitt

ance

4000 3000 2000 1000

131776

123942

80951

(b)

Figure 5 FTIR spectra of (a) bulk g-CN and (b) g-CN NSs (reproduced and adapted from [70])

g-C3N4

C 1s

N 1s

600Binding Energy (eV)

Binding Energy (eV)Binding Energy (eV)

Inte

nsity

(au

)

Inte

nsity

(au

)

Inte

nsity

(au

)(d)(c)

(a)

N 1sC 1s 3983 eV

3999 eV4006 eV

2846 eV

2860 eV

2881 eV

0 100 200 300 400 500

280 282 284 286 288 290 292 294 394 396 398 400 402 404 406 408

Figure 6 XPS spectra of g-CN (reproduced and adapted from [73])

Table 7 Percentage of atomic composition obtained from XPS analysis

C N O CNAtomic concentration 4118 5658 224 073


graphite (d 0335 nm) [78] is result suggests a typicalg-CN structure [79] Both NSs and bulk g-CN show strongemission peaks respectively at 445 nm and 464 nm whenexposed to visible light excitation using a photo-luminescence experimental setup ese peaks correspondto the band gap energies of 278 eV and 267 eV for the NSsand bulk g-CN respectively [54 62 74 80]

e optical band deviation (Eg) was also estimated fromabsorbance measurements using the Tauc model [71 81]

(αhv) B hv minus Eg1113872 1113873m

(1)

where α is the absorption coefficient h] is the photon en-ergy Eg the optical band gap B is a constant and m is anexponent that characterizes the optical absorption processFor the direct authorized transition m 12 for the indirectauthorized transition m 2 for the direct forbidden tran-sition m 32 and for the indirect forbidden transitionm 3

e plotting of [(αh])1m] as a function of the energy ofthe photon (h]) and the extrapolation of the linear part of

the curve to [(αh])1m 0] on the energy axis provides thevalue of the optical band gap (Eg) e value of m 12 issuitable for g-CN because it has a direct allowed band gap[74] By using the Tauc model Huang et al [56] found theband gaps for bulk g-CN and g-CN NSs to be approximately272 eV and 282 eV respectively ey attributed this in-crease in the band gap energy from bulk to nanolayers by theeffect of quantum confinement

5 Gas-Sensing Investigations

51 Gas-SensingMechanisms e physical principle of a gassensor is based on charge transfer process in which thedetection material acts as a charge donor or a charge ac-ceptor [5 16 34 82] Upon exposure to different gases thecharge transfer reaction occurs in different directions be-tween the sensing material and the adsorbed gases whichleads to different changes in the resistance of the material[83] In absence of adsorbed gas molecules or upon reex-position to air the original resistance of the material isrecovered Figure 9 shows a schematic that describes thechange of resistance related to charge transfer processesfrom adsorbed gases Considering an n-type material ex-posed to an electron donor gas (reducing gas) electrons aretransferred from the gas molecules to the n-type materialcausing an increase in the density of majority of chargecarriers (electrons) Consequently the resistance of then-type material decreases Seemingly in the case of an n-typematerial exposed to an acceptor gas (oxidizing gas) theelectrons are transferred from the material to the gasmolecules resulting in a decrease of the majority of chargecarriersrsquo density in the material As a result the resistance ofthe n-type material increases

Similar processes occur in the case of a p-type materialIts exposure to a reducing gas causes electron to transferfrom the gas molecules to the material hence decreasing thedensity of the majority of charge carriers (holes) in thep-type material and resulting in a decrease of the p-type

Ram

an In

tens

ityc

ps

Wavenumber (cm-1)2000 1600 1200 800 400

2400

2000

1600

1200

800

400

0

Bulk

1 layer

1616 1555

1481

1234

751

705

543

479

1250

(a)

Ram

an In

tens

itya

u

Wavenumber (cm-1)1600 1400 600 400

Bulk

1 layer

1602 15

6915

10

1224

726

685

616

555

1232

(b)

Figure 7 (a) Experimental Raman spectra of bulk and signal-layer g-CN and (b) calculated Raman spectra of bulk and signal-layer g-CN(reproduced from [76])

10 20 30 40 50 60 70 80

(100)

(002)

g-CN NSs

g-CN bulk

Inte

nsity

(au

)

2θ (deg)

Figure 8 XRD patterns of bulk g-CN and g-CN NSs


materialrsquos resistance In contrast if the adsorbed gas isoxidizing electrons are transferred from the material to thegas molecules resulting in an increase of the charge carriersrsquodensity in the material As a result the resistance of thep-type material decreases

52 Graphene-Sensing Performance Studies have provedthat defects and dopants in Gr increase its gas sensitivityconsiderably [84ndash87] Modification of Gr with boron ni-trogen and defect increases its adsorption energy with gasessuch as ammonia as well as oxides of nitrogen and carbon[84] Doping Gr with metals such as Mg Co Fe and Niincreases sensitivity of Gr for gases such as H2S SO2 and O2Table 8 shows sensing characteristics of various dopants withGr for various gases

Microsensors made of mechanically exfoliated Gr arecapable of sensing even single molecules of NO2 in highvacuum [21]e adsorption of electron acceptingmoleculessuch as NO2 and H2S onto Gr leads to a decrease of itsresistivity due to an increase in holes concentrationMeanwhile electron donor molecules such as CO and NH3increase resistivity of Gr when adsorbed to it which is due toincrease in electron concentration as shown in Figure 10

A 35ndash5 nm thick mechanically exfoliated Gr used as agas sensor has shown commendable sensitivity reproduc-ibility and selectivity in response to NO2 at 100 ppm asshown in Figure 11 Sensors based on CVD made Gr showsignificant sensitivity to various gases at a minimum con-centration of 1 ppq [90] Schottky diode sensors made of Grn-si have proven to be potential H2S gas-sensing device [91]

Graphene oxides (GrO) are promising gas-sensingmaterials owing to their oxygen-rich functional groupsSingle-layer to few-layer GrO (dimensions ranging from 27to 500 microm) based sensors fabricated by drop casting show ap-type response in both oxidizing and reducing environ-ments [92] GrO based sensors fabricated by dielec-trophoresis are used to sense hydrogen gas [93] GrO withacoustic wave propagated surface is used to detect H2 andNO2 in the atmosphere [94 95] Dense functional groups of

oxygen in GrO maintain its sensitivity even in harsh con-ditions such as high humidity and strong acidic or basicconditions and also sense harsh volatile content like chlo-roform [96]

Reduced graphene oxide (r-GrO) is widely used insensing gases r-GrO is preferred over Gr due to its low costand tailorable structure and properties [22] e enhance-ments in the r-GrO response to gases are associated with thecarbon atoms holes or vacancies created due to thermaltreatments Sensors fabricated by r-GrO (made by annealingof GrO at 300degC) show conductance that is 43 more thanthat of mechanically exfoliated Gr [21] Cost-effective gassensors based on r-GrO were fabricated on paper substratesto sense NO2 at lower ppm levels It is also noted that sensingbehavior depends on both the thickness and size of ther-GrO flakes [97] e poor selectivity of Gr constitutes onemain drawback for its usage in gas-sensing devices Nev-ertheless its functionalization with metallic or metal oxidenanoparticles has been shown to enhance its selectivity[98ndash102] In fact pristine Gr shows insignificant change inresistance when hydrogen gas molecules are adsorbed ontoit Meanwhile nano-Pd decorated Gr shows considerablechanges in resistance because Pd hydride on the surface ofGr donates more electrons [99] r-GrO decorated withpalladium can sense NO from 2 to 420 ppb r-GrO func-tionalized with ndashSO3H and decorated with nano-Ag showeda superior performance in measuring NO2 and NH3 gases[102 103] Table 9 shows details of gases sensed by differentGr decorated by various nanoparticles

Regardless of its comparison with g-CN Gr remains aninteresting 2D material suitable for gas sensing due to itslarge specific surface area high carriersrsquo mobility highsensitivity fast response low power consumption and itsoperation under ambient conditions [120] Moreover whenGr is associated with perovskites [121] polymers [122] ororganic molecules [123] its sensing performance was foundto be improved at room temperature Indeed the compositeform of Gr whether with a polymer or a perovskite ororganic molecules provides specific reaction sites for gasadsorption hence improving the sensor selectivity at room

n-type

Resistance

Time

Reducinggas

e-

n-type

Resistance

Time

Oxidizinggas

e-

Figure 9 e detection mechanism of an n-type gas sensor


temperature When Gr was used in conjunction with g-CN[124] g-CN showed superior performance compared to Grin both gas sensing and catalysis which was attributed to theincreased interaction sites offered by 2D g-CN structure

53 g-CN Sensing Performance Several works have beenreported on the influence of the g-CN content on its gas-sensing performances Karthik et al [103] reported that thinlayers (elaborated by a spray pyrolysis) of TiO2 porousnanospheres decorated with g-CN showed excellent detec-tion performance of CO2 gas with very fast response andrecovery e results show that 10 wt g-CN decoratedTiO2 composite layer exhibits an exceptional detection

response of 88 and a great stability for CO2 gas at 450degCunder 1500 ppm e enhanced detection response is at-tributed to the increased surface area of 1085m2g due tothe porous nature of g-CN (157 nm) Zhang et al [58]showed that gas detection properties such as gas selectivityand sensitivity of SnO2 to acetic acid as well as the operatingtemperature were enhanced by the incorporation of g-CNinto SnO2 eir results indicate that the operating tem-perature for the detection of acetic acid was decreased from230degC to 185degC In particular the g-CN-SnO2 nano-composite-based gas sensor containing 10 by weight ofg-CN revealed the highest sensitivity of 877 to 1000 ppmacetic acid the fastest response lower recovery time and thelowest detection limit down to 01 ppm Besides calcinationtemperatures calcination times and precursor ratios werealso reported to significantly affect the performance ofsensors to target gases For example Hu et al [14] have

Table 8 Characteristics of graphene with dopants

Ref Gas Dopant Minimumconcentration (ppt)

Detectionlimit (ppt)

eoretical adsorptionenergy (Ead) (eV)

eoretical Mullikencharge (Q) (e)

[86 87]

NO

Pristine 10 0158 0029 0018[82] Pristine mdash mdash minus030 004[82] Boron mdash mdash minus107 015[82] Nitrogen mdash mdash minus040 001[86 87]

NO2

Pristine 20 206 0067 minus0099[82] Pristine mdash mdash minus048 minus019[82] Boron mdash mdash minus137 minus034[82] Nitrogen mdash mdash minus098 minus055[86 87]

NH3

Pristine 200 332 0031 0027[82] Pristine mdash mdash minus011 002[82] Boron mdash mdash minus050 040[82] Nitrogen mdash mdash minus012 004[87] N2O Pristine 200 103 mdash mdash[87] O2 Pristine 200 388 mdash mdash[86]

CO

Pristine mdash mdash 0014 0012[82] Pristine mdash mdash minus012 minus001[82] Boron mdash mdash minus014 minus002[82] Nitrogen mdash mdash minus014 0[87] CO2 Pristine 200 136 mdash mdash[82 87] SO2

Pristine 200 674 0012 minus0077[83] Boron mdash mdash 0205 minus0110

NH3

CO

H2O

NO2

I II III IV

0 500 1000t (s)

4

2

0

-2

-4

Δρρ

()

Figure 10 Change in resistivity when Gr is exposed to variousgases [88]

Air Air Air AirNO2 NO2 NO2

100 ppm NO2 gasBias voltage 1 V

Time (s)1000 1500 20000 500

240

235

230

225

220

215

Curr

ent (

mA

)

Figure 11 Reversibility of gas sensors [89]


examined the effect of elaboration conditions on the de-tection performance of g-CN-SnO2 nanocomposites using500 ppm acetone as the target gase 200100 ratio betweenmelamine and SnCl2 middot 2H2O and the calcination for 3 hoursat 500degC appeared to offer better detection properties Forinstance these preparation conditions enhanced the de-tection sensitivity 22 times compared to pure SnO2 at a fastresponse and recovery time (7 s8 s) while achieving very lowdetection limit of 67 ppb In addition the element ratios(melamine and SnCl2 middot 2H2O) were also used to determinethe important role of g-CN in the g-CN-SnO2 nano-composite sensor In parallel Absalan et al [25] havesynthesized CO gas sensors based on PdSnO2g-CNnanocomposites by the hydrothermal method at different Pdand g-CN contents e nanocomposites made of 5 PdSnO25 g-CN presented remarkable CO detection capa-bilities such as good selectivity and stability superior re-sponse short response and low recovery times at very lowoperating temperature of 125degC e exceptional gas de-tection performances of these nanocomposites were at-tributed to the large specific surface area of g-CN SimilarlyChu et al [125] examined the g-CN-WO3 composite syn-thetized by hydrothermal treatment eir results revealedthat adding a suitable quantity of g-CN toWO3 was found toenhance the selectivity and sensitivity to acetone vapor esensor based on 2 wt g-CN-WO3 composite at an idealoperating temperature of 310degC presented a response to1000 ppm acetone of RaRg 582 Moreover Zhang et al[126] studied g-CNMgFe2O4 composites synthesized by aone-step solvothermal process as acetone gas sensor e gasdetection properties of the models were determined andcompared to a sensor based on pure MgFe2O4 e highersensing performance was achived at 10 wt g-CN contentwhere the sensitivity to acetone was enhanced by approxi-mately 145 times while the best possible operating

temperature was 320degC e MgFe2O4g-CN-10wt basedsensor exhibits outstanding acetone detection performancehigh sensitivity and selectivity rapid response and lowrecovery time and thus favorable stability

Additionally the gas sensors based on chemically ex-foliated g-CN NSs were found to exhibit very low detectionlimits and ultrahigh sensitivity towards NO2 gas comparedto Gr as reported by Hang et al [127] Precisely 15 wt ofg-CN NSs associated with Gr showed a better response thanthe sole Gr based sensor towards NO2 gas Similar gas-sensing enhancement was reported to occur for othercompounds associated with g-CN such as ZnOg-CNcomposite [128] For instance when ZnOg-CN compositewas irradiated with 460 nm light it displayed the maximumresponse of 448 under 7 ppm of NO2 with a response andrecovery times of 142 s and 190 s respectively and a de-tection limit of 38 ppb

Table 10 summarizes the g-CN based nanocompositesfor gas sensor applications including their characteristicselaboration methods and gas-sensing performances

All aforementioned gas-sensing performances did notinclude specific sensing conditions that greatly influence thedetection capabilities such as the relative humidity or mixedgases In fact humidity is a key factor that needs to be takeninto account when analyzing the gas-sensing performancesFor instance the responsivity of g-CN gas sensors towardsNO2 was found to be altered in the presence of high levels ofwater vapor (about 90) as shown in Figure 12(a) [129] esensing performance was decreased by 3 times for 90 RHcompared to 50 RH

Hence the presence of humidity might compromise thedetection of target gases is result has to be consideredwith special care as this limitation is commonly overcome byincreasing the operating temperature this implies that thegas sensors need to be stable at intermediate temperatureswhile keeping their gas sensitivity unchanged As an exampleof the sensing selectivity Figure 12(b) is provided to illus-trate the gas selectivity of g-CN sensors towards severalcommon gases where the highest selectivity was obtained onNO2

6 Simulated Gas-Sensing Performances

eoretical calculations show the adsorption energies be-tween selected gas molecules (CO2 NO2 and HF) and g-CNmonolayer e comparison with Gr and r-GrO is shownusing HF as a selected adsorption gas e first-principlescalculations are based on the density functional theory(DFT) using generalized gradient approximation (GGA)with the Perdew-Burke-Ernzerhof (PBE) exchange-corre-lation functional [81 130] implemented in QuantumEspresso code [131] In the optimized process the vacuumspaces of 15 A were set for the three compounds to separatethe interactions between the layers A (3times 3times1) k-point wasused in the structure optimization and total energy calcu-lations To study the stability of g-CN Gr and r-GrOsurfaces with considered gas molecules the adsorptionenergy of system was computed using the following relation[132 133]

