Microporous and Mesoporous Materials 168 (2013) 57–64

Contents lists available at SciVerse ScienceDirect

Microporous and Mesoporous Materials

journal homepage: www.elsevier .com/locate /micromeso

Efficient electrosynthesis of highly active Cu3(BTC)2-MOF and its catalyticapplication to chemical reduction

R. Senthil Kumar a, S. Senthil Kumar b, M. Anbu Kulandainathan a,⇑a Electro Organic Division, Central Electrochemical Research Institute, Karaikudi, Indiab Department of Chemistry and Biochemistry, The University of Texas at Austin, USA

a r t i c l e i n f o a b s t r a c t

Article history:Received 16 July 2012Received in revised form 28 August 2012Accepted 27 September 2012Available online 6 October 2012

Keywords:Electrochemical synthesisMetal organic frameworkCu3(BTC)2

Chemical reductionp-Nitrophenol

1387-1811/$ - see front matter � 2012 Elsevier Inc. Ahttp://dx.doi.org/10.1016/j.micromeso.2012.09.028

⇑ Corresponding author. Tel.: +91 4565 241550; faxE-mail address: manbu123@yahoo.com (M. Anbu

Cu3(BTC)2 (Metal organic frameworks-MOF) synthesized through electrochemical route and is used as ancatalyst for chemical reduction of nitrophenol in the presence of excess NaBH4. Optimization studies forthe electrochemical parameters have been demonstrated in order to get 97.51% yield with respect to cop-per dissolution. Synthesized Cu3(BTC)2 is characterized by XRD, FT-IR, SEM, TEM, EDX, BET, TGA and XPSand the results reveal that supporting electrolyte, current density play a crucial role in controlling theparticle size and also improving the yield of MOF. The SEM and TEM studies show that the morphologyof the synthesized particles is cubic in nature and the particle size is �10–20 nm. The oxidation state ofCu in the synthesized Cu3(BTC)2 found to be +2 from XPS studies. Synthesized Cu3(BTC)2-MOF function asan effective catalyst to activate the reduction of p-nitrophenol to p-aminophenol in the presence of excessNaBH4 and the calculated apparent rate constant of 8.69 � 10�2 s�1 is found to be higher than the othersupported noble metal nanoparticle and polymer nanocomposites.

� 2012 Elsevier Inc. All rights reserved.

1. Introduction

In the past few decades, many researchers gave much attentionto develop newer synthetic protocols for preparing highly crystal-line porous Metal organic frameworks (MOF), which consists ofboth inorganic and organic moieties exclusively linked by strongbonds. Based on the metal ions, metal clusters and organic ligandsmore diversity in the synthesis was possible. Since extra-large poresolids with relatively high thermal stability have been synthesizedand these exhibit novel fascinating three-dimensional (3D) topolo-gies. MOFs can exhibit tunable chemical functionality, exception-ally high surface areas (500–6500 m2 g�1) with large pore sizes(3–35 A�) [1] and tailorable nanoporous host materials as robustsolids with high thermal and mechanical stability. These materialsare having rigid pores, which are not collapsed upon addition or re-moval of solvent or other guest molecules occupying the pores.Several framework materials are derived from benzene-1,3,5-tri-carboxylic acid (BTC), in combination with different metal ionsand clusters. Among them, HKUST-1 (Cu3(BTC)2) is the mostimportant material [2], which exhibits highly porous nature andhas promised material for a number of diverse potential applica-tions including gas storage, gas separation and catalysis in organicsynthesis [3–15].

The conventional routes for the synthesis of MOF have somelimitation on scaling up. Moreover, some authors attempted faster

ll rights reserved.

