Surface Modification Reaction of Photocatalytic Titanium Dioxide with Triethoxysilane for Improving Dispersibility

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1 Surfce Modifiction Rection of Titnium Dioxide with Triethoxysilne Bull. Koren Chem. Soc., Vol. 3, No DOI.5/bkcs Surfce Modifiction Rection of Photoctlytic Titnium Dioxide with Triethoxysilne for Improving Dispersibility Myung Jin Lee, Ji Ho Kim, nd Young Te Prk * Deprtment of Chemistry, Keimyung University, Degu 74-7, Kore. * E-mil: ytprk@kmu.c.kr Received Jnury 3,, Accepted Mrch 8, We hve crried out the surfce modifiction of photoctlytic TiO with triethoxysilne through dehydrogention rection nd chrcterized the modified photoctlyst by spectroscopic methods, such s FT-IR, solid-stte 9 Si MAS NMR, XPS, nd XRF, etc. We lso exmined photoctlytic ctivity of the immobilized photoctlytic titnium dioxide with triethoxysilne by decoloriztion rection of dyes such s cong red nd methylene blue under visible light. Dispersion test showed tht the photoctlytic titnium dioxide immobilized with triethoxysilne group hs kept higher dispersibility thn titnium dioxide itself. No pprecible precipittion tkes plce even fter stnding for 4 h in the 4:6 mixture rtio of ethnol nd wter. Key Words: Titnium dioxide, Photoctlyst, Surfce modifiction, Triethoxysilne, Chrcteriztion Introduction Photoctlytic titnium dioxide (TiO ) hs ttrcted considerble ttention for their potentil pplictions s photoctlyst for decomposition of undesirble substnces from environment nd lso s wter splitting rections for hydrogen evolution. This phenomenon is bsed on the strong redox power of electron-hole pirs generted in ctlytic TiO when its vlence electrons re converted to conducting-bnd s electrons by photo irrdition. The rective species creted my interct with dsorbed wter nd oxygen to give rdicl species ttcking the undesirble orgnic molecules. -4 Extensive studies hve been focused on incresing photoctlytic ctivity of titnium dioxide by doping with trnsition metl ions such s iron, vndium, nd gold, 5-7 or with nonmetl elements such s crbon, 8 boron, nd nitrogen, 9 nd by entrpping with iodine in nnovoid-structured TiO. Efficient dye sensitized solr cell ws lso chieved by photoinduced electron injection from moleculr excited-stte into the conduction bnd of TiO film using phthlocynine sensitizer. Recently, surfce-modifictions such s fluorintion rection nd solid-liquid rection with hydride functionl siloxne oil 3,4 hve been reported in order to increse photoctlytic ctivity nd photoinduced hydrophilicity of titnium dioxide, respectively. Functionliztion of textile mterils using modified titnium dioxide with minotrimethoxysilne ws lso reported very recently. 5 However, surfce modifiction of TiO using lkoxyhydrosilnes hs not yet been reported so fr. The im of this study is to prepre photoctlytic titnium dioxide surfce-modified by triethoxysilnes nd therefore in order to improve the dispersibility of immobilized titnium dioxide in mixture solvent of wter nd ethnol. Herein, we now report the coupling rections of titnium dioxide with triethoxysilne (EtO) 3Si-O-TiO (3) through utilizing dehydrogention in the presence of toluene s solvent. The photoctlytic mterils immobilized with triethoxysilne were chrcterized by FT-IR nd solid-stte 9 Si MAS NMR spectrophotometer in solid stte s well s XPS, XRF, nd XRD, etc. Furthermore, the new mterils obtined cn be expected to hve photoctlytic ctivity under UV or visible light. In prticulr, we hve crried out studying their chrcteriztion of the newly prepred photoctlytic titnium dioxide mterils immobilized with triethoxysilne by using surfce nlysis technique nd photoctlytic ctvivity s well s dispersibility in polr solvents such s mixture of wter nd ethnol. Results nd Discussion Surfce modifiction of photoctlytic TiO with triethoxysilne. Photoctlytic TiO () ws prepred by the hydrolysis rection of regent-grde TiCl 4 s precursor, neutrliztion of rection mixture with mmoni, nd then clcintion of the precipitted mteril t 4 o C under oxygen tmosphere for 3 h following reported procedure. 6 The prepred photoctlyst TiO OH + H Si Toluene TiO O Si + H 3. (.8% Si) (.8% Si) 3c (5.7% Si) 3d (7.56% Si) Scheme