Table 9 Sensitivity of metal nanopowders decorated graphenesensors

Ref Gas Nanometal-Gr Sensitivity () Response time(min)

[97]

H2

Pd-Gr ΔR 5 10[98] Pd-gr ΔR 33 1[99] Pt-gr ΔR 3 mdash[104] Pt-gr ΔV 661 125[105] ZnO-Gr0 ΔR 250 035[106] Pd-Wo3-rGrO ΔG 7200 059[107] Pt-rGrO ΔV 22 mdash[108]

NO2

SnO2-gr ΔR minus6 315[109] WO3-gr ΔR 96 042ndash33[110] CNT-GrO ΔR 20 60[111] NiO-GrO ΔR 200 mdash[112] ZnO-GrO ΔR 256 275[113] CO3O4-GrO ΔR 80 lt1ndash2[114] SnO2-rGrO ΔR 231 225[115] WO3-rGrO ΔR 102 mdash[116]

CO2

SnO2-gr ΔRlt 60 026[117] Al2O3-gr ΔR 1084 024[116] Sb2O3-gr ΔRlt 60 026[118] LPG Bi2O3-gr ΔR 400 026[119] MnO2-rGrO ΔR 50 027


Tabl

e10

eperformancesof

nano

compo

sites

basedon

g-CN

forgassensor

applications

Material

Metho

dRe

spon

seG

asRe

spon

se

recovery

time

(s)

ppm

level

Operatio

nT

(deg C)

Detectio

nlim

itCom

ment

Ref

TiO2

Spraypyrolysis

techniqu

e

RaRg

25

H2S

sim5260

1500

450

U

eim

provem

entinthedetectionperformance

ofthe

sensor

isdu

eto

theintrod

uctio

nof

10

oftheg-CN

nano

sheets

[103]

RaRg

22

CO2

4555

g-CN

(10wt

)TiO2

RaRg

67

H2S

sim3052

RaRg

88

CO2

3527

SnO2

Hydrothermal

metho

d

RaRg

134

acetic

acid

94160

1000

230degC

UIm

provem

ento

fthe

operatingtemperature

andthe

sensitivity

byintrod

uctio

nof

10wt

ofg-CNin

SnO2

[58]

10wt

ofg-

CN-SnO

2

RaRg

877

CH

3COOH

U185degC

01pp

m

g-CN-SnO

2One-stepcalcinationmetho

dVgVa

83

aceton

e78

500

380degC

67pp

bA

significantimprovem

entin

sensor

performance

bycalciningmelam

ineSn

O2po

wderfor3ho

urs

[14]

5Pd

SnO

25

g-CN

Hydrothermal

metho

d(Rg-Ra

)Ra

905CO

1013

1000

125degC

75pp

mg-CN-5

nano

sheets

with

SnO2nano

particles

effectiv

elyim

proved

therespon

seof

thegassensors

towards

CO

[25]

2wt

g-CN-

WO3

Hydrothermal

metho

dRa

Rg

582

aceton

e5329

1000

310degC

05pp

mA

gassensor

basedon

2g-CN

compo

siteshow

sa

high

errespon

seto

aceton

ethan

pure

WO3

[125]

10wt

g-CN

MgFe 2O4

One-stepsolvotherm

almetho

dRa

Rg

275

aceton

e4929

500

320degC

30pp

b

eintrod

uctio

nof

10

ofg-CN

nano

sheets

inMgFe 2O4im

proves

theirdetectionperformance

[126]

Grg-CN

Dropcoatingmetho

d(Rg-Ra

)Ra

42N

O2

U5

100degC

600pp

bGraph

iticcarbon

nitridenano

sheetswith

15of

g-CN

exhibith

ighdetectionperformance

comparedto

bulk

g-CN

andpu

regraphene

[127]

10wt

g-CN

ZnO

Synthesiz

edviaultrason

icmixingandsubsequent

calcinationprocess

RgRa

448

NO2

142190

7U

38pp

mDetectio

nperformance

isactiv

ated

byLE

Dlight

sources460nm

LED

(127Wm

2 )[128]

ldquoUrdquoun

availablecitatio

nitisno

tcitedin

thestud

yVgVaelectricvoltagesinthetargetgasesa

ndatmosph

ericairrespectiv

elyRa

Rgelectricresis

tances

intheatmosph

ericaira

ndtargetgasesrespectiv

ely


Resis

tanc

e (M

Ω)

Time (s)

90

80

70

60

50

40

30

20

10

0100 200 300 400

50 RH70 RH90 RH

(a)

Resp

onse

(Ra

Rg o

r Rg

Ra)

50

40

30

20

10

0

NO2

CO NH3 C6H6 H2 Cl2N2OEtha

nol

Ace

tone

RaRg CO NH3 C6H6 H2 Ethanol AcetoneRgRa NO2 N2O Cl2

(b)

Figure 12 (a) Humidity effect on the response of gas sensors based on g-C3N4 to 3 ppm NO2 (b) gas selectivity of g-C3N4 sensors towardsseveral common gases [129]

Table 11 Side and top views of the equilibrium adsorption configuration of NO2 CO2 andHF on g-CN andHF adsorbed on Gr and r-GrO

Systems Structure before optimization Optimized structure

g-CN-NO2

25 Aring 313 Aring

g-CN-CO2

25 Aring 324 Aring

g-CN-HF

25 Aring 129 Aring

r-GrO-HF

25 Aring 326 Aring

Gr-HF

25 Aring 370 Aring


Ea ds minus E(compoun dminusgaz) minus Ecompoun d + Egas1113872 1113873 (2)

where E(compoundminusgas) Ecompound and Egas are the total energyof gas molecules adsorbed by the surface of the compoundcompound and gas molecule respectively A positive ad-sorption energy value shows that the adsorption is ener-getically unfavorable and the reaction is endothermic andhence unstable A negative value indicates that the reaction isexothermic and hence stable and energetically favorableeposition of the nitrogen atom (N) in g-CN according to [134]shows that the adsorption energies of CO2 gas on a nitrogenatom at two coordinates are more negative than those ofother positions e monolayer model was obtained byremoving other layers in the unit cell of bulk

e adsorbed CO2 NO2 and HF molecules were con-structed by placing a single gas molecule parallel on thesurface of compounds e values of d for all compound-gassystems are 25 Ae gas molecules CO2 NO2 and HF havebond lengths between atoms of 116 A 14 A and 086 Arespectively Top views of systems adsorbed by gas moleculesare shown in Table 11 e five adsorbed models weregeometrically optimized to obtain the adsorption energiesand they were compared successively

According to the optimization of the g-CN-gas system(see Table 12) the CO2 and NO2 molecules are moved awayfrom the surface while the HF molecule is brought closer tothe surface e distances between the surface of g-CN andthe atoms of the molecules are 25 A before optimizationAfter adsorption on the g-CN surface the molecules alsoexhibit some deformation e angles and bond lengthschange while the angles O-C-O and O-N-O in CO2 andNO2 respectively are decreased e N-O and H-F bondlengths increase and the C-O bond length decreases edistance between the surface of g-CN and the atom closest tothe surface in gas molecules is noted with d-g-CN-gas

e DFT calculation results show that all the adsorptionenergies are negative indicating that the adsorption of thethree gases on g-CN is exothermic It can be briefly sum-marized that g-CN exhibits a relatively high adsorptioncapacity for HF (minus103 eV) and CO2 (minus059 eV) and a lowadsorption intensity for NO2 (minus0166 eV) erefore theadsorption behavior of g-CN corresponds to efficient ad-sorption of reagents which is very beneficial for gas sensorperformance e adsorption results of CO2 NO2 and HFgas molecules on g-CN showed that the Eads of these gases onvirgin g-CN follows the order of NO2gtCO2gtHFe resultssuggest that the g-CN nanolayer is more stable with HF than

other gases with an adsorption energy of minus103 eV eresults revealed that the g-CN system is a suitable candidatefor HF gas sensors due to their high adsorption capacity Inaddition the results indicate that the interaction betweeng-CN and HF gas is significantly higher than that of othergases Table 13 shows other gases detected by g-CN and theiradsorption energies

For Gr and GrO the DFT calculation results show thatthe interaction of HF gas with the latter two is relatively lowcompared to the adsorption of HF on g-CN e optimizedstructures of HF adsorbed on Gr and r-GrO are shown inTable 14 e length of the HF bond is less modifiedcompared to its initial state of a little near sim094 A eadsorption energies of HF on Gr and r-GrO are respectivelyminus004 eV and minus074 eV lower than those of HF on g-CNis calculation shows that g-CN can be used for the de-tection of HF gas

Gr-based gas sensors show commendable effect invarious sensing gases Pristine Gr shows insignificant effectin gas sensing and hence its sensitivity is enriched by eitherdoping the Gr with suitable metal dopants such as Mg CoFe and Ni or hybridizing with other nanoparticles Stabilityof the GrO sensors at higher temperatures is generally lowerthan that of g-CN based sensors Ye et al showed that TiO2hybridized with GrO senses NH3 gas and the same TiO2when hybridized with g-CN shows better sensitivity for CO2even at 400degC GrO based sensors are used in acidic or al-kaline conditions and can sense high volatile chemicals suchas chloroform SnO2-Gr proves to be an excellent candidatefor sensing humidity

Table 12 e angle between the bonds the bond lengths and the distance between the gases and the surface of g-CN before and afteroptimization

CO2 NO2 HFBefore After Before After Before After

Angle (deg) 180deg 17942deg 13442deg 12969deg mdash mdashBond lengths (5 A) 1181 11721170 1203 12191225 0869 0957d g-CN-gas (A) 25 324 25 313 25 129Eads minus059 eV minus016 eV minus103 eV

Eads literatureminus0226 eV [135] 03975 eV

[134] minus0231 eV [136] mdash

Table 13 Other potential gases detected by g-CN and their ad-sorption energies

H2 H2O N2 CO CH4 NOEads (eV) minus0078 minus0513 minus0117 minus0155 minus0163 eV minus0059 eVRef [135] [137]

Table 14 e distance between the gases and the surface of g-CNGr and r-GrO before and after optimization

Gr r-GrO g-CNBefore After Before After Before After

Bond lengths (A) 0869 0938 0869 094 0869 0957d GrrGrO-HF (A) 25 370 25 326 25 129Eads (eV) minus004 eV minus074 eV minus103 eV


7 Conclusion

In this work an overview of both Gr and g-CN low-di-mensional materials was outlined in terms of elaborationand characterization with respect to their gas-sensing per-formances Subsequently theoretical calculations along withsimulated gas-sensing performances of both nanomaterialswere carried out to address the researcherrsquos paradigm re-garding their optimization as potential gas sensors issensor would exhibit high sensitivity low detection limitfast response and low operating temperature Based on ourinvestigation g-CN which reveals interesting gas-sensingperformances over Gr by 10-folds may offer new oppor-tunities for the design and manufacturing of high-perfor-mance gas sensors is is mainly related to itssemiconducting character and its porosity that provideslarge adsorption sites for the target gases Besides theconductivity and the tailorable functional groups of Grprovide a great advantage as resistive sensors Consequentlyfor NO2 NH3 and organic gases such as ethanol and ac-etone Gr would show high performances e main bot-tlenecks are large-scale production of Gr-based sensors andsensitivity of these sensors for specific gases e specific gassensitivity can be improved by (1) increasing the surface areaof Gr and combination with other specific nanomaterialsand (2) focusing on the morphology of various GrO withspecific gas adsorption [138 139]

Data Availability

Data collected from the literature can be consulted in therelevant articles the authorsrsquo data are available upon requestto Professor Mustapha Jouiad at mustaphajouiadu-picardiefr

Conflicts of Interest

e authors declare that they have no conflicts of interest

Acknowledgments

is research was funded by a seed grant provided byMAScIR ldquo2DndashHFndashDetect 240004055rdquo

References

[1] A Salas C Medina J T Vial et al ldquoUltrafast carbonnanotubes growth on recycled carbon fibers and theirevaluation on interfacial shear strength in reinforced com-positesrdquo Scientific Reports vol 11 no 1 pp 1ndash11 2021

[2] S-H Chung J T Kim and D H Kim ldquoHybrid carbonthermal interface materials for thermoelectric generatordevicesrdquo Scientific Reports vol 10 no 1 pp 1ndash11 2020

[3] B Podlesny B Olszewska Z Yaari et al ldquoEn route to single-step two-phase purification of carbon nanotubes facilitatedby high-throughput spectroscopyrdquo Scientific Reports vol 11no 1 pp 1ndash11 2021

[4] S Yonezawa T Chiba Y Seki and M Takashiri ldquoOrigin ofn type properties in single wall carbon nanotube films withanionic surfactants investigated by experimental and

theoretical analysesrdquo Scientific Reports vol 11 no 1 pp 1ndash92021

[5] G Deokar J Casanova-Chafer N S Rajput et al ldquoWafer-scale few-layer graphene growth on CuNi films for gassensing applicationsrdquo Sensors and Actuators B Chemicalvol 305 p 127458 2020

[6] D D Evanoff and G Chumanov ldquoSynthesis and opticalproperties of silver nanoparticles and arraysrdquo Chem-PhysChem vol 6 no 7 pp 1221ndash1231 2005

[7] A K Bodenmann and A H MacDonald ldquoGraphene ex-ploring carbon flatlandrdquo Physics Today vol 60 no 8pp 35ndash41 2007

[8] Y Si and E T Samulski ldquoSynthesis of water soluble gra-phenerdquo Nano Letters vol 8 no 6 pp 1679ndash1682 2008

[9] D R Dreyer S Park C W Bielawski and R S Ruoff ldquoechemistry of graphene oxiderdquo Chemical Society Reviewsvol 39 no 1 pp 228ndash240 2010

[10] G Wang J Yang J Park et al ldquoFacile synthesis andcharacterization of graphene nanosheetsrdquo Journal of PhysicalChemistry C vol 112 no 22 pp 8192ndash8195 2008

[11] G Wang X Shen B Wang J Yao and J Park ldquoSynthesisand characterisation of hydrophilic and organophilic gra-phene nanosheetsrdquo Carbon vol 47 no 5 pp 1359ndash13642009

[12] X Li X Wang L Zhang S Lee and H Dai ldquoChemicallyderived ultrasmooth graphene nanoribbon semiconduc-torsrdquo Science vol 319 no 5867 pp 1229ndash1232 2008

[13] P Blake P D Brimicombe R R Nair et al ldquoGraphene-based liquid crystal devicerdquo Nano Letters vol 8 no 6pp 1704ndash1708 2008

[14] J Hu C Zou Y Su et al ldquoOne-step synthesis of 2D C3N4-tin oxide gas sensors for enhanced acetone vapor detectionrdquoSensors and Actuators B Chemical vol 253 pp 641ndash6512017

[15] Z Yuan R Tang Y Zhang and L Yin ldquoEnhanced pho-tovoltaic performance of dye-sensitized solar cells based onCo9S8 nanotube array counter electrode and TiO2g-C3N4heterostructure nanosheet photoanoderdquo Journal of Alloysand Compounds vol 691 pp 983ndash991 2017

[16] S Zhang N Hang Z Zhang H Yue and W YangldquoPreparation of g-C3N4graphene composite for detectingNO2 at room temperaturerdquo Nanomaterials vol 7 no 1pp 12ndash11 2017

[17] S K Ghosh V K Perla and K Mallick ldquoEnhancement ofdielectric and electric-field-induced polarization of bismuthfluoride nanoparticles within the layered structure of carbonnitriderdquo Scientific Reports vol 10 no 1 pp 1ndash11 2020

