Preparation and photocatalytic activity of nano-TiO2 codoped with fluorine and ferric

玻纤负载TiO 2/g-C 3N 4光催化膜的制备及降解染料性能高海燕1，2，3，安仁德1，2，赵永男1，2（1.天津工业大学天津市先进纤维与储能技术重点实验室，天津300387；2.天津工业大学材料科学与工程学院，天津300387；3.南开大学先进能源材料化学教育部重点实验室，天津300071）摘要：为解决光催化剂效率不高、粉末难回收且易造成二次污染等问题，采用浸渍法制备了玻璃纤维负载TiO 2/g-C 3N 4光催化膜（命名为TCNGF ）。

TiO 2和g-C 3N 4纳米颗粒通过静电自组装在玻璃纤维表面形成了均匀无裂痕的薄膜，重量法测得催化剂负载量（质量分数）为4%。

降解实验结果表明：以TCNGF 为催化剂，在模拟太阳光下，10mg/L 的罗丹明B （RhB ）溶液在40min 的降解率达到98%，4次循环降解实验的脱色降解率均高于99%，且溶液中无絮状沉淀产生，表明催化剂优异的催化活性、附着牢度和循环稳定性。

催化结果表明：适量提高TiO 2和g-C 3N 4的质量比，催化膜内异质结量增多，促使光生活性自由基增多，染料降解速率增快；初始染料浓度对TCNGF 光催化降解性能无明显影响。

自由基捕获实验证明：超氧自由基（·O 2-）和羟基自由基（·OH ）在光催化反应过程中为主要活性物种；光催化反应机理研究表明，TCNGF 属于Z 型光催化体系。

关键词：浸渍法；TiO 2；g-C 3N 4；玻璃纤维；光催化剂；染料降解；光催化膜中图分类号：TB383；O643.36文献标志码：A文章编号：员远苑员原园圆源载（圆园23）园6原园园47原07Fabrication and dye degradation performances of glass fiber supported TiO 2/g-C 3N 4catalyst filmGAO Haiyan 1，2，3，AN Rende 1，2，ZHAO Yongnan 1，2（1.Tianjin Key Laboratory of Advanced Fibers and Energy Storage Technology ，Tiangong University ，Tianjin 300387，China ；2.School of Material Science and Engineering ，Tiangong University ，Tianjin 300387，China ；3.Key Laboratory of Advanced Energy Materials Chemistry ，Ministry of Education ，Nankai University ，Tianjin 300071，China ）Abstract ：In order to solve the problems of low catalytic efficiency袁the unrecyclability and possible secondary pollution ofpowder photocatalysts袁glass fiber-supported TiO 2/g-C 3N 4catalyst film渊denoted as TCNGF冤was fabricated by impregnation method.Homogeneous crack-free film formed on the glass fiber by self-assembled TiO 2and g-C 3N 4nanoparticles through electrostatic interaction.Gravimetric determination gave the catalyst loading content of 4%.The degradation experiments show that using TCNGF as the catalyst under mimic sunlight袁the degradation rate of 10mg/L RhB solution reaches 98%within 40min.The degradation rates of four-cycle degradation reactions are all higher than 99%without any flocculent precipitation in the solution.These results reveale the high catalytic efficiency袁excellent adhesion fastness and cycling stability of the catalyst.The catalytic results also demonstrate that increasing the mass ratio of TiO 2院g -C 3N 4within a certain range elevate the amount of heterojunction to augment the photo -induced active free radicals and accelerate the dye degradation rate.The initial dye concentration has no detectable effect on the photocatalytic degradation performance of TCNGF.Free radical capture experiments have proved that superoxide radicals渊窑O 2-冤and hydroxyl radicals渊窑OH冤are themain active species in the photocatalytic reaction process袁and the study of the photocatalytic reaction mechanismhas shown that TCNGF belongs to the Z-type photocatalytic system.Key words ：dipping method曰TiO 2曰g-C 3N 4曰glass fiber曰photocatalysts曰dye degradation曰photocatalytic film收稿日期：2022-03-23基金项目：国家自然科学基金资助项目（21703152）；天津市教委科研计划项目（自然科学）（2018KJ197）；南开大学先进能源材料化学教育部重点实验室开放课题通信作者：高海燕（1986—），女，博士，副教授，主要研究方向为储能材料与器件。