2 76 Bull. Koren Chem. Soc., Vol. 3, No. 5 Myung Jin Lee et l. Os Tip Counts /s r r r r r r : ntse r: rutile Cs Sip Figure. XPS survey spectrum of. Binding Energy (ev) θ (degree) Figure 3. XRD ptterns of,, nd. Intensity (. u.) 5 5 ppm Figure 4. Solid-stte 9 Si MAS NMR spectrum of Binding Energy (ev) Figure. High-resolution XPS spectrum of the O s in nd its decomposition. hs the phse rtio of 75:5 in ntse nd rutile ccording to XRD pttern, 6 in which the mixture phse of ntse nd rutile my cuse slight shift to longer wvelengths nd extension of the bsorption bnd in the visible region of UV-vis spectr compred to the ntse ctlyst (vide infr). As shown in Scheme, the surfce modifiction rection ws crried out in dried toluene t 6 o C for 8 h under rgon by the dehydrosilyltion rections of with triethoxysilne () to yield the surfce modified TiO -d. 7 Chrcteriztion of surfce-modified TiO. Firstly, the surfce-modified photoctlytic TiO mterils -d hve been chrcterized by X-ry fluorescence spectr (XRF). The quntittive elementl nlysis by XRF indicted tht the contents of Si tom in the surfced-modified powder,, 3c, nd 3d were.8%,.8%, 5.7%, nd 7.56% by weights, respectively. The Fourier trnsform infrred (FT-IR) spectrum of fter wshed with chloroform exhibits tht the strong peks between 45 nd 5 cm pper due to the Si-O stretching vibrtion frequencies nd the peks t 97 cm due to the liphtic C-H stretching vibrtion motions, respectively. 8,9 According to the FT-IR spectrum of fter wshed with chloroform, the chrcteristic pek t round 6 cm ttributed to the Si-H stretching vibrtion frequency does not show up t ll, 8,9 suggesting tht the dehydrosilyltion rection of with underwent completely under this rection condition. Figure shows the X-ry photoelectron spectroscopy (XPS) survey spectrum of fter wshed with chloroform. It contins C s nd Si p peks s well s the Ti p 3/ nd O s peks. The binding energies of Ti (p 3/), O (s), Si (p), nd C (s) re observed t 459.5, 53.63,.9, nd ev, respectively, which indictes the presence of the ethoxysilne group in the smple. Furthermore, C s nd Si p peks long with the Ti p 3/ nd O s peks re lso observed for ll the smples -c. Figure shows the high-resolution XPS spectr of O s peks of nd its decomposition. The O s region my be decomposed into three contributions, which is tht the peks t 53.4, 53.3, nd 53.4 ev correspond to Ti-O in TiO, hydroxyl groups (OH ), nd Ti-O-Si long with Si-O-Et, respectively. 4,, As shown in Figure 3 of the X-ry diffrction (XRD) ptterns of, nd, it is obvious tht the modifiction rection of dehydrosiltion does not chnge the bulk crystl structure of prepred TiO. Therefore the decrese or increse of the degrdtion rection rte of dye on surfce-modified TiO might be due to surfce influence, including surfce morphology chnge, defect nd roughness increse, s well s rectnt dsorption improvement, etc. Figure 4 shows the solid-stte 9 Si mgic ngle spinning nucler mgnetic resonnce (MAS NMR) spectr of, in which new 9 Si NMR pek is observed t between 9 nd 8 ppm

UV-vis spectr of (solid line) nd (dotted line). Figure 7. Photoctlytic ctivities of the smples nd -d for () methylene blue (MB) nd congo red (CR) under visible light.