[18] S Kumar S Karthikeyan and A Lee ldquog-C3N4-basednanomaterials for visible light-driven photocatalysisrdquo Cat-alysts vol 8 no 2 p 74 2018

[19] S V Morozov K S Novoselov and A K Geim ldquoElectrontransport in graphenerdquo Physics-Uspekhi vol 51 no 7pp 744ndash748 2008

[20] A N Sruti and K Jagannadham ldquoElectrical conductivity ofgraphene composites with in and In-Ga alloyrdquo Journal ofElectronic Materials vol 39 no 8 pp 1268ndash1276 2010

[21] F Schedin A K Geim S V Morozov et al ldquoDetection ofindividual gas molecules adsorbed on graphenerdquo NatureMaterials vol 6 no 9 pp 652ndash655 2007

[22] G Lu L E Ocola and J Chen ldquoReduced graphene oxide forroom-temperature gas sensorsrdquo Nanotechnology vol 20no 44 p 445502 2009

[23] S Li Z Wang X Wang et al ldquoOrientation controlledpreparation of nanoporous carbon nitride fibers and related


composite for gas sensing under ambient conditionsrdquo NanoResearch vol 10 no 5 pp 1710ndash1719 2017

[24] Q Ma B Kutilike N Kari S Abliz and A Yimit ldquoStudy onsurface sensitization of g-C3N4 by functioned differentaggregation behavior porphyrin and its optical propertiesrdquoMaterials Science in Semiconductor Processing vol 121p 105316 2021

[25] S Absalan S Nasresfahani and M H Sheikhi ldquoHigh-performance carbon monoxide gas sensor based on palla-diumtin oxideporous graphitic carbon nitride nano-compositerdquo Journal of Alloys and Compounds vol 795pp 79ndash90 2019

[26] G Deokar J Avila I Razado-Colambo et al ldquoTowards highquality CVD graphene growth and transferrdquo Carbon vol 89pp 82ndash92 2015

[27] H Asgar K M Deen U Riaz Z U Rahman U H Shahand W Haider ldquoSynthesis of graphene via ultra-sonic ex-foliation of graphite oxide and its electrochemical charac-terizationrdquo Materials Chemistry and Physics vol 206pp 7ndash11 2018

[28] K S Novoselov A Mishchenko A Carvalho andA H Castro Neto ldquo2D materials and van der Waals het-erostructuresrdquo Science vol 353 no 6298 p 353 2016

[29] M Yi and Z Shen ldquoA review on mechanical exfoliation forthe scalable production of graphenerdquo Journal of MaterialsChemistry vol 3 no 22 pp 11700ndash11715 2015

[30] G Deokar A Genovese and P M F J Costa ldquoFast wafer-scale growth of a nanometer-thick graphite film on Ni foiland its structural analysisrdquo Nanotechnology vol 31 no 48p 485605 2020

[31] G Deokar J-L Codron C Boyaval X Wallart andD Vignaud ldquoCVD graphene growth on Ni films andtransferrdquo in Proceedings of the 4th Graphene ConferenceGraphene Toulouse France July 2014

[32] D Mouloua A Kotbi G Deokar et al ldquoRecent progress inthe synthesis of MoS2 thin films for sensing photovoltaicand plasmonic applications a reviewrdquo Materials vol 14no 12 p 3283 2021

[33] Q Yu J Lian S Siriponglert H Li Y P Chen and S-S PeildquoGraphene segregated on Ni surfaces and transferred toinsulatorsrdquo Applied Physics Letters vol 93 no 11pp 113103-113104 2008

[34] G Deokar A Genovese S G Surya C Long K N Salamaand P M F J Costa ldquoSemi-transparent graphite filmsgrowth on Ni and their double-sided polymer-free transferrdquoScientific Reports vol 10 no 1 pp 1ndash15 2020

[35] X Li W Cai J An et al ldquoLarge-area synthesis of high-quality and uniform graphene films on copper foilsrdquo Sciencevol 324 no 5932 pp 1312ndash1314 2009

[36] A K Geim ldquoGRAPHENE STATUS and prospects A KGeim manchester centre for mesoscience and nanotech-nologyrdquo Prospects vol 324 pp 1ndash8 2009

[37] K V Emtsev A Bostwick K Horn et al ldquoTowards wafer-size graphene layers by atmospheric pressure graphitizationof silicon carbiderdquo Nature Materials vol 8 no 3pp 203ndash207 2009

[38] K S Kim Y Zhao H Jang et al ldquoLarge-scale pattern growthof graphene films for stretchable transparent electrodesrdquoNature vol 457 no 7230 pp 706ndash710 2009

[39] S Bae H Kim Y Lee et al ldquoRoll-to-roll production of 30-inch graphene films for transparent electrodesrdquo NatureNanotechnology vol 5 no 8 pp 574ndash578 2010

[40] X Li C W Magnuson A Venugopal et al ldquoGraphene filmswith large domain size by a two-step chemical vapor

deposition processrdquo Nano Letters vol 10 no 11pp 4328ndash4334 2010

[41] K S Novoselov A K Geim S V Morozov et al ldquoTwo-dimensional gas of massless Dirac fermions in graphenerdquoNature vol 438 no 7065 pp 197ndash200 2005

[42] R Kaindl G Jakopic R Resel et al ldquoSynthesis of graphene-layer nanosheet coatings by PECVDrdquo Materials TodayProceedings vol 2 no 8 pp 4247ndash4255 2015

[43] N Li Z Zhen R Zhang Z Xu Z Zheng and L HeldquoNucleation and growth dynamics of graphene grown byradio frequency plasma-enhanced chemical vapor deposi-tionrdquo Scientific Reports vol 11 no 1 pp 1ndash10 2021

[44] N Woehrl O Ochedowski S Gottlieb K Shibasaki andS Schulz ldquoPlasma-enhanced chemical vapor deposition ofgraphene on copper substratesrdquo AIP Advances vol 4 no 4p 47128 2014

[45] C Yang H Bi D Wan F Huang X Xie and M JiangldquoDirect PECVD growth of vertically erected graphene wallson dielectric substrates as excellent multifunctional elec-trodesrdquo Journal of Materials Chemistry vol 1 no 3pp 770ndash775 2013

[46] S Hussain E Kovacevic J Berndt et al ldquoLow-temperaturelow-power PECVD synthesis of vertically aligned graphenerdquoNanotechnology vol 31 no 39 p 395604 2020

[47] S Chugh R Mehta N Lu F D Dios M J Kim andZ Chen ldquoComparison of graphene growth on arbitrary non-catalytic substrates using low-temperature PECVDrdquoCarbonvol 93 pp 393ndash399 2015

[48] B Gurunlu Ccedil Tasdelen Yucedag and M R BayramogluldquoGreen synthesis of graphene from graphite in molten saltmediumrdquo Journal of Nanomaterials vol 2020 Article ID7029601 12 pages 2020

[49] G Varshney S R Kanel D M Kempisty et al ldquoNanoscaleTiO2 films and their application in remediation of organicpollutantsrdquo Coordination Chemistry Reviews vol 306pp 43ndash64 2016

[50] B Priyadarshini M Rama and U Vijayalakshmi ldquoBioactivecoating as a surface modification technique for biocom-patible metallic implants a reviewrdquo Journal of Asian CeramicSocieties vol 7 no 4 pp 397ndash406 2019

[51] L Ye and S Chen ldquoFabrication and high visible-light-drivenphotocurrent response of g-C3N4 film the role of thioureardquoApplied Surface Science vol 389 pp 1076ndash1083 2016

[52] R Tejasvi and S Basu ldquoFormation of C3N4 thin filmsthrough the stoichiometric transfer of the bulk synthesizedgC3N4 using RFM sputteringrdquo Vacuum vol 171 p 1089372020

[53] Y Shi L He F Guang L Li Z Xin and R Liu ldquoA reviewpreparation performance and applications of silicon oxy-nitride filmrdquo Micromachines vol 10 no 8 pp 552ndash6232019

[54] N A Mohamed J Safaei A F Ismail et al ldquoe influencesof post-annealing temperatures on fabrication graphiticcarbon nitride (g-C3N4) thin filmrdquo Applied Surface Sciencevol 489 pp 92ndash100 2019

[55] X Sun X An S Zhang et al ldquoPhysical vapor deposition(PVD) a method to fabricate modified g-C3N4 sheetsrdquo NewJournal of Chemistry vol 43 no 17 pp 6683ndash6687 2019

[56] J Huang J Hu Y Shi et al ldquoEvaluation of self-cleaning andphotocatalytic properties of modified g-C3N4 based PVDFmembranes driven by visible lightrdquo Journal of Colloid andInterface Science vol 541 pp 356ndash366 2019

[57] G Zhang J Zhang M Zhang and X Wang ldquoPolycon-densation of thiourea into carbon nitride semiconductors as


visible light photocatalystsrdquo Journal of Materials Chemistryvol 22 no 16 pp 8083ndash8091 2012

[58] Y Zhang J Liu X Chu S Liang and L Kong ldquoPreparationof g-C3N4-SnO2 composites for application as acetic acidsensorrdquo Journal of Alloys and Compounds vol 832p 153355 2020

[59] D Wang W Gu Y Zhang et al ldquoNovel C-rich carbonnitride for room temperature NO2 gas sensorsrdquo RSC Ad-vances vol 4 no 35 pp 18003ndash18006 2014

[60] X Li J Xiong X Gao et al ldquoRecent advances in 3D g-C3N4composite photocatalysts for photocatalytic water splittingdegradation of pollutants and CO2 reductionrdquo Journal ofAlloys and Compounds vol 802 pp 196ndash209 2019

[61] M Ismael Y Wu D H Taffa P Bottke and M WarkldquoGraphitic carbon nitride synthesized by simple pyrolysisrole of precursor in photocatalytic hydrogen productionrdquoNew Journal of Chemistry vol 43 no 18 pp 6909ndash69202019

[62] W Zhang Z Zhao F Dong and Y Zhang ldquoSolvent-assistedsynthesis of porous g-C 3 N 4 with efficient visible-lightphotocatalytic performance for NO removalrdquo ChineseJournal of Catalysis vol 38 no 2 pp 372ndash378 2017

[63] S Yao S Xue S Peng et al ldquoSynthesis of graphitic carbonnitride via direct polymerization using different precursorsand its application in lithium-sulfur batteriesrdquo AppliedPhysics A vol 124 no 11 pp 1ndash10 2018

[64] J Tian Z Chen J Jing C Feng M Sun and W Li ldquoEn-hanced photocatalytic performance of the MoS2g-C3N4heterojunction composite prepared by vacuum freeze dryingmethodrdquo Journal of Photochemistry and Photobiology AChemistry vol 390 p 112260 2020

[65] W Iqbal B Yang X Zhao et al ldquoFacile one-pot synthesis ofmesoporous g-C3N4 nanosheets with simultaneous iodinedoping and N-vacancies for efficient visible-light-driven H2evolution performancerdquo Catalysis Science and Technologyvol 10 no 2 pp 549ndash559 2020

[66] R M Yadav R Kumar A Aliyan et al ldquoFacile synthesis ofhighly fluorescent free-standing films comprising graphiticcarbon nitride (g-C3N4) nanolayersrdquo New Journal ofChemistry vol 44 no 6 pp 2644ndash2651 2020

[67] Y Wang F Wang Y Zuo X Zhang and L-F Cui ldquoSimplesynthesis of ordered cubic mesoporous graphitic carbonnitride by chemical vapor deposition method using mela-minerdquo Materials Letters vol 136 pp 271ndash273 2014

[68] Z Wei Z Zhi-Hong G Huai-Xi X Yi and F Xiang-JunldquoCorrosion resistance properties and preparation of α-C3N4thin filmsrdquo Wuhan University Journal of Natural Sciencesvol 4 no 2 pp 171ndash174 1999

[69] Z Xiong and L Cao ldquoNanostructure and optical propertytuning between the graphitic-like CNx and fullerene-likeβ-C3N4 via Fe doping and substrate temperaturerdquo Journal ofAlloys and Compounds vol 775 pp 100ndash108 2019

[70] L Cai X Wei H Feng et al ldquoAntimicrobial mechanisms ofg-C3N4 nanosheets against the oomycetes Phytophthoracapsici disrupting metabolism and membrane structuresand inhibiting vegetative and reproductive growthrdquo Journalof Hazardous Materials vol 417 p 126121 2021

[71] Y Bu Z Chen J Yu and W Li ldquoA novel application ofg-C3N4 thin film in photoelectrochemical anticorrosionrdquoElectrochimica Acta vol 88 pp 294ndash300 2013

[72] V Guigoz L Balan A Aboulaich R Schneider andT Gries ldquoHeterostructured thin LaFeO3g-C3N4 films forefficient photoelectrochemical hydrogen evolutionrdquo

International Journal of Hydrogen Energy vol 45 no 35pp 17468ndash17479 2020

[73] W Zhang L Zhou and H Deng ldquoAg modified g-C3N4composites with enhanced visible-light photocatalytic ac-tivity for diclofenac degradationrdquo Journal of MolecularCatalysis A Chemical vol 423 pp 270ndash276 2016

[74] H Miao G Zhang X Hu et al ldquoA novel strategy to prepare2D g-C3N4 nanosheets and their photoelectrochemicalpropertiesrdquo Journal of Alloys and Compounds vol 690pp 669ndash676 2017

[75] G Yang T Chen B Feng et al ldquoImproved corrosion re-sistance and biocompatibility of biodegradable magnesiumalloy by coating graphite carbon nitride (g-C3N4)rdquo Journalof Alloys and Compounds vol 770 pp 823ndash830 2019

[76] J Jiang L Ou-Yang L Zhu et al ldquoDependence of electronicstructure of g-C 3 N 4 on the layer number of its nanosheetsa study by Raman spectroscopy coupled with first-principlescalculationsrdquo Carbon vol 80 pp 213ndash221 2014

[77] J Kavil S Pilathottathil M S ayyil and P PeriyatldquoDevelopment of 2D nano heterostructures based ong-C3N4 and flower shaped MoS2 as electrode in symmetricsupercapacitor devicerdquo Nano-Structures amp Nano-Objectsvol 18 p 100317 2019

[78] N Duraisamy and K Kandiah ldquoBinder-free heterostructure(g-C3N4PPy) based thin film on semi-flexible nickel foamvia hybrid spray technique for energy storage applicationrdquoProgress in Natural Science Materials International vol 30no 3 pp 298ndash307 2020

[79] Q Gu Y Liao L Yin J Long X Wang and C XueldquoTemplate-free synthesis of porous graphitic carbon nitridemicrospheres for enhanced photocatalytic hydrogen gen-eration with high stabilityrdquo Applied Catalysis B Environ-mental vol 165 pp 503ndash510 2015

[80] S Panimalar R Uthrakumar E T Selvi et al ldquoStudies ofMnO2g-C3N4 hetrostructure efficient of visible lightphotocatalyst for pollutants degradation by sol-gel tech-niquerdquo Surfaces and Interfaces vol 20 p 100512 2020

[81] A Kotbi B Hartiti S Fadili A Ridah and P eveninldquoExperimental and theoretical studies of CuInS2 thin filmsfor photovoltaic applicationsrdquo Journal of Materials ScienceMaterials in Electronics vol 30 no 24 pp 21096ndash211052019

[82] G Deokar P Vancso R Arenal et al ldquoMoS2 -carbonnanotube hybrid material growth and gas sensingrdquo Ad-vanced Materials Interfaces vol 4 no 24 pp 1700801ndash1700810 2017