: +91 4565 227713.Kulandainathan).

and more efficient synthetic routes like microwave synthesis [16]and sonochemical synthesis [17] of MOFs. But, there are only afew reports available based on electrochemistry and patterned filmgrowth on metal surface by anodic oxidation [18] or by galvanicdisplacement method [19], which are less complicated, avoids sev-eral steps and less cleaning procedure. Mueller et al., have studiedthe generation of MOFs via electrosynthesis in methanol medium[20] and also developed a series of MOFs using metal ion with var-ious linkers particularly terephthalic acid, naphthalene dicarbox-ylic acid and benzene tricarboxylic acid [21,22]. However, theabove studies have limitation over the yield, particle size and sur-face area. Chui et al., reported that each of the four coordinationsites of three Cu2+ ions are bound to twelve carboxylate oxygenatoms of the two BTC ligands to form a face centered crystal latticewith Fm3m symmetry which possesses a three-dimensional chan-nel system with a bimodal pore size distribution based on theirstructural studies of Cu3(BTC)2 [2]. Further, the above authors havecalculated the copper–copper distance as 0.263 nm with a porediameter of 0.9 nm were formed from 12 paddle-wheel subunitsforming a cubic octahedron.

The active copper species have free binding sites in the nano-spaces, which facilitate the formation of adducts with electroactivemolecule. Such unique properties may provide benefits that makea Cu-MOF a good candidate for catalytic reaction. Cu3(BTC)2 haswidely been used as a heterogenous catalyst in acetalization ofaldehydes with methonol [23], quinoline synthesis [24], a-pineneoxide rearrangement [25], trimethylsilylazide addition to carbonylcompounds [9], oxidation of benzylic compounds with t-butyl

58 R. Senthil Kumar et al. / Microporous and Mesoporous Materials 168 (2013) 57–64

hydroperoxide [26], ring opening of epoxides with methanol [27],alkylation of amines with dimethyl cabonate [28], oxidation ofcyclohexene to allylic products [29], cyclopropanation of styrenesand cycloaddition of phenyl acetylene with benzyl azide [30]. AlsoCu3(BTC)2 along with TEMPO was proved to be a catalyst for (i) theoxidation of benzylic alcohol [22] and (ii) heterogeneous chemose-lective reduction of C–C multiple bonds [31] on which the catalyticactivity may depend on (a) availability of significant numbers ofaccessible sites due to the open MOF crystal structure, (b) revers-ible coordination of organic linkers with the metal atom and (c)the influence of the electrostatic field in the cavity by the partiallycharged framework [31]. Our group has already demonstrated theelectrochemical catalysis of Fe based MOF for the electrochemicalconversion of hydroxide [32].

In this work, we reported the optimized condition for the elec-trochemical synthesis of Cu3(BTC)2 by anodically dissolving copperion to link/bind with BTC molecules (organic linker) by applyingconstant voltage using similar area of copper plates, as a cathodeand anode with tetrabutylammoniumtetrafluoroborate (TBATFB)as supporting electrolyte. The advantages of this synthetic protocolprovides higher yield, high surface area and purity than the earlierprocedures and also demonstrate for the first time that Cu3(BTC)2

as a novel heterogeneous catalyst for p-nitrophenol (4-NP)conversion.

Scheme 1. Schematic representation for synthesis of activated Cu3(BTC)2 byelectrochemical method.

2. Experimental

2.1. Materials and methods

Cu-plates with 99.9% purity are used as electrode material. Ben-zene tricarboxylic acid (BTC Acros organics, India), Tetrabutylam-moniumtetrafluoroborate (TBATFB, Acros organics, India) areanalytical grade, methanol (Sisco Research Laborotories) HPLCgrade were used as received.

2.2. Experimental procedure

Two copper electrodes having similar area (10.5 cm2) were usedas an anode and cathode for the synthesis of Cu3(BTC)2. The organiclinker (0.1 M BTC) and supporting electrolyte (TBATFB) were dis-solved in 50 ml methanol solution in the electrolysis cell and stir-red for 15 min for complete dispersion. Electrolysis was carried outin an electrochemical cell under constant voltage electrolysis (withkeeping current varying to make voltage constant) for more than2.5 h to complete the reaction. Finally the sky blue color precipitateof Cu3(BTC)2 was collected from the electrolysis cell and allowed todry in a hot air oven at 120 �C for 12 h and activated at 200 �C for2 h. The sky blue color which appeared initially was changed todark blue after activation, i.e., change in color indicates that theco-ordination number of Cu in the complex state is changed fromsix to four [33]. A detailed flowchart is presented as Scheme 1. Fur-ther, optimization of experimental parameters like supportingelectrolyte concentrations, applied voltage and reaction time werecarried out in order to get good yield and highly crystalline Cu3(-BTC)2. The yield of the product corresponding to the amount ofweight loss in the copper anode is 97.51%.