Chemical Engineering Journal 181–182 (2012) 196–205Contents lists available at SciVerse ScienceDirectChemical EngineeringJournalj o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /c ejPreparation of coupled ZnO/SnO 2photocatalysts using a rotating packed bedChia-Chang Lin ∗,Yu-Ju ChiangDepartment of Chemical and Materials Engineering,Chang Gung University,Taoyuan,Taiwan,ROCa r t i c l ei n f oArticle history:Received 9June 2011Received in revised form 31October 2011Accepted 17November 2011Keywords:Rotating packed bed Photocatalysts ZnO/SnO 2Methylene bluea b s t r a c tZn(OH)2/Sn(OH)4was prepared by continuously pumping two aqueous solutions of ZnSO 4/SnCl 4and NaOH into a rotating packed bed (RPB),where co-precipitation occurred to form Zn(OH)2/Sn(OH)4.Cou-pled ZnO/SnO 2photocatalysts were formed by calcining these precursors (Zn(OH)2/Sn(OH)4)at 600◦C for 10h.The photocatalytic activity of coupled ZnO/SnO 2photocatalysts,evaluated using the photocat-alytic degradation of methylene blue,was found to be related to the molar ratio of zinc salt to tin salt,the concentrations of the reactants,the concentration of the precipitant,the rotating speed of the RPB,the flow rates of the reactants and precipitant,and the zinc source.The photocatalytic activity of coupled ZnO/SnO 2photocatalysts was highest at ZnSO 4and SnCl 4concentrations of 0.10mol/kg and 0.05mol/kg,respectively,an NaOH concentration of 0.40mol/kg,a rotating speed of 600rpm,and flow rates of the solutions of ZnSO 4/SnCl 4and NaOH of 500mL/min.The photocatalytic degradation of methylene blue using coupled ZnO/SnO 2photocatalysts obeyed the pseudo-first-order kinetic model.© 2011 Elsevier B.V. All rights reserved.1.IntroductionSince Fujishima and Honda [1]discovered the photoelectrolysis of water on TiO 2electrodes in 1972,TiO 2,which is a semiconductor,has attracted considerable interest [2].Semiconductors other than TiO 2,such as ZnO [3–7],Fe 2O 3[6,7],and CuO [7],have been studied as photocatalysts for degrading most organics pollutants in waste water and waste gas under UV irradiation.When these photocata-lysts are illuminated,providing an energy equal to or greater than the band gap of the photocatalysts,the electrons are transferred from the valence band to the conduction band,and electron/hole pairs are simultaneously photogenerated.The electrons are oxi-dizing and the holes are reducing.Photocatalysis can occur if the photoexcited electrons and holes can migrate to the surface of the photocatalysts [7].However,the recombination rate of photogen-erated electron/hole pairs is very high,inhibiting the practical use of the photocatalysts.Coupled photocatalysts have recently been developed to enhance the photocatalytic activity of conventional photocata-lysts by reducing the degree of recombination and increasing the charge separation.They include TiO 2/ZnO [8–10],TiO 2/WO 3[11],TiO 2/Fe 2O 3[12],SnO 2/TiO 2[13,14],ZnO/SnO 2[15–22],and ZnO/TiO 2/SnO 2[23].According to inter-particle electron transfer theory [24],the photoexcited electrons can be trans-ferred between the conduction bands of coupled photocatalysts.∗Corresponding author.Tel.:+88632118800x5760;fax:+88632118800x5702.E-mail address:higee@.tw (C.-C.Lin).Accordingly,the lifetime of the charge carriers is extended,and the charge separation is enhanced.For example,the photocatalytic activity of coupled ZnO/SnO 2photocatalysts has been evaluated using the photocatalytic degradation of methyl orange,and exper-imental results have shown that the photocatalytic activity of coupled ZnO/SnO 2photocatalysts exceeds that of pure ZnO or SnO 2[15,17–19].According to these investigations,the increase in the photocatalytic activity of coupled ZnO/SnO 2photocatalysts veri-fies that photoexcited electrons are indeed transferred from the conduction band of ZnO to that of SnO 2.Recently,several methods for preparing coupled ZnO/SnO 2pho-tocatalysts have been developed.They include co-precipitation [15–19],the hydrothermal method [20,21],the sol–gel method [25,26],ball-milling [27–29],thermal evaporation [30],and sput-tering deposition [31–33].However,most of them are very difficult to produce coupled ZnO/SnO 2photocatalysts in a continuous mode.Therefore,the conventional methods for the large-scale produc-tion of coupled ZnO/SnO 2photocatalysts have some limitations such as long operating time and expensive equipment.Based on high-gravity reactive precipitation,a novel method without these weaknesses is developed to improve the conventional methods for preparing coupled ZnO/SnO 2photocatalysts in large-scale opera-tion.The high-gravity reactive precipitation method uses a rotating packed bed (RPB)or a spinning disk reactor (SDR)as a reactor,in which a precipitation reaction proceeds.Under high-gravity con-ditions,reactant solutions could been spread or split into tiny droplets and thin films,under the influence of a large centrifugal force [34].Accordingly,high mass transfer,uniform supersatura-tion and homogeneous nucleation are achieved [34].Therefore,1385-8947/$–see front matter © 2011 Elsevier B.V. All rights reserved.doi:10.1016/j.cej.2011.11.062C.-C.Lin,Y.-J.Chiang/Chemical Engineering Journal181–182 (2012) 196–205197Fig.1.Photograph of RPB used in this investigation.the high-gravity reactive precipitation method generates small nanoparticles with a narrow particle size distribution at low oper-ating cost[34].The method has a large production capacity[34].The high-gravity reactive precipitation method has been extensively utilized in preparing nanoparticles via gas–liquid, liquid–liquid,and gas–liquid–solid multiphase reactions,including nanoparticles of CaCO3[35],TiO2[36],ZnS[37],Mg(OH)2[38],and Ag[39,40].However,very little work,if any,has been performed on the preparation of coupled ZnO/SnO2photocatalysts by the high-gravity reactive precipitation method.The main goal of this investigation was to study the preparation of coupled ZnO/SnO2 photocatalysts in the RPB by the co-precipitation method.Also,the effects of the molar ratio of zinc salt to tin salt,the concentrations of the reactants,the concentration of the precipitant,the rotating speed of the RPB,theflow rates of the reactants and precipitant,and the zinc source on the photocatalytic activity of coupled ZnO/SnO2 photocatalysts were explored.2.Experimental2.1.Preparation of coupled ZnO/SnO2photocatalystsFig.1presents a photograph of the RPB applied herein to prepare coupled ZnO/SnO2photocatalysts.The packed bed in the RPB had an internal radius of2.1cm,an external radius of3.9cm,and an axial height of2.3cm.Hence,the depth(radial length)of the packed bed was1.8cm,and its total volume was78cm3.Stainless steel wire mesh was used as the packings.It comprised interconnected filaments with a mean diameter of0.22mm.The packings had a specific surface area of874m2/m3and a voidage of0.95.The RPB was operated at a rotating speed of600–1800rpm.These rotating speeds provided a centrifugal acceleration that was12–109times the gravitational acceleration on the basis of the arithmetic mean radius of the RPB.Based on the literature[15,17],the formation of coupled ZnO/SnO2photocatalysts in the RPB by the co-precipitation method involves the following chemical reactions.ZnSO4(aq)+2NaOH(aq)→Zn(OH)2↓+Na2SO4(aq)(1) SnCl4(aq)+4NaOH(aq)→Sn(OH)4(s)↓+4NaCl(aq)(2)Zn(OH)2/Sn(OH)4(s)−→ZnO/SnO2(s)+3H2O(g)↑(3)Fig.2schematically depicts the experimental setup for the preparation of coupled ZnO/SnO2photocatalysts in the RPB by the above chemical reactions.ZnSO4·7H2O(J.T.Baker,99.9%)and SnCl4·5H2O(J.T.Baker,99.7%)were the starting reactants,and NaOH(Mallinckrodt,99.0%)was the precipitant.2L of NaOH solu-tion at a known concentration was placed in tank A.ZnSO4·7H2O and SnCl4·5H2O in the given molar ratio were dissolved in2L of deionized water.Then,the solutions with the given[Zn2+]/[Sn4+] ratio was placed in tank B.Solutions from both tanks A and B were pumped into the packed bed through the liquid distributors at aflow rate that was controlled usingflowmeters.The product, Zn(OH)2/Sn(OH)4,which was formed in the rapid co-precipitation reaction(Eq.(1))in the RPB,was expelled into a collection vessel. The product slurry wasfiltered and washed several times in deion-ized water.Thefilter cake was dried at60◦C in air for48h.Then, the precursors of coupled ZnO/SnO2photocatalysts were obtained by milling these dry cakes using a ceramic mortar.The dehydration temperature of the precursors,Zn(OH)2/ Sn(OH)4,was measured using a thermogravimetric analyzer(TGA, TA instrument,TGA2050).Fig.3indicates the TGA result,reveal-ing that the temperature more than450◦C should be suitable for the transformation of the precursors to coupled ZnO/SnO2 photocatalysts,as an earlier investigation[15].Therefore,the cal-cination condition was set to600◦C for10h.Finally,coupled ZnO/SnO2photocatalysts were produced(Eq.(3))after the pre-cursors,Zn(OH)2/Sn(OH)4,had been calcined in air at600◦C for 10h.2.2.Characterization of coupled ZnO/SnO2photocatalystsThe crystal structure of coupled ZnO/SnO2photocatalysts was determined using an X-ray diffractometer(XRD,Siemems,D5005) with Cu K␣radiation and a scanning speed of4◦/min.The mor-phology and particle size of coupled ZnO/SnO2photocatalysts were determined using afield-emission scanning electron microscope (FE-SEM,Hitachi,S5000).The UV–visible absorption spectra of coupled photocatalysts were recorded using a UV–visible spec-trophotometer(UV–vis,Jasco,V-630).198 C.-C.Lin,Y.-J.Chiang /Chemical Engineering Journal 181–182 (2012) 196–205Fig.2.Experimental setup for preparing coupled ZnO/SnO 2photocatalysts in RPB.2.3.Measurement of photocatalytic activityThe photocatalytic activity of coupled ZnO/SnO 2photocatalysts was evaluated by photodegrading methylene blue (Fluka,96.0%).Photocatalytic experiments were performed in a Pyrex glass reac-tor that had been charged with 3L of aqueous methylene blue and 0.5g/L ZnO/SnO 2powder.The initial concentration of methylene blue in the aqueous solution was 10mg/L.Two UV lamps with the maximum emission at 365nm and the intensity of 12mW/cm 2were used as a light source and placed within the reactor.The pH of the reaction suspensions was adjusted to 8by adding concentrated aqueous NaOH.Air was fed continuously into the reactor from the bottom at a flow rate of 400mL/min.In all photocatalytic exper-iments,reaction suspensions were stirred using a DC stirrer,and their temperature was maintained at 25◦C using a circulator.After the pH and the temperature of the reaction suspensions had been constant for around 30min,UV lamps were turned on and the photocatalytic degradation was sustained for 2h.At known time intervals,analytic samples of around 10mL were taken from the reaction suspensions,and filtered through a 0.45␮m100200 300 400 500 600700707580859095100w e i g h t p e r c e n t a g e (%)Temperature (ºC)Fig.3.TGA analysis of Zn(OH)2/Sn(OH)4.millipore filter to remove the ZnO/SnO 2powder.The filtrate was then analyzed.The methylene blue concentration in the filtrate was analyzed using a spectrophotometer (Thermo Electron,Genesys 20)at the maximum absorption wavelength of 633nm.According to earlier studies [41–45],a blank experiment with-out UV irradiation but with coupled ZnO/SnO 2photocatalysts was performed at pH 8,25◦C,and a ZnO/SnO 2dosage of 0.5g/L.Fig.4(a)indicates the adsorption performance of coupled ZnO/SnO 2photo-catalysts,revealing that methylene blue was not adsorbed onto the surface of coupled ZnO/SnO 2photocatalysts.According to earlier investigations [46–48],another blank experiment without coupled ZnO/SnO 2photocatalysts but with UV irradiation was performed at pH 8and 25◦C.Fig.4(b)displays the photolysis of methylene blue,demonstrating that no methylene blue was degraded only with UV irradiation.3.Results and discussion3.1.Effect of molar ratio of zinc salt to tin saltTo study the effect of the [Zn 2+]/[Sn 4+]ratio on the photocat-alytic activity of coupled ZnO/SnO 2photocatalysts,other operating variables were fixed:the of rotating speed was maintained at 1800rpm;the flow rates of the solutions of salts and NaOH were set to 500mL/min,and the NaOH concentrations were determined from the stoichiometric ratio in the co-precipitation reactions (Eqs.(1)and (2)).Pure ZnO and SnO 2photocatalysts were also prepared under the same operating conditions expect for the fact that the starting reactants were ZnSO 4·7H 2O for ZnO and SnCl 4·5H 2O for SnO 2,respectively.The corresponding Zn 2+,Sn 4+,and NaOH con-centrations at various [Zn 2+]/[Sn 4+]ratios were listed in Table 1.Fig.5displays the photocatalytic activities of coupled ZnO/SnO 2photocatalysts prepared at various [Zn 2+]/[Sn 4+]ratios.Fig.5reveals that coupled ZnO/SnO 2photocatalysts were pre-pared at a [Zn 2+]/[Sn 4+]ratio of 2/1performed better than those prepared at other ratios in the degradation of methylene blue,because the photoexcited electrons were effectively transferred between ZnO and SnO 2at this ratio.Similar result have been achieved in the literature [17],indicating that the optimal Sn con-tent in coupled ZnO/SnO 2photocatalysts that were prepared byC.-C.Lin,Y.-J.Chiang /Chemical Engineering Journal 181–182 (2012) 196–205199Table 1Zn 2+Sn 4+,and NaOH concentrations at various [Zn 2+]/[Sn 4+]ratios.[Zn 2+]/[Sn 4+][Zn 2+](mol/kg)[Sn 4+](mol/kg)[OH −](mol/kg)1/00.200.000.405/10.200.040.562/10.200.100.801/10.200.20 1.201/20.100.20 1.001/50.040.200.880/10.000.200.80the conventional co-precipitation method,in the degradation of methyl orange,is 33.3mol%.Additionally,the photocatalytic activ-ity of these photocatalysts prepared at a [Zn 2+]/[Sn 4+]ratio of 2/1exceeded those of pure ZnO and SnO 2,consistent with ear-lier investigations [15,17–19].This result verifies that coupled photocatalysts reduce the recombination rate of photogenerated electron/hole pairs and promote the charge separation.Fig.6shows XRD analyses of coupled ZnO/SnO 2photocata-lysts that were prepared at various [Zn 2+]/[Sn 4+]ratios.Notably,the crystal structures of all coupled ZnO/SnO 2photocatalysts com-prised mixtures of ZnO and SnO 2.No Zn 2SnO 4phase (JCPDS 74-2184)was present in any of them,because the calcination temperature,600◦C,was lower than the formation tempera-ture (700◦C)of Zn 2SnO 4that was prepared by the conventional co-precipitation method,as proposed by Wang et al.[17].The intensities of the diffraction peaks from coupled ZnO/SnO 2photo-catalysts were weaker than those from pure ZnO or SnO 2,revealing that the ZnO and SnO 2phases in coupled ZnO/SnO 2photocatalysts inhibited the formation of the other.However,as the Sn content in coupled ZnO/SnO 2photocatalysts increased,the characteristic(a)10020304050607080901001101200.00.10.20.30.40.50.60.70.80.91.0C /C 0C /C 0Reactiontime (min)(b)0.00.10.20.30.40.50.60.70.80.91.0Reactiontime (min)Fig.4.(a)Adsorption and (b)photolysis of methylene blue.C /C 0Reaction Time (min)Fig.5.Effect of [Zn 2+]/[Sn 4+]ratio on photocatalytic activity of coupled ZnO/SnO 2photocatalysts.peaks of SnO 2at around 25.5◦and 51.8◦(JCPDS 21-1250)were obvious,and the characteristic peak of ZnO at around 36.3◦(JCPDS 36-1451)was weak.This finding is consistent with the literature in which the inhibition of the growth of ZnO grains by SnO 2increased with the SnO 2content [17].3.2.Effect of concentration of precipitantIn this section,according to the above results,the [Zn 2+]/[Sn 4+]ratio was kept at 2/1with a Zn 2+concentration of 0.2mol/kg and an Sn 4+concentration of 0.1mol/kg.The NaOH concentrations were set to 0.4mol/kg (insufficient),0.8mol/kg (stoichiometric),and 1.6mol/kg (excess)to elucidate the effect of NaOH concentration on the photocatalytic activity of coupled ZnO/SnO 2photocatalysts.The other operating variables were fixed:the rotating speed was maintained at 1800rpm and the flow rates of the solutions of salts and NaOH were set to 500mL/min.Fig.7shows the effect of the NaOH concentration on the photocatalytic activities of coupled ZnO/SnO 2photocatalysts.From Fig.7,coupled ZnO/SnO 2photocat-alysts that were prepared at the stoichiometric NaOH concentration of 0.8mol/kg exhibited a higher photocatalytic activity than those prepared at other NaOH concentrations.When the NaOH concentration was insufficient,the main prod-uct of the Zn(OH)2/Sn(OH)4slurry was Sn(OH)4,and the final pH2025303540455055606570I n t e n s i t y (c o u n t s )(a)(c)(b)(d)(e)2 (degree)(g)(f)Fig. 6.XRD patterns of coupled ZnO/SnO 2photocatalysts prepared at various[Zn 2+]/[Sn 4+]ratios:(a)pure SnO 2;(b)1/5;(c)1/2;(d)1/1;(e)2/1;(f)5/1;(g)pure ZnO.200 C.-C.Lin,Y.-J.Chiang /Chemical Engineering Journal 181–182 (2012) 196–205C /C 0Reaction Time (min)Fig.7.Effect of NaOH concentration on photocatalytic activity of coupled ZnO/SnO 2photocatalysts.of this slurry was around 4.8,revealing that the co-precipitation reaction was incomplete.This finding may be explained by the fact that the solubility product constant (K sp )(1.0×10−56)of Sn(OH)4is much lower than that (1.2×10−17)of Zn(OH)2[49].Therefore,the ZnO content in coupled ZnO/SnO 2photocatalysts was much lower than the SnO 2content.This result was supported by the XRD analyses,presented in Fig.8,in which the characteristic peaks of SnO 2were greater than those of ZnO at the insufficient NaOH concentration.Accordingly,coupled ZnO/SnO 2photocatalysts that were prepared at the insufficient NaOH concentration of 0.4mol/kg performed as if they were pure SnO 2.However,at the excess NaOH concentration,the final pH of the Zn(OH)2/Sn(OH)4slurry was around 12.8.Under this basic con-dition,almost all of the Sn(OH)4and some of the Zn(OH)2in the Zn(OH)2/Sn(OH)4slurry formed complex ions,which dissolved in the basic solution.Hence,the major product obtained from the Zn(OH)2/Sn(OH)4slurry was Zn(OH)2.As displayed in Fig.8,most of the diffraction peaks from coupled ZnO/SnO 2photocatalysts were consistent with pure ZnO;the characteristic peaks of SnO 2were not observed.Thus,coupled ZnO/SnO 2photocatalysts that were pre-pared at the excess NaOH concentration of 1.6mol/kg performed as if they were pure ZnO.2025303540455055606570I n t e n s i t y (c o u n t s )(a)(b)2 (degree)(c)Fig.8.XRD patterns of coupled ZnO/SnO 2photocatalysts prepared at various NaOHconcentrations:(a)excess;(b)stoichiometric;(c)insufficient.C /C 0Reaction Time (min)Fig.9.Effect of Zn 2+and Sn 4+concentrations on photocatalytic activity of coupled ZnO/SnO 2photocatalysts.3.3.Effect of concentrations of reactantsIn this experiment,with the rotating speed fixed at 1800rpm,the flow rates of the solutions of salts and NaOH were 500mL/min;the NaOH concentration was stoichiometric;and the Zn 2+and Sn 4+concentrations were varied,while maintaining a [Zn 2+]/[Sn 4+]ratio of 2/1,to determine their effect on the photocatalytic activity of coupled ZnO/SnO 2photocatalysts.Fig.9presents the photocatalytic results.The figure demonstrates that the highest photocatalyst activity was observed at a Zn 2+concentration of 0.10mol/kg and an Sn 4+concentration of 0.05mol/kg,perhaps because coupled ZnO/SnO 2photocatalysts that were prepared at these reactant concentrations agglomerated slightly.However,lower reactant concentrations are associated with a lower produc-tion capacity.Therefore,further work must be conducted on how to reduce the agglomeration at high reactant concentrations.Fig.10shows the effect of reactant concentrations on the phases in cou-pled ZnO/SnO 2photocatalysts.The reactant concentrations did not significantly affect the crystal structure of coupled ZnO/SnO 2pho-tocatalysts,because the [Zn 2+]/[Sn 4+]ratio was fixed and the NaOH concentration was stoichiometric.2025303540455055606570I n t e n s it y (c o u n t s )(a)(b)(c)2 (degree)(d)Fig.10.XRD patterns of coupled ZnO/SnO 2photocatalysts prepared at various Zn 2+and Sn 4+concentrations:(a)[Zn 2+]=0.60mol/kg and [Sn 4+]=0.30mol/kg;(b)[Zn 2+]=0.40mol/kg and [Sn 4+]=0.20mol/kg;(c)[Zn 2+]=0.20mol/kg and [Sn 4+]=0.10mol/kg;(d)[Zn 2+]=0.10mol/kg and [Sn 4+]=0.05mol/kg.C.-C.Lin,Y.-J.Chiang /Chemical Engineering Journal 181–182 (2012) 196–205201C /C 0Reaction Time (min)Fig.11.Effect of rotating speed on photocatalytic activity of coupled ZnO/SnO 2photocatalysts.3.4.Effect of rotating speed and liquid flow rateTo investigate the effect of varying the rotating speed from 600to 1800rpm on the photocatalytic activity of coupled ZnO/SnO 2photocatalysts,the Zn 2+and Sn 4+concentrations were 0.10mol/kg and 0.05mol/kg,respectively,the NaOH concentration was set to 0.40mol/kg,and the flow rates of the solutions of salts and NaOH were fixed at 500mL/min.Fig.11presents the results of the photo-catalytic experiments.Fig.11demonstrates that coupled ZnO/SnO 2photocatalysts that were prepared at a rotating speed of 600rpm had the greatest photocatalytic activity in the degradation ofmethylene blue.Fig.12presents the effect of the rotating speed on the morphology of coupled ZnO/SnO 2photocatalysts.As the rotat-ing speed was increased,the increased centrifugal force spread the solutions of salts and NaOH or split them into much tinier droplets,shrinking the coupled ZnO/SnO 2photocatalysts,implying that the photocatalytic activity was independent of particle size.Therefore,a rotating speed of 600rpm yielded the best combination of ZnO and SnO 2for enhancing the transfer of the photoexcited electrons and the lifetime of charge carriers,increasing the photocatalytic activity of coupled ZnO/SnO 2photocatalysts.As shown in Fig.12(a),the shapes of coupled ZnO/SnO 2photo-catalysts that were prepared at a rotating speed of 600rpm were approximately cubic,with smaller,hexagon-like particles clearly attached to the cubic particles.With respect to the crystal struc-tures of ZnO and SnO 2,the hexagon-like particles were thought to be ZnO and the larger cubic particles were thought to be SnO 2.The solubility product constants of Sn(OH)4and Zn(OH)2are con-sidered again.When co-precipitation reaction occurred,the cubic particles of Sn(OH)4were the first to form.Then,hexagon-like par-ticles of Zn(OH)2formed,and were deposited on the cubic particles,asshown in Fig.12(a).To describe the effect of the flow rate of the solutions of salts and NaOH on the photocatalytic activity of ZnO/SnO 2coupled photocat-alysts,Zn 2+and Sn 4+concentrations of 0.10mol/kg and 0.05mol/kg,respectively,an NaOH concentration of 0.40mol/kg,and a rotat-ing speed of 600rpm,were used.The results reveal that coupled ZnO/SnO 2photocatalysts prepared at a flow rate of 500mL/min outperformed the others in the degradation of methylene blue,as shown in Fig.13.The photocatalytic activity of coupled ZnO/SnO 2photocatalysts was directly related to the combination of ZnO and SnO 2.As shown in Fig.14,the best combination of ZnO and SnO 2was observed at a higher flow rate of 500mL/min.Additionally,theFig.12.FE-SEM analyses of coupled ZnO/SnO 2photocatalysts prepared at various rotating speeds:(a)600rpm;(b)1000rpm;(c)1400rpm;(d)1800rpm.202 C.-C.Lin,Y.-J.Chiang /Chemical Engineering Journal 181–182 (2012) 196–205C /C 0Reaction Time (min)Fig.13.Effect of flow rate of solutions of salts and NaOH on photocatalytic activity of coupled ZnO/SnO 2photocatalysts.same combination of ZnO and SnO 2was found at two flow rate of 100and 300mL/min.Therefore,a higher flow rate of 500mL/min was associated with a higher photocatalytic activity of coupled ZnO/SnO 2photocatalysts.3.5.Effect of zinc sourceSeveral zinc compounds have been adopted as zinc sources for producing coupled ZnO/SnO 2photocatalysts [15–22],including zinc sulfate,zinc chloride,zinc nitrate and zinc acetate.Coupled ZnO/SnO 2photocatalysts that are produced from different zinc sources exhibit different photocatalytic activities.In this section,the effects of four zinc salts,ZnSO 4·7H 2O,ZnCl 2,Zn(NO 3)2·6H 2O,and Zn(CH 3COO)2·2H 2O,on the photocatalytic activity of cou-pled ZnO/SnO 2photocatalysts were explored.The Zn 2+and Sn 4+concentrations were 0.10mol/kg and 0.05mol/kg,respectively;the NaOH concentration was 0.40mol/kg;the rotating speed was 600rpm,and the flow rates of the solutions of salts and NaOH were 500mL/min.According to Fig.15,the zinc sources significantly affected the photocatalytic activity of coupled ZnO/SnO 2photocatalysts.Furthermore,coupled ZnO/SnO 2photocatalysts had the high-est photocatalytic activity when ZnSO 4·7H 2O was used as the zinc source,because the absorbance at a wavelength of 365nm of coupled ZnO/SnO 2photocatalysts that were prepared using ZnSO 4·7H 2O exceeded those of coupled ZnO/SnO 2photocatalysts that were prepared using other zinc salts,as displayed in Fig.16.This result suggests that coupled ZnO/SnO 2photocatalysts that were prepared using ZnSO 4·7H 2O could produce the most elec-tron/hole pairs under UV-365nm,and therefore had the greatest photocatalytic activity.As mentioned earlier,coupled ZnO/SnO 2photocatalysts with superior photocatalytic activity were prepared using ZnSO 4·7H 2O and SnCl 4·5H 2O as the starting reactants and NaOH as the copre-cipitant under the following operating variables;theZn 2+and Sn 4+concentrations were 0.10mol/kg and 0.05mol/kg,respectively;the NaOH concentration was 0.40mol/kg,the rotating speed was 600rpm,and the flow rates of the solutions of the salts and NaOH were 500mL/min.In the presence of both of the above photo-catalysts and UV,with an initial methylene blue concentration of 10mg/L,around 100%of methylene blue was photodegraded after 2h,as shown in Fig.15.Also,the BET surface area of the above photocatalysts measured using a surface area analyzer (Micromer-titics,ASAP-2020)was 33m 2/g,agreeing with the results obtained using the conventional co-precipitation method,as proposed byFig.14.FE-SEM analyses of coupled ZnO/SnO 2photocatalysts prepared at vari-ous flow rates of solutions of salts and NaOH:(a)100mL/min;(b)300mL/min;(c)500mL/min.Wang et al.[15].Moreover,the particle size of the above photocat-alysts estimated using a particle size analyzer (Malvern,Zatasier Nano ZS)and an image (Fig.17)obtained by a transmission electron microscopy (TEM,Hitachi,H7500)was 954nm.parison of photocatalystFor the purposes of comparison,coupled ZnO/SnO 2photocata-lysts was prepared using the RPB at ZnSO 4and SnCl 4concentrations of 0.10mol/kg and 0.05mol/kg,respectively,an NaOH concentra-tion of 0.40mol/kg,a rotating speed of 600rpm,and flow rates of the solutions of ZnSO 4/SnCl 4and NaOH of 500mL/min.Addi-tionally,coupled ZnO/SnO 2photocatalysts was prepared usingC.-C.Lin,Y.-J.Chiang /Chemical Engineering Journal 181–182 (2012) 196–205203C /C 0Reaction Time (min)Fig.15.Effect of zinc source on photocatalytic activity of coupled ZnO/SnO 2photo-catalysts.200300400500600 700 800 900 10001100(d)(c)(b)A b s o r b a n c eWavelength (nm)(a)Fig.16.UV–vis analyses of coupled ZnO/SnO 2photocatalysts prepared using vari-ous zinc sources:(a)ZnSO 4;(b)ZnCl 2;(c)Zn(NO 3)2;(d)Zn(CH 3COO)2.the conventional co-precipitation method at ZnSO 4and SnCl 4concentrations of 0.10mol/kg and 0.05mol/kg,respectively,an NaOH concentration of 0.40mol/kg.The photocatalytic degrada-tion of methylene blue was carried out at pH 8,25◦C,an initial concentration of methylene blue of 10mg/L,and a ZnO/SnO 2dosageTable 2k -values at various [Zn 2+]/[Sn 4+]ratios.[Zn 2+]/[Sn 4+]k (1/min)R 21/00.00440.99845/10.00750.99722/10.01800.99911/10.00560.98051/20.00090.98421/50.00020.98360/10.00300.9954of 0.5g/L,as shown in Fig.18.Coupled ZnO/SnO 2photocatalysts prepared using the RPB had a higher photocatalytic activity with methylene blue than coupled ZnO/SnO 2photocatalysts prepared using the conventional co-precipitation method.This result is attributable to the fact that the RPB provided a better combina-tion of ZnO and SnO 2in coupled ZnO/SnO 2photocatalysts than the conventional co-precipitation method,as presented in Fig.19.Therefore,the RPB can improve the conventional co-precipitation method in the preparation of coupled ZnO/SnO 2photocatalystswith higher photocatalytic activity and large-scale preparation.3.7.Kinetics of photocatalytic degradation of methylene blueThe kinetic data of photocatalytic degradation of methylene blue using coupled ZnO/SnO 2photocatalysts were analyzed using a pseudo-first-order kinetic model as follows [46–48]:dCdt=−kC (4)where C represents the concentration of methylene blue at time t and k is the apparent degradation rate coefficient (k ).The integra-tion of Eq.(4)yields Eq.(5)as follows:lnC 0C=kt(5)Plotting ln(C 0/C )as a function of time yields the k values.Here,C 0is the initial concentration of methylene blue.A linear relation between ln(C 0/C )and t was observed in the plot (not shown here).Then,the k values for the photocatalytic degradation of methylene blue using coupled ZnO/SnO 2photocatalysts prepared at various [Zn 2+]/[Sn 4+]ratios were determined graphically;they are listed in Table 2.The agreement between experimental data and the results obtained using the model (Eq.(5))was evaluated from the coef-ficients of determination (R 2).The high values of R 2in all ratios revealed that the photocatalytic degradation of methylene blueFig.17.TEM image of coupled ZnO/SnO 2photocatalysts.。