[83] N Joshi T Hayasaka Y Liu H Liu O N Oliveira andL Lin ldquoA review on chemiresistive room temperature gassensors based on metal oxide nanostructures graphene and2D transition metal dichalcogenidesrdquo Microchimica Actavol 185 no 4 2018

[84] Y-H Zhang Y-B Chen K-G Zhou et al ldquoImproving gassensing properties of graphene by introducing dopants anddefects a first-principles studyrdquo Nanotechnology vol 20no 18 p 185504 2009

[85] L Shao G Chen H Ye et al ldquoSulfur dioxide adsorbed ongraphene and heteroatom-doped graphene a first-principlesstudyrdquo e European Physical Journal B vol 86 no 2pp 2ndash6 2013

[86] Y-H Zhang L-F Han Y-H Xiao D-Z Jia Z-H Guo andF Li ldquoUnderstanding dopant and defect effect on H2Ssensing performances of graphene a first-principles studyrdquoComputational Materials Science vol 69 pp 222ndash228 2013


[87] C Ma X Shao and D Cao ldquoNitrogen-doped graphene as anexcellent candidate for selective gas sensingrdquo Science ChinaChemistry vol 57 no 6 pp 911ndash917 2014

[88] Z Rajesh Gao A T Charlie Johnson N PuriA Mulchandani and D K Aswal ldquoScalable chemical vapordeposited graphene field-effect transistors for biochemicalassayrdquo Applied Physics Reviews vol 8 no 1 p 011311 2021

[89] G Ko H-Y Kim J Ahn Y-M Park K-Y Lee and J KimldquoGraphene-based nitrogen dioxide gas sensorsrdquo CurrentApplied Physics vol 10 no 4 pp 1002ndash1004 2010

[90] G Chen T M Paronyan and A R Harutyunyan ldquoSub-pptgas detection with pristine graphenerdquo Applied Physics Let-ters vol 101 no 5 p 053119 2012

[91] W Kang and S Park ldquoH2S gas sensing properties of CuOnanotubesrdquo Applied Science and Convergence Technologyvol 23 no 6 pp 392ndash397 2014

[92] S Prezioso F Perrozzi L Giancaterini et al ldquoGrapheneoxide as a practical solution to high sensitivity gas sensingrdquoJournal of Physical Chemistry C vol 117 no 20pp 10683ndash10690 2013

[93] J Wang B Singh J-H Park et al ldquoDielectrophoresis ofgraphene oxide nanostructures for hydrogen gas sensor atroom temperaturerdquo Sensors and Actuators B Chemicalvol 194 pp 296ndash302 2014

[94] S Drewniak T Pustelny M Setkiewicz et al ldquoInvestigationsof SAW structures with oxide graphene layer to detection ofselected gasesrdquo Acta Physica Polonica A vol 124 no 3pp 402ndash405 2013

[95] T Pustelny S Drewniak M Setkiewicz et al ldquoe sensitivityof sensor structures with oxide graphene exposed to selectedgaseous atmospheresrdquo Bulletin of the Polish Academy ofSciences Technical Sciences vol 61 no 3 pp 705ndash710 2013

[96] S Some Y Xu Y Kim et al ldquoHighly sensitive and selectivegas sensor using hydrophilic and hydrophobic graphenesrdquoScientific Reports vol 3 no 1 pp 19ndash22 2013

[97] J Hassinen J Kauppila J Leiro et al ldquoLow-cost reducedgraphene oxide-based conductometric nitrogen dioxide-sensitive sensor on paperrdquo Analytical and BioanalyticalChemistry vol 405 no 11 pp 3611ndash3617 2013

[98] Y Pak S-M Kim H Jeong et al ldquoPalladium-decoratedhydrogen-gas sensors using periodically aligned graphenenanoribbonsrdquo ACS Applied Materials amp Interfaces vol 6no 15 pp 13293ndash13298 2014

[99] M G Chung D-H Kim D K Seo et al ldquoFlexible hydrogensensors using graphene with palladium nanoparticle deco-rationrdquo Sensors and Actuators B Chemical vol 169pp 387ndash392 2012

[100] A Kaniyoor R Imran Jafri T Arockiadoss andS Ramaprabhu ldquoNanostructured Pt decorated graphene andmulti walled carbon nanotube based room temperaturehydrogen gas sensorrdquo Nanoscale vol 1 no 3 pp 382ndash3862009

[101] W Li X Geng Y Guo et al ldquoReduced graphene oxideelectrically contacted graphene sensor for highly sensitivenitric oxide detectionrdquo ACS Nano vol 5 no 9pp 6955ndash6961 2011

[102] A Gutes B Hsia A Sussman et al ldquoGraphene decorationwith metal nanoparticles towards easy integration forsensing applicationsrdquo Nanoscale vol 4 no 2 pp 438ndash4402012

[103] P Karthik P Gowthaman M Venkatachalam andM Saroja ldquoDesign and fabrication of g-C3N4 nanosheetsdecorated TiO2 hybrid sensor films for improved

performance towards CO2 gasrdquo Inorganic Chemistry Com-munications vol 119 p 108060 2020

[104] L Zhu Y Jia G Gai X Ji J Luo and Y Yao ldquoAmbipolarityof large-area Pt-functionalized graphene observed in H2sensingrdquo Sensors and Actuators B Chemical vol 190pp 134ndash140 2014

[105] J Yu M Shafiei J Ou K Shin andWWlodarski ldquoA study ofhydrogen gas sensing performance of PtGrapheneGaN de-vicesrdquo 2011 IEEE SENSORS Proceedings pp 1017ndash1020 2011

[106] K Anand O Singh M P Singh J Kaur and R C SinghldquoHydrogen sensor based on grapheneZnO nanocompositerdquoSensors and Actuators B Chemical vol 195 pp 409ndash4152014

[107] A Esfandiar A Irajizad O Akhavan S Ghasemi andM R Gholami ldquoPd-WO3reduced graphene oxide hierar-chical nanostructures as efficient hydrogen gas sensorsrdquoInternational Journal of Hydrogen Energy vol 39 no 15pp 8169ndash8179 2014

[108] M Shafiei R Arsat J Yu and W Wlodarski ldquoPtgraphenenano-sheet based hydrogen gas sensorrdquo IEEE vol 2009pp 295ndash298 2009

[109] X Liu J Cui J Sun and X Zhang ldquo3D graphene aerogel-supported SnO2 nanoparticles for efficient detection ofNO2rdquo RSC Advances vol 4 no 43 pp 22601ndash22605 2014

[110] S Srivastava K Jain V N Singh et al ldquoFaster response ofNO2sensing in graphene-WO3nanocompositesrdquo Nano-technology vol 23 no 20 p 205501 2012

[111] H Y Jeong D-S Lee H K Choi et al ldquoFlexible room-temperature NO2 gas sensors based on carbon nanotubesreduced graphene hybrid filmsrdquo Applied Physics Lettersvol 96 no 21 pp 213105ndash213197 2010

[112] L T Hoa H N Tien V H Luan J S Chung and S H HurldquoFabrication of a novel 2D-graphene2D-NiO nanosheet-based hybrid nanostructure and its use in highly sensitiveNO2 sensorsrdquo Sensors and Actuators B Chemical vol 185pp 701ndash705 2013

[113] S Liu B Yu H Zhang T Fei and T Zhang ldquoEnhancingNO2 gas sensing performances at room temperature basedon reduced graphene oxide-ZnO nanoparticles hybridsrdquoSensors and Actuators B Chemical vol 202 pp 272ndash2782014

[114] N Chen X Li X Wang et al ldquoEnhanced room temperaturesensing of Co3O4-intercalated reduced graphene oxidebased gas sensorsrdquo Sensors and Actuators B Chemicalvol 188 pp 902ndash908 2013

[115] H Zhang J Feng T Fei S Liu and T Zhang ldquoSnO2nanoparticles-reduced graphene oxide nanocomposites forNO2 sensing at low operating temperaturerdquo Sensors andActuators B Chemical vol 190 pp 472ndash478 2014

[116] X An J C Yu Y Wang Y Hu X Yu and G Zhang ldquoWO3nanorodsgraphene nanocomposites for high-efficiencyvisible-light-driven photocatalysis and NO2 gas sensingrdquoJournal of Materials Chemistry vol 22 no 17 pp 8525ndash8531 2012

[117] K R Nemade and S A Waghuley ldquoRole of defects con-centration on optical and carbon dioxide gas sensingproperties of Sb2O3graphene compositesrdquo Optical Mate-rials vol 36 no 3 pp 712ndash716 2014

[118] K R Nemade and S A Waghuley ldquoHighly responsivecarbon dioxide sensing by grapheneAl2O3 quantum dotscomposites at low operable temperaturerdquo Indian Journal ofPhysics vol 88 no 6 pp 577ndash583 2014


[119] K R Nemade and S A Waghuley ldquoLPG sensing applicationof grapheneBi2O3 quantum dots compositesrdquo Solid StateSciences vol 22 pp 27ndash32 2013

[120] X Tang M Debliquy D Lahem Y Yan and J-P Raskin ldquoAreview on functionalized graphene sensors for detection ofammoniardquo Sensors vol 21 no 4 pp 1443ndash1528 2021

[121] B Electrochemical and A Overview An Overview[122] X Huang N Hu R Gao et al ldquoReduced graphene oxide-

polyaniline hybrid preparation characterization and itsapplications for ammonia gas sensingrdquo Journal of MaterialsChemistry vol 22 no 42 pp 22488ndash22495 2012

[123] D Sahni A Jea J AMata et al ldquoBiocompatibility of pristinegraphene for neuronal interfacerdquo Journal of NeurosurgeryPediatrics vol 11 no 5 pp 575ndash583 2013

[124] A I Cooper and M J Bojdys ldquoCarbon nitride vs graphene -now in 2Drdquo Materials Today vol 17 no 10 pp 468-4692014

[125] X Chu J Liu S Liang L Bai Y Dong and M EpifanildquoFacile preparation of g-C3N4-WO3 composite gas sensingmaterials with enhanced gas sensing selectivity to acetonerdquoJournal of Sensors vol 2019 Article ID 6074046 8 pages2019

[126] R Zhang Y Wang Z Zhang and J Cao ldquoHighly sensitiveacetone gas sensor based on g-C3N4 decorated MgFe2O4porous microspheres compositesrdquo Sensors vol 18 no 7p 2211 2018

[127] N T Hang S Zhang and W Yang ldquoEfficient exfoliation ofg-C3N4 and NO2 sensing behavior of grapheneg-C3N4nanocompositerdquo Sensors and Actuators B Chemicalvol 248 pp 940ndash948 2017

[128] H Wang J Bai M Dai et al ldquoVisible light activated ex-cellent NO2 sensing based on 2D2D ZnOg-C3N4 heter-ojunction compositesrdquo Sensors and Actuators B Chemicalvol 304 p 127287 2020

[129] S Yang C Jiang and S-h Wei ldquoGas sensing in 2D ma-terialsrdquoApplied Physics Reviews vol 4 no 2 p 021304 2017

[130] J P Perdew K Burke and M Ernzerhof ldquoGeneralizedgradient approximation made simplerdquo Physical ReviewLetters vol 77 no 18 pp 3865ndash3868 1996

[131] P Giannozzi S Baroni N Bonini et al ldquoQuantum espressoa modular and open-source software project for quantumsimulations of materialsrdquo Journal of Physics CondensedMatter vol 21 no 39 p 395502 2009

[132] H W Zuo C H Lu Y R Ren Y Li Y F Zhang andW K Chen ldquoPt4 clusters supported on monolayer graphiticcarbon nitride sheets for oxygen adsorption a first-principlesstudyrdquo Wu Li Hua Xue Xue BaoActa Physico - ChimicaSinica vol 32 pp 1183ndash1190 2016

[133] H-Z Wu L-M Liu and S-J Zhao ldquoe effect of water onthe structural electronic and photocatalytic properties ofgraphitic carbon nitriderdquo Physical Chemistry ChemicalPhysics vol 16 no 7 pp 3299ndash3304 2014

[134] B Zhu L Zhang D Xu B Cheng and J Yu ldquoAdsorptioninvestigation of CO2 on g-C3N4 surface by DFTcalculationrdquoJournal of CO2 Utilization vol 21 pp 327ndash335 2017

[135] Y Ji H Dong H Lin L Zhang T Hou and Y LildquoHeptazine-based graphitic carbon nitride as an effectivehydrogen purification membranerdquo RSC Advances vol 6no 57 pp 52377ndash52383 2016

[136] H Basharnavaz A Habibi-Yangjeh and S H Kamali ldquoAfirst-principle investigation of NO2 adsorption behavior onCo Rh and Ir-embedded graphitic carbon nitride lookingfor highly sensitive gas sensorrdquo Physics Letters A vol 384no 2 p 126057 2020

[137] K Bai Z Cui E Li et al ldquoAdsorption of gas molecules ongroup III atoms adsorbed g-C3N4 a first-principles studyrdquoVacuum vol 175 p 109293 2020

[138] I T Jolliffe and J Cadima ldquoPrincipal component analysis areview and recent developmentsrdquo Philosophical Transactionsof the Royal Society A Mathematical Physical amp EngineeringSciences vol 374 no 2065 p 20150202 2016

[139] R Haney N Siddiqui J Andress J Fergus R Overfelt andB Prorok ldquoPrincipal component analysis (PCA) applicationto FTIR spectroscopy data of COCO2 contaminants of airrdquo41st International Conference on Environmental Systemsvol 2011 pp 1ndash12 2011


Gas sensing is one of the important applications of Grand associated 2D nanomaterials owing mainly to severalinteresting properties such as (i) large surface area (for Gr2630m2g) (ii) good conductivity (iii) high gas sensitivity(iv) and the possibility of tailored surface functionalizationfor a specific gas absorption In Gr the gas absorption is aresult of a pull electron effect [19 20] In fact the adsorbedmolecules change the Fermi level of Gr and hence itsconductivity due to hybridization and coupling on itssurface ey act as electron donors in case their valenceband energy is higher than the Fermi level of Gr and aselectron acceptors in the opposite case when the valenceband energy is lower than Fermi level of Gr [21 22]

Nowadays highly performing portable sensors havebecome a key necessity for all technological advances Whilemetal-oxide-semiconductor based gas sensors are farcommonly used their performances remain very limited dueto their short life poor selectivity temperature instabilitiesand high sensitivity to environmentrsquos perturbations e useof nanostructured materials with higher gas-sensing capa-bilities has therefore become inevitable [5]

Besides the development of g-CN based gas sensorscompared to those based on Gr or transition metal disulfidenanosheets is becoming more attractive [23] Many ap-proaches have been adopted so far for the development ofthis material in view of its incorporation in gas-sensingapplications In this sense researchers attempted to combineg-CN with other materials to improve its performances [24]For instance the use of porous g-CN in nanostructuredesigns as gas sensors appeared to greatly improve theirselectivity and their sensitivity in ambient conditionsSimilarly hybridization of g-CN with other materials wasfound as a promising route for further enhancement indetection performances [23] e resulting heterostructuresmade of metal oxide nanoparticles attached to the surface of2D materials were found to exhibit higher detectionproperties [14] For instance g-CNMOX heterostructuresrevealed much superior detection performances comparedto a pure MOX sensor (MnO2 ZnO and TiO2) Howeversome drawbacks remain which prevent the direct appli-cation of these sensors such as the high working temper-ature and the slow sensing response [25] eseachievements are attributed on one hand to the increasedsurface area obtained by the combination of 2D g-CN withthe MOx leading to an increased number of gas-materialinteraction sites [20] and to the low operating temperaturewhile improving the gas sensitivity and selectivity on theother hand [23] Despite these interesting gas-sensingperformances g-CN presents some limitations when com-pared to Gr such as its moderate band gap that requires ahigh excitation voltage and its fast electron-hole pairs re-combination leading to low responsivity In addition g-CNadsorbs most of gases and liquids while Gr is known to beimpermeable to most of fluids which reduces the operatingtemperature of graphene compared to g-CN

