Journal of Photochemistry and Photobiology B: Biology 144 (2015) 68–74

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Journal of Photochemistry and Photobiology B: Biology

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Photocatalytic destruction of Escherichia coli in water by V2O5/TiO2

http://dx.doi.org/10.1016/j.jphotobiol.2015.02.0031011-1344/� 2015 Elsevier B.V. All rights reserved.

⇑ Corresponding author.E-mail addresses: velsak_r@yahoo.com, rsakthivel@immt.res.in (S. Ramasamy).

Diptipriya Sethi a, Naresh Jada b, Ashish Tiwari b, Sakthivel Ramasamy b,⇑, Tapan Dash b, Sony Pandey b

a Academy of Scientific and Innovative Research (AcSIR), Anusandhan Bhawan, 2 Rafi Marg, New Delhi 110 001, Indiab CSIR-Institute of Minerals and Materials Technology, Bhubaneswar 751013, India

a r t i c l e i n f o

Article history:Received 10 October 2014Received in revised form 6 January 2015Accepted 5 February 2015Available online 17 February 2015

a b s t r a c t

Vanadia modified titania (V2O5/TiO2) photo-catalysts are prepared by incipient wet impregnation methodusing aqueous ammonium metavanadate and anatase (Aldrich) titania. Titania with various loading con-centrations of vanadia from 0 to 10 wt.% have been prepared and characterized by X-ray diffraction(XRD), Thermogravimetry (TGA), Laser Raman Spectroscopy, Fourier Transform Infrared Spectroscopy(FTIR), X-ray Photoelectron Spectroscopy (XPS), UV–Visible Spectrophotometry and Transmission Elec-tron Microscopy (TEM). XRD study reveals that vanadia loading on titania does not bring any phasechange of titania, however, diffuse (UV–Vis) reflectance spectra show that absorption edge of titaniashifted from UV to visible region. TEM confirms that titania and vanadia modified titania have the particlesize below 50 nm. XPS shows alteration of 2p3/2 peak of V(V) in the V2O5/TiO2 samples whereas no suchchange is noticed in pure V2O5 indicating the interaction between vanadia and titania support. Antibac-terial activity of each sample has been investigated against Escherichia coli present in the water underboth UV–Visible irradiation and UV alone. V2O5/TiO2 catalysts exhibit better photocatalytic effect thanthe unmodified titania and pure V2O5. It is observed that with increasing loading concentrations ofV2O5 from 0 to 10 wt.% on titania support, the photocatalytic annihilation of E. coli is also increasedand found to be little higher under UV alone than the UV–Visible irradiation.

� 2015 Elsevier B.V. All rights reserved.

1. Introduction

Titanium dioxide has been of immensely studied semiconductormaterial ever since its photocatalytic properties were established[1]. TiO2 is found in numerous applications like paints, coatings,paper, filler in plastics, inks, cosmetics, sunscreens, food coloring,pharmaceuticals etc. Its ability in the photo-catalytic degradationof organic contaminants in soil [2], water [3] and air [4] is of specialresearch area that stimulates to develop safer and more efficientcatalytic systems for better performance in the energy productionand environmental remediation. Heterogeneous photocatalysis onTiO2 has been much applied to water purification due to its strongphotocatalytic oxidation activity and super hydrophilicity [5]. Tita-nium dioxide is a non-toxic, chemically and biologically inert mate-rial and highly stable against photo-corrosion [6]. Nevertheless, itslarge band gap (3.2 eV for anatase titania) confines its usage as aphotocatalyst exclusively to the ultra violet region that constitutesonly 5% of the solar spectrum [7]. Inducing photo-response oftitania in the visible spectrum that constitutes 40% of the typicalsunlight helps for efficient utilization of solar radiation and makesthe catalytic process more viable and economical.