J. Chem. Chem. Eng. 6 (2012) 744-747The Physical Properties and Photocatalytic Activity of Cu/TEA Doped TiO2-Nanoparticles Prepared by theSol-Gel ProcessWeerachai Sangchay*, Weerachai Mudtharak, Kuntapon Mahamad and Aurasa NamesaiFaculty of Industrials Technology, Songkhla Rajabhat University, Songkhla 90000, ThailandReceived: July 08, 2012 / Accepted: August 02, 2012 / Published: August 25, 2012.Abstract: Cu/TEA-doped TiO2 nanoparticles were prepared by the sol-gel process. Titanium (IV) isoproxide, copper (II) nitrate trihydrate and triethanolamine were used as precursors and calcined at a temperature of 400°C for 2 h with a heating rate of 10 °C/min to produce powders. Different interstitial amounts of TEA were added in the range of 0 mol% to 15 mol% of TiO2. The X-ray diffractrometer patterns show the TiO2 nanocomposites have a high anatase phase. It was also apparent that doped TEA has an effect on the crystallite size of TiO2 composite nanoparticles. The morphology of the composite powders was characterized by scanning electron microscope. The photocatalytic activity of Cu/TEA-doped TiO2 nanoparticles was evaluated through the degradation of methylene blue under UV irradiation. The results showed that 1 mol% TEA of TiO2 nanocomposites exhibited high photocatalytic activity and a small crystallite size.Key words: TiO2, Cu, TEA, nanoparticles, sol-gel.1. IntroductionTiO2 (Titanium dioxide) is widely used as a photocatalyst because it is photochemically stable, non-toxic and low cost [1]. However, the efficiency of the photocatalytic reaction is limited by the high recombination rate of photoinduced electron-hole pairs formed in photocatalytic processes and by the absorption capability of UV light of photocatalysts.In recent years, many studies have been devoted to the improvement of the photocatalytic efficiency of TiO2, for instance, depositing noble metals and doping metal or nonmetal ions[2]. Generally, the introduction of doped ions can result in the formation of a doping energy level between the conduction and valence bands of TiO2. In principle, it should be possible for the absorption of doped TiO2 to be extended into the UV region effectively.*Corresponding author: Weerachai Sangchay, Mr., research field:nanomaterials.E-mail:************************.Many approaches have been used to obtain TiO2 powders, including inert gas condensation [3], hydrothermal processing [4], solution combustion [5], and the sol-gel method [6, 7]. The sol-gel method has recently been developed as a general and powerful approach to preparing inorganic materials such as ceramics and glass. In this method, a soluble precursor molecule is hydrolyzed to form a colloidal dispersion (the sol). Further reactions cause bonds to form among the sol particles, resulting in an infinite network of particles (the gel). The gel is then typically heated to yield the desired material. This method for the synthesis of inorganic materials has a number of advantages over more conventional synthetic procedures. For example, high-purity materials can be synthesized at low temperatures [8, 9]. In addition, homogeneous multi-component systems can be obtained by mixing precursor solutions, which allow for the easy chemical doping of the materials prepared.In this paper, we report on the synthesis andAll Rights Reserved.The Physical Properties and Photocatalytic Activity of Cu/TEADoped TiO2-Nanoparticles Prepared by the Sol-Gel Process745characterization of Cu/TEA-doped TiO2 nanoparticles prepared by using a modified sol-gel method. Based on our previous studies, the amount of Cu was equal to 1 mol% of TiO2. The effects of physical properties, such as phase, morphology and crystallinity on the photocatalytic activity of the TiO2 powders are discussed in this paper.2. Experiments2.1 Raw MaterialsTitanium (IV) isoproxide (TTIP, 99.95%, Fluka Sigma-Aldrich), copper (II) nitrate trihydrate (Cu(NO3)2·3H2O) and triethanolamine (TEA, C6H15NO3) were used as raw materials. Ethanol (C2H5OH, 99.9%, Merck Germany) was used as a solvent.2.2 Sample Preparation•TiO2 (TP): 2 mol HNO3 was added drop-wise and stirred into a solution containing 10 mL TTIP in 150 mL ethanol to fix the pH at 3-4. The mixture was continuously stirred at room temperature until a clear and homogeneous solution was obtained;•TiO2/Cu (TC): A mixture composed of TTIP 10 mL, ethanol 150 mL, and Cu(NO3)2·3H2O 1 mol% of TiO2 was stirred for 15 min and 2 mol HNO3 were added to fix the pH at 3-4 and the mixture further stirred for 30 min.•TiO2/Cu/TEA (TCT): 1 mol%, 5 mol%, 10 mol% and 15 mol% of TEA samples were designated as TCT1, TCT5, TCT10 and TCT15, respectively,which were prepared in the same way as the TC;The three solutions were dried at 100 °C for 24 h until white TiO2 powders were obtained. Finally, the powders were ground using a mortar in order to reduce the agglomerations of grains and then calcined at 400 °C for 2 h with a heating rate of 10 °C/min.2.3 Materials CharacterizationThe morphology and particle size of the synthesized powders were characterized by SEM (scanning electron microscope) (Quanta400). The phase composition was characterized using an XRD (X-ray diffractometer) (Phillips X’pert MPD, Cu-K). The crystallite size was calculated by the Scherer equation, Eq. 1 [10].D = 0.9 λ/β cosθB(1) Where D is the average crystallite size, λ is the wavelength of the Cu Kα line (0.15406), θis the Bragg angle and βis the FWHM (full-width at half-maximum) in radians.2.4 Photocatalytic Activity TestPhotocatalytic activity was evaluated from an analysis of the photodegradation of methylene blue (MB) aqueous solution. MB solution having an initial concentration of 1 × 10-5 M was mixed with 0.0375 g of photocatalyst powder. The suspension was kept in the dark for 60 min to achieve adsorption/desorption equilibrium before being irradiated under a UV lamp (black light) of 50 W. The distance between the testing substrate and the light source was 32 cm. The photocatalytic reaction test was conducted in a dark chamber by UV irradiation times of 0, 1, 2, 3, 4, 5 and 6 h. After being centrifuged, the supernatant solutions were measured for MB absorption at 665 nm using a UV-vis spectrophotometer. The percentage degradation of the MB was calculated by Eq. (2) [11].Percentage of degradation = 100(C0-C)/C0 (2) Where C0 is the concentration of MB aqueous solution at the beginning (1 ×10-5 M) and C is the concentration of MB aqueous solution after exposure to a light source.3. Results and Discussion3.1 CharacterizationThe XRD patterns of the TiO2 powders in all cases calcined at 400 °C for 2 h at a heating rate of 10 °C/min demonstrated the anatase phases shown in Fig. 1. The Cu-compound phase could not be verifiedAll Rights Reserved.The Physical Properties and Photocatalytic Activity of Cu/TEA Doped TiO 2-Nanoparticles Prepared by the Sol-Gel Process746in these XRD peaks because of the very small amount of Cu doping and because of other organic matter being completely removed during calcination at 400 °C. The anatase phase fraction in the TiO 2 powders seemed to decrease with increases in the TEA doping. The crystallite sizes of the anatase phases are 44.2, 9.2, 16.5 21.7, 23.6, and 25.3 nm for TP, TC, TCT1, TCT5, TCT10 and TCT15, respectively. It was found that the crystallite size increases with increases in TEA doping due to the contribution of the TEA effect. The morphologies of the TC and TCT15 revealed by the SEM micrographs are shown in Fig. 2. All the samples had a similar morphology consisting of agglomerations of smaller particles.Fig. 1 XRD patterns of TiO 2 powders.3.2 Photocatalytic ActivityPhotocatalytic activity was evaluated using degradation of the MB solution under UV irradiation during 0-6 hours and the results are shown in Fig. 3. The TCT1 powder exhibits the best decomposition results under UV irradiation. After 6 hours of testing, the degradation percentage of the TCT1 powders shown in Fig. 4 under UV irradiation was 67.02% compared to those of the TP powders which were 30.05% due to the small crystallite size. It can be concluded that 1 mol% TEA is the best condition for Cu/TEA-doped TiO 2 nanoparticles producing a small crystallite size and a high degree of crystallinity of the anatase phase.Fig. 3 Photocatalytic activity of TiO 2 powders under UV irradiation.Fig. 2 SEM cross-sectional morphologies images of TiO 2 powders (magnification 60,000 ×).TC TCT15All Rights Reserved.The Physical Properties and Photocatalytic Activity of Cu/TEADoped TiO2-Nanoparticles Prepared by the Sol-Gel Process747Fig. 4 The degradation percentage of MB of TiO2 powders under UV irradiation.4. ConclusionsNanocomposite powders were prepared by the sol-gel process using pure TiO2, TiO2/Cu and TiO2/Cu doped with 1-15 mol% TEA and was calcined at a temperature of 400°C for 2 h with a heating rate of 10 °C/min. The physical properties and photocatalytic activity were investigated and concluded as followings, The XRD patterns showed that the TiO2 nanocomposites had a 100% anatase phase. The TiO2/Cu with 1 mol% TEA showed a high photocatalytic MB degradation rate of 67.02% under 6 h of UV irradiation.The addition of TEA affects the crystallinity of the anatase phase, resulting in good photocatalytic activity of the Cu/TEA-doped TiO2 nanoparticles.AcknowledgmentThe authors would like to acknowledge Department of Mining and Materials Engineering, Faculty of Engineering, Prince of Songkla University, Thailand for financial support of this research. References[1]Fujishima, A.; Rao, T. N.; Tryk, D. A. Titanium DioxidePhotocatalysis. J. Photochem. and Photobiol. 2000,C1,1-21.[2]Baifu, X.; Peng, W.; Dandan, D.; Jia, U.; Zhiyu, R.;Honggang, F. Effect of Surface Species on Cu-TiO2Photocatalytic Activity. J. Applied Surface Sci. 2008,254, 2569-2574.[3]Marcial, Z.; Tessy, L.; Ricardo, G.; Maximilinno, A.; Ruth,M. Acetone Gas Phase Condensation on Akaline MetalsDope TiO2 Sol-Gel Catalysts. J. Applied Surface Sci. 2005,252, 828-832.[4]Fanda, S.; Meltem, A.; Sadiye, S.; Sema, E.; Murat, E.;Hikmet, S. Hydrothermal Syhthesis, Characterization andPhotocatalytic Activity of Nanozied TiO2 Based Catalystsfor Rhodamine B Degradation. J. Chem. 2007,31,211-221.[5]Mimani, T.; Patil, K. C. Solution Combustion Synthesis ofNanoscale Oxides and Their Composites. Mater. Phys.Mech. 2001,4, 134-137.[6]Schmidt, H.; Jonschker, G.; Goedicke, S.; Mening, M. TheSol-Gel Process as a Basic Technology for Nanoparticle-Dispersed Inorganic-Organic Composites. J.Sol-Gel Sci. Tech. 2000,19, 39-51.[7]Xianfeng, Y.; Feng, C.; Jinlong, Z. Effect of Calcinationon the Physical and Photocatalytic Properties of TiO2Powders Prepared by Sol-Gel Template Method. J.Sol-Gel Sci. Tech. 2005,34, 181-187.[8]Jerzy, Z. Past and Present of Sol-Gel Science Technology.J. Sol-Gel Sci. Tech. 1997,8, 17-22.[9]Tianfa, W.; Jianping, G.; Juyun, S.; Zhongshen, Z.Preparation and Characterization of TiO2 Thin Films bythe Sol-Gel Process. J. Materials Sci. 2001,36,5923-5926.[10]Sangchay, W.; Sikong, L.; Kooptarnobd, K. Comparisonof Photocatalytic Reaction of Commercial P25 andSyntertic TiO2-AgCl Nanoparticles. J. Procedia.Engineering2012,32, 590-596.[11]Weerachai, S.; Lek, S.; Kalayanee, K. Phootocatalytic andSelf-Cleaning Properties of TiO2-Cu Thin Films on GlassSubstrate. J. Applied Mechanics and Materials2012,152-154, 409-413.All Rights Reserved.。