In the following we intend to provide a detailed over-view of both CNM in terms of fabrication and character-ization with special emphasis on their gas-sensingperformances en theoretical calculations using density

functional theory (DFT) will be carried out to determine theadsorption mechanisms of selected gas molecules namelyCO2 NO2 and HF and to examine the g-CN sensingperformances to be compared to other graphitic nano-materials such as Gr or reduced graphene oxide (r-GrO)

2 Synthesis of Graphene

Several methods are most commonly used for the fabricationof Gr layers including (i) micromechanical exfoliation (ii)reduction of graphene oxide (iii) chemical vapor deposition(CVD) [5 26] or plasma-enhanced chemical vapor depo-sition (PECVD) and (iv) epitaxial growth on insulatingmaterials e choice of a fabrication route is mainly de-pendent upon the material quality and overall productioncost required for given application

e structural and vibrational properties of Gr areusually examined by Fourier-transform infrared spectros-copy (FTIR) X-ray diffraction (XRD) and Raman spec-troscopy respectively and given in Figure 1 [27]

Transmission spectra (Figure 1(a)) show an obvioussimilarity for all three materials mainly due to the C-C bondpeaks present in the 2325ndash1981 cmminus1 range e XRD dia-gram (Figure 1(b)) shows a narrow diffraction peak at 265deg(2θ) corresponding to the characteristic (002) plane ofgraphite is peak is broadened and downshifted in gra-phene towards 239deg representing an increased spacing ofC-C layer in sp2 bonding e Raman spectra (Figure 1(c))show a characteristic vibration peak at 1601 cmminus1 (G-band)related to the original graphitic structure for all three ma-terials However a wider peak at 1352 cmminus1 (D-band) ap-pears for graphite oxide and Gr sheets related to the presenceof defects in these structures e ratio of these bandsrsquo in-tensities (IDIG) is a good indicator of the graphitizationrsquosquality in these layers

21 Mechanical Exfoliation Mechanical exfoliation is thefirst process through which Gr was isolated by Novoselovet al [28] It is a top-down approach in which Gr layers areexfoliated from bulk graphite using adhesive tape eprocedure involves repeated pealing of Gr from flakes ofgraphite e tape containing Gr is finally placed on an SiSiO2 surface and gently pressed to get Gr attached to the Sisubstrate is method allows investigating the basicproperties of Gr For in-depth investigations of Gr prop-erties for technical applications scalable methods are beingdeveloped [29]

22 Chemical Vapor Deposition Chemical vapor deposition(CVD) is the most commonmethod used to produce Gr on asubstrate with commendable quality and tailored dimen-sions Growth mechanism and number of layers grown onthe substrate depend on the catalyst metal substrate usedsuch as Cu [26] Ni [30 31] Cu-Ni alloy [1] and Co Figure 2shows a schematic of CVD setup used to grow carbonnanomaterials

For Gr grown on Ni substrate the Ni foil is annealed inhydrogen atmosphere and then carbon source gas such as




Wavenumber (cm-1)

T

rans

mitt

ance

4000 3500 3000 2500 2000 1500 1000

Graphite Oxide

Graphene Sheets

Graphite

(a)

2θ (degree)

Inte

nsity

(au

)

10 20 30 40 50 60 70 805 15 25 35 45 55 65 75

Graphite Oxide

Graphene Sheets

Graphite

(002)

(001)

(002)

(b)

Wavenumber (cm-1)

Inte

nsity

(au

)

1000 1250 1500 1750 2000

Graphite Oxide

Graphene Sheets

Graphite

D band G band

(c)


Heating Coil

Heating Coil


Sample

NitrogenAccetylene

Alumina Crucible










3 Synthesis of g-CN











Advantages













Power(KW)

RF power(MHz) Ref



Brodie




4 cycles



Graphene oxide

Staudenmaier





Graphene oxide


Hummer

Graphite + NaNO3




Graphene oxide











Spin-coating



[49 50]





[49 52]


Melamine(C3H6N6)


iourea(CH4N2S)

Cyanamide (CH2N2)


Urea(CH4N2O)

500-

580deg

C

520-

550deg

C

460-

650deg

C

550deg

C

550deg

C























Depositiontime

Power(W)

RF power(MHz) Ref



Wavenumber (cm-1)

Tran

smitt

ance

500 1000 1500 2000 2500 3000 3500 4000

3124

161214

57

1250

1320

1419

889

802

(a)

Wavenumber (cm-1)

Tran

smitt

ance

4000 3000 2000 1000

131776

123942

80951

(b)


g-C3N4

C 1s

N 1s



Inte

nsity

(au

)

Inte

nsity

(au

)

Inte

nsity

(au

)(d)(c)

(a)

N 1sC 1s 3983 eV

3999 eV4006 eV

2846 eV

2860 eV

2881 eV

0 100 200 300 400 500

280 282 284 286 288 290 292 294 394 396 398 400 402 404 406 408








(1)







Ram

an In

tens

ityc

ps

Wavenumber (cm-1)2000 1600 1200 800 400

2400

2000

1600

1200

800

400

0

Bulk

1 layer

1616 1555

1481

1234

751

705

543

479

1250

(a)

Ram

an In

tens

itya

u

Wavenumber (cm-1)1600 1400 600 400

Bulk

1 layer

1602 15

6915

10

1224

726

685

616

555

1232

(b)


10 20 30 40 50 60 70 80

(100)

(002)

g-CN NSs

g-CN bulk

Inte

nsity

(au

)

2θ (deg)











n-type

Resistance

Time

Reducinggas

e-

n-type

Resistance

Time

Oxidizinggas

e-











[86 87]

NO


NO2


NH3


CO



NH3

CO

H2O

NO2

I II III IV

0 500 1000t (s)

4

2

0

-2

-4

Δρρ

()




Time (s)1000 1500 20000 500

240

235

230

225

220

215

Curr

ent (

mA

)













[97]

H2


NO2


CO2



Tabl

e10

eperformancesof

nano

compo

sites

basedon

g-CN

forgassensor

applications

Material

Metho

dRe

spon

seG

asRe

spon

se

recovery

time

(s)

ppm

level

Operatio

nT

(deg C)

Detectio

nlim

itCom

ment

Ref

TiO2

Spraypyrolysis

techniqu

e

RaRg

25

H2S

sim5260

1500

450

U

eim

provem


ofthe

sensor

isdu

eto

theintrod

uctio

nof

10

oftheg-CN

nano

sheets

[103]

RaRg

22

CO2

4555

g-CN

(10wt

)TiO2

RaRg

67

H2S

sim3052

RaRg

88

CO2

3527

SnO2

Hydrothermal

metho

d

RaRg

134

acetic

acid

94160

1000

230degC

UIm

provem

ento

fthe


andthe

sensitivity

byintrod

uctio

nof

10wt

ofg-CNin

SnO2

[58]

10wt

ofg-

CN-SnO

2

RaRg

877

CH

3COOH

U185degC

01pp

m

g-CN-SnO


dVgVa

83

aceton

e78

500

380degC

67pp

bA

significantimprovem

entin

sensor

performance

bycalciningmelam

ineSn

O2po

wderfor3ho

urs

[14]

5Pd

SnO

25

g-CN

Hydrothermal

metho

d(Rg-Ra

)Ra

905CO

1013

1000

125degC

75pp

mg-CN-5

nano

sheets

with

SnO2nano

particles

effectiv

elyim

proved

therespon

seof

thegassensors

towards

CO

[25]

2wt

g-CN-

WO3

Hydrothermal

metho

dRa

Rg

582

aceton

e5329

1000

310degC

05pp

mA

gassensor

basedon

2g-CN

compo

siteshow

sa

high

errespon

seto

aceton

ethan

pure

WO3

[125]

10wt

g-CN

MgFe 2O4

One-stepsolvotherm

almetho

dRa

Rg

275

aceton

e4929

500

320degC

30pp

b

eintrod

uctio

nof

10

ofg-CN

nano

sheets

inMgFe 2O4im

proves


[126]

Grg-CN

Dropcoatingmetho

d(Rg-Ra

)Ra

42N

O2

U5

100degC

600pp

bGraph

iticcarbon

nitridenano

sheetswith

15of

g-CN

exhibith


comparedto

bulk

g-CN

andpu

regraphene

[127]

10wt

g-CN

ZnO

Synthesiz

edviaultrason


calcinationprocess

RgRa

448

NO2

142190

7U

38pp

mDetectio

nperformance

isactiv

ated

byLE

Dlight

sources460nm

LED

(127Wm

2 )[128]

ldquoUrdquoun

availablecitatio

nitisno

tcitedin

thestud


ndatmosph

ericairrespectiv

elyRa

Rgelectricresis

tances

intheatmosph

ericaira


ely


Resis

tanc

e (M

Ω)

Time (s)

90

80

70

60

50

40

30

20

10

0100 200 300 400

50 RH70 RH90 RH

(a)

Resp

onse

(Ra

Rg o

r Rg

Ra)

50

40

30

20

10

0

NO2


nol

Ace

tone


(b)




g-CN-NO2

25 Aring 313 Aring

g-CN-CO2

25 Aring 324 Aring

g-CN-HF

25 Aring 129 Aring

r-GrO-HF

25 Aring 326 Aring

Gr-HF

25 Aring 370 Aring





















7 Conclusion


Data Availability




Acknowledgments


References

























































































































































Wavenumber (cm-1)

T

rans

mitt

ance

4000 3500 3000 2500 2000 1500 1000

Graphite Oxide

Graphene Sheets

Graphite

(a)

2θ (degree)

Inte

nsity

(au

)

10 20 30 40 50 60 70 805 15 25 35 45 55 65 75

Graphite Oxide

Graphene Sheets

Graphite

(002)

(001)

(002)

(b)

Wavenumber (cm-1)

Inte

nsity

(au

)

1000 1250 1500 1750 2000

Graphite Oxide

Graphene Sheets

Graphite

D band G band

(c)


Heating Coil

Heating Coil


Sample

NitrogenAccetylene

Alumina Crucible










3 Synthesis of g-CN











Advantages













Power(KW)

RF power(MHz) Ref



Brodie




4 cycles



Graphene oxide

Staudenmaier





Graphene oxide


Hummer

Graphite + NaNO3




Graphene oxide











Spin-coating



[49 50]





[49 52]


Melamine(C3H6N6)


iourea(CH4N2S)

Cyanamide (CH2N2)


Urea(CH4N2O)

500-

580deg

C

520-

550deg

C

460-

650deg

C

550deg

C

550deg

C























Depositiontime

Power(W)

RF power(MHz) Ref



Wavenumber (cm-1)

Tran

smitt

ance

500 1000 1500 2000 2500 3000 3500 4000

3124

161214

57

1250

1320

1419

889

802

(a)

Wavenumber (cm-1)

Tran

smitt

ance

4000 3000 2000 1000

131776

123942

80951

(b)


g-C3N4

C 1s

N 1s



Inte

nsity

(au

)

Inte

nsity

(au

)

Inte

nsity

(au

)(d)(c)

(a)

N 1sC 1s 3983 eV

3999 eV4006 eV

2846 eV

2860 eV

2881 eV

0 100 200 300 400 500

280 282 284 286 288 290 292 294 394 396 398 400 402 404 406 408








(1)







Ram

an In

tens

ityc

ps

Wavenumber (cm-1)2000 1600 1200 800 400

2400

2000

1600

1200

800

400

0

Bulk

1 layer

1616 1555

1481

1234

751

705

543

479

1250

(a)

Ram

an In

tens

itya

u

Wavenumber (cm-1)1600 1400 600 400

Bulk

1 layer

1602 15

6915

10

1224

726

685

616

555

1232

(b)


10 20 30 40 50 60 70 80

(100)

(002)

g-CN NSs

g-CN bulk

Inte

nsity

(au

)

2θ (deg)











n-type

Resistance

Time

Reducinggas

e-

n-type

Resistance

Time

Oxidizinggas

e-











[86 87]

NO


NO2


NH3


CO



NH3

CO

H2O

NO2

I II III IV

0 500 1000t (s)

4

2

0

-2

-4

Δρρ

()




Time (s)1000 1500 20000 500

240

235

230

225

220

215

Curr

ent (

mA

)













[97]

H2


NO2


CO2



Tabl

e10

eperformancesof

nano

compo

sites

basedon

g-CN

forgassensor

applications

Material

Metho

dRe

spon

seG

asRe

spon

se

recovery

time

(s)

ppm

level

Operatio

nT

(deg C)

Detectio

nlim

itCom

ment

Ref

TiO2

Spraypyrolysis

techniqu

e

RaRg

25

H2S

sim5260

1500

450

U

eim

provem


ofthe

sensor

isdu

eto

theintrod

uctio

nof

10

oftheg-CN

nano

sheets

[103]

RaRg

22

CO2

4555

g-CN

(10wt

)TiO2

RaRg

67

H2S

sim3052

RaRg

88

CO2

3527

SnO2

Hydrothermal

metho

d

RaRg

134

acetic

acid

94160

1000

230degC

UIm

provem

ento

fthe


andthe

sensitivity

byintrod

uctio

nof

10wt

ofg-CNin

SnO2

[58]

10wt

ofg-

CN-SnO

2

RaRg

877

CH

3COOH

U185degC

01pp

m

g-CN-SnO


dVgVa

83

aceton

e78

500

380degC

67pp

bA

significantimprovem

entin

sensor

performance

bycalciningmelam

ineSn

O2po

wderfor3ho

urs

[14]

5Pd

SnO

25

g-CN

Hydrothermal

metho

d(Rg-Ra

)Ra

905CO

1013

1000

125degC

75pp

mg-CN-5

nano

sheets

with

SnO2nano

particles

effectiv

elyim

proved

therespon

seof

thegassensors

towards

CO

[25]

2wt

g-CN-

WO3

Hydrothermal

metho

dRa

Rg

582

aceton

e5329

1000

310degC

05pp

mA

gassensor

basedon

2g-CN

compo

siteshow

sa

high

errespon

seto

aceton

ethan

pure

WO3

[125]

10wt

g-CN

MgFe 2O4

One-stepsolvotherm

almetho

dRa

Rg

275

aceton

e4929

500

320degC

30pp

b

eintrod

uctio

nof

10

ofg-CN

nano

sheets

inMgFe 2O4im

proves


[126]

Grg-CN

Dropcoatingmetho

d(Rg-Ra

)Ra

42N

O2

U5

100degC

600pp

bGraph

iticcarbon

nitridenano

sheetswith

15of

g-CN

exhibith


comparedto

bulk

g-CN

andpu

regraphene

[127]

10wt

g-CN

ZnO

Synthesiz

edviaultrason


calcinationprocess

RgRa

448

NO2

142190

7U

38pp

mDetectio

nperformance

isactiv

ated

byLE

Dlight

sources460nm

LED

(127Wm

2 )[128]

ldquoUrdquoun

availablecitatio

nitisno

tcitedin

thestud


ndatmosph

ericairrespectiv

elyRa

Rgelectricresis

tances

intheatmosph

ericaira


ely


Resis

tanc

e (M

Ω)

Time (s)

90

80

70

60

50

40

30

20

10

0100 200 300 400

50 RH70 RH90 RH

(a)

Resp

onse

(Ra

Rg o

r Rg

Ra)

50

40

30

20

10

0

NO2


nol

Ace

tone


(b)




g-CN-NO2

25 Aring 313 Aring

g-CN-CO2

25 Aring 324 Aring

g-CN-HF

25 Aring 129 Aring

r-GrO-HF

25 Aring 326 Aring

Gr-HF

25 Aring 370 Aring





















7 Conclusion


Data Availability




Acknowledgments


References






























































































































































3 Synthesis of g-CN











Advantages













Power(KW)