Doping of semiconductors alters the band gap energy and con-sequently exhibits distinct changes in optical and electronicproperties. Moreover, the ability to change these characteristicproperties of a semiconductor through selective doping empha-sizes its undisputable candidature in photocatalysis. Titaniumdioxide is photo-catalytically active only when irradiated withultra violet light. However, when doped with various metals [8]and nonmetals [9] and composited with other lesser band gapenergy metal oxides [10]/semiconductors [11], it lowers theoriginal bandwidth to exhibit visible activity. These visible lightresponsive materials have been employed in various practicalapplications such as dye-sensitized solar cells [12], dilute magneticsemiconductors [13], H2 fuel production [14], self-cleaning surfacecoatings [15] and air/water purification.

Visible response of a catalyst helps to exploit the wider range ofvisible region of solar radiation to exhibit improved photocatalyticyield. However, the ability to produce reactive oxygen species(ROS) is another main characteristic of an efficient photocatalystapart from its visible absorption. Transition metal doping improvesthe visible absorption and betters electron trapping and reducesthe electron–hole recombination and thereby the net separationof charge carriers is enhanced [16,17]. The separated e�–h+ pairsspontaneously react with H2O and O2 to generate reactive oxygen

D. Sethi et al. / Journal of Photochemistry and Photobiology B: Biology 144 (2015) 68–74 69

species (ROS) such as �OH radicals, O2�� and H2O2 on the material

surface to annihilate alien species.Vanadium (V) oxide, with its high oxidation state, is a well

demonstrated catalyst of commercial interest in manufacturingsulfuric acid and maleic anhydride, and oxidizing o-xylene tophthalic anhydride. The special structural characteristics of vana-dium oxide nanostructures find potential applications in chemicalsensors [18], energy-conserving coatings [19], transparent conduc-tors [20], switching materials [21], actuators [22] and lithium-ionbatteries [23]. Several authors have investigated vanadium oxidedoped-TiO2 materials/composites and their photo-response in visi-ble region suggesting their use in various practical applications.Ivanova et al. [24] prepared mixed titanium-vanadium oxide thinfilms having admirable optical properties. Zhao et al. [19] foundthat titanium-vanadium oxide film electrodes exhibit conspicuousphoto-response in visible region. Wang and Huang [25] successful-ly used TiO2/V2O5 composites as an efficient photo-chargeablematerial in photoelectrochemical cells. Bettinelli et al. [20] exam-ined the photocatalytic activity of V-doped TiO2 materials formethylene blue degradation. V2O5 loaded N-doped TiO2 [26] andC-doped TiO2 [27] were found visible active and performed wellin photocatalytic degradation of gaseous toluene. Having all theseinformation on various applications of titania, it has been a greatchallenge to provide safe drinking water for humanity due toincreasing population and industrial revolution. Water treatmentusing chemicals leads to retaining of them even after treatmentprocess is completed; causing health hazards and makes the pro-cess not eco-friendly. Therefore, there is a compelling need fordevelopment of non-toxic and cost effective method for efficientwater disinfection. This investigation demonstrates the effect ofvarious concentrations of vanadia loading on titania and their pho-tocatalytic destruction of Escherichia coli in water separately underUV and UV–Visible irradiations.

2. Materials and methods

2.1. Preparation of V2O5/TiO2

Vanadia modified titania samples were synthesized fromammonium metavanadate (purity 99.5.00 %, CDH Analytical) andanatase TiO2 (purity 99.7%, Sigma Aldrich) precursors by usingincipient wet impregnation method. Known amount of ammoniummetavanadate (NH4VO3) crystals (weight corresponding to theloading percentage) were dissolved in 100 mL distilled water whilestirring and gentle heating. Then the appropriate amount of TiO2

was impregnated with required quantity of aqueous NH4VO3 solu-tion upon stirring for 15 min and oven dried at 120 �C. Then thedried samples were thoroughly ground in an agate mortar withpestle and finally calcined at 400 �C for 3 h in a muffle furnace.The concentrations of V2O5 on titania is varied from 0 to 10 wt.%.

