Interntionl Journl of ChemTech Reserch CODEN (USA): IJCRGG ISSN: 0974-4290 Vol.8, No.2, pp 424-429, 2015 ICEWEST-2015 [05 th - 06 th Feb 2015] Interntionl Conference on Energy, Wter nd Environmentl Science & Technology PG nd Reserch Deprtment of Chemistry, Presidency College (Autonomous), Chenni-600 005, Indi Investigtion of Photo-Ctlytic Activity of TiO2- Grphene Composite in Hydrogen Production by Method of Wter Splitting 1 Llith Kumr B*, 1 Bhoopthy B G, 1 Siddhrthn A, 2 Knmni S 1 Deprtment of Mechnicl Engineering, Ann University, Chenni-600 025, Indi 2 Centre for Environmentl Studies, Ann University, Chenni-600 025, Indi Abstrct: TiO 2 nnophotoctlysts were prepred by methods of sol-gel nd hydrotherml using sme precursor Titnium Tetr Iso-Propoxide. It ws observed TiO 2 prepred by hydrotherml gve higher hydrogen yield which ws used in further synthesis of nnocomposites. TiO 2-grphene (TiO 2-GR) hybrids were prepred vi solvotherml rection of grphene oxide nd TiO 2 using ethnol s solvent. The s-prepred TiO 2-GR nnocomposites were chrcterized by X-ry diffrction (XRD), Scnning electron microscopy (SEM), Fourier Trnsform Infrred (FT-IR) spectroscopy nd ultrviolet-visible (UV-vis) diffuse reflectnce spectroscopy. The results indicted tht TiO 2-GR nnocomposites possessed enhnced light bsorption bility nd chrge seprtion efficiency thn TiO 2. The hydrogen evolution from queous EDTA nd wter (30:70) solution under solr-lmp illumintion in bench scle tubulr rector (BTR). The optimum mss rtio of GR to TiO 2 in the hybrids ws 1 wt. % which produced 1562 µmol h -1 g -1 of hydrogen from splitting of wter. Keywords: Grphene, TiO 2, solvotherml reduction, hydrogen production, hydrotherml reduction Introduction The incresingly serious energy crisis nd the environmentl contmintion cused by the burning of fossil fuels hve led to n ggressive serch for renewble nd environmentl friendly energy resources. Hydrogen energy hs been recognized s potentilly significnt form of storble nd clen energy for the future. Since the discovery of the first wter splitting system bsed on TiO 2 nd Pt in 1972 by Fujishim nd Hond 1, mny kinds of mterils nd derivtives hve been discovered s photoctlysts for this rection 2. Currently, TiO 2 is still one of the most widely used photoctlysts due to its exceptionl opticl nd electronic properties, strong oxidizing power, non-toxicity, chemicl stbility, nd low cost 3. Typiclly, photo-excited electron-hole pirs cn be generted under the light irrdition with wvelength lower thn tht corresponding to the bnd gp energy of TiO 2. However, the photo-generted electrons nd holes in TiO 2 my experience
Llith Kumr B et l /Int.J. ChemTech Res. 2015,8(2),pp 424-429. 425 rpid recombintion, which is one of key fctor limiting further improvement of its photoctlytic efficiency 4. Therefore, one of the most chllenging issues on photoctlysis is to overcome the quick recombintion of photo-generted electrons nd holes. Severl strtegies hve been employed to improve the photoctlytic performnce of TiO 2, for exmple, texturl design 5, coupling TiO 2 with metl or other semiconductors 6, etc. In prticulr, gret interest hs been devoted to combining crbon nnomterils 7, prticulrly crbon nnotubes (CNTs) 8, with TiO 2 to enhnce its photoctlytic performnce. Grphene (GR) s new crbon nnomteril hs mny exceptionl properties, such s high electron mobility, high trnsprency, flexible structure, nd lrge theoreticl specific surfce re 9. Thus, the combintion of TiO 2 nd grphene is promising to improve the