RF power(MHz) Ref



Brodie




4 cycles



Graphene oxide

Staudenmaier





Graphene oxide


Hummer

Graphite + NaNO3




Graphene oxide











Spin-coating



[49 50]





[49 52]


Melamine(C3H6N6)


iourea(CH4N2S)

Cyanamide (CH2N2)


Urea(CH4N2O)

500-

580deg

C

520-

550deg

C

460-

650deg

C

550deg

C

550deg

C























Depositiontime

Power(W)

RF power(MHz) Ref



Wavenumber (cm-1)

Tran

smitt

ance

500 1000 1500 2000 2500 3000 3500 4000

3124

161214

57

1250

1320

1419

889

802

(a)

Wavenumber (cm-1)

Tran

smitt

ance

4000 3000 2000 1000

131776

123942

80951

(b)


g-C3N4

C 1s

N 1s



Inte

nsity

(au

)

Inte

nsity

(au

)

Inte

nsity

(au

)(d)(c)

(a)

N 1sC 1s 3983 eV

3999 eV4006 eV

2846 eV

2860 eV

2881 eV

0 100 200 300 400 500

280 282 284 286 288 290 292 294 394 396 398 400 402 404 406 408








(1)







Ram

an In

tens

ityc

ps

Wavenumber (cm-1)2000 1600 1200 800 400

2400

2000

1600

1200

800

400

0

Bulk

1 layer

1616 1555

1481

1234

751

705

543

479

1250

(a)

Ram

an In

tens

itya

u

Wavenumber (cm-1)1600 1400 600 400

Bulk

1 layer

1602 15

6915

10

1224

726

685

616

555

1232

(b)


10 20 30 40 50 60 70 80

(100)

(002)

g-CN NSs

g-CN bulk

Inte

nsity

(au

)

2θ (deg)











n-type

Resistance

Time

Reducinggas

e-

n-type

Resistance

Time

Oxidizinggas

e-











[86 87]

NO


NO2


NH3


CO



NH3

CO

H2O

NO2

I II III IV

0 500 1000t (s)

4

2

0

-2

-4

Δρρ

()




Time (s)1000 1500 20000 500

240

235

230

225

220

215

Curr

ent (

mA

)













[97]

H2


NO2


CO2



Tabl

e10

eperformancesof

nano

compo

sites

basedon

g-CN

forgassensor

applications

Material

Metho

dRe

spon

seG

asRe

spon

se

recovery

time

(s)

ppm

level

Operatio

nT

(deg C)

Detectio

nlim

itCom

ment

Ref

TiO2

Spraypyrolysis

techniqu

e

RaRg

25

H2S

sim5260

1500

450

U

eim

provem


ofthe

sensor

isdu

eto

theintrod

uctio

nof

10

oftheg-CN

nano

sheets

[103]

RaRg

22

CO2

4555

g-CN

(10wt

)TiO2

RaRg

67

H2S

sim3052

RaRg

88

CO2

3527

SnO2

Hydrothermal

metho

d

RaRg

134

acetic

acid

94160

1000

230degC

UIm

provem

ento

fthe


andthe

sensitivity

byintrod

uctio

nof

10wt

ofg-CNin

SnO2

[58]

10wt

ofg-

CN-SnO

2

RaRg

877

CH

3COOH

U185degC

01pp

m

g-CN-SnO


dVgVa

83

aceton

e78

500

380degC

67pp

bA

significantimprovem

entin

sensor

performance

bycalciningmelam

ineSn

O2po

wderfor3ho

urs

[14]

5Pd

SnO

25

g-CN

Hydrothermal

metho

d(Rg-Ra

)Ra

905CO

1013

1000

125degC

75pp

mg-CN-5

nano

sheets

with

SnO2nano

particles

effectiv

elyim

proved

therespon

seof

thegassensors

towards

CO

[25]

2wt

g-CN-

WO3

Hydrothermal

metho

dRa

Rg

582

aceton

e5329

1000

310degC

05pp

mA

gassensor

basedon

2g-CN

compo

siteshow

sa

high

errespon

seto

aceton

ethan

pure

WO3

[125]

10wt

g-CN

MgFe 2O4

One-stepsolvotherm

almetho

dRa

Rg

275

aceton

e4929

500

320degC

30pp

b

eintrod

uctio

nof

10

ofg-CN

nano

sheets

inMgFe 2O4im

proves


[126]

Grg-CN

Dropcoatingmetho

d(Rg-Ra

)Ra

42N

O2

U5

100degC

600pp

bGraph

iticcarbon

nitridenano

sheetswith

15of

g-CN

exhibith


comparedto

bulk

g-CN

andpu

regraphene

[127]

10wt

g-CN

ZnO

Synthesiz

edviaultrason


calcinationprocess

RgRa

448

NO2

142190

7U

38pp

mDetectio

nperformance

isactiv

ated

byLE

Dlight

sources460nm

LED

(127Wm

2 )[128]

ldquoUrdquoun

availablecitatio

nitisno

tcitedin

thestud


ndatmosph

ericairrespectiv

elyRa

Rgelectricresis

tances

intheatmosph

ericaira


ely


Resis

tanc

e (M

Ω)

Time (s)

90

80

70

60

50

40

30

20

10

0100 200 300 400

50 RH70 RH90 RH

(a)

Resp

onse

(Ra

Rg o

r Rg

Ra)

50

40

30

20

10

0

NO2


nol

Ace

tone


(b)




g-CN-NO2

25 Aring 313 Aring

g-CN-CO2

25 Aring 324 Aring

g-CN-HF

25 Aring 129 Aring

r-GrO-HF

25 Aring 326 Aring

Gr-HF

25 Aring 370 Aring





















7 Conclusion


Data Availability




Acknowledgments


References



























































































































































Advantages













Power(KW)

RF power(MHz) Ref



Brodie




4 cycles



Graphene oxide

Staudenmaier





Graphene oxide


Hummer

Graphite + NaNO3




Graphene oxide











Spin-coating



[49 50]





[49 52]


Melamine(C3H6N6)


iourea(CH4N2S)

Cyanamide (CH2N2)


Urea(CH4N2O)

500-

580deg

C

520-

550deg

C

460-

650deg

C

550deg

C

550deg

C























Depositiontime

Power(W)

RF power(MHz) Ref



Wavenumber (cm-1)

Tran

smitt

ance

500 1000 1500 2000 2500 3000 3500 4000

3124

161214

57

1250

1320

1419

889

802

(a)

Wavenumber (cm-1)

Tran

smitt

ance

4000 3000 2000 1000

131776

123942

80951

(b)


g-C3N4

C 1s

N 1s



Inte

nsity

(au

)

Inte

nsity

(au

)

Inte

nsity

(au

)(d)(c)

(a)

N 1sC 1s 3983 eV

3999 eV4006 eV

2846 eV

2860 eV

2881 eV

0 100 200 300 400 500

280 282 284 286 288 290 292 294 394 396 398 400 402 404 406 408








(1)







Ram

an In

tens

ityc

ps

Wavenumber (cm-1)2000 1600 1200 800 400

2400

2000

1600

1200

800

400

0

Bulk

1 layer

1616 1555

1481

1234

751

705

543

479

1250

(a)

Ram

an In

tens

itya

u

Wavenumber (cm-1)1600 1400 600 400

Bulk

1 layer

1602 15

6915

10

1224

726

685

616

555

1232

(b)


10 20 30 40 50 60 70 80

(100)

(002)

g-CN NSs

g-CN bulk

Inte

nsity

(au

)

2θ (deg)











n-type

Resistance

Time

Reducinggas

e-

n-type

Resistance

Time

Oxidizinggas

e-











[86 87]

NO


NO2


NH3


CO



NH3

CO

H2O

NO2

I II III IV

0 500 1000t (s)

4

2

0

-2

-4

Δρρ

()




Time (s)1000 1500 20000 500

240

235

230

225

220

215

Curr

ent (

mA

)













[97]

H2


NO2


CO2



Tabl

e10

eperformancesof

nano

compo

sites

basedon

g-CN

forgassensor

applications

Material

Metho

dRe

spon

seG

asRe

spon

se

recovery

time

(s)

ppm

level

Operatio

nT

(deg C)

Detectio

nlim

itCom

ment

Ref

TiO2

Spraypyrolysis

techniqu

e

RaRg

25

H2S

sim5260

1500

450

U

eim

provem


ofthe

sensor

isdu

eto

theintrod

uctio

nof

10

oftheg-CN

nano

sheets

[103]

RaRg

22

CO2

4555

g-CN

(10wt

)TiO2

RaRg

67

H2S

sim3052

RaRg

88

CO2

3527

SnO2

Hydrothermal

metho

d

RaRg

134

acetic

acid

94160

1000

230degC

UIm

provem

ento

fthe


andthe

sensitivity

byintrod

uctio

nof

10wt

ofg-CNin

SnO2

[58]

10wt

ofg-

CN-SnO

2

RaRg

877

CH

3COOH

U185degC

01pp

m

g-CN-SnO


dVgVa

83

aceton

e78

500

380degC

67pp

bA

significantimprovem

entin

sensor

performance

bycalciningmelam

ineSn

O2po

wderfor3ho

urs

[14]

5Pd

SnO

25

g-CN

Hydrothermal

metho

d(Rg-Ra

)Ra

905CO

1013

1000

125degC

75pp

mg-CN-5

nano

sheets

with

SnO2nano

particles

effectiv

elyim

proved

therespon

seof

thegassensors

towards

CO

[25]

2wt

g-CN-

WO3

Hydrothermal

metho

dRa

Rg

582

aceton

e5329

1000

310degC

05pp

mA

gassensor

basedon

2g-CN

compo

siteshow

sa

high

errespon

seto

aceton

ethan

pure

WO3

[125]

10wt

g-CN

MgFe 2O4

One-stepsolvotherm

almetho

dRa

Rg

275

aceton

e4929

500

320degC

30pp

b

eintrod

uctio

nof

10

ofg-CN

nano

sheets

inMgFe 2O4im

proves


[126]

Grg-CN

Dropcoatingmetho

d(Rg-Ra

)Ra

42N

O2

U5

100degC

600pp

bGraph

iticcarbon

nitridenano

sheetswith

15of

g-CN

exhibith


comparedto

bulk

g-CN

andpu

regraphene

[127]

10wt

g-CN

ZnO

Synthesiz

edviaultrason


calcinationprocess

RgRa

448

NO2

142190

7U

38pp

mDetectio

nperformance

isactiv

ated

byLE

Dlight

sources460nm

LED

(127Wm

2 )[128]

ldquoUrdquoun

availablecitatio

nitisno

tcitedin

thestud


ndatmosph

ericairrespectiv

elyRa

Rgelectricresis

tances

intheatmosph

ericaira


ely


Resis

tanc

e (M

Ω)

Time (s)

90

80

70

60

50

40

30

20

10

0100 200 300 400

50 RH70 RH90 RH

(a)

Resp

onse

(Ra

Rg o

r Rg

Ra)

50

40

30

20

10

0

NO2


nol

Ace

tone


(b)




g-CN-NO2

25 Aring 313 Aring

g-CN-CO2

25 Aring 324 Aring

g-CN-HF

25 Aring 129 Aring

r-GrO-HF

25 Aring 326 Aring

Gr-HF

25 Aring 370 Aring





















7 Conclusion


Data Availability




Acknowledgments


References




























































































































































Spin-coating



[49 50]





[49 52]


Melamine(C3H6N6)


iourea(CH4N2S)

Cyanamide (CH2N2)


Urea(CH4N2O)

500-

580deg

C

520-

550deg

C

460-

650deg

C

550deg

C

550deg

C























Depositiontime

Power(W)

RF power(MHz) Ref



Wavenumber (cm-1)

Tran

smitt

ance

500 1000 1500 2000 2500 3000 3500 4000

3124

161214

57

1250

1320

1419

889

802

(a)

Wavenumber (cm-1)

Tran

smitt

ance

4000 3000 2000 1000

131776

123942

80951

(b)


g-C3N4

C 1s

N 1s



Inte

nsity

(au

)

Inte

nsity

(au

)

Inte

nsity

(au

)(d)(c)

(a)

N 1sC 1s 3983 eV

3999 eV4006 eV

2846 eV

2860 eV

2881 eV

0 100 200 300 400 500

280 282 284 286 288 290 292 294 394 396 398 400 402 404 406 408








(1)







Ram

an In

tens

ityc

ps

Wavenumber (cm-1)2000 1600 1200 800 400

2400

2000

1600

1200

800

400

0

Bulk

1 layer

1616 1555

1481

1234

751

705

543

479

1250

(a)

Ram

an In

tens

itya

u

Wavenumber (cm-1)1600 1400 600 400

Bulk

1 layer

1602 15

6915

10

1224

726

685

616

555

1232

(b)


10 20 30 40 50 60 70 80

(100)

(002)

g-CN NSs

g-CN bulk

Inte

nsity

(au

)

2θ (deg)











n-type

Resistance

Time

Reducinggas

e-

n-type

Resistance

Time

Oxidizinggas

e-











[86 87]

NO


NO2


NH3


CO



NH3

CO

H2O

NO2

I II III IV

0 500 1000t (s)

4

2

0

-2

-4

Δρρ

()




Time (s)1000 1500 20000 500

240

235

230

225

220

215

Curr

ent (

mA

)













[97]

H2


NO2


CO2



Tabl

e10

eperformancesof

nano

compo

sites

basedon

g-CN

forgassensor

applications

Material

Metho

dRe

spon

seG

asRe

spon

se

recovery

time

(s)

ppm

level

Operatio

nT

(deg C)

Detectio

nlim

itCom

ment

Ref

TiO2

Spraypyrolysis

techniqu

e

RaRg

25

H2S

sim5260

1500

450

U

eim

provem


ofthe

sensor

isdu

eto

theintrod

uctio

nof

10

oftheg-CN

nano

sheets

[103]

RaRg

22

CO2

4555

g-CN

(10wt

)TiO2

RaRg

67

H2S

sim3052

RaRg

88

CO2

3527

SnO2

Hydrothermal

metho

d

RaRg

134

acetic

acid

94160

1000

230degC

UIm

provem

ento

fthe


andthe

sensitivity

byintrod

uctio

nof

10wt

ofg-CNin

SnO2

[58]

10wt

ofg-

CN-SnO

2

RaRg

877

CH

3COOH

U185degC

01pp

m

g-CN-SnO


dVgVa

83

aceton

e78

500

380degC

67pp

bA

significantimprovem

entin

sensor

performance

bycalciningmelam

ineSn

O2po

wderfor3ho

urs

[14]

5Pd

SnO

25

g-CN

Hydrothermal

metho

d(Rg-Ra

)Ra

905CO

1013

1000

125degC

75pp

mg-CN-5

nano

sheets

with

SnO2nano

particles

effectiv

elyim

proved

therespon

seof

thegassensors

towards

CO

[25]

2wt

g-CN-

WO3

Hydrothermal

metho

dRa

Rg

582

aceton

e5329

1000

310degC

05pp

mA

gassensor

basedon

2g-CN

compo

siteshow

sa

high

errespon

seto

aceton

ethan

pure

WO3

[125]

10wt

g-CN

MgFe 2O4

One-stepsolvotherm

almetho

dRa

Rg

275

aceton

e4929

500

320degC

30pp

b

eintrod

uctio

nof

10

ofg-CN

nano

sheets

inMgFe 2O4im

proves


[126]