Phase identification of vanadia loaded TiO2 catalyst system wasdetermined by X-ray diffraction (Diffractometer: X’PERT PRO,PANalytical, Netherlands) using Cu Ka radiation source(k = 0.154056 nm). The diffuse reflectance UV–Visible spectra(DRS) were recorded from 300 to 800 nm wavelength by using Var-ian Cary UV–Visible Spectrophotometer. The Raman spectra wererecorded in a dispersive type micro-Raman Spectrometer (Ren-ishaw in via Reflex, UK) in the wave number range of 100–1200 cm�1. The morphology of samples was observed under TEM(TECHNAI G2, FEI operated at 200 kV). Thermogravimetry analysiswas made with Mettler Toledo instrument (TGA/SDTA851e). Fouri-er Transform Infrared (FTIR) spectra were recorded in the range of400–4000 cm�1 on a Fourier Transform Infrared spectrophotome-ter (Model: Spectrum GX) supplied by Perkin Elmer India Pvt.Ltd, Kolkata and KBr was used as a reference. In order to identify

the oxidation state of V in V2O5/TiO2 samples, X-ray PhotoelectronSpectroscopy (XPS) measurements were carried out by employingthe model XPS: S/N-10001, Prevac Poland with a VG Scienta-R3000hemispherical energy analyzer. Spectra were recorded using Al Ka(hm = 1486.6 eV) X-ray radiation source operating at 200 W (10 kVand 20 mA). Instrument base pressure of 8 � 10�10 mbar wasmaintained during data acquisition. The spectrometer is wellcalibrated with Ag standard and referring to the binding energyof the Ag3d5/2 (368.2 eV). General resolution of the instrument is0.2 eV.

2.2. Photocatalytic activity

The antibacterial activity of various vanadia modified titaniasamples was carried out against E. coli (MTCC 739), a referencestrain obtained from Microbial Type Culture Collection and GeneBank, an International Depository Authority, Chandigarh, India.For this experiment, a bioreactor was fabricated which consistsof UV-C (Philips TUV 8 W G8 T5) and visible light (Philips T58 W) sources at the top and a magnetic stirrer at the bottom onwhich a beaker containing test solution was placed. Test solutionis composed of sterilized tap water with 0.85% NaCl to maintainthe osmotic balance of bacterial cells during the experiment, aninitial E. coli concentration of 108 CFU/ml and 0.5 mg/ml catalystsample. The height of 12 cm was maintained from test solutionsurface to the light source. The measured intensities of 8 W UVand 8 W visible light sources were found to be 50 lm/m2 and505 lm/m2 respectively at the solution surface. To carry out experi-ments only with visible light irradiation, at first 8 W fluorescentlamp at the top emitting intensity 505 lm/m2 was used. To observethe intensity effect, three fluorescent visible lamps having 15 Wvisible light at the top (12 cm height) and 8 W visible light sourcesat both sides (17.5 cm from wall) were used together; the totalintensity of these lamps were measured to be 2642 lm/m2. At var-ious intervals of irradiation time, 1 ml sample was drawn from thereaction vessel and serially diluted up to 10�4 and from each dilut-ed solution 0.1 ml was drawn for spread plating on LBA plates andincubated at 37 �C under dark condition for 24 h. After incubation,the numbers of colonies present in the plates were counted. TheColony Forming Units (CFU) per ml was calculated for each sampleby using the following formula:

CFU=ml ¼ No: of colonies� Dilution factor=Volume incubated

Where dilution factor is the reciprocal of the dilution in whichthe plate count was taken and volume inoculated is 0.1 ml. Theexperiment was carried out separately under UV and Visible lightand also under both UV and Visible light together at ambient atmo-spheric conditions. Our preliminary experiments conducted withcatalyst loading of 1 mg/mL showed very high photocatalytic inac-tivation of E. coli in a very short period of irradiation time whichcreated difficulties in seeing the differences in catalytic behaviorof various samples. Therefore, we decided to use a lower quantityof catalyst loading (0.5 mg/mL) for better distinction of the inacti-vation rate of various catalysts.