2.3. Characterisation

The surface morphology and microstructure of synthesizedsamples were characterized by scanning electron microscope(SEM Hitachi S-3000H from Japan). The morphology and particlesize was determined by using transmission electron microscopy(Philips CM 200). The synthesized product was characterized byXRD (‘Xpert PROPANalyticalPW3040/ 60‘X’PertPRO’) using Cu–Ka

radiation (k = 1.5418� A), with the voltage and current were heldat 40 kV and 30 mA (2h = 5–50�) at a scan rate of 1� min�1. FourierTransform Infrared spectrum has been recorded on a Nicolet 5DX-FTIR spectroscopy using KBr pellet in the range of 400–4000 cm�1.The surface area and pore volume of the Cu3(BTC)2 are determinedfrom BET adsorption isotherms of nitrogen at 77 K using a staticvolumetric apparatus Micrometrics, ASAP 2020 V3.00H.

X-ray photoelectron spectroscopy (XPS) of synthesized samplehas been investigated using VG electron spectroscopy, were re-corded using an X-ray source (Al Ka radiation) with a scan rangeof 0–1200 eV binding energy. The collected high-resolution XPSspectra were analyzed using XPS peak fitting software program.The energy scale was adjusted using carbon peak, C1s spectra at284.5 eV. The EDX spectrum (Thermo Electron Corporation, USA)was collected at an accelerating voltage of 20.0 kV and a magnifi-cation of 700�. Thermogravimetric analysis was performed usinga Q 500 instrument manufactured by TA Instruments and experi-ments were conducted with a constant heating rate of 5 �C min�1

in nitrogen atmosphere.

2.4. Chemical catalysis

The catalytic reduction reaction was carried out in a standardquartz cell with a 1 cm path length and about 3 ml volume. Theprocedure entailed in mixing excess NaBH4 (15 mM) with 4-NP(0.1 mM) solution in water in the quartz cell. Mixing leads to thecolor change from light yellow to green yellow. The absorptionspectra were recorded immediately after the addition of Cu3(BTC)2

(5 ll of 5 lg of Cu3(BTC)2 in aqueous dispersion) with a time inter-val of 30 s in a scanning range of 200–600 nm at 25 �C.

3. Results and discussion

3.1. Optimization of electrolysis condition

Fig. 1a presents the effect of concentration of supporting elec-trolyte and applied voltage on the yield of the product, which

Fig. 1. The plots corresponding to (a) concentration of supporting electrolyte vs yield and voltage vs yield (b) the yield vs reaction time and current vs reaction time.

R. Senthil Kumar et al. / Microporous and Mesoporous Materials 168 (2013) 57–64 59

clearly showed that while increasing the concentration and appliedvoltage the yield also increases. Fig. 1b depicts the yield vs reactiontime and current vs reaction time. The yield mainly depends onreaction time but as the reaction time goes on the availability ofBTC decreases and thereby current decreases. However, it is wor-thy to mention that, while increasing the concentration ofTBATFB > 0.02 M and the applied voltage more than 15 V, the par-ticles are agglomerated and cubic shapes are getting collapsed (seeSupporting information SI-1). Hence, the optimized experimentalconditions are so important to get regular shapes without agglom-eration with good yield of crystalline Cu3(BTC)2. Since all theparameters for the synthesis are electrochemically controllable,the above process can be said to be scalable.

The criteria for optimized electrochemical condition in order toget maximum yield, high surface area, controlled Cu dissolutionand good crystallinity without agglomerisation for the synthesisof Cu3(BTC)2 is presented as Scheme 1.

3.2. Characterisation

Fig. 2a shows the morphological structure (SEM image) of theelectrochemically synthesized Cu3(BTC)2 sample under optimized

Fig. 2. (a) Scanning electron microscopic image, higher magnification (inset) and (b) TrCu3(BTC)2.

experimental condition. Morphological studies clearly shows thesynthesized Cu3(BTC)2 is highly porous in nature and the figure in-set represents higher magnification of the SEM image exhibiting auniform decoration of cubic shaped particles of the Cu3(BTC)2.