Grg-CN

Dropcoatingmetho

d(Rg-Ra

)Ra

42N

O2

U5

100degC

600pp

bGraph

iticcarbon

nitridenano

sheetswith

15of

g-CN

exhibith


comparedto

bulk

g-CN

andpu

regraphene

[127]

10wt

g-CN

ZnO

Synthesiz

edviaultrason


calcinationprocess

RgRa

448

NO2

142190

7U

38pp

mDetectio

nperformance

isactiv

ated

byLE

Dlight

sources460nm

LED

(127Wm

2 )[128]

ldquoUrdquoun

availablecitatio

nitisno

tcitedin

thestud


ndatmosph

ericairrespectiv

elyRa

Rgelectricresis

tances

intheatmosph

ericaira


ely


Resis

tanc

e (M

Ω)

Time (s)

90

80

70

60

50

40

30

20

10

0100 200 300 400

50 RH70 RH90 RH

(a)

Resp

onse

(Ra

Rg o

r Rg

Ra)

50

40

30

20

10

0

NO2


nol

Ace

tone


(b)




g-CN-NO2

25 Aring 313 Aring

g-CN-CO2

25 Aring 324 Aring

g-CN-HF

25 Aring 129 Aring

r-GrO-HF

25 Aring 326 Aring

Gr-HF

25 Aring 370 Aring





















7 Conclusion


Data Availability




Acknowledgments


References









































































































































































Depositiontime

Power(W)

RF power(MHz) Ref



Wavenumber (cm-1)

Tran

smitt

ance

500 1000 1500 2000 2500 3000 3500 4000

3124

161214

57

1250

1320

1419

889

802

(a)

Wavenumber (cm-1)

Tran

smitt

ance

4000 3000 2000 1000

131776

123942

80951

(b)


g-C3N4

C 1s

N 1s



Inte

nsity

(au

)

Inte

nsity

(au

)

Inte

nsity

(au

)(d)(c)

(a)

N 1sC 1s 3983 eV

3999 eV4006 eV

2846 eV

2860 eV

2881 eV

0 100 200 300 400 500

280 282 284 286 288 290 292 294 394 396 398 400 402 404 406 408








(1)







Ram

an In

tens

ityc

ps

Wavenumber (cm-1)2000 1600 1200 800 400

2400

2000

1600

1200

800

400

0

Bulk

1 layer

1616 1555

1481

1234

751

705

543

479

1250

(a)

Ram

an In

tens

itya

u

Wavenumber (cm-1)1600 1400 600 400

Bulk

1 layer

1602 15

6915

10

1224

726

685

616

555

1232

(b)


10 20 30 40 50 60 70 80

(100)

(002)

g-CN NSs

g-CN bulk

Inte

nsity

(au

)

2θ (deg)











n-type

Resistance

Time

Reducinggas

e-

n-type

Resistance

Time

Oxidizinggas

e-











[86 87]

NO


NO2


NH3


CO



NH3

CO

H2O

NO2

I II III IV

0 500 1000t (s)

4

2

0

-2

-4

Δρρ

()




Time (s)1000 1500 20000 500

240

235

230

225

220

215

Curr

ent (

mA

)













[97]

H2


NO2


CO2



Tabl

e10

eperformancesof

nano

compo

sites

basedon

g-CN

forgassensor

applications

Material

Metho

dRe

spon

seG

asRe

spon

se

recovery

time

(s)

ppm

level

Operatio

nT

(deg C)

Detectio

nlim

itCom

ment

Ref

TiO2

Spraypyrolysis

techniqu

e

RaRg

25

H2S

sim5260

1500

450

U

eim

provem


ofthe

sensor

isdu

eto

theintrod

uctio

nof

10

oftheg-CN

nano

sheets

[103]

RaRg

22

CO2

4555

g-CN

(10wt

)TiO2

RaRg

67

H2S

sim3052

RaRg

88

CO2

3527

SnO2

Hydrothermal

metho

d

RaRg

134

acetic

acid

94160

1000

230degC

UIm

provem

ento

fthe


andthe

sensitivity

byintrod

uctio

nof

10wt

ofg-CNin

SnO2

[58]

10wt

ofg-

CN-SnO

2

RaRg

877

CH

3COOH

U185degC

01pp

m

g-CN-SnO


dVgVa

83

aceton

e78

500

380degC

67pp

bA

significantimprovem

entin

sensor

performance

bycalciningmelam

ineSn

O2po

wderfor3ho

urs

[14]

5Pd

SnO

25

g-CN

Hydrothermal

metho

d(Rg-Ra

)Ra

905CO

1013

1000

125degC

75pp

mg-CN-5

nano

sheets

with

SnO2nano

particles

effectiv

elyim

proved

therespon

seof

thegassensors

towards

CO

[25]

2wt

g-CN-

WO3

Hydrothermal

metho

dRa

Rg

582

aceton

e5329

1000

310degC

05pp

mA

gassensor

basedon

2g-CN

compo

siteshow

sa

high

errespon

seto

aceton

ethan

pure

WO3

[125]

10wt

g-CN

MgFe 2O4

One-stepsolvotherm

almetho

dRa

Rg

275

aceton

e4929

500

320degC

30pp

b

eintrod

uctio

nof

10

ofg-CN

nano

sheets

inMgFe 2O4im

proves


[126]

Grg-CN

Dropcoatingmetho

d(Rg-Ra

)Ra

42N

O2

U5

100degC

600pp

bGraph

iticcarbon

nitridenano

sheetswith

15of

g-CN

exhibith


comparedto

bulk

g-CN

andpu

regraphene

[127]

10wt

g-CN

ZnO

Synthesiz

edviaultrason


calcinationprocess

RgRa

448

NO2

142190

7U

38pp

mDetectio

nperformance

isactiv

ated

byLE

Dlight

sources460nm

LED

(127Wm

2 )[128]

ldquoUrdquoun

availablecitatio

nitisno

tcitedin

thestud


ndatmosph

ericairrespectiv

elyRa

Rgelectricresis

tances

intheatmosph

ericaira


ely


Resis

tanc

e (M

Ω)

Time (s)

90

80

70

60

50

40

30

20

10

0100 200 300 400

50 RH70 RH90 RH

(a)

Resp

onse

(Ra

Rg o

r Rg

Ra)

50

40

30

20

10

0

NO2


nol

Ace

tone


(b)




g-CN-NO2

25 Aring 313 Aring

g-CN-CO2

25 Aring 324 Aring

g-CN-HF

25 Aring 129 Aring

r-GrO-HF

25 Aring 326 Aring

Gr-HF

25 Aring 370 Aring





















7 Conclusion


Data Availability




Acknowledgments


References























































































































































Wavenumber (cm-1)

Tran

smitt

ance

500 1000 1500 2000 2500 3000 3500 4000

3124

161214

57

1250

1320

1419

889

802

(a)

Wavenumber (cm-1)

Tran

smitt

ance

4000 3000 2000 1000

131776

123942

80951

(b)


g-C3N4

C 1s

N 1s



Inte

nsity

(au

)

Inte

nsity

(au

)

Inte

nsity

(au

)(d)(c)

(a)

N 1sC 1s 3983 eV

3999 eV4006 eV

2846 eV

2860 eV

2881 eV

0 100 200 300 400 500

280 282 284 286 288 290 292 294 394 396 398 400 402 404 406 408








(1)







Ram

an In

tens

ityc

ps

Wavenumber (cm-1)2000 1600 1200 800 400

2400

2000

1600

1200

800

400

0

Bulk

1 layer

1616 1555

1481

1234

751

705

543

479

1250

(a)

Ram

an In

tens

itya

u

Wavenumber (cm-1)1600 1400 600 400

Bulk

1 layer

1602 15

6915

10

1224

726

685

616

555

1232

(b)


10 20 30 40 50 60 70 80

(100)

(002)

g-CN NSs

g-CN bulk

Inte

nsity

(au

)

2θ (deg)











n-type

Resistance

Time

Reducinggas

e-

n-type

Resistance

Time

Oxidizinggas

e-











[86 87]

NO


NO2


NH3


CO



NH3

CO

H2O

NO2

I II III IV

0 500 1000t (s)

4

2

0

-2

-4

Δρρ

()




Time (s)1000 1500 20000 500

240

235

230

225

220

215

Curr

ent (

mA

)













[97]

H2


NO2


CO2



Tabl

e10

eperformancesof

nano

compo

sites

basedon

g-CN

forgassensor

applications

Material

Metho

dRe

spon

seG

asRe

spon

se

recovery

time

(s)

ppm

level

Operatio

nT

(deg C)

Detectio

nlim

itCom

ment

Ref

TiO2

Spraypyrolysis

techniqu

e

RaRg

25

H2S

sim5260

1500

450

U

eim

provem


ofthe

sensor

isdu

eto

theintrod

uctio

nof

10

oftheg-CN

nano

sheets

[103]

RaRg

22

CO2

4555

g-CN

(10wt

)TiO2

RaRg

67

H2S

sim3052

RaRg

88

CO2

3527

SnO2

Hydrothermal

metho

d

RaRg

134

acetic

acid

94160

1000

230degC

UIm

provem

ento

fthe


andthe

sensitivity

byintrod

uctio

nof

10wt

ofg-CNin

SnO2

[58]

10wt

ofg-

CN-SnO

2

RaRg

877

CH

3COOH

U185degC

01pp

m

g-CN-SnO


dVgVa

83

aceton

e78

500

380degC

67pp

bA

significantimprovem

entin

sensor

performance

bycalciningmelam

ineSn

O2po

wderfor3ho

urs

[14]

5Pd

SnO

25

g-CN

Hydrothermal

metho

d(Rg-Ra

)Ra

905CO

1013

1000

125degC

75pp

mg-CN-5

nano

sheets

with

SnO2nano

particles

effectiv

elyim

proved

therespon

seof

thegassensors

towards

CO

[25]

2wt

g-CN-

WO3

Hydrothermal

metho

dRa

Rg

582

aceton

e5329

1000

310degC

05pp

mA

gassensor

basedon

2g-CN

compo

siteshow

sa

high

errespon

seto

aceton

ethan

pure

WO3

[125]

10wt

g-CN

MgFe 2O4

One-stepsolvotherm

almetho

dRa

Rg

275

aceton

e4929

500

320degC

30pp

b

eintrod

uctio

nof

10

ofg-CN

nano

sheets

inMgFe 2O4im

proves


[126]

Grg-CN

Dropcoatingmetho

d(Rg-Ra

)Ra

42N

O2

U5

100degC

600pp

bGraph

iticcarbon

nitridenano

sheetswith

15of

g-CN

exhibith


comparedto

bulk

g-CN

andpu

regraphene

[127]

10wt

g-CN

ZnO

Synthesiz

edviaultrason


calcinationprocess

RgRa

448

NO2

142190

7U

38pp

mDetectio

nperformance

isactiv

ated

byLE

Dlight

sources460nm

LED

(127Wm

2 )[128]

ldquoUrdquoun

availablecitatio

nitisno

tcitedin

thestud


ndatmosph

ericairrespectiv

elyRa

Rgelectricresis

tances

intheatmosph

ericaira


ely


Resis

tanc

e (M

Ω)

Time (s)

90

80

70

60

50

40

30

20

10

0100 200 300 400

50 RH70 RH90 RH

(a)

Resp

onse

(Ra

Rg o

r Rg

Ra)

50

40

30

20

10

0

NO2


nol

Ace

tone


(b)




g-CN-NO2

25 Aring 313 Aring

g-CN-CO2

25 Aring 324 Aring

g-CN-HF

25 Aring 129 Aring

r-GrO-HF

25 Aring 326 Aring

Gr-HF

25 Aring 370 Aring





















7 Conclusion


Data Availability




Acknowledgments


References


























































































































































(1)







Ram

an In

tens

ityc

ps

Wavenumber (cm-1)2000 1600 1200 800 400

2400

2000

1600

1200

800

400

0

Bulk

1 layer

1616 1555

1481

1234

751

705

543

479

1250

(a)

Ram

an In

tens

itya

u

Wavenumber (cm-1)1600 1400 600 400

Bulk

1 layer

1602 15

6915

10

1224

726

685

616

555

1232

(b)


10 20 30 40 50 60 70 80

(100)

(002)

g-CN NSs

g-CN bulk

Inte

nsity

(au

)

2θ (deg)











n-type

Resistance

Time

Reducinggas

e-

n-type

Resistance

Time

Oxidizinggas

e-











[86 87]

NO


NO2


NH3


CO



NH3

CO

H2O

NO2

I II III IV

0 500 1000t (s)

4

2

0

-2

-4

Δρρ

()




Time (s)1000 1500 20000 500

240

235

230

225

220

215

Curr

ent (

mA

)













[97]

H2


NO2


CO2



Tabl

e10

eperformancesof

nano

compo

sites

basedon

g-CN

forgassensor

applications

Material

Metho

dRe

spon

seG

asRe

spon

se

recovery

time

(s)

ppm

level

Operatio

nT

(deg C)

Detectio

nlim

itCom

ment

Ref

TiO2

Spraypyrolysis

techniqu

e

RaRg

25

H2S

sim5260

1500

450

U

eim

provem


ofthe

sensor

isdu

eto

theintrod

uctio

nof

10

oftheg-CN

nano

sheets

[103]

RaRg

22

CO2

4555

g-CN

(10wt

)TiO2

RaRg

67

H2S

sim3052

RaRg

88

CO2

3527

SnO2

Hydrothermal

metho

d

RaRg

134

acetic

acid

94160

1000

230degC

UIm

provem

ento

fthe


andthe

sensitivity

byintrod

uctio

nof

10wt

ofg-CNin

SnO2

[58]

10wt

ofg-

CN-SnO

2

RaRg

877

CH

3COOH

U185degC

01pp

m

g-CN-SnO


dVgVa

83

aceton

e78

500

380degC

67pp

bA

significantimprovem

entin

sensor

performance

bycalciningmelam

ineSn

O2po

wderfor3ho

urs

[14]

5Pd

SnO

25

g-CN

Hydrothermal

metho

d(Rg-Ra

)Ra

905CO

1013

1000

125degC

75pp

mg-CN-5

nano

sheets

with

SnO2nano

particles

effectiv

elyim

proved

therespon

seof

thegassensors

towards

CO

[25]

2wt

g-CN-

WO3

Hydrothermal

metho

dRa

Rg

582

aceton

e5329

1000

310degC

05pp

mA

gassensor

basedon

2g-CN

compo

siteshow

sa

high

errespon

seto

aceton

ethan

pure

WO3

[125]

10wt

g-CN

MgFe 2O4

One-stepsolvotherm

almetho

dRa

Rg

275

aceton

e4929

500

320degC

30pp

b

eintrod

uctio

nof

10

ofg-CN

nano

sheets

inMgFe 2O4im

proves


[126]

Grg-CN

Dropcoatingmetho

d(Rg-Ra

)Ra

42N

O2

U5

100degC

600pp

bGraph

iticcarbon

nitridenano

sheetswith

15of

g-CN

exhibith


comparedto

bulk

g-CN

andpu

regraphene

[127]

10wt

g-CN

ZnO

Synthesiz

edviaultrason


calcinationprocess

RgRa

448

NO2

142190

7U

38pp

mDetectio

nperformance

isactiv

ated

byLE

Dlight

sources460nm

LED

(127Wm

2 )[128]

ldquoUrdquoun

availablecitatio

nitisno

tcitedin

thestud


ndatmosph

ericairrespectiv

elyRa

Rgelectricresis

tances

intheatmosph

ericaira


ely


Resis

tanc

e (M

Ω)

Time (s)

90

80

70

60

50

40

30

20

10

0100 200 300 400

50 RH70 RH90 RH

(a)

Resp

onse

(Ra

Rg o

r Rg

Ra)