3. Results and discussion

X-ray diffraction patterns of various crystalline phases of V2O5/TiO2 samples are depicted in Fig. 1. It shows very prominentdiffraction peaks only for anatase titania even with vanadia loadingup to 5 wt.%, whereas samples with 7.5 and 10 wt.% of vanadialoading show strong intensity peaks corresponding to anatase tita-nia and weak intensity peaks to orthorhombic vanadia phase.Absence of vanadia peaks in the samples with < 7.5 wt.% of V2O5

implies that the V2O5 species are well dispersed in the TiO2 support

Fig. 1. XRD patterns of V2O5/TiO2 catalysts.

Fig. 3. FTIR spectra of V2O5/TiO2 catalysts.

Table 1FTIR spectral assignments of V2O5/TiO2 samples.

Band position(cm�1)

Spectral assignment

3693 OAH stretching of surface hydroxyl groups3600–2800 OAH stretching of physically adsorbed water molecule1626 HAOAH bending of physically adsorbed water

molecule1022 V@O stretching vibration996 VAOv stretching mode580–630 3VAOc stretching and the bridging VAObAV

deformation

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and are not detectable by XRD due to low concentration. On theother hand, higher loading leads to show separate phase of vanadiaindicating the accommodation limit of titania support. Presence ofanatase titania and vanadia phases in the samples is confirmed bywell matching with the corresponding standard JCPDS data filesNo. 01-071-1167 and 00-001-0359 respectively. However, for pur-pose of comparison XRD patterns of pure V2O5 and TiO2 are alsodepicted in the same Fig. 1.

TGA curve of uncalcined sample, 2.5% V2O5/TiO2 is shown inFig. 2. It represents the weight loss of sample against increasingtemperature. It shows a gradual fall in weight throughout the tem-perature range. The initial weight loss up to 210 �C could be due todehydration of both physisorbed and lattice water molecules. Theweight loss occurred between 210 and 450 �C is due to release ofammonia from the impregnated ammonium metavanadate and itis expected to form V2O5 on the titania support at 450 �C. It hasbeen reported in literature [28] that pure ammonium metavana-date releases ammonia to yield V2O5 at 260 �C. But the same isdecomposed at a higher temperature that could be due to the

Fig. 2. TGA curve of uncalcined 2.5 wt.%V2O5/TiO2 sample.

interaction between impregnated ammonium metavanadate andtitania support.

Fourier Transform Infrared Spectra of V2O5, TiO2 and vanadia-modified TiO2 samples are shown in Fig. 3. The respective spectralassignments for various peaks observed are furnished in Table 1.The band at 1626 cm�1 and a broad band observed between3600 and 2800 cm�1 are attributed to the HAOAH bending andOAH stretching vibration modes of physically adsorbed watermolecule respectively [29,30]. A band at 3693 cm�1 correspondsto the OAH stretching of surface hydroxyl groups [31]. For vanadia,peaks at 1022 cm�1 (V@O vibration), 996 cm�1 (VAOv stretchingmode) and group of bands < 630 cm�1 (edge-shearing 3VAOC

stretching and the bridging VAObAV deformation) are observed[32,33]. But in V2O5/TiO2 samples the characteristic V@O and VAOv

bands appeared as a broad feature particularly in the case of highervanadia loadings (>5%). This observation confirms the highly dis-persed V2O5 species as a monolayer at smaller loadings and forma-tion of V2O5 crystalline phase for higher loadings of vanadia overTiO2 support which is in excellent agreement with the XRD data.

Raman spectra of V2O5/TiO2 catalysts are shown in Fig. 4. Thespectral assignments for various Raman bands observed for unmo-dified and V2O5-modified TiO2 and pure V2O5 samples are given inTable 2. It has been reported that the position and width of Ramanbands of a material directly confer its vibrational and structuralproperties [34]. The Raman bands observed at 144, 194, 397, 518and 638 cm�1 are ascribed to anatase titania and are well support-ed by various reports [35,36]. As the V2O5 loading is increased onTiO2 support, Raman intensities of all vibrations in modifiedsamples are reduced. This indicates the increased perturbation ofanatase bands due to V2O5 clusters’ coverage over titania support.