如何准备体育测试英语作文英文回答：Preparation for physical tests requires a multifaceted approach encompassing both physical and mental conditioning. Implementing a comprehensive training regimen that targets specific fitness components is crucial.1. Establish a Personalized Training Plan: Determine your current fitness level through an assessment and establish realistic goals. Tailor a plan that aligns with your abilities and caters to the demands of the specific test.2. Aerobic Endurance Enhancement: Engage in activities that elevate your heart rate, such as running, cycling, or swimming. Gradually increase the intensity and duration of these exercises to improve cardiovascular efficiency.3. Muscular Strength and Power Development: Incorporateresistance training exercises like squats, lunges, andpull-ups into your routine. Gradually increase the weight or resistance to enhance muscular power and strength.4. Flexibility Improvement: Dedicate time to stretching exercises that target the major muscle groups involved in the test. This enhances range of motion and reduces therisk of injuries.5. Practice Test Simulations: Replicate the conditions of the actual test by conducting practice drills. This allows you to familiarize yourself with the movements and pace, boosting confidence and performance on test day.6. Nutrition Optimization: Fuel your body with a balanced and nutrient-rich diet that supports your training efforts. Adequate hydration is also essential for maintaining optimal performance.7. Rest and Recovery: Allow your body sufficient time to rest and repair after intense workouts. Sleep is crucial for muscle recovery and overall rejuvenation.Mental Preparation:1. Goal Visualization: Picture yourself successfully completing the test and focus on positive outcomes. This fosters a mindset conducive to peak performance.2. Stress Management Techniques: Develop strategies to cope with pre-test anxiety through techniques such as deep breathing, meditation, or visualization.3. Positive Self-Talk: Engage in affirmations and positive self-talk to reinforce belief in your abilities. This fosters a mindset of confidence and resilience.4. Performance Visualization: Rehearse the test mentally, visualizing each step and anticipating potential challenges. This enhances mental preparation and reduces uncertainty.中文回答：如何准备体育测试。