Transmission electron microscopy (TEM) analysis is used to findout the individual particle size of the cubic structure of Cu3(BTC)2

are shown in Fig. 2b. Inset in the TEM image of Fig. 2b shows theSAED pattern, in which the bright circular rings representing thehighly polycrystalline nature of the synthesized Cu3(BTC)2 parti-cles, which is in good agreement with the electron diffraction re-sults. As can be seen in the TEM image, 10–20 nm Cu3(BTC)2

particles form a network structure in cubic shape of 0.2–0.5 lmdue to Van-der walls force. Higher magnification image (see Sup-porting information SI-2) clearly shows that the nanocrystals of10 nm particles closely bound together forms the cubic shape.Hence, SEM, TEM and SAED pattern unambiguously proved thatthe discrete state as well as the Cu3(BTC)2 nanoparticles were for-mulated in cubic manner.

The XRD pattern of synthesized Cu–BTC is shown in Fig. 3. Thediffraction peaks of electrochemically synthesized sample are wellconsistent with available literature [34,35] and the simulated pat-tern published by Chui et al., [2] calculated using single crystal data

ansmission electron microscopy image, selected area diffraction pattern (inset) of

Fig. 3. Powder X-ray diffraction pattern of electrochemically synthesizedCu3(BTC)2.

60 R. Senthil Kumar et al. / Microporous and Mesoporous Materials 168 (2013) 57–64

are comparable. The observed XRD peaks are very sharp indicatesthat highly crystalline nature of the synthesized material. Thesepeaks correspond to the face centered cubic structure of Cu3(BTC)2

nanoparticles [34]. Moreover, it is interesting to note that the syn-thesized Cu3(BTC)2 from optimized experimental condition doesnot exhibit any peaks corresponding to CuO (2h = 35.5� and38.7�) or Cu2O (2h = 36.43�) and also in particular no significantimpurities peak at 2h = 11.0� [36] as observed by Hartmann et al.,who synthesized Cu3(BTC)2 by hydrothermal method which con-firms that higher purity Cu3(BTC)2 was obtained from the presentmethod using optimized electrochemical experimental conditions .

Therefore, electrochemically synthesized Cu3(BTC)2 under opti-mized experimental condition exhibits the highly crystalline struc-ture of Cu3(BTC)2 in which twelve carboxylate oxygen atom fromtwo BTC molecules (electrochemically reduced at cathode) andeach of the three Cu2+ ions (electrochemically oxidized from Cu an-ode) forms Cu3(BTC)2 like structure with paddle-wheel units of fcclattice [2]. The formation of Cu3(BTC)2 is shown in reaction scheme2.

In order to confirm the nature of bonding between benzene tri-carboxylic acid and Cu2+, vibrational spectral analyses was carriedout and are shown in Fig. 4. The band observed around 1715 cm�1

can be significantly assigned to acidic C@@O stretching vibrationpresent in the BTC, which after complexation with Cu2+ is shiftedto 1665 cm�1 suggesting that deprotonated has happened in acidicC@@O. This unambiguously indicates that the carboxylate ion partic-ipates in the complex formation. The absence of peaks at 410, 500,610 and 615 cm�1 indicates that the synthesized materials arefree from CuO and Cu2O [37] crystals during the nucleation of

3CCu2++ ++

1

2

HO

O

1,3,5-

O

-Benzene tricarboxylic acid

O

OH

O

OHH

MeeOH/

R

/TBA

R.T

-O

ATFB

O

B

Scheme 2. Reaction scheme for the synthesis of Cu

Cu3(BTC)2. Moreover, the characteristic vibration at 714 cm�1

may be attributed to Cu–O stretching vibration, in which the oxy-gen atom is coordinated with Cu. The broad band observed at2500–3300 cm�1 region in benzene tricarboxylic acid is due toO–H stretching in carboxylic group, which is shifted to 3100–3600 cm�1 region in the complex indicating the presence of looselybound water molecules in Cu3(BTC)2.