Fig. 4. Raman spectra of V2O5/TiO2 catalysts.

D. Sethi et al. / Journal of Photochemistry and Photobiology B: Biology 144 (2015) 68–74 71

Further, no distinct V2O5 Raman bands are present in any of theV2O5/TiO2 system, however, at higher V2O5 loading (>5 wt.%), weakfeatures are observed at 704 and 994 cm�1 for V2O5 [37]. A similareffect is also seen in the XRD results. TEM micrographs of anatasetitania and 7.5%V2O5/TiO2 are shown in Fig. 5. It shows that particlesize of both samples is less than 50 nm. However, vanadia loadingon titania causes slight agglomeration.

The diffuse UV–Visible reflectance spectra of pure titania,vanadia and V2O5-modified titania samples are depicted inFig. 6. It shows that pure titania absorbs only in UV region ataround 390 nm wavelength. However, this absorption edgered-shifts in case of vanadia modified TiO2 samples and the shiftincreases with increasing loading concentration of V2O5. DensityFunctional Theory (DFT) calculations for transition metal dopedtitania system provide that the delocalization of V-3d states

Table 2Raman spectral assignments for V2O5/TiO2 samples.

Band position (cm�1) TiO2 Spectral assignment Band p

144 Eg -symmetric TiO2 144, 1194 Eg -symmetric TiO2 284, 4398 B1g OATiAO bending 303, 4518 A1g + B1g TiAO stretching 526638 Eg -symmetric TiO2 704

994

Fig. 5. TEM micrographs of unmo

contributes to the formation of impurity energy levels just belowthe conduction band edge of TiO2 by hybridizing with Ti-3dstates. This leads to the formation of a new conduction bandminimum at a lower energy that results in the band gapnarrowing [38]. Hence, the observed red-shifted absorptions inV2O5/TiO2 system are clearly understandable. The sample with10 wt.% V2O5 loading shows strong absorption at 525 nmwavelength.

Chemical composition and surface properties of selected cata-lysts are determined by XPS studies. All XPS spectra for V2O5/TiO2 samples are corrected with respect to C 1s level of adventi-tious carbon at 284.6 eV. Three different core level XPS spectrafor oxygen (O1s), vanadium (V2p) and titanium (Ti2p) are consid-ered for detailed study. The collected spectra are de-convolutedassuming Gaussian line profile. The spin–orbital spitting of Ti2pinto Ti 2p3/2 and 2p1/2 states gives rise to the binding energy peaksat 458.8 eV and 464.5 eV respectively (Fig. 7a) indicating the exis-tence of Ti4+ ions in titania support [39]. The de-convoluted corelevel spectrum of O1s in Fig. 7b renders two peaks at 529.4 and532.06 eV for oxygen in TiO2 lattice and oxygen due to surfacehydroxyl groups respectively [40,41]. These surface hydroxylgroups are also evidenced by FTIR (Fig. 3) and become the catalyticsites that can produce hydroxyl radicals to oxidize organic con-taminants. The de-convoluted XPS spectra of V2p in V2O5/TiO2 sys-tem are depicted in Fig. 7c. V2p splitting in pure V2O5 spectrumshows two peaks; one at 517.28 eV (2p3/2) and another at523.86 eV (2p1/2) confirming V in V5+ state [39]. However, in thespectra of V2O5/TiO2 samples (5%, 7.5%, 10 wt.% V2O5), an addition-al peak with moderate intensity at around 519 eV is observed,which lies in between V5+2p3/2 and V5+2p1/2 states. This additionalpeak could be due to the interaction between titania support andvanadia over layer. Moreover, it is very interesting to note thatthe red shifts in binding energies of V5+2p3/2 and V5+2p1/2 withincreasing V2O5 content (Fig. 7c) confirms the increased interactionbetween V2O5 and the titania support and provides a hint that V5+

undergoes a partial reduction.

osition (cm�1) V2O5 Spectral assignment

96 Lattice vibration04 V@O bending vibration83 VAOAV bending vibration

Triply coordinated oxygen (V3AO) stretchingDoubly coordinated oxygen (V2AO) stretchingTerminal oxygen (V@O) stretching

dified and modified titania.