50

40

30

20

10

0

NO2


nol

Ace

tone


(b)




g-CN-NO2

25 Aring 313 Aring

g-CN-CO2

25 Aring 324 Aring

g-CN-HF

25 Aring 129 Aring

r-GrO-HF

25 Aring 326 Aring

Gr-HF

25 Aring 370 Aring





















7 Conclusion


Data Availability




Acknowledgments


References































































































































































n-type

Resistance

Time

Reducinggas

e-

n-type

Resistance

Time

Oxidizinggas

e-











[86 87]

NO


NO2


NH3


CO



NH3

CO

H2O

NO2

I II III IV

0 500 1000t (s)

4

2

0

-2

-4

Δρρ

()




Time (s)1000 1500 20000 500

240

235

230

225

220

215

Curr

ent (

mA

)













[97]

H2


NO2


CO2



Tabl

e10

eperformancesof

nano

compo

sites

basedon

g-CN

forgassensor

applications

Material

Metho

dRe

spon

seG

asRe

spon

se

recovery

time

(s)

ppm

level

Operatio

nT

(deg C)

Detectio

nlim

itCom

ment

Ref

TiO2

Spraypyrolysis

techniqu

e

RaRg

25

H2S

sim5260

1500

450

U

eim

provem


ofthe

sensor

isdu

eto

theintrod

uctio

nof

10

oftheg-CN

nano

sheets

[103]

RaRg

22

CO2

4555

g-CN

(10wt

)TiO2

RaRg

67

H2S

sim3052

RaRg

88

CO2

3527

SnO2

Hydrothermal

metho

d

RaRg

134

acetic

acid

94160

1000

230degC

UIm

provem

ento

fthe


andthe

sensitivity

byintrod

uctio

nof

10wt

ofg-CNin

SnO2

[58]

10wt

ofg-

CN-SnO

2

RaRg

877

CH

3COOH

U185degC

01pp

m

g-CN-SnO


dVgVa

83

aceton

e78

500

380degC

67pp

bA

significantimprovem

entin

sensor

performance

bycalciningmelam

ineSn

O2po

wderfor3ho

urs

[14]

5Pd

SnO

25

g-CN

Hydrothermal

metho

d(Rg-Ra

)Ra

905CO

1013

1000

125degC

75pp

mg-CN-5

nano

sheets

with

SnO2nano

particles

effectiv

elyim

proved

therespon

seof

thegassensors

towards

CO

[25]

2wt

g-CN-

WO3

Hydrothermal

metho

dRa

Rg

582

aceton

e5329

1000

310degC

05pp

mA

gassensor

basedon

2g-CN

compo

siteshow

sa

high

errespon

seto

aceton

ethan

pure

WO3

[125]

10wt

g-CN

MgFe 2O4

One-stepsolvotherm

almetho

dRa

Rg

275

aceton

e4929

500

320degC

30pp

b

eintrod

uctio

nof

10

ofg-CN

nano

sheets

inMgFe 2O4im

proves


[126]

Grg-CN

Dropcoatingmetho

d(Rg-Ra

)Ra

42N

O2

U5

100degC

600pp

bGraph

iticcarbon

nitridenano

sheetswith

15of

g-CN

exhibith


comparedto

bulk

g-CN

andpu

regraphene

[127]

10wt

g-CN

ZnO

Synthesiz

edviaultrason


calcinationprocess

RgRa

448

NO2

142190

7U

38pp

mDetectio

nperformance

isactiv

ated

byLE

Dlight

sources460nm

LED

(127Wm

2 )[128]

ldquoUrdquoun

availablecitatio

nitisno

tcitedin

thestud


ndatmosph

ericairrespectiv

elyRa

Rgelectricresis

tances

intheatmosph

ericaira


ely


Resis

tanc

e (M

Ω)

Time (s)

90

80

70

60

50

40

30

20

10

0100 200 300 400

50 RH70 RH90 RH

(a)

Resp

onse

(Ra

Rg o

r Rg

Ra)

50

40

30

20

10

0

NO2


nol

Ace

tone


(b)




g-CN-NO2

25 Aring 313 Aring

g-CN-CO2

25 Aring 324 Aring

g-CN-HF

25 Aring 129 Aring

r-GrO-HF

25 Aring 326 Aring

Gr-HF

25 Aring 370 Aring





















7 Conclusion


Data Availability




Acknowledgments


References































































































































































[86 87]

NO


NO2


NH3


CO



NH3

CO

H2O

NO2

I II III IV

0 500 1000t (s)

4

2

0

-2

-4

Δρρ

()




Time (s)1000 1500 20000 500

240

235

230

225

220

215

Curr

ent (

mA

)













[97]

H2


NO2


CO2



Tabl

e10

eperformancesof

nano

compo

sites

basedon

g-CN

forgassensor

applications

Material

Metho

dRe

spon

seG

asRe

spon

se

recovery

time

(s)

ppm

level

Operatio

nT

(deg C)

Detectio

nlim

itCom

ment

Ref

TiO2

Spraypyrolysis

techniqu

e

RaRg

25

H2S

sim5260

1500

450

U

eim

provem


ofthe

sensor

isdu

eto

theintrod

uctio

nof

10

oftheg-CN

nano

sheets

[103]

RaRg

22

CO2

4555

g-CN

(10wt

)TiO2

RaRg

67

H2S

sim3052

RaRg

88

CO2

3527

SnO2

Hydrothermal

metho

d

RaRg

134

acetic

acid

94160

1000

230degC

UIm

provem

ento

fthe


andthe

sensitivity

byintrod

uctio

nof

10wt

ofg-CNin

SnO2

[58]

10wt

ofg-

CN-SnO

2

RaRg

877

CH

3COOH

U185degC

01pp

m

g-CN-SnO


dVgVa

83

aceton

e78

500

380degC

67pp

bA

significantimprovem

entin

sensor

performance

bycalciningmelam

ineSn

O2po

wderfor3ho

urs

[14]

5Pd

SnO

25

g-CN

Hydrothermal

metho

d(Rg-Ra

)Ra

905CO

1013

1000

125degC

75pp

mg-CN-5

nano

sheets

with

SnO2nano

particles

effectiv

elyim

proved

therespon

seof

thegassensors

towards

CO

[25]

2wt

g-CN-

WO3

Hydrothermal

metho

dRa

Rg

582

aceton

e5329

1000

310degC

05pp

mA

gassensor

basedon

2g-CN

compo

siteshow

sa

high

errespon

seto

aceton

ethan

pure

WO3

[125]

10wt

g-CN

MgFe 2O4

One-stepsolvotherm

almetho

dRa

Rg

275

aceton

e4929

500

320degC

30pp

b

eintrod

uctio

nof

10

ofg-CN

nano

sheets

inMgFe 2O4im

proves


[126]

Grg-CN

Dropcoatingmetho

d(Rg-Ra

)Ra

42N

O2

U5

100degC

600pp

bGraph

iticcarbon

nitridenano

sheetswith

15of

g-CN

exhibith


comparedto

bulk

g-CN

andpu

regraphene

[127]

10wt

g-CN

ZnO

Synthesiz

edviaultrason


calcinationprocess

RgRa

448

NO2

142190

7U

38pp

mDetectio

nperformance

isactiv

ated

byLE

Dlight

sources460nm

LED

(127Wm

2 )[128]

ldquoUrdquoun

availablecitatio

nitisno

tcitedin

thestud


ndatmosph

ericairrespectiv

elyRa

Rgelectricresis

tances

intheatmosph

ericaira


ely


Resis

tanc

e (M

Ω)

Time (s)

90

80

70

60

50

40

30

20

10

0100 200 300 400

50 RH70 RH90 RH

(a)

Resp

onse

(Ra

Rg o

r Rg

Ra)

50

40

30

20

10

0

NO2


nol

Ace

tone


(b)




g-CN-NO2

25 Aring 313 Aring

g-CN-CO2

25 Aring 324 Aring

g-CN-HF

25 Aring 129 Aring

r-GrO-HF

25 Aring 326 Aring

Gr-HF

25 Aring 370 Aring





















7 Conclusion


Data Availability




Acknowledgments


References

































































































































































[97]

H2


NO2


CO2



Tabl

e10

eperformancesof

nano

compo

sites

basedon

g-CN

forgassensor

applications

Material

Metho

dRe

spon

seG

asRe

spon

se

recovery

time

(s)

ppm

level

Operatio

nT

(deg C)

Detectio

nlim

itCom

ment

Ref

TiO2

Spraypyrolysis

techniqu

e

RaRg

25

H2S

sim5260

1500

450

U

eim

provem


ofthe

sensor

isdu

eto

theintrod

uctio

nof

10

oftheg-CN

nano

sheets

[103]

RaRg

22

CO2

4555

g-CN

(10wt

)TiO2

RaRg

67

H2S

sim3052

RaRg

88

CO2

3527

SnO2

Hydrothermal

metho

d

RaRg

134

acetic

acid

94160

1000

230degC

UIm

provem

ento

fthe


andthe

sensitivity

byintrod

uctio

nof

10wt

ofg-CNin

SnO2

[58]

10wt

ofg-

CN-SnO

2

RaRg

877

CH

3COOH

U185degC

01pp

m

g-CN-SnO


dVgVa

83

aceton

e78

500

380degC

67pp

bA

significantimprovem

entin

sensor

performance

bycalciningmelam

ineSn

O2po

wderfor3ho

urs

[14]

5Pd

SnO

25

g-CN

Hydrothermal

metho

d(Rg-Ra

)Ra

905CO

1013

1000

125degC

75pp

mg-CN-5

nano

sheets

with

SnO2nano

particles

effectiv

elyim

proved

therespon

seof

thegassensors

towards

CO

[25]

2wt

g-CN-

WO3

Hydrothermal

metho

dRa

Rg

582

aceton

e5329

1000

310degC

05pp

mA

gassensor

basedon

2g-CN

compo

siteshow

sa

high

errespon

seto

aceton

ethan

pure

WO3

[125]

10wt

g-CN

MgFe 2O4

One-stepsolvotherm

almetho

dRa

Rg

275

aceton

e4929

500

320degC

30pp

b

eintrod

uctio

nof

10

ofg-CN

nano

sheets

inMgFe 2O4im

proves


[126]

Grg-CN

Dropcoatingmetho

d(Rg-Ra

)Ra

42N

O2

U5

100degC

600pp

bGraph

iticcarbon

nitridenano

sheetswith

15of

g-CN

exhibith


comparedto

bulk

g-CN

andpu

regraphene

[127]

10wt

g-CN

ZnO

Synthesiz

edviaultrason


calcinationprocess

RgRa

448

NO2

142190

7U

38pp

mDetectio

nperformance

isactiv

ated

byLE

Dlight

sources460nm

LED

(127Wm

2 )[128]

ldquoUrdquoun

availablecitatio

nitisno

tcitedin

thestud


ndatmosph

ericairrespectiv

elyRa

Rgelectricresis

tances

intheatmosph

ericaira


ely


Resis

tanc

e (M

Ω)

Time (s)

90

80

70

60

50

40

30

20

10

0100 200 300 400

50 RH70 RH90 RH

(a)

Resp

onse

(Ra

Rg o

r Rg

Ra)

50

40

30

20

10

0

NO2


nol

Ace

tone


(b)




g-CN-NO2

25 Aring 313 Aring

g-CN-CO2

25 Aring 324 Aring

g-CN-HF

25 Aring 129 Aring

r-GrO-HF

25 Aring 326 Aring

Gr-HF

25 Aring 370 Aring





















7 Conclusion


Data Availability




Acknowledgments


References























































































































































Tabl

e10

eperformancesof

nano

compo

sites

basedon

g-CN

forgassensor

applications

Material

Metho

dRe

spon

seG

asRe

spon

se

recovery

time

(s)

ppm

level

Operatio

nT

(deg C)

Detectio

nlim

itCom

ment

Ref

TiO2

Spraypyrolysis

techniqu

e

RaRg

25

H2S

sim5260

1500

450

U

eim

provem


ofthe

sensor

isdu

eto

theintrod

uctio

nof

10

oftheg-CN

nano

sheets

[103]

RaRg

22

CO2

4555

g-CN

(10wt

)TiO2

RaRg

67

H2S

sim3052

RaRg

88

CO2

3527

SnO2

Hydrothermal

metho

d

RaRg

134

acetic

acid

94160

1000

230degC

UIm

provem

ento

fthe


andthe

sensitivity

byintrod

uctio

nof

10wt

ofg-CNin

SnO2

[58]

10wt

ofg-

CN-SnO

2

RaRg

877

CH

3COOH

U185degC

01pp

m

g-CN-SnO


dVgVa

83

aceton

e78

500

380degC

67pp

bA

significantimprovem

entin

sensor

performance

bycalciningmelam

ineSn

O2po

wderfor3ho

urs

[14]

5Pd

SnO

25

g-CN

Hydrothermal

metho

d(Rg-Ra

)Ra

905CO

1013

1000

125degC

75pp

mg-CN-5

nano

sheets

with

SnO2nano

particles

effectiv

elyim

proved

therespon

seof

thegassensors

towards

CO

[25]

2wt

g-CN-

WO3

Hydrothermal

metho

dRa

Rg

582

aceton

e5329

1000

310degC

05pp

mA

gassensor

basedon

2g-CN

compo

siteshow

sa

high

errespon

seto

aceton

ethan

pure

WO3

[125]

10wt

g-CN

MgFe 2O4

One-stepsolvotherm

almetho

dRa

Rg

275

aceton

e4929

500

320degC

30pp

b

eintrod

uctio

nof

10

ofg-CN

nano

sheets

inMgFe 2O4im

proves


[126]

Grg-CN

Dropcoatingmetho

d(Rg-Ra

)Ra

42N

O2

U5

100degC

600pp

bGraph

iticcarbon

nitridenano

sheetswith

15of

g-CN

exhibith


comparedto

bulk

g-CN

andpu

regraphene

[127]

10wt

g-CN

ZnO

Synthesiz

edviaultrason


calcinationprocess

RgRa

448

NO2

142190

7U

38pp

mDetectio

nperformance

isactiv

ated

byLE

Dlight

sources460nm

LED

(127Wm

2 )[128]

ldquoUrdquoun

availablecitatio

nitisno

tcitedin

thestud


ndatmosph

ericairrespectiv

elyRa

Rgelectricresis

tances

intheatmosph

ericaira


ely


Resis

tanc

e (M

Ω)

Time (s)

90

80

70

60

50

40

30

20

10

0100 200 300 400

50 RH70 RH90 RH

(a)

Resp

onse

(Ra

Rg o

r Rg

Ra)

50

40

30

20

10

0

NO2


nol

Ace

tone


(b)




g-CN-NO2

25 Aring 313 Aring

g-CN-CO2

25 Aring 324 Aring

g-CN-HF

25 Aring 129 Aring

r-GrO-HF

25 Aring 326 Aring

Gr-HF

25 Aring 370 Aring





















7 Conclusion


Data Availability




Acknowledgments


References























































































































































Resis

tanc

e (M

Ω)

Time (s)

90

80

70

60

50

40

30

20

10

0100 200 300 400

50 RH70 RH90 RH

(a)

Resp

onse

(Ra

Rg o

r Rg

Ra)

50

40

30

20

10

0

NO2


nol

Ace

tone


(b)




g-CN-NO2

25 Aring 313 Aring

g-CN-CO2

25 Aring 324 Aring

g-CN-HF

25 Aring 129 Aring

r-GrO-HF

25 Aring 326 Aring

Gr-HF

25 Aring 370 Aring





















7 Conclusion


Data Availability




Acknowledgments


References










































































































































































7 Conclusion


Data Availability




Acknowledgments


References























































































































































Review Article Graphene and g-C3N4-Based Gas Sensors

Documents

Transcript of Review Article Graphene and g-C3N4-Based Gas Sensors