To find out the exact specific pore volume and surface area ofelectrochemically synthesized and activated Cu3(BTC)2, the BETnitrogen gas adsorption/desorption isotherm studies were carriedout. The nitrogen adsorption data yield a specific pore volume of0.43 cm3 g�1 and surface area of 1498 m2 g�1. While comparingthe reported values of Cu3(BTC)2, the specific surface area is almostsimilar 1510 [35], 1587 m2 g�1 [38] and pore volume value is alsosimilar with the results of Pradip Chowdhury et al.,(0.425 cm3 g�1)[39] and Chui et al., (0.333 cm3 g�1) [2]. Nanoporous nature is alsoconfirmed from the steep rise at the high relative pressure in theisotherm.

X-ray photoelectron spectroscopy is carried out on particlesrecovered after complete evaporation of solvent, separating thesupporting electrolyte and starting materials if any, which shownin Fig. 5. The main peaks observed in the survey scan as C1s,Cu2p3/2, Cu2p1/2 and O1s centered at 284.5, 934.14, 954.27 and531.1 eV respectively. The binding energy of C1s emission peak ob-served at 284.5 eV, which was used as the reference in the presentXPS measurements. In Cu2p core level photoelectron spectra forCu3(BTC)2 displayed doublets i.e., Cu2p3/2 and Cu2p1/2 at 934.14and 954.27 eV respectively. The Cu2p3/2 and Cu2p1/2 main doubletswere separated by �20 eV and their satellite peaks at �8 eV fromthe main peaks were also observed. Further, the similar satellitepeaks were also observed in CuO indicating that Cu in the synthe-sized MOF is in divalent nature, which is consistent with our FT-IRand XRD results. The binding energy of O1s core level is observedat 531.1 eV corresponds to the characteristics of O2� ions in thecrystalline network. These results are in good agreement withthe previously reported work [40]. The chemical composition andthe purity of electrochemically synthesized Cu3(BTC)2 was deter-mined using energy dispersive X-ray analysis. It clearly showsthe Cu without any impurities other than carbon and oxygen.The effective atomic weight percentage of Cu, C, and O are listedin the Table 1. Since there are no peaks corresponding to Boronand Fluoride, we conclude that electrochemically synthesizedCu3(BTC)2 does not contain any impurities (like supportingelectrolyte).

The nature of thermal stability and the molecules that are des-orbed or buried in the synthesized Cu3(BTC)2 with respect to tem-perature was studied by TGA and compared with literature and ispresented in Fig. 6. The synthesized Cu3(BTC)2 was heated in nitro-gen atmosphere with a heating rate of 5 �C min�1. The thermogramshows three different regions viz., (1) the first weight loss (19.5%)region between 50 and 120 �C indicating the loss of moisture (2)

O

O

O

O O- Cu

O-

u2+ -

O

Copper

-O

(II

O

O

I)1,3

O

,5-Benzenetricarboxylic acid

OC

O-

O

u2+

Cu

O

O-u2+

3(BTC)2 from 1,3,5-Benzene tricarboxylic acid.

Fig. 4. FT-IR spectra of (a) 1,3,5-benzene tricarboxylic acid and (b) Cu3(BTC)2.

Fig. 5. X-ray photoelectron spectrum of (a) Cu2P region and (b) O1s region of the synthesized Cu3(BTC)2.

R. Senthil Kumar et al. / Microporous and Mesoporous Materials 168 (2013) 57–64 61

Table 1Element composition determined by EDX analysis for Cu3(BTC)2 sample.

Sl. no. Element Weight%

1 % of C 25.572 % of O 34.533 % of Cu 39.90

Fig. 6. Thermo-gravimetric analysis of Cu3(BTC)2.

62 R. Senthil Kumar et al. / Microporous and Mesoporous Materials 168 (2013) 57–64

the region between 120 to 293 �C corresponding to the loss of twowater molecule from the MOF with the weight loss of 6%. It isinteresting to note that Cu co-ordination has been reduced fromsix to four takes place at this stage(Scheme 3), which was con-firmed by the color change during activation [33] and (3) the thirdregion starts at 293 �C, at that temperature the structure of MOFcollapse and the organic linker is buried. This weight loss is com-pleted at 438 �C and stable up to 800 �C and the residue is foundto be 35% which is comparatively higher than the reported valueof 24% and is ascribed to the availability of Cu2+ in the open struc-ture for catalysis. While comparing the results of Harman et al.[35], they observed that the trapping of supporting electrolytemethyltributylammoniummethyl sulfate (MTBS) in the pores ofCu3(BTC)2, but in the present case the supporting electrolytenamely TBATFB is not trapped inside the pores of the Cu3(BTC)2,which can be explained from the higher Cu2+ content and lowerweight loss of the organic linkers.