Fig. 6. UV–Visible diffuse reflectance spectra of V2O5/TiO2 catalysts.

Fig. 7a. XPS spectrum of titanium (Ti2p) in V2O5/TiO2 photocatalyst system.

Fig. 7b. XPS spectrum of oxygen (O1s) in V2O5/TiO2 photocatalyst system.

72 D. Sethi et al. / Journal of Photochemistry and Photobiology B: Biology 144 (2015) 68–74

The photocatalytic activity of TiO2, V2O5 and various V2O5/TiO2

catalysts are examined against E. coli with increasing irradiationtime separately under UV and Visible and combindly under UV–Visible light. All samples tested under visible light irradiation aloneshow no inactivation of E. coli even with high intensity and atlonger irradiation time (figure not shown). However, experimentsconducted separately under UV and UV–Visible irradiations exhibitsignificant inactivation of E. coli, which are depicted in Figs. 8a and8b respectively. They show that all samples are able to photoanni-hilate the E. coli at a faster rate up to a range of 4–5.5 log reductionfrom the initial concentration during the first 10 min of irradiation,whereas a gradual log reduction is observed with subsequent irra-diation time. E. coli destruction is induced by the strong oxidizingability of reactive oxygen species (ROS) such as �OH, H2O2, andO2�� generated during photocatalysis and their attack on polyun-

saturated phospholipids and subsequent DNA damage in bacteria.The reasons for high rate of killing of E. coli during the initial periodof irradiation could be due to fresh attack of photo-catalyticallygenerated reactive oxygen species (ROS) on E. coli. Though thisattack is continued subsequently, there is a competition for ROS

among the remaining active E. coli cells and cell materials releasedduring photocatalysis [42,43] thereby leading to show a slowerrate of killing. However, photocatalytic activity differs for eachsample. Prestine V2O5 shows inferior activity than TiO2. However,when titania is modified with vanadia, its photocatalytic effecttoward inactivation of E. coli is enhanced compared to TiO2. It isinteresting to observe that the activity increases with increasingloading concentrations of V2O5 from 0 to 10 wt.% on titania. UnderUV irradiation condition, pure vanadia and titania show only 5.8and 6 log reductions respectively at 75 min from the initial E. coliconcentration (108 CFU/mL). This log reduction value is furtherincreased to 7 with 1.2 wt.% loading of V2O5 on titania at the sameirradiation time. At higher loadings of 2.5, 5, 7.5 and 10 wt.% ofV2O5, 8 log reductions are observed indicating complete inactiva-tion of bacteria at irradiation times of 75, 60, 45 and 30 min respec-tively (Fig. 8a). These observations show that increased logreduction can be achieved with increasing loading concentrationsof V2O5 on titania. However, while comparing these UV resultswith UV–Visible irradiation condition (Fig. 8b), log reduction valueat any given irradiation time between 15 and 60 min is higher inUV alone. This concludes that vanadia loading helps to improvethe activity of titania more under UV irradiation than UV–Visible.Although samples with 7.5 and 10 wt.% V2O5 show 8 log reductionvalues at different irradiation time of 45 and 30 min under UV andUV–Visible irradiation respectively, they show their variation inlog reduction values lower under UV–Visible irradiation than UValone during irradiation time below 45 and 30 min respectively.Photocatalytic degradation activity of V2O5 modified TiO2 catalystreported in the literature is compared with the selected sample.It has been observed by Kim et al. [44] that 5% vanadia loadingon TiO2 sample reduces/shows no significant effect in the photo-catalytic activity compared to pure titania under 8 W (2 � 4 W)UV irradiation with the initial E. coli concentrations of 105 CFU/ml. In this study, we have obtained much improved results forthe same 5% vanadia loading concentration with 8 W UV irra-diation and the initial E. coli concentrations of 108 CFU/ml. Thisresult indicates that the sample, 5% V2O5/TiO2, studied in this workshows relatively better activity than that of the 5% V2O5/TiO2 sam-ple reported by Kim et al. [44].