photoctlytic performnce of TiO 2. Most recently TiO 2-grphene shows n enhncement of photoctlytic ctivity for the degrdtion of methylene blue 10. TiO 2-grphene showed higher photoctlytic ctivity for H 2 evolution from queous solution contining N 2S nd N 2SO 3 s scrificil gents thn P25 11. It hs been reported tht GO cn be reduced to GR by solvotherml rection of GO in the ethnol solvent 12. In this pper, photoctlytic ctivity of TiO 2-grphene composites prepred by fcile solvotherml rectio hs been nlyzed. Experimentl Methods Preprtion of Photoctlyst Preprtion of TiO 2 by Sol-Gel (S-TiO 2) nd hydrotherml method (H-TiO 2) involves sme precursor mteril Titnium tetr isopropoxide s reported in 13 nd 14 respectively. Grphite powder ws used for the synthesis of Grphene Oxide (GO) by modified Hummers method 15. The synthesised GO is reduced to Grphene (GR) long with the TiO 2 Nnoprticles to form the required TiO 2-X% GR composite, X% = 0.5, 1, 5 nd 10, respectively by solvo-therml reduction 16. Bench-Scle Tubulr Photoctlytic Rector Tubulr rector ws chosen to evlute the performnce of the phtoctlyst. By hving the rector in cylindricl shpe nd surrounding it with the lmps (UV nd Visible), most of the light energy could be used to ctivte the ctlyst. The schemtic picture of the rector is given in the Fig 1. The working volume of 100 ml ws tken with 70 ml wter nd 30 ml EDTA (Scrificil regent). The photoctlyst powder, wter nd scrificil regent were dded through the inlet vlve of liquid. The ir spce bove the solution in the rector ws flushed with N 2 for 1 h in ech experiment. The temperture of the photorector (25 o C) ws mintined by using exhust fns. The evolved gs ws collected in the collection tnk by downwrd displcement of wter. The evolved hydrogen ws collected nd nlyzed by Gs Chromtogrphy (Shimdzu - GC 2014ATF: 6890N). The volume of hydrogen ws mesured t every 15 min intervl. Mesurements reported re the verge of three reding. Fig 1. Schemtic Digrm of the Tubulr Photoctlytic Rector Chrcteriztion Studies In order to evlute the performnce of photoctlyst Fourier Trnsform Infrred (FTIR) spectr of the smples, recorded using Bruker FTIR spectrometer (Model IFS 66 v) in the rnge 4000 500 cm -1 ws done for the confirmtion of the presence orgnic group in the powder. Diffuse reflectnce (DR) UV-visible spectr were recorded using CARY 5E UV-Vis-NIR spectrophotometer in the spectrl rnge of 200 800 nm to clculte bnd gp energy. The morphology of smple powders sputtered with gold were seen using SEM (JEOL, JSM 5610LV microscope). X-ry diffrctometer (XRD) were recorded using X Pert Pro diffrctometer
Llith Kumr B et l /Int.J. ChemTech Res. 2015,8(2),pp 424-429. 426 by Ni-filtered Cu K α rdition (λ= 1.5418 Å) in the rnge of 10 90 with step size of 0.5 nd the verge grin size of the mterils ws clculted by Scherrer eqution. Results nd Discussion Photoctlytic Hydrogen Production The photoctlytic H 2 evolution (Fig. 2) of H-TiO 2 nd S-TiO 2 ws found to be 28 ml/h nd 30 ml/h respectively. So the ctivity of H-TiO 2 is found to be higher thn tht of S-TiO 2. Therefore H-TiO 2 ws selected for further studies to TiO 2 -grphene composite. The hydrogen evolution rte of TiO 2-X% GR (X% = 0.5, 1, 5 nd 10) composite were observed to be 32 ml/h, 35 ml/h, 25 ml/h nd 20 ml/h respectively. Among which hydrogen production of TiO 2-1% GR composite shows 1.2 times higher thn tht of H-TiO 2 prticles. These results were in ccordnce to Ping et l, 16 who reported 12 ml/h with TiO 2-GR nnocomposite. The role of grphene in