3 Surfce Modifiction Rection of Titnium Dioxide with Triethoxysilne ().3 nm 9.46 nm 3.66 nm 3.99 nm 3. nm.86 nm.5 nm.43 nm 6. nm.7 nm nm nm Figure 5. TEM imges of () nd MB Concentrtion Chnge, In (C /C) () Bull. Koren Chem. Soc., Vol. 3, No. 5 3c 3d 4 3c 3d Absorbnce Wvelength (nm) CR Concentrtion Chnge, In (C /C) Irrdition Time (min) 3c3c 3d3d Irrdition Time (min) Figure 6. UV-vis spectr of (solid line) nd (dotted line). Figure 7. Photoctlytic ctivities of the smples nd -d for () methylene blue (MB) nd congo red (CR) under visible light. when compred with the resonnce observed t 59 ppm for triethoxysilne used s rectnt. According to the solid-stte 9 Si MAS NMR spectr of, it lso indictes clerly tht the structure of must contin Q unit of silicon-modified (EtO)3 Si-O-TiO on the surfce of these prticles. The prticle sizes of nd were nlyzed by trnsmission electron microscopy (TEM). TEM imges demonstrte the sizes of prticle rnging from nm to nm, s shown in Figure 5. While the prticle size nlyses by electron light scttering (ELS) in ethnol nd wter s solvents for were turned out to be 8.9 nm nd 56.4 nm, respectively, the prticle sizes of in ethnol nd wter were found to be 9. nm nd 4.7 nm, respectively. These results of prticle size mesured by using ELS re greter thn those mesured by TEM, probbly due to the cogultion of photoctlytic TiO prticle in solution sttes of these solvents. As shown in Figure 6 of diffuse reflectnce UV-vis bsorption spectr of nd, the modifiction rection of by dehydrosiltion does not chnge much the bsorption of prepred TiO. Diffuse reflectnce UV-vis bsorption spectr show steep fll in bsorbnce observed from the bsorption edge t 4 nm ttributed to the interbnd trnsition. The onset bsorption of the photoctlytic TiO is extrpolted to 3. ev corresponding to the bnd-gp energy.3 It lso exhibits wek but significntly brodended bnd t longer wvelengths thn 4 nm up to 53 nm, which might be cused to bsorb visible light due to the mixture phse rtio of 75:5 in ntse nd rutile. Photoctlytic properties nd dispersion test. In order to study the photoctlytic properties of nd -d, decoloriztion rections of congo red (CR) nd methylene blue (MB) were crried out in queous solution contining the photoctlysts TiO under irrdition of visible light t room temperture. Figure 7 shows the comprison of photoctlytic decomposition of congo red nd methylene blue on nd -d with vrying Si contents under visible light irrdition. In the cse of MB, -d shows better photoctlytic ctivity thn. However, in the cse of CR, shows better photoctlytic ctivity thn -d. These results indicte tht the optimum composition of Si tom might be round.8% by weight in the cse of photoctlytic mterils -d for the photoctlytic ctivity of surfce-modified TiO by using triethoxysilne. We lso tried to compre the dispersibility of.5% (w/v) solutions of with in mixture solvent of wter nd ethnol, s shown in Figure 8. It clerly shows tht hs higher dispersibility without pprecible precipittion thn even fter stnding for 4 h in the 4:6 mixture rtio solvent of ethnol nd wter.

78 Bull. Koren Chem. Soc., Vol. 3, No. 5 Myung Jin Lee et l. () - - b- b- -3-4 -5 b-3 b-4 b-5 Figure 8. Dispersibility test comprison of ().

The mixture rtios of wter nd ethnol for b-, b-, b-3, b-4, nd b-5 re :, 9:, 8:, 6:4, nd 5:5, respectively.