Scheme 3. Schematic representation of coordinated

3.3. Chemical reduction of p-nitrophenol

Due to the enhanced properties of the synthesized Cu3(BTC)2, asa proof of concept, an attempt is being made to demonstrate Cu3(-BTC)2 as an effective catalyst for the chemical reduction of p-nitro-phenol. Cu3(BTC)2 was used in the reduction of p-nitrophenol inwater along with excess NaBH4 (see reaction scheme 4). The pro-cess of reduction was monitored by measuring UV–Vis spectra re-corded at different time t. Every 30 s UV spectrum was recordedand presented in Fig. 7a. The absorption peak of p-nitrophenolundergoes a red shift from 317 to 401 nm immediately upon addi-tion of aqueous NaBH4 solution (15 mM) with an associated colorchange from light yellow to yellow–green (corresponding to thegeneration of p-nitrophenolate anion) [41]. The absorption peakat 401 nm remains unchanged for extended periods of time show-ing that even an excess concentration of NaBH4 is unable to bringout reduction of p-nitrophenolate anion. Interestingly, addition ofvery small aliquots [5 lL i.e.,(5 lg)] of Cu3(BTC)2 dispersion(1 mg of MOF was dispersed in 1 ml of acetone) into the abovesolution was found to cause fading and finally decoloration ofthe yellow–green color of p-nitrophenolate in aqueous solution.This is clearly proved by the gradual disappearance of absorptionpeak at 401 nm after the addition of Cu3(BTC)2 MOF, with a concur-rent appearance of two new peaks at 310 nm and 230 nm, corre-sponding to the formation of p-aminophenol as shown in Fig. 7b(corresponding plot of ln(A) vs time for the disappearance of p-nitrophenol absorption at 401 nm upon reduction in the presenceof excess borohydride in solution). Thus, the kinetics of the reduc-tion reaction can be treated as pseudo-first-order with respect to p-nitrophenol concentration. Here the ratio of the absorbance A(t) ata given time t to the absorbance Ao measured at t = 0 is directlyproportional to the ratio of the c/c0. From this, the rate constantof p-nitrophenol reduction reaction is calculated to be8.69 � 10�2 s�1. The rate constant obtained from slope of the ki-netic curves has been related to catalyst concentration. That is, asthe concentration of the catalyst increases (more surface area forthe reaction to occur) the rate is also found to increase. The con-centration of NaBH4 was chosen to exceed the concentration ofp-nitrophenol by far. Because the chemical conversion of nitrophe-nol to aminophenol takes place only in the presence of excessNaBH4 [42]. In the absence of BH4 ions, the reaction does not hap-pen even noble metal catalyst like Pt used for this reaction. The roleof excess NaBH4 is only to change the solution pH form neutral tomore than 12 and to remove or abstract the acidic proton fromnitrophenol to nitrophenolate. After that, the catalyst (Cu3(BTC)2

MOF) will catalyze the chemical reduction of nitrophenolate toaminophenolate. So whenever the availability of catalyst is more,

and decoordinated forms of water in Cu3(BTC)2.

P-Nitrophenol

OH

NO2

EX

Cu

.N

3(B

aB

T

H4

C)2

P-Aminophenol

OH

NH2

Scheme 4. Reduction scheme of p-nitrophenol to p-aminophenol using synthesizedCu3(BTC)2.

Fig. 7. (a) UV–Vis absorption spectra recorded at different times t using Cu3(BTC)2

(a—0 s, b—30 s, c—60 s, d—90 s, e—120 s) and (b) a plot of concentration withrespect to time (i.e., ln(A) vs time plot) of the above UV absorption spectra.