2006年第14卷合成化学Vo l.14,2006第4期,388~391Chinese Jo ur nal of Sy nthetic Chemistry N o.4,388~391 #研究简报#H2O2络合凝胶法制备纳米T iO2/SiO2复合催化剂及其光催化性能*王耀红1a,1b,储伟1a,1b,徐建春1a,1b,罗仕忠1b(1.四川大学a.建筑与环境学院; b.化工学院,四川成都610065)摘要:采用H2O2络合凝胶法获得钛的络合物[T iO(H2O2)]2+水溶胶,并与SiO2水溶胶包覆复合,制备了纳米T iO2/SiO2复合半导体催化剂,其结构经X RD和BET表征。

以含阳离子艳红染料模拟废水降解为模型反应,考察了复合催化剂的光催化性能。

实验结果表明:经650e焙烧后的复合催化剂中T iO2粒径为9.8nm,光催化活性最好,SiO2的最佳掺杂量为25%。

关键词:纳米T iO2/SiO2复合催化剂;制备;光催化性能;废水降解中图分类号:O643.3文献标识码:A文章编号:1005-1511(2006)04-0388-04Preparation of TiO2/SiO2Nanoparticles Composite Catalysts by H2O2Complex-gel Method and Their Photocatalytic ActivityWANG Yao-hong1a,1b,CH U Wei1a,1b,XU Jian-chun1a,1b,LUO S-i zhong1b(a.Scho ol o f Env ir onment and Ar chitectur e; b.Scho ol of Chem ical Engineering,1.Sichuan U niversity,Chengdu610065,China)A bstract:Nanosized TiO2/SiO2composite semic onductor catalysts were prepared by so-l gel method basedon the complex reac tion between Ti4+and H2O2.Their struc ture and properties were c haracterized by XRD and BET.Their photocatalytic properties were investigated via photocatalytic degradation of the waste wa-ter of Cationic Brilliant Red5GN under UV irradiation in a fluidized photoreactor as a model reac tion.The results showed that the size of nanopaticle calcined at650e is9.8nm and the corresponding catalyst ex-hibits better photocatalytic activity.The optimum content of silica doped was25%.Ke yw ord s:TiO2/SiO2photocatalyst;preparation;photoc atalytic ac tivity;degradation of waste water半导体光催化具有低能耗、易操作、无二次污染等特点,在有机合成、环境治理等领域显示了其广阔的应用前景,在废水处理中的应用潜力,已有许多文献报道[1~5]。

第33卷第3期2013年3月环境科学学报Acta Scientiae CircumstantiaeVol．33，No．3Mar．，2013基金项目：辽宁省科技厅自然科学基金项目（No．201202091）；辽宁省教育厅自然科学基金项目（No．L2012006）；辽宁省教育厅特色学科建设项目；辽宁省水环境生物监测与水生态安全重点实验室项目；辽宁大学“211”工程建设项目（No．HJ211007）；辽宁环境科研教育“123工程”（No．CEPF2009-123-2-10）Supported by the Natural Science Foundation of Liaoning Province Science and Technology Department （No．201202091），the Natural Science Foundation of Liaoning Province Education Department （No．L2012006），the Environmental Science Key Discipline Construction Project of Liaoning Province Education Department ，the Program of the Key Laboratory of Water Environment Biomonitoring and Ecological Security of Liaoning Province ，the “211”Project of Liaoning University （No．HJ211007）and the “123Engineering ”Program of Education of Environment Scientific Research of Liaoning Province （No．CEPF2009-123-2-10）作者简介：王丽涛（1964—），女，E-mail ：wlt631225@163．com ；*通讯作者（责任作者），E-mail ：lnuhjhx@sina．com Biography ：WANG Litao （1964—），female ，E-mail ：wlt631225@163．com ；*Corresponding author ，E-mail ：lnuhjhx@sina．com王丽涛，李芳轶，张朝红，等．2013．氮氟掺杂二氧化钛（N ，F-TiO 2）的制备及可见光催化活性的研究［J ］．环境科学学报，33（3）：742-748Wang L T ，Li F Y ，Zhang Z H ，et al ．2013．Preparation of N ，F-codoped TiO 2and its photocatalytic activity under visible light ［J ］．Acta Scientiae Circumstantiae ，33（3）：742-748氮氟掺杂二氧化钛（N ，F-TiO 2）的制备及可见光催化活性的研究王丽涛，李芳轶，张朝红*，张丰秋，景逵，黄丽荣，刘丹妮，郜炜辽宁大学环境学院，沈阳110036收稿日期：2012-05-20修回日期：2012-07-21录用日期：2012-07-30摘要：以氨水为氮源，氢氟酸为氟源，采用溶胶-凝胶法制备了氮氟掺杂二氧化钛（N ，F-TiO 2）光催化剂，并通过X －射线衍射（XRD ）和扫描电镜（SEM ）技术对其晶型和形态进行表征．最后以酸性红B 为模型污染物，探讨了N 和F 加入量、焙烧温度、焙烧时间、照射时间、催化剂用量、溶液初始浓度和照射功率等因素对N ，F-TiO 2可见光催化活性的影响．结果表明，制备的N ，F-TiO 2以锐钛型为主，N 和F 的掺杂对TiO 2的晶相没有明显改变，但可以扩大TiO 2的可见光响应范围．当N 和F 的加入量均为2．0%，且在500ħ下焙烧40min 时，得到的N ，F-TiO 2的可见光催化活性明显高于单N 或单F 掺杂的TiO 2（N-TiO 2或F-TiO 2）．对于50mL 浓度为10．0mg ·L －1的酸性红B 溶液，当催化剂加入量为1．5g ·L －1，128W 光照3．0h ，溶液pH =5．6时，去除率为85．40%．适当延长光照时间至4．0h ，降解率几乎可达100%．另外，研究还证明了N ，F-TiO 2催化可见光降解过程中有·OH 自由基生成．关键词：氮氟掺杂；二氧化钛；制备；可见光；催化活性文章编号：0253-2468（2013）03-742-07中图分类号：X131文献标识码：APreparation of N ，F-codoped TiO 2and its photocatalytic activity under visible lightWANG Litao ，LI Fangyi ，ZHANG Zhaohong *，ZHANG Fengqiu ，JING Kui ，HUANG Lirong ，LIU Danni ，GAO WeiSchool of Environment ，Liaoning University ，Shenyang 110036Received 20May 2012；received in revised form 21July 2012；accepted 30July 2012Abstract ：Preparation of N ，F-codoped TiO 2（N ，F-TiO 2）photocatalyst using ammonia water as nitrogen sources and hydrofluoric acid as fluorine sources by sol-gel method was proposed．The crystal form and morphology of the as-prepared photocatalysts were characterized by X-ray diffraction （XRD ）and scanning electron microscope （SEM ）．The influence of N-to-Ti and F-to-Ti molar ratio ，calcination temperature and time ，irradiation time ，catalyst dose ，initial concentration of solution and light power on catalytic activity of N ，F-TiO 2under visible light was investigated using acid red B as a model contaminant．The results showed that anatase is the main crystal form of N ，F-TiO 2．Also ，the doping of nitrogen and fluorine produced no significant change in the crystalline phase of TiO 2，but it could expand the range of response of TiO 2to visible light．The highest catalytic activity of N ，F-TiO 2could be obtained at 2．0%molar ratio of N ，F /Ti while calcining at 500ħfor 40min ，and it was obviously higher than that of N-TiO 2or F-TiO 2．The degradation ratio reached 85．40%for 50mL solution with 10mg ·L －1acid red B at 1．5g ·L －1N ，F-TiO 2dose ，3．0h light irradiation ，128W light power and pH =5．6．The removal ratio could reach nearly 100%by increasing the irradiation time to 4．0h with no change of other conditions．In addition ，the hydroxyl radicals （·OH ）were proved to be generated in the catalyzed degradation by N ，F-TiO 2under visible light．Keywords ：N ，F-codoped ；TiO 2；preparation ；visible light ；catalytic activity3期王丽涛等：氮氟掺杂二氧化钛（N，F-TiO2）的制备及可见光催化活性的研究1引言（Introduction）二氧化钛（TiO2）因具有无毒、化学性质稳定、催化活性高、成本低等优点，成为倍受人们青睐的光催化剂，并在污水处理、空气净化及灭菌消毒等领域显示出巨大的应用价值（Gong et al．，2012；Wang et al．，2011）．但由于TiO2的带隙能为3．2eV，只有用波长小于387．5nm的紫外光激发才会产生空穴（h+）-电子（e－）对，推动一系列化学反应的发生，进而显示出较强的光催化活性（张朝红等，2010）．太阳光中紫外光只占2% 4%，大部分是可见光，这就极大地限制了TiO2光催化剂对太阳能的利用；并且h+和e－在TiO2粒子内部和表面易复合，导致其光催化活性降低（Shen et al．，2009）．近年来，一些研究表明，通过金属或非金属元素的掺杂可以扩大TiO2对可见光的响应范围，使TiO2在可见光的照射下也具有光催化活性．例如，单一的非金属（N、F、S或C）掺杂可在一定程度上增大TiO2对可见光的响应范围，提高其光催化活性（孙剑辉等，2006；Wang et al．，2010）．然而，也有研究表明，非金属元素的共掺杂可进一步提高TiO2的光催化活性（Rengifo Herrera et al．，2008；Yang et al．，2010）．N元素的掺杂可以使TiO2的激发光波长向可见光区移动，而F元素的掺杂尽管不能明显改变TiO2的光吸收区域，却能明显提高TiO2的光吸收强度．因此，可以预测N和F的共同掺杂能够提高TiO2的光催化效率（Pelaez et al．，2009）．目前，国内外已有一些关于非金属N或F的单掺杂研究，而关于N和F共掺杂TiO2的研究却相对较少（Huo et al．，2009；Pelaez et al．，2010）．因此，本研究直接以氨水为氮源，氢氟酸为氟源，采用溶胶－凝胶法制备N，F共掺杂TiO2（N，F-TiO2）．同时，以酸性红B为目标污染物，对制备的N，F-TiO2的可见光催化活性进行研究，并与N或F单掺杂的TiO2（N-TiO2或F-TiO2）进行比较．此外，系统考察N或F加入量、焙烧时间、焙烧温度、光照时间、催化剂用量、溶液初始浓度和照射功率等因素对N，F-TiO2的可见光催化活性的影响，探讨N，F-TiO2的可见光催化反应机理，并验证N，F-TiO2存在时可见光催化降解过程中是否有·OH自由基生成．2材料和方法（Materials and methods）2．1仪器与试剂仪器：Cary50型紫外-可见光谱仪（美国Varian 公司），pHS-3C型酸度计（上海雷磁分析仪器厂），FL40T8EXD/36型三基色灯（日本Toshiba公司，波长范围470 700nm，功率64 192W），D8ADVANCE 型全自动X-射线衍射仪（XRD）（德国Brukeraxs公司），JSM-6301F型扫描电镜（SEM，英国LEO公司），Dionex IonPac型离子色谱仪（美国Dionex公司），TOC测定仪（德国GmbH公司），RH basic2型加热搅拌器（德国IKA公司），KSY-4D-16型马弗炉（沈阳长城工业电炉厂）．试剂：酸性红B（C20H12N2Na2O7S2，AR-B，结构式如图1）、钛酸丁酯（C16H36O4Ti，TTBT）、冰醋酸（CH3COOH）、氨水（NH3·H2O）、氢氟酸（HF）、无水乙醇（C2H5OH）、浓硝酸（HNO3）、四氯化碳（CCl4）、苯（C6H6）、二苯卡巴肼（C13H14N4O，DPCI）、维生素C（C6H8O6，VC）均为市售分析纯试剂．实验用水为二次蒸馏水．图1酸性红B分子结构Fig．1Molecular structure of acid red B2．2实验方法2．2．1N，F-TiO2光催化剂的制备及表征将10．0 mL钛酸丁酯缓慢滴入到30．0mL无水乙醇和4．0 mL冰乙酸混合溶液中，磁力搅拌器快速搅拌，再逐滴加入5．0mL的氢氟酸溶液（0.06mol·L－1），搅拌形成透明混合溶液A；将5．0mL的氨水溶液（0.06 mol·L－1）与10．0mL无水乙醇混合，用1．0mol·L－1HNO3调节pH至2．0，配成溶液B．将溶液B缓慢滴入溶液A中，搅拌，得到均匀透明的溶胶．陈化24 h，得到固体凝胶，在80ħ下干燥12h，研磨成粉末，于马弗炉中一定温度下焙烧，得到N和F掺杂的TiO2粉末．分别改变HF酸溶液或NH3·H2O浓度（0.06 0．24mol·L－1），同样方法制备可得不同N 和F掺杂量的TiO2粉末．分别改变焙烧温度（300 700ħ）或焙烧时间（20 80min），考察它们对N，347环境科学学报33卷F-TiO2粉末光催化活性的影响．作为对照，溶液A或溶液B中氢氟酸溶液或氨水溶液用乙醇代替，制备可得N或F单掺的TiO2粉末．采用XRD和SEM技术对制备的样品进行表征．2．2．2可见光催化降解实验将酸性红B配制成浓度分别为10．0、20．0、30．0、40．0和50．0mg·L－1的标准溶液（pH=5．6），测516nm处吸光度（A），得出A与浓度C（mol·L－1）成线性关系：A= 0.0275C+0．0008，R2=0．9998，符合朗伯-比耳定律．以此标准曲线作为酸性红B定量分析的依据．称取在500ħ下焙烧40min所制备的催化剂0．075g于100mL锥形瓶中，加入50mL浓度为10 mg·L－1的酸性红B溶液，搅拌，光照一定时间，离心，取上清液，测其紫外-可见吸收光谱．作为对照，单独光照和单独催化剂吸附的结果也被给出．改变N和F的加入量、焙烧温度、焙烧时间、光照时间、催化剂加入量和照射功率，并取516nm处的吸光度换算，按公式η=［（C0－C x）/C0］ˑ100%计算酸性红B的降解率η，其中，C为原液浓度（mg·L－1），C x为样品浓度（mg·L－1）．另外，改变光照时间测其离子色谱，并分别测定酸性红B原液和光照4h后溶液的TOC值．离子色谱测定条件为：AS9-HC型离子色谱柱，电导检测器，淋洗液为9．0mmol·L－1的NaCO3溶液，流速为1．0mL·min－1，进样量为20!L．TOC测定条件为：红外检测器，载气0．95 1．00bar（1bar=0．1MPa），流速为200 mL·min－1，进样量为10!L．2．2．3N，F-TiO2催化可见光降解反应中·OH自由基的测定分别取4份50mL的DPCI溶液于锥形瓶中，分别标记为A、B、C、D．向A、C和D瓶中分别加入0．075g催化剂，另向D瓶中加入VC，混匀．A 瓶避光放置，B、C、D瓶同时光照4．0h后，离心，取上清液（5．0mL）于分液漏斗中，用萃取剂（苯与四氯化碳1ʒ1混合溶液5．0mL）萃取，静置，取下层红色溶液测定．用萃取剂作参比，测定563nm处的吸光度．3结果与讨论（Results and discussion）3．1N，F-TiO2的XRD分析图2为500ħ下焙烧40min制备的TiO2和N，F-TiO2的XRD图．可以看出，在2θ=25．4ʎ、38.0ʎ、48．0ʎ、54．7ʎ和63．1ʎ附近都表现出明显的锐钛型特征衍射峰，表明TiO2和N，F-TiO2均以锐钛型为主，也说明N和F的掺杂并未改变TiO2的晶相．与TiO2相比，N，F-TiO2衍射峰稍微变宽．根据Scherrer公式D=0．89Kλ/（bˑcosθ）（λ=0．154 nm，b为半峰宽（rad），θ为半衍射角（ʎ），θ=12．7ʎ）计算（Ling et al．，2008），可得出TiO2和N，F-TiO2的平均晶粒尺寸（D）分别为21．82和16．17nm，说明N和F共掺杂导致TiO2的粒径变小．平均粒径的变小有助于光催化活性的提高．图2TiO2和N，F-TiO2的XRD图Fig．2XRD patterns of TiO2and N，F-TiO23．2N，F-TiO2的SEM分析图3是500ħ焙烧40min制备的TiO2和N，F-TiO2的SEM图．可以看出，与TiO2相比，N，F-TiO2尽管有些团聚，但仍呈现较小的粒径分布，大部分N，F-TiO2粒子的粒径分布在25 35nm范围内．而TiO2粒子的粒径则分布在35 50nm范围内，有些甚至更大．这与Scherrer公式计算的结果比较符合．测试结果表明，N和F共掺杂可有效抑制TiO2粒径的增长，粒径的变小也有利于光催化活性的增加．图3TiO2和N，F-TiO2的SEM图Fig．3SEM image of TiO2and N，F-TiO23．3酸性红B的紫外-可见（UV-Vis）光谱图4是采用500ħ焙烧40min制备的各种4473期王丽涛等：氮氟掺杂二氧化钛（N ，F-TiO 2）的制备及可见光催化活性的研究TiO 2光催化剂可见光降解酸性红B 的UV-Vis 光谱图．由图可知，酸性红B 在200 250nm 、250 350nm 和450 600nm 范围内有3组吸收峰，分别对应着不同的萘环和偶氮键．与原液相比，单独可见光照射或单独加入N ，F-TiO 2后，酸性红B 的吸收峰只有较小的下降，这说明单独可见光照射使酸性红B 只有很小的降解，而单独加入N ，F-TiO 2对酸性红B 有一定的吸附作用．然而，当N ，F-TiO 2结合可见光照射一定时间后，吸收峰大幅降低．且远远低于N或F 单掺TiO 2结合可见光照射后的吸收峰．表明当可见光和N ，F-TiO 2联合作用时，可使大多数酸性红B 氧化分解，且N ，F-TiO 2的光催化活性明显高于单掺N 或单掺F 的TiO 2．图4酸性红B 的紫外光谱（酸性红B 10．0mg ·L －1，功率128W ，光照3．0h ，催化剂1．5g·L －1，pH =5．6）Fig．4UV-Vis spectra of acid red B （AR －B 10．0mg ·L －1，128W ，3．0h ，1．5g ·L －1catalyst ，pH =5．6）3．4N 和F 的加入量对N ，F-TiO 2催化活性的影响改变N 和F 的加入量（N 、F 与TiO 2质量比）分别为1．0%、2．0%、4．0%，400ħ下焙烧1．0h ，考察N 和F 加入量对TiO 2光催化活性的影响．图5结果表明，随着N 和F 加入量的增加，N ，F-TiO 2的光催化活性先增加后降低，这说明N 和F 的掺杂对TiO 2的光催化活性有明显的影响．在酸性红B10.0mg ·L －1、催化剂1．0g ·L －1、pH =5．6、128W 光照2.0h 的条件下，当N 和F 的加入量均为2．0%时，催化剂的活性最高，酸性红B 的去除率达82%．当加入量高于或者低于2．0%时，催化活性均有所降低．这可能是因为当N 和F 掺杂量适当时可使N ，F-TiO 2杂质能级或缺陷能级增多，有利于拓展可见光的响应范围，提高可见光吸收强度．当加入量达到一定程度后，继续增加掺杂量，会使晶体表面的缺陷过多，而易造成光生电子与空穴的复合，降低N ，F-TiO 2的量子产率，导致其可见光催化活性降低（Chen et al ．，2011）．图5氮氟加入量对催化剂催化活性的影响Fig．5Effect of N and F doses on catalytic activity of catalyst3．5焙烧温度和时间对N ，F-TiO 2催化活性的影响图6焙烧温度（a ）和时间（b ）对催化剂催化活性的影响Fig．6Effect of （a ）heat-treated temperature and （b ）time on catalytic activity of catalyst在酸性红B 10．0mg ·L －1、催化剂1．0g ·L －1、pH =5．6、功率128W 光照1．0h 的条件下，改变焙烧温度（300 700ħ）和焙烧时间（20 80min ），考察它们对催化剂光催化活性的影响．图6a 显示（焙烧40min ），当焙烧温度为300ħ时，酸性红B 的去除率最高．通过吸附实验可知，当焙烧温度为300ħ时，吸附率较大，这是由于所制备的催化剂晶化还未完成，此时催化剂的作用主要以吸附为主．当随着焙烧温度升高，样品晶化程度不断提高，晶粒逐渐长大，比表面逐渐减小，吸附能力也逐渐降低．当547环境科学学报33卷温度达到500ħ时，吸附率也达到最小，但仍显示出良好的可见光催化活性．当焙烧温度继续升高时，N ，F-TiO 2颗粒的粒径继续随着温度升高而变大，内部孔隙减少，比表面积减少；另外，当焙烧温度超过500ħ时，也会出现（向金红石转变的）转晶现象，这些都会导致催化活性降低．此外，由图6b 可知（焙烧温度400ħ），焙烧时间为40min 时，催化剂的可见光催化活性最高，焙烧时间过短和过长都会导致催化活性的下降．当时间少于40min 时，由于焙烧时间过短，可能干凝胶未能完全脱去水和醇，不能完全转化为锐钛型的晶型，所以其活性不高．焙烧时间过长，则共掺杂N ，F-TiO 2颗粒会产生团聚，使光催化剂的平均粒径增大，比表面积迅速减小，导致催化活性降低．图7照射时间对酸性红B 溶液去除的影响（a ）和反应动力学（b ）（酸性红B 10．0mg ·L －1，功率128W ，催化剂1．5g ·L －1，pH =5．6）Fig．7Effect of irradiation time on （a ）removal and （b ）reaction kinetics （AR-B 10．0mg ·L －1，128W ，1．5g ·L －1catalyst ，pH =5．6）3．6光照时间对酸性红B 去除率的影响图7a 表明，在N ，F-TiO 2催化结合可见光照射下，酸性红B 的降解率随着照射时间的增加而逐渐增大．当光照240min 时，去除率几乎达100%，表明酸性红B 溶液已基本被去除完全．通过不同照射时间下酸性红B 溶液浓度的自然对数－ln （C t /C 0）随光照时间t 的变化，得到去除反应动力学曲线（图7b ）．由图7b 可知，此去除反应符合一级动力学过程，反应速率常数为0．0112min －1．为了进一步证明酸性红B 的矿化情况，对酸性红B 光照4．0h 的溶液进行了TOC 和离子色谱的测定．结果表明，与原液TOC 值相比，酸性红B 降解液的TOC 去除率约为100%．这与紫外光谱所得结果相一致（见图4）．另外，图8显示不同光照时间后酸性红B 溶液的离子色谱中都出现了NO －3和SO 2－4离子峰，且随着可见光照射时间的增加两个离子峰逐渐增强．这是由于酸性红B 分子中的偶氮键和碳硫键被逐渐破坏而得到NO －3和SO 2－4．离子色谱和TOC 的结果表明，在N ，F-TiO 2催化可见光照射下，酸性红B 可被矿化为CO 2、H 2O 和无机离子．图8不同时间下酸性红B 离子色谱图（酸性红B 10.0mg ·L －1，功率128W ，催化剂1．5g ·L －1，pH =5．6）Fig．8Ion chromatogram of acid red B solution at different irradiation time （AR －B 10．0mg ·L －1，128W ，1．5g ·L －1catalyst ，pH =5．6）3．7催化剂加入量和酸性红B 的初始浓度对去除的影响在酸性红B 10．0mg ·L －1、pH =5．6、128W 光照4．0h 的条件下，改变催化剂加入量（0 2.5g ·L －1），考察N ，F-TiO 2加入量对酸性红B 去除的影响（图9a ）．由图9a 可以看出，随着催化剂用量增大，去除率先升高后下降．当用量为1．5g ·L －1时，去除率可达100%．当催化剂量过多时（大于1.5g ·L －1），由于相互屏蔽阻止催化剂对可见光的吸收，因而去除率逐渐减小．此外，在催化剂1．5g ·L －1、pH =5．6、128W 光照3．0h 的条件下，改变酸性红B 的初始浓度（5．0 25．0mg ·L －1），考察初6473期王丽涛等：氮氟掺杂二氧化钛（N ，F-TiO 2）的制备及可见光催化活性的研究始浓度对酸性红B 去除的影响（图9b ）．由图9b 可知，酸性红B 的去除率随着初始液浓度的增加而减小，说明初始浓度较低时有利于去除．在初始浓度为5．0mg·L －1时，去除率几乎可达到100%．一般来说，催化剂的催化活性是有限的．对于N ，F-TiO 2，在可见光激发下，水中可产生的·OH 自由基的数目是一定的．因此，单位时间内酸性红B 被氧化分解的数量是有限的．另外，高浓度的染料能可阻止催化剂对可见光的吸收，从而导致去除率下降．图9催化剂加入量（a ）和初始浓度（b ）对去除的影响Fig．9Effect of （a ）catalyst dose and （b ）initial concentration on degradation3．8照射功率对酸性红B 去除的影响在酸性红B 10．0mg ·L －1、催化剂1．5g ·L －1、pH =5．6、光照2．0h 的条件下，由图10可知，随着可见光照射功率的增加，酸性红B 的去除率逐渐增大．当照射功率达到192W 时，酸性红B 的去除率接近90%．这是因为提高照射功率，光强增加，光子数增加，所产生的光生电子与空穴也随之增多，致使体系中的活性氧物种浓度增加，从而加速了有机物的去除．图10照射功率对去除的影响Fig．10Effect of light power on removal3．9·OH 自由基的测定在N ，F-TiO 2光催化反应过程中，·OH 自由基的生成可通过二苯卡巴肼（DPCI ）的氧化来鉴定（Wang et al ．，2011）．图11显示了不同条件下DPCI 的UV-Vis 光谱变化．当DPCI 捕获·OH 后可被氧化，生成二苯卡巴腙（DPCO ），溶液呈红色，在563nm 处有强吸收．然而当遇到·OH 的猝灭剂如抗坏血酸（VC ）后，DPCO 的吸收峰有明显的下降，这说明N ，F-TiO 2催化可见光降解过程中产生了·OH ，将DPCI 氧化为DPCO．图11不同条件下二苯卡巴肼溶液的UV-Vis 光谱Fig．11UV-Vis spectra of DPCI solutions at different conditions3．10光催化活性机理的探讨TiO 2只在紫外光照射下可被激发，产生电子（e －）-空穴（h +）对，h +能将水中的OH －和H 2O 转化为·OH 自由基，使有机物氧化降解．由于TiO 2的禁带宽度为3．2eV ，导致它对可见光的利用率很低．N 掺杂的TiO 2可形成N —Ti —O 键，在TiO 2价带上方引入一个杂质能级，可拓宽TiO 2对可见光的响应范围（Pelaez et al ．，2010）．同时，掺杂N 还可导致TiO 2表面产生O 空位，提高TiO 2的可见光催化活性．掺杂F ，由于其较高的电负性，能够促进e －-h +对的分离，抑制e －-h +的复合；另一方面，F 掺杂促747环境科学学报33卷进了TiO2表面酸性位点的形成，而酸性位点有助于提高光催化剂对反应物的吸附能力，且表面强酸性位点也起到电子捕获体的作用，进而加剧了e－-h+对的分离．因此，N和F共掺杂可改变TiO2粒子的能级结构与表面性质，从而扩大其可见光响应范围，抑制载流子复合，提高量子效率和光催化活性（Pelaez et al．，2009；Li et al．，2010）．4结论（Conclusions）1）以氨水为氮源，氢氟酸为氟源，采用溶胶-凝胶法成功制备了氮氟掺杂的二氧化钛（N，F-TiO2）光催化剂，表征结果表明，制备的N，F-TiO2以锐钛型为主，N和F共掺杂可有效抑制TiO2粒径的增长．2）当N和F的加入量为2．0%，500ħ下焙烧40min时，N，F-TiO2的可见光催化活性明显高于N-TiO2，F-TiO2或未掺杂TiO2．3）N，F-TiO2结合可见光照射可使酸性红B矿化为CO2、H2O和无机离子．对于10mg·L－1酸性红B，催化剂加入量1．5g·L－1，溶液pH=5．6，可见光（128W）照射4．0h，降解率几乎达100%．此降解反应是一级动力学反应，反应速度常数为0.0112min－1．4）可见光照射N，F-TiO2催化降解过程中有·OH自由基的生成．责任作者简介：张朝红（1968—），理学博士，教授，主要从事水污染控制方面的研究，主持国家自然科学基金和省部级以上科研项目多项，在国内外学术刊物发表研究论文100余篇，被SCI和EI检索收录65篇．参考文献（References）：Chen S F，Yang Y G，Liu W．2011．Preparation，characterization and activity evaluation of TiN/F-TiO2photocatalyst［J］．J Hazard 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Vol 137No 13・72・化　工　新　型　材　料N EW CH EMICAL MA TERIAL S 第37卷第3期2009年3月基金项目:江苏省生态环境材料重点实验室开放基金(XKY2007002)作者简介:王旭(1974-),男,硕士,讲师,从事功能材料的研究。

溶胶2凝胶法制备TiO 2及其光催化性能研究王　旭　程俊华　陈嘉兴(盐城工学院材料工程学院,盐城224009)摘　要　采用溶胶2凝胶法制备TiO 2,以甲基橙为模型污染物,考察了影响TiO 2光催化活性的主要因素,并采用SEM 和XRD 等方法对样品进行了表征。

结果表明:在450℃下煅烧2h 后,可以制得具有较高光催化活性的TiO 2粉末。

当甲基橙溶液中TiO 2的质量浓度为1.0g/L 时,光催化效果最佳;TiO 2粉末主要具有锐钛矿型晶体结构。

关键词　溶胶2凝胶法,TiO 2粉末,光催化Study on photocatalytic activity of TiO 2prepared by sol 2gel methodWang Xu Cheng J unhua Chen Jiaxing(School of Materials Engineering ,Yancheng Instit ute of Technology ,Yancheng 224009)Abstract TiO 2powder was prepared by sol 2gel method.It was determined the influencing factors by the methyl or 2ange as model pollutants.The obtained TiO 2were characterized though XRD ,SEM ,etc.The results showed that TiO 2ex 2presses optimal photocatalytic activity when the powder was calcinated for 2hours at 450℃and the proper dosage of TiO 2was 110g /L ,and the prepared TiO 2powder was anatase phase.K ey w ords sol 2gel method ,TiO 2powder ,photo catalysis TiO 2作为一种新型多功能材料,以其无毒、光催化活性高、稳定性高、氧化能力强、能耗低、可重复使用等优点而成为最优良的光催化材料[1]。

ReviewA review on the formation of titania nanotube photocatalysts by hydrothermal treatmentChung Leng Wong,Yong Nian Tan,Abdul Rahman Mohamed *School of Chemical Engineering,Engineering Campus,Universiti Sains Malaysia,14300Nibong Tebal,Pulau Pinang,Malaysiaa r t i c l e i n f oArticle history:Received 14August 2010Received in revised form 15January 2011Accepted 6March 2011Available online 29March 2011Keywords:Titania nanotubesHydrothermal method MechanismStarting materialSonication pretreatment Hydrothermal temperaturea b s t r a c tTitania nanotubes are gaining prominence in photocatalysis,owing to their excellent physical and chemical properties such as high surface area,excellent photocatalytic activity,and widespread avail-ability.They are easily produced by a simple and effective hydrothermal method under mild temperature and pressure conditions.This paper reviews and analyzes the mechanism of titania nanotube formation by hydrothermal treatment.It further examines the parameters that affect the formation of titania nanotubes,such as starting material,sonication pretreatment,hydrothermal temperature,washing process,and calcination process.Finally,the effects of the presence of dopants on the formation of titania nanotubes are analyzed.Ó2011Elsevier Ltd.All rights reserved.1.IntroductionIn the environmental technology sector,industrial wastewater treatment is gaining importance for the removal of organic pollut-ants (Neves et al.,2009).Large amounts of organic pollutants consumed in the industries are being released into the eco-system over the past few decades and they constitute a serious threat to the environment (Mahmoodi and Arami,2009).As chemical and agri-cultural wastes,these contaminants are frequently carcinogenic and toxic to the aquatic system because of their aromatic ring structure,optical stability and resistance to biodegradation (Mahmoodi and Arami,2009).Catalytic technologies are gaining recognition in the field of environmental protection (Yu et al.,2007b ).In past decades,the traditional physical techniques for the removal of organic pollut-ants from wastewaters have included adsorption,biological treat-ment,coagulation,ultra filtration and ion exchange on synthetic resins (Mahmoodi and Arami,2009and Sayilkan et al.,2006).Those methods have not always been effective and they may not actually break down the pollutants in wastewater.For example,adsorption technology does not degrade the contaminants,but essentially transfers the contaminants from one medium to another,hence,contributing to secondary pollution (Mahmoodi and Arami,2009and Sayilkan et al.,2006).Moreover,such operations are expen-sive because the pollutants are treated before the adsorption process while the adsorbent medium has to be regenerated for re-use (Mahmoodi and Arami,2009).Traditional biological treatments are often ineffective in removing and degrading pollutants because the molecules,being mostly aromatic,are chemically and physically stable (Xu et al.,2009).Hence,biodegradation of organic pollutants is usually incomplete and selective (Xu et al.,2009).In fact,some of the degradation intermediates may be even more toxic and carci-nogenic than the original pollutants (Xu et al.,2009).Chlorination and ozonation have also been used in contaminant removal,but their operating costs are high compared with other methods (Sayilkan et al.,2006).Finally,although coagulation treatments using alums,ferric salts,or limes are inexpensive,they often pose waste disposal problems of their own (Mahmoodi and Arami,2009).With the discovery of photocatalytic splitting on TiO 2electrodes by Fujishima and Honda in 1972,heterogeneous photocatalysis has attracted much attention as a new puri fication technique for air and water (Fujishima and Honda,1972;Yu et al.,2006,Yu et al.,2007a and Yu et al.,2007b ).Heterogeneous photocatalysis has been successfully used in the oxidation,decontamination or minerali-zation of organic and inorganic contaminants in wastewater without generating harmful byproducts (Thiruvenkatachari et al.,2008).This approach has attracted much attention for its ease of*Corresponding author.Tel.:þ60045996410;fax:þ60045941013.E-mail address:chrahman@m.my (A.R.Mohamed).Contents lists available at ScienceDirectJournal of Environmental Managementjournal homepage:www.elsev /locat e/jenvman0301-4797/$e see front matter Ó2011Elsevier Ltd.All rights reserved.doi:10.1016/j.jenvman.2011.03.006Journal of Environmental Management 92(2011)1669e 1680application in oxidizing and degrading organic pollutants at rela-tively lower costs(Sayilkan et al.,2006).Currently,many semiconductors have been applied in hetero-geneous photocatalysis(Costa and Prado,2009).Semiconductor photocatalysts such as CdS,SnO2,WO3,TiO2,ZrTiO4,and ZnO (Nawin et al.,2008;Seo et al.,2001and Seo et al.,2009),titania (TiO2)semiconductor photocatalysts have demonstrated advan-tages that include transparency(Nawin et al.,2008),wide band gap (Wang et al.,2008),biological and chemical inertness(Lee et al., 2007;Mahmoodi and Arami,2009;Yu et al.,2006,Yu et al., 2007a,Yu et al.,2007b and Zhang et al.,2010),strong oxidizing power(Lee et al.,2007;Yu et al.,2006and Yu et al.,2007a)and non-toxicity(Lee et al.,2007;Mahmoodi and Arami,2009;Neves et al., 2009;Yu et al.,2006,2007a and Zhang et al.,2010).Considerable effort has been made to develop TiO2semi-conductor photocatalysts for environmental protection procedures such as air and water purification(Lee et al.,2007;Nawin et al., 2008;Yu et al.,2006and Yu et al.,2007b),antibacterial protec-tion(Vuong et al.,2009),water disinfection(Yu et al.,2006and Yu et al.,2007b),treatment of harmful gas emission(Nawin et al., 2008)and hazardous water remediation(Yu et al.,2006and Yu et al.,2007b).TiO2has been used in many areas such as in photo-catalysis,in the generation of hydrogen from water(photocatalytic water splitting),in photocatalytic oxidation of organic or inorganic compounds,and in solar cells.Despite the enormous potential of TiO2semiconductor photocatalysts,its low efficiency limits its role in present day photooxidation technology(Lee et al.,2007;Yu et al., 2006and Yu et al.,2007a).Thus,significant improvements and optimizations to TiO2semiconductor photocatalysts are needed before their many promising applications can be realized(Yu et al., 2006and Yu et al.,2007a).With appropriate modification and optimization,TiO2semiconductor photocatalysts can be develop to generate active charge carriers to degrade organic pollutants into the harmless products(Yu et al.,2006).The performance of TiO2semiconductor photocatalysts is strongly influenced by the physical and chemical properties that determine its morphology,dimension and crystallite phase(Vuong et al.,2009).From research carried with TiO2nanocrystals,it has been shown that the smaller particle size(giving rise to larger surface area-to-volume ratio)of TiO2nanocrystals increases pho-tocatalytic efficiency(Wang et al.,2008and Yu et al.,2007a).The disadvantages of TiO2semiconductor photocatalysts include the requirement of large amounts of TiO2semiconductor photo-catalysts,difficulty in re-cycling TiO2semiconductor photocatalysts, problems encountered in its recovery byfiltration or centrifugation, and the problematic agglomeration of TiO2nanocrystals into large particles(Costa and Prado,2009;Gupta et al.,2006and Ribbens et al.,2008).The separation processes required to recover the TiO2 semiconductor photocatalysts at the end of the photocatalytic treatment are difficult to perform because of the small size of the TiO2semiconductor photocatalysts and the high stability of the TiO2 semiconductor photocatalyst hydrocolloid(Costa and Prado,2009). TiO2semiconductor photocatalysts also have the tendency to lose efficiency when they agglomerate into larger particles(Ribbens et al.,2008).This also adds to the complications in their disposal. While immobilized TiO2nanocrystals are an option for large scale application,the overall photocatalytic efficiency is compromised due to the reduction in surface area and the limitation in mass transfer(Yu et al.,2007a).To overcome these difficulties,different titanate nanostructure preparations are being investigated with the aim of increasing photocatalytic efficiency(Costa and Prado,2009 and Okour et al.,2009).Nanostructured materials such as nanofibers,nanoparticles, nanorods,nanospheres,nanotubes and nanowires present new features and opportunities for enhanced performance in many promising applications(Costa and Prado,2009;Seo et al.,2009; Wang et al.,2007and Wang et al.,2008).Nanostructured mate-rials are of special significance owing to their excellent physi-cochemical properties that are catalytic,electronic,magnetic, mechanical and optical in nature(Poudel et al.,2005).They are widely applied in air and water purification technologies,photo-catalysis,gas sensors,high effect solar cells and microelectronic devices(Nakahira et al.,2004and Yu and Yu,2006).For example, O’Regan et al.stated that titania nanotubes have been used in high quality,efficient solar cells(Nakahira et al.,2004).Nanostructured materials with different morphologies have varying specific prop-erties and,hence,the new applications of such materials are related to the shape and size of the nanostructured materials(Wang et al., 2007).The synthesis of nanostructured materials with specific shape and size,as well as the understanding of their formation mechanism are two important research aspects in material science and technology(Wang et al.,2007).Nanowires,nanotubes and nanofibres of TiO2have been successfully prepared by electro-chemical synthesis,template based synthesis and a chemical based route although the effectiveness and practicality of some of these materials as photocatalysts are still being evaluated(Okour et al., 2009and Yu and Yu,2006).The discovery of the carbon nanotubes in the1990s by Iijima opened newfields in the material science sector(Costa and Prado, 2009).Nanotubular materials are considered important in photo-catalysis owing to their special electronic and mechanical properties, high photocatalytic activity,large specific surface area and high pore volume(Idakiev et al.,2005and Yu and Yu,2006).Several studies have shown that titania nanotubes have better physical and chemical properties in photocatalysis compared with other forms of titanium dioxide.For example,titania nanotubes have a relatively higher interfacial charge transfer rate and surface area compared with the spherical TiO2particles(Colmenares et al.,2009).The transfer of the charge carriers along the length of titania nanotubes can reduce the recombination of positive hole and electron(Colmenares et al., 2009).Li et al.(2009)found that hollow titania nanotubes were highly efficient in the photocatalytic decomposition of methyl orange compared with rutile phase TiO2nanopowders.Xu et al.(2006)stated that titania nanotubes were excellent photocatalysts,which were more reactive than TiO2nanopowder(anatase P25)in long cycles. Thus,titania nanotubes have raised expectations in what nanotech-nology can achieve because of their interesting microstructure and potential photoelectrochemical applications in dye-sensitized solar cells,gas sensors,organic light-emitting diodes and photocatalysts (Yu et al.,2007a).Considerable effort is now being devoted to the production of well-structured TiO2nanotubes with novel properties such as high surface area and pore volume(Idakiev et al.,2005).The approaches in developing TiO2nanotubes include chemical vapor deposition(CVD),anodic oxidation,seeded growth,the wet chemical(hydrothermal method and the sol gel method)(Guo et al., 2008;Morgan et al.,2008and Wang et al.,2007).Among these, hydrothermal method is often the method of choice because of its many advantages like cost-effectiveness,low energy consumption, mild reaction condition and simple equipment requirement(Guo et al.,2008).This method also allows for the manipulation of a large number of variable factors by which the morphology of TiO2 nanotubes that are produced is controlled.Photocatalysis is a“green”technology with promising applica-tions in a wide assortment of chemical and environmental tech-nologies(Colmenares et al.,2009).It has been singled out as a particularly attractive means by which to oxidize and remove toxic compounds,including carcinogenic chemicals,from industrial effluent.The pollutants are chemically transformed and completely mineralized to harmless compounds such as carbon dioxide,water and salts(Gupta et al.,2006).C.L.Wong et al./Journal of Environmental Management92(2011)1669e1680 1670This process is an example of an advanced oxidation process (AOP),which is defined as the chemical treatment process designed to produce strong hydroxyl radicals to oxidize and remove the organic and inorganic materials in the wastewater(Thiruvenkatachari et al., 2008).Photocatalysis is a chemical process that uses light to acti-vate a catalyst that alters the reaction rate without being involved itself.In heterogeneous photocatalysis,three main components are essential for photocatalytic reaction to take place:catalyst,light source and reactant(Thiruvenkatachari et al.,2008).Heterogeneous photocatalysis using titania nanotubes as pho-tocatalysts has recently gained importance in wastewater treat-ment.It has several advantages compared with other processes:(a) no mass transfer limitations,(b)complete mineralization of organic compounds to carbon dioxide,salts and water,(c)no addition of chemicals(d)no waste-solids disposal problems,(e)utilization of sunlight or near-UV light for irradiation and(f)only mild temper-ature and pressure conditions(atmospheric oxygen is used as oxidant)are necessary(Gogate and Pandit,2004;Konstantinou and Albanis,2004and Mahmoodi and Arami,2009).TiO2nanotubes have high cation-exchange ability that allows for large active catalyst loadings with high and uniform spreading. In the photocatalytic reaction,access to active sites is optimized by three main characteristics:high specific surface area,unavailability of micropores of reactants and open mesoporous morphology of TiO2nanotubes.The high performance of TiO2nanotubes in pho-tocatalysis is due to the semiconducting behavior of titania that produces a powerful electronic interaction between titania nano-tubes and their supports to increase the catalytic activity.As titania nanotubes are very resilient during heat treatment,their applica-tion as catalysts in photocatalysis is attractive.2.Fabrication of titania nanotubesThe fabrication of titania nanotubes is achieved by one of several methods:the surfactant-directed method,alumina templating synthesis,microwave irradiation,electrochemical synthesis and the hydrothermal method.Alumina templating synthesis has been a popular method to produce TiO2nanotubes over the last decades(Bavykin et al.,2006). TiO2nanotubes produced by template replication are uniform and well-aligned(Bavykin et al.,2006).However,this method is not suitable for the preparation of smaller nanotubes because of the limitation of the pore size of the mold prepared from porous alumina(Ma et al.,2006).TiO2nanotubes produced by the alumina templating method normally have large diameters(greater than 50nm)and the walls of TiO2nanotubes are composed of nano-particles(Costa and Prado,2009and Nawin et al.,2008).They are difficult to split from their template components that are then destroyed and discarded,thus adding to operating cost(Bavykin et al.,2006and Nawin et al.,2008).TiO2nanotubes produced by the surfactant-directed method have smaller diameters and thinner walls as compared with products fabricated using the other methods(Ma et al.,2006).In addition, there are two main disadvantages of the surfactant-directed method: it is elaborate and time consuming to undertake(Ma et al.,2006).With the direct anodizaiton method,titania nanotubes are not split in an organized manner and the tubes do not have well-developed gaps in between(Bavykin et al.,2006).Besides,during the preparation of titania nanotubes,they have been immobilized on the surface of titanium effectively(Bavykin et al.,2006).Thus, they can be applied in different applications such as photocatalysis, hydrogen sensors,photoanodes for water splitting,and so on (Bavykin et al.,2006).The microwave irradiation method is another means by which TiO2nanotubes are synthesized.Wu et al.(Zhao et al.,2009)synthesized TiO2nanotubes by treating TiO2(anatase or rutile) with8e10M sodium hydroxide(NaOH)aqueous solution.On applying195W microwave power,TiO2nanotubes(8e12nm in diameter and100e1000nm in length,with multi-wall and open-ended structure)were produced.Notwithstanding the methods mentioned above,high quality of TiO2nanotubes with small diameters of about10nm are normally produced via a simple hydrothermal treatment of crystalline tita-nium dioxide nanoparticles with highly concentrated sodium hydroxide(Bavykin et al.,2006;Costa and Prado,2009and Nawin et al.,2008).Alkali titanate nanotubes are generated in hydro-thermal treatment where alkali ions are exchanged with photons to form the H-titanates.In order to produce TiO2nanotubes with different crystallographic phases such as anatase,rutile and broo-kite,thermal dehydration reactions in air are carried out at high temperatures.Kasuga et al.reported thefirst evidence for the production of small sized titania nanotubes through the hydrothermal process in the absence of molds for template and replication(Idakiev et al., 2005and Kasuga et al.,1998).The hydrothermal synthesis method is widely regarded as a convenient and inexpensive method to produce high quality TiO2nanotubes(Yu et al.,2006).In general,TiO2nanotubes show vast pore structure and high aspect ratio owing to their unique nanotubular structure(Yu et al.,2006). This renders the nanotubes attractive candidates for photocatalytic and photoelectrochemical systems.3.Hydrothermal method:formation mechanism of titania nanotubesThe fabrication of titania nanotubes by hydrothermal synthesis is performed by reacting titania nanopowders with an alkaline aqueous solution.While the hydrothermal method of titania nan-otube production has been comprehensively investigated in the past decade,the formation mechanisms,compositions,crystalline structures,thermal stabilities and post-treatment functions still remain areas of debate(Guo et al.,2007and Qamar et al.,2008).As a low temperature technology,hydrothermal synthesis is environmentally friendly in that the reaction takes place in aqueous solutions within a closed system,using water as the reaction medium(Sayilkan et al.,2006;Wang et al.,2008and Yu et al., 2007b).This technique is usually carried out in an autoclave (a steel pressure vessel)under controlled temperature and/or pressure.The operating temperature is held above the water boiling point to self-generate saturated vapor pressure(Chen and Mao,2007and Wang et al.,2008).The internal pressure gener-ated in the autoclave is governed by the operating temperature and the presence of aqueous solutions in the autoclave(Chen and Mao, 2007).TiO2nanotubes are obtained when TiO2powders are mixed with2.5e20M sodium hydroxide aqueous solution maintained at 20e110 C for20h in the autoclave(Chen and Mao,2007).The hydrothermal method is widely applied in titania nanotubes production because of its many advantages,such as high reactivity, low energy requirement,relatively non-polluting set-up and simple control of the aqueous solution(Lee et al.,2007).The reaction pathway is very sensitive to the experimental conditions,such as pH, temperature and hydrothermal treatment time,but the technique achieves a high yield of tinania nanotubes cheaply and in a relatively simpler manner under optimized conditions.There are three main reaction steps in hydrothermal method:(a