The reason for the observed higher photocatalytic activities forvanadia modified TiO2 mixed oxide system than its individual oxi-des could be due to the interaction between the guest vanadia spe-cies and the TiO2 support. Lin et al. reported that the strength ofBrønsted acidity positively increases with increasing V2O5 loading

Fig. 7c. XPS spectra of vanadium in V2O5/TiO2 photocatalyst system.

Fig. 8a. Photocatalytic activity of V2O5/TiO2 catalysts against E. coli under UVirradiation.

Fig. 8b. Photocatalytic activity of V2O5/TiO2 catalysts against E. coli under UV–Visible irradiation.

D. Sethi et al. / Journal of Photochemistry and Photobiology B: Biology 144 (2015) 68–74 73

on titania whereas Lewis acidity remains almost constant but thesurface area decreases [45]. They concluded that the increased cat-alytic activity of the V2O5/TiO2 materials is attributed to theincreased surface Brønsted acidity rather than the surface area.Therefore, the interaction between metal oxides helps to generatesurface hydroxyl groups that are considered as the active sites forexhibiting photocatalytic activity [46] as more hydroxyl groups canproduce more number of �OH radicals to attack the bacterial cell[47]. The interaction between these two oxides was evidenced inthe XPS spectra (Fig. 7c), which show an additional broad peak ataround 519 eV that lies between V5+ 2p3/2 (517.28 eV) and V5+

2p1/2 (523.86 eV). Red shifting of these V5+ 2p3/2 and 2p1/2 peaksare the indications for the partial reduction of V5+ induced by inter-

action of V2O5 with TiO2 support. Further, it is expected to havehigh activity for V2O5/TiO2 samples under UV–Visible irradiationthan UV alone as they absorb strongly in the visible region asobserved in Fe-doped TiO2 system [48]. But the obtained resultsshow lower activity under UV–Visible condition which is verymuch disappointing and it implies that the absorption of visiblelight alone is not important in bringing out catalysis, follow upaction after absorption such as formation of e�–h+ pairs and theirseparation from recombination is very much relevant for catalysis.Perhaps, visible light absorption in V2O5/TiO2 system might notinvolve in photo-excitation to yield e�–h+ pairs or induces thee�–h+ recombination to lower the photocatalytic effect. SinceV2O5/TiO2 system shows high photocatalytic inactivation under

74 D. Sethi et al. / Journal of Photochemistry and Photobiology B: Biology 144 (2015) 68–74

UV irradiation, it gives a scope to use them in the UV based waterpurification systems at ambient atmospheric conditions.

4. Conclusions

V2O5/TiO2 catalysts prepared by wet impregnation methodshow superior photocatalytic activity for E. coli destruction thanits individual metal oxides under UV and UV–Visible irradiation.The rate of killing of bacteria is a little higher in UV alone than thatunder UV–Vis irradiation. As the vanadia concentration loading ontitania increases, the photocatalytic inactivation of E. coli alsoincreases progressively, indicating for inevitable importance ofsurface modification of titania to achieve high photocatalytic activ-ity. Increasing V2O5 content leads to increased interaction of V5+

ions with the TiO2 support as we evidenced a red shift in theV2p binding energies in XPS spectra of V2O5/TiO2 samples. Thesesurface interactions resulted from the electron transfer betweenguest V2O5 and host TiO2 give rise to a better photocatalytic activ-ity of the synthesized hybrid catalysts than that of pristine materi-als. Hence, V2O5/TiO2 catalyst could be a good choice material forUV based water disinfection systems working at ambient atmo-spheric conditions.

Acknowledgements

Author wishes to thank Ministry of Environment and Forest,New Delhi for financial support and also thank Director, CSIR-Insti-tute of Minerals and Materials Technology, Bhubaneswar forencouragement. One of the author Diptipriya Sethi wishes to thankMinistry of Social Justice and Empowerment, New Delhi for award-ing Rajiv Gandhi National Fellowship.

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