4 78 Bull. Koren Chem. Soc., Vol. 3, No. 5 Myung Jin Lee et l. () - - b- b b-3 b-4 b-5 Figure 8. Dispersibility test comprison of ().5% (w/v) solutions of nd in mixture solvents of wter nd ethnol fter stnding for 4 h. The mixture rtios of wter nd ethnol for -, -, -3, -4, nd -5 re 5:5, 6:4, 8:, 9:, nd :, respectively. The mixture rtios of wter nd ethnol for b-, b-, b-3, b-4, nd b-5 re :, 9:, 8:, 6:4, nd 5:5, respectively. Conclusion We hve successfully prepred the surfce-modified photoctlytic TiO -d by using triethoxysilne through dehydrogention rection, nd chrcterized the modified photoctlyst 9 by spectroscopic methods such s FT-IR, solid-stte Si MAS NMR, XPS, nd XRF, etc. We lso exmined photoctlytic ctivity of the immobilized photoctlytic TiO with triethoxysilne by decoloriztion rection of dyes such s cong red nd methylene blue under visible light. Dispersibility test shows tht the photoctlytic titnium dioxide immobilized with triethoxysilne group hs kept better dispersed solution without pprecible precipittion thn titnium dioxide itself even fter 4 h in the 4:6 mixture rtio of ethnol nd wter. Experimentl Section Generl procedures. All the chemicls were purchsed from Aldrich Chemicls Inc. All solvent were purified prior to use ccording to stndrd literture methods: toluene ws distilled 4 from sodium benzophenone ketyl. All glsswre ws ssembled nd ws then flme-dried while being swept with rgon. Solid stte 9Si MAS nucler mgnetic resonnce (NMR) spectroscopy ws performed on Vrin Unity INOVA 6 MHz FTNMR spectrometer t the Degu Brnch of the Kore Bsic Science Institute. Fourier trnsform infrred (FR-IR) spectr were recorded on Bruker IFS-48 FT-IR spectrometer using DRIFT method. Powder X-ry diffrction (XRD) ptterns were recorded on Philips X Pert APD diffrctometer with Cu Kα rdition. X-ry photoelectron spectroscopy (XPS) mesurements were crried out on VG Scientifics ESCALAB 5 spectrometer. X-ry fluorescence spectr (XRF) were recorded on Philips PW 4 spectrometer. Trnsmission electron microscope (TEM) ws conducted with Hitchi H-76. The sizes of prepred TiO prticles were observed with electrophoretic light scttering (ELS) spectrophotometer using n Otusk ELS 8 t the Chuncheon Brnch of the Kore Bsic Science Institute. Diffuse reflectnce UV-vis bsorption spectr in solid were collected by Shimdzu UV-3 PC spectrophotometer. UVvis bsorption spectr in solution were lso recorded by Shimdzu UV-6 spectrometer. Photoctlytic TiO () ws prepred by hydrolysis rection of regent-grde TiCl4 s precursor using ice-wter bth, neutrliztion of the rection mixture with mmoni wter (.5 M), nd then clcintion of the precipitted mteril t 4 oc under oxygen tmosphere for 3 h, ccording to the previously reported 6 method. Surfce modifiction of TiO with triethoxysilne. A ml round bottomed flsk ws equipped with reflux condenser, Teflon covered mgnetic stirring br, nd heting mntle. The flsk ws chrged with the prepred TiO (6. g, 75 mmol) o (dried t C for h), triethoxysilne () (.37g,.3 mmol), nd dried toluene ( g) under n rgon tmosphere. The reo ction mixture ws stirred t 6 C for 8 h. After then, the solvent ws removed by rotry evportion. The crude product ws wshed with chloroform three times nd dried t reduced pressure. In this wy the purified product ws obtined s white 9 powder, 5.86 g; Si CP/MAS NMR (5 MHz): δ 9 ~ 8; IR (DRIFT): ν 97 (-CH), 54, 5, 45 (Si-O-C) cm ; XPS (binding energy, ev): Ti (p3/, 459.5), O (s, 53.63), Si (p,.9), C (s, 84.96). The content of Si tom in surfcemodified TiO powder ws.8% (by weight) determined by XRF. Surfce modifictions of (6. g, 75 mmol) with (.3 g, 7.5 mmol), (.85 g,.3 mmol), nd (.59 g, 5.8 mmol) were crried out in the sme mnner nd the purified product s white powders (5.7 g), 3c (6. g), nd 3d (5.79 g) obtined, respectively. For, XPS (binding energy, ev): Ti (p3/, ), O (s, 53.8), Si (p,.37), C (s, 85.5). For 3c, XPS (binding energy, ev): Ti (p3/, 459.), O (s, 53.87), Si (p, 3.5), C (s, 84.69). The contents of Si tom in surfce-