TiO 2 nd its enhnced evolution of H 2 is described elsewhere 17. TiO 2 composite with higher percentge of grphene thn 1, decresed the hydrogen production due to the shielding effect 18. The gs collected from the inverted jr subjected to gs chromtogrphy technique ws confirmed to be hydrogen. Fig. 2 The time course of hydrogen production from n queous solution with suspended photoctlysts (H-TiO 2, S-TiO 2 nd TiO 2-X% GR) (0.1 g) Chrcteristion of Synthezised Photoctlysts Moleculr Vibrtions The FTIR spectrum of H-TiO 2 is shown in Fig. 3. The pek corresponding to 2918.18 cm -1 ws due to C-H stretching vibrtion of lknes. Presence of Oleic cid ws confirmed by the vibrtion t 1525.20 nd 1435.27 cm -1 tht ws used during synthesis. There were bnds t bout 1100 cm -1 due to C-O stretching nd t 1371 cm -1 due to CH 2 bending modes of ethnol used for wshing. The bnd close to 600 cm -1 ws ssigned to TiO 2 vibrtion nd it ws mtched with the results reported by Li et l. 19. The FTIR spectrum of grphene oxide is shown in Fig. 6. The intense brod pek between 2200 nd 3700 cm -1 ws due to O-H stretching vibrtion of H 2O. Presence of H 2O ws confirmed by bending vibrtion close to 1630 cm -1.The pek corresponding to 3383.34 cm -1 ws due to C-H stretching vibrtion of romtics. Presence of oxygen bond ws confirmed by the vibrtion t 1705.12 nd 1022.38 cm -1 tht corresponds to C=O stretch nd C O stretch. b Fig. 3 ) FTIR spectrum of H-TiO 2 nd b) grphene oxide
Llith Kumr B et l /Int.J. ChemTech Res. 2015,8(2),pp 424-429. 427 Bnd Gp Energy The energy bnd gps were clculted s 3.18, 3.12 nd 2.83 ev corresponding to H-TiO 2, S-TiO 2 nd TiO 2 1% GR composite respectively from DR-UV spectr shown in Fig. 4. These vlues re in ccordnce to 3.2 ev for ntnse phse TiO 2 nd 2.96 ev for TiO 2 GR composite Ping Cheng et l, 16. The nrrowing of the bnd gp in the cse of TiO 2 1% GR composite ws ttributed to the interction between TiO 2 nd GR, similr to tht observed for the crbon-doped TiO 2 composites. But on incresing the mount of GR ffected the opticl property of light bsorption for the TiO 2 GR composite significntly which is in ccordnce with the hydrogen yield dt. Fig. 4 DR UV-visible spectr of () S-TiO 2, (b) H-TiO 2 nd (c) TiO 2 1% GR Morphology nd Prticle size The microgrphs of H-TiO 2 nd S-TiO 2 powders shown in Fig.5 () nd (b) respectively were sphericl in shpe with different sizes. The prticles prepred by Sol gel method Fig.5 () were fused together which is not in the cse of prticles prepred by Hydrotherml where individul seprte sphericl prticles were seen in Fig.5 (b). The verge prticle size of H-TiO 2 nd S-TiO 2 is found to be in the rnge of 100-300 nm nd 300-500 nm using imge j softwre. Flke like structures of Grphene were seen in Fig. 5 (c). The morphology of TiO 2-Grphene composite shown in Fig. 5 (d) ws similr to tht of H-TiO 2. This is becuse of the use of H-TiO 2 in the synthesis of TiO 2-Grphene composite. But the powders in TiO 2-Grphene composite were fused together with the grphene nd forms islnd like morphology. b c d Fig. 5 SEM microgrphs of () H- TiO 2, (b) S-TiO 2, (c) Grphene nd (d) TiO 2- Grphene composite Grin size The XRD pttern of grphene in Fig. 6 () showed one intense pek t 11.32 o corresponding to (002) plne of Grphene Oxide nd brod pek between 15 o nd 30 o corresponding to grphene (020) plne which is in ccordnce with Li et l. 19. In generl crbon (002) stndrd pek will be observed t 26 o. Becuse of the single lyer of crbon rings in the grphene mkes the XRD pek t 26 o broder.