R. Senthil Kumar et al. / Microporous and Mesoporous Materials 168 (2013) 57–64 63

obviously the rate of conversion is also more, because reaction be-haves like pseudo first order kinetics. The obtained value of therate constant is higher than the rate of reduction of p-nitrophenol(0.1 mM) in aqueous NaBH4 in the presence of Au(NP)/PEDOT/PSSand Au(NP)/PMMA was found to be 0.0439 and 0.0073 s�1 respec-tively [41,42].

4. Conclusions

The problem associated with the scalable synthesis is unveiledhere by optimizing the electrochemical parameters as well as by

selecting the suitable supporting electrolyte in order to get pureCu3(BTC)2. The yield corresponding to the electrochemical dissolu-tion of Cu is 97.51%. The advantage of the present synthetic route isthat the Cu content is about 32% than the previously reported valueof 22% and the thermal stability of the Cu3(BTC)2 is as high as293 �C. The surface area and pore volume of the synthesized Cu3(-BTC)2 were found to be 1469 m2 g�1, 0.43 cm3 g�1 respectively. Fi-nally, it was demonstrated that the presence of high Cu content(exposed open structured Cu which is Lewis acidic in the paddlewheel structure of Cu3(BTC)2) is responsible for highly effectiveconversion of p-nitrophenol to p-aminophenol. The rate constantcorresponding to p-nitrophenol reduction reaction is as high as8.69 � 10�2 s�1.

Acknowledgements

The authors are grateful to CSIR, New Delhi for EMPOWER Pro-ject funding. R. Senthil Kumar thanks CSIR, New Delhi for SeniorResearch Fellowship.

Appendix A. Supplementary data

Supplementary data associated with this article can be found, inthe online version, at http://dx.doi.org/10.1016/j.micromeso.2012.09.028.

References

[1] L. Yang, S. Kinoshita, T. Yamada, S. Kanda, H. Kitagawa, M. Tokunaga, T.Ishimoto, T. Ogura, R. Nagumo, A. Miyamoto, M. Koyama, Angew. Chem. Int.Ed. 122 (2010) 5476.

[2] S.S. Chui, M.F. Y, S. Lo, J.P.H. Charmant, A.G. Orpen, I.D. Williams, Science 283(1999) 1148.

[3] (a) A.U. Czaja, N. Trukhan, U. Muller, Chem. Soc. Rev. 38 (2009) 1284;(b) L.J. Murray, M. Dinca, J.R. Long, Chem. Soc. Rev. 38 (2009) 1294.

[4] J.R. Li, R.J. Kuppler, H.C. Zhou, Chem. Soc. Rev. 38 (2009) 1477.[5] R. Kitaura, G. Onoyama, H. Sakamoto, R. Matsuda, S. Noro, S. Kitagawa, Angew.

Chem. Int. Ed. 43 (2004) 2684.[6] D. Jiang, T. Mallat, F. Krumeich, A. Baiker, J. Catal. 257 (2008) 390.[7] A.G. Hu, H.L. Ngo, W.B. Lin, J. Am. Chem. Soc. 125 (2003) 11490.[8] Z. Xie, L. Ma, K.E. Dekrafft, A. Jin, W. Lin, J. Am. Chem. Soc. 132 (2010) 922.[9] K. Schlichte, T. Kratzke, S. Kaskel, Micropor. Mesopor. Mater. 73 (2004) 81.

[10] L. Harmon, C. Serre, T. Devic, T. Loiseau, F. Millange, G. Ferey, G.D. Weireld, J.Am. Chem. Soc. 131 (2009) 8775.

[11] Partha Mahata, Debajit Sarma, C. Madhu, A. Sundaresen, N. Srinivasan, DaltonTrans. 40 (2011) 1952.

[12] T. Meek Scott, A. Greathouse Jeffery, D. Allendorf Mark, Adv. Mater. 23 (2011)249.