5 Surfce Modifiction Rection of Titnium Dioxide with Triethoxysilne Bull. Koren Chem. Soc., Vol. 3, No modified TiO powders, 3c, nd 3d were.8%, 5.7%, nd 7.56% (by weights) determined by XRF, respectively. The XRD ptterns nd UV-vis spectr in the solid stte s well s TEM imges re described in Result nd Discussion. Mesurement of photoctlytic ctivities. The photoctlytic ctivities of nd -d were mesured by decoloriztion rection of congo red nd methylene blue in queous solution contining the photoctlysts nd -d under 5 W highpressure mercury lmp irrdition with UV-filter. A. g portion of or -d ws mixed with ml of the queous congo red solution (5 ppm) or methylene blue solution (5 ppm) in opticlly mtched Pyrex vessel, nd the mixed solution ws simultneously irrdited with vigorous stirring using mgnetic stirrer under visible light. After certin period of irrdition, ech solution ws filtered by using. µm membrne filter to remove the solid photoctlysts, followed by tking the filtrte solution to mesure the bsorption spectrl chnge of congo red or methylene blue to monitor decoloriztion rection. Dispersion test. The dispersibility of nd -d ws compred by precipittion of the TiO prticle in mixture solvent with the vrious rtios of wter nd ethnol. The photogrphs of dispersion solution nd discussion re described in Result nd Discussion. Acknowledgments. This work ws supported by the Progrm for the Trining of Grdute Students in Regionl Innovtion which ws conducted by the Ministry of Commerce Industry nd Energy of the Koren Government nd prtly by the Keimyung University. References. Fujishim, A.; Hond, K. Nture 97, 38, 37.. Somorji, G. A. Chemistry in Two Dimensions: Surfce; Bker, G. F., Ed.; Cornell University Press: New York, Childs, L. P.; Ollis, D. F. J. Ctl. 98, 66, Diebold, U. Surf. Sci. Rep. 3, 48, Wng, X. H.; Li, J.-G.; Kmiym, H.; Ktd, M.; Ohshi, N.; Moriyoshi, Y.; Ishigki, T. J. Am. Chem. Soc. 5, 7, Choi, H.-J.; Kim, J.-S.; Kng, M. Bull. Koren Chem. Soc. 7, 8, Li, H.; Bin, Z.; Zhu, J.; Huo, Y.; Li, H.; Lu,Y. J. Am. Chem. Soc. 7, 9, Vlentin, C. D.; Pcchioni, G.; Selloni, A. Chem. Mter. 5, 7, Ashi, R.; Morikw, T.; Ohwki, T.; Aoki, K.; Tg, Y. Science, 93, 69.. Usseglio, S.; Dmin, A.; Scrno, D.; Bordig, S.; Zecchin, A.; Lmberti, C. J. Am. Chem. Soc. 7, 9, 8.. Morndeir, A.; Lopez-Durte, I.; Mrtinez-Diz, M. V.; O Regn, B.; Shuttle, C.; Hji-Zinulbidin, N. A.; Torres, T.; Plomres, E.; Durrnt, J. R. J. Am. Chem. Soc. 7, 9, 95.. Tng, J.; Qun, H.; Ye, J. Chem. Mter. 7, 9, Nkbyshi, A. In Orgnosilicon Chemistry V. From Molecules to Mterils; Auner, N., Weis, J. Eds.; Wiley-VCH Verlg GmbH & Co. KGA: Weinheim, Germny, 3; p Zn, L.; Liu, Z.; Zhong, J.; Peng, Z. J. Mter. Sci. 4, 39, Sójk-Ledkowicz, J.; Lewrtowsk, J.; Kudzin, M.; Leonowicz, M.; Jesionowski, T.; Siwińsk-Stefńsk, K.; Krysztfkiewicz, A. J. Mter. Sci. 9, 44, Kim, S-M.; Yun, T-K.; Hong, D-I. J. Kor. Chem. Soc. 5, 49, Kim, J. H.; Lee, M. J.; Yun, T. K.; Yun, S. B.; Jung, I. K.; Jung, J. W.; Prk, Y. T. Repub. Kore ptent KR -8793, 7 Nov 8, Appl , 3 My Pretsch, E.; Bühlmnn, P.; Affolter, C. In Structure Determintion of Orgnic Compounds, Tbles of Spectrl Dt, 3rd ed.; Springer- Verlg: Berlin,. 9. Bellmy, L. J. In The Infr-red of Complex Molecules, 3rd ed.; John Wiley nd Sons: New York, Erdem, B.; Hunsicker, R. A.; Simmons, G. W.; Sudol, E. D.; Dimonie, V. L.; El-Asser, M. S. Lngmuir, 7, Hwng Y. K.; Ptil, K. R.; Kim, H.-K.; Sthye, S. D.; Hwng, J.-S.; Prk, S.-E.; Chng, J.-S. Bull. Koren Chem. Soc. 5, 6, 55.. Willims, E. In The Chemistry of Orgnic Silicon Compounds; Pti, S., Rppoport, Z., Eds.; John Wiley & Sons: Avon, Gret Britin, 989; Prt, Chpter Yoon, M.; Seo, M.; Jeong, C.; Jng, J. H.; Jeon, K. S. Chem. Mter. 5, 7, Armrego, W. L. F.; Perrin, D. D. Purifiction of Lbortory Chemicls, 4th ed.; Butterworth-Heinemnn: Oxford, 996.

Preparation and visible light photocatalytic activity of Bi 2 O 3 /CaO photocatalysts

Preparation and visible light photocatalytic activity of Bi 2 O 3 /CaO photocatalysts Rec Kinet Mech Ct (2010) 99:235 241 DOI 10.1007/s11144-009-0130-1 Preprtion nd visible light photoctlytic ctivity of Bi 2 O 3 /CO photoctlysts Limin Song Shujun Zhng Received: 2 June 2009 / Accepted: 20