Llith Kumr B et l /Int.J. ChemTech Res. 2015,8(2),pp 424-429. 428 b Fig. 6 XRD pttern of () Grphene nd (b) H-TiO 2 nd S-TiO 2 The XRD ptterns of H-TiO 2 nd S-TiO 2 re shown in Fig. 6 (b). The peks were very much shrp nd not brodened enough to be nnoprticles (i.e. 1-100 nm). Both XRD ptterns were similr nd they mtched with the ntse form. The peks were indexed using JCPDS Crd No. 21-1272. The verge crystl size of H- TiO 2 nd S-TiO 2, clculted by Scherrer Eqution were 20.39 nm nd 16.13 nm respectively using peks corresponding to (xxx) plne. Conclusions TiO 2 powders synthesized by hydrotherml method gve higher hydrogen production thn TiO 2 prepred by sol gel method. The hydrogen yield of TiO 2-Grphene composites ws mximum t 1% GR which shows 1.2 times higher thn tht of H-TiO 2 prticles nd then decresed with increse in grphene percentge thn 1%. Results obtined from this reserch indicted tht the synthesized novel solr UV light responsive nnocomposite TiO 2-1% GR effectively decomposed the H 2O in n lkline solution long with genertion of clen H 2. References 1. Fujishim A. Electrochemicl photolysis of wter t semiconductor electrode. Nture., 1972, 238: 37-38. 2. Ashokkumr M. An overview on semiconductor prticulte systems for photoproduction of hydrogen. Int J Hydrogen Energy., 1998, 23:427-38. 3. Hung BS, Wey MY. Properties nd H2 production bility of Pt photodeposited on the ntse phse trnsition of nitrogen doped titnium dioxide. Int J Hydrogen Energy., 2011, 36:9479-86. 4. Bk T, Nowotny J, Reks M, Sorrell C. Photo-electrochemicl hydrogen genertion from wter using solr energy. Mterils-relted spects. Int J Hydrogen Energy., 2002, 27: 991-1022. 5. Tomkiewicz M. Scling properties in photoctlysi. Ctl Tody., 2000, 58:115-23. 6. Tryb B, Tsumur T, Jnus M, Morwski AW, Ingki M. Crbon-coted ntse: dsorption nd decomposition of phenol in wter. Appl Ctl B., 2004, 50:177-83. 7. Ingki M, Kojin F, Tryb B, Toyod M. Crbon coted ntse: the role of the crbon lyer for photoctlytic performnce. Crbon., 2005, 43:1652-9. 8. Won K, Pyrgiotkis G, Sigmund W. Photoctlytic crbon-nnotube-tio2 composites. Adv Mter., 2009, 21: 2233-9. 9. Nir RR, Blke P, Grigorenko AN, Novoselov KS, Booth TJ, Stuber T. Fine structure constnt defines visul trnsprency of grpheme. Science., 2008, 320:1308. 10. Zhng H, Lv XJ, Li YM, Wng Y, Li JH. P25-grphene composite s high performnce photoctlyst. ACS Nno., 2010, 4:380-6. 11. Zhng XY, Li HP, Cui XL, Lin YH, Grphene/TiO2 nnocomposites: synthesis, chrcteriztion nd ppliction in hydrogen evolution from wter photoctlytic splitting. J Mter Chem, 2010, 20:2801-6. 12. Nethrvthi C, Rjmthi M. Chemiclly modified grphene sheets produced by the solvotherml reduction of colloidl dispersions of grphite oxide. Crbon., 2008, 46:1994-8.
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