[13] L. Ma, C. Abney, W. Lin, Chem. Soc. Rev. 38 (2009) 1248.[14] W. Lin, W.J. Rieter, K.M.L. Taylor, Angew. Chem. Int. Ed. 48 (2009) 650.[15] W.J.K.M. Rieter, Pott, K.M.L. Taylor, W. Lin, J. Am. Chem. Soc. 130 (2008)

11584.[16] Z. Ni, R.I. Masel, J. Am. Chem. Soc. 128 (2006) 12394.[17] Da-Won Jung, Da-Ae Yang, Jun Kim, Jaheon Kim, Wha-Seung Ahn, Dalton

Trans. 39 (2010) 2883.[18] Rob Ameloot, Linda Stappers, Jan Fransaer, Luc Alaerts, F. Sels Bert, D.E. De Vos,

Chem. Mater. 21 (2009) 2580.[19] Rob Ameloot, Lesley Pandey, Mark Vander Auweraer, Luc Alaerts, F. Selsa Bert,

D.E. De Vos, Chem. Commun. 46 (2010) 3735.[20] U. Mueller, H. Puetter, M. Hesse, H. Wessel, WO 2005/049892, 2005.[21] M. Schubert, M. Hesse, U. Mueller, H. Puetter, M. Tonigold, US 7910732 B2,

2011.[22] U. Mueller, H. Puetter, M. Hesse, M. Schubert, H. Wessel, J. Huff, M. Guzmann,

US 2007/0227898 A1, 2007.[23] A. Dhakshinamoorthy, M. Alvaro, H. Garcia, Adv. Synth. Catal. 352 (2010) 3022.[24] E. Perez-Mayoral, Cejka, J. Chem. Cat. Chem. 3 (2011) 157.[25] L. Alaerts, E. Seguin, H. Poelman, F. Thibault, P.A. Jacobs, D.E. De Vos, Chem.-

Eur. J. 12 (2006) 7353.[26] A. Dhakshinamoorthy, M. Alvaro, H. Garcia, J. Catal. 267 (2009) 1.[27] A. Dhakshinamoorthy, M. Alvaro, H. Garcia, Chem.-Eur. J. 16 (2010) 8530.[28] A. Dhakshinamoorthy, M. Alvaro, H. Garcia, Appl. Catal. A: General 378 (2010)

19.[29] F. Yanghe, S. Dengrong, Q. Meng, H. Renkun, L. Zhaohui, RSC. Adv. 2 (2012)

3309.[30] Avelino Corma, Marta Iglesias, Francesc X. Llabres i Xamena, Felix Sanchez,

Chem.-Eur. J. 16 (2010) 9789.[31] I. Luz, F.X. Llabres i Xamena, A. Corma, J. Catal. 27 (6) (2010) 134.

64 R. Senthil Kumar et al. / Microporous and Mesoporous Materials 168 (2013) 57–64

[32] K. Firoz Babu, M. Anbu Kulandainathan, Ioannis Katsounaros, Liza Rassaei,Andrew D. Burrows, R. Paul Raithby, Frank Marken, Electrochem. Commun. 12(2010) 632.

[33] Y. Cheng, A. Kondo, H. Noguchi, H. Kajiro, K. Urita, T. Ohba, K. Kaneko, H.Kanoh, Langmuir 25 (2009) 4510.

[34] B. Panella, M. Hirscher, H. Putter, U. Muller, Adv. Funct. Mater. 16 (2006) 520.[35] A. Dhakshinamoorthy, M. Alvaro, H. Garcia, ACS. Catal. 1 (2011) 48.[36] Martin Hartmann, Sebastian Kunz, Dieter Himsl, Oliver Tangermann, Langmuir

24 (2008) 8634.[37] Ioan Ardelean, Simona Cora, J. Mat. Sci. Mat. Electron. 19 (2008) 584.

[38] Z.H. Xiang, Z. Hu, D.P. Cao, W.T. Yang, J.M. Lu, B.Y. Han, W.C. Wang, Angew.Chem. Int. Ed. 50 (2011) 491.

[39] P. Chowdhury, C. Bikkina, D. Meister, F. Dreisbach, S. Gumma, Micropor.Mesopor. Mater. 117 (2009) 406.

[40] C. Nithya, R. Thirunakaran, A. Sivashanmugam, S. Gopukumar, J. Power Sources195 (2010) 939.

[41] S. Senthil kumar, C. Siva kumar, J. Mathiyarasu, K.L.N. Phani, Langmuir 23(2007) 3401.

[42] S. Saha, A. Pal, S. Kundu, S. Basu, T. Pal, Langmuir 26 (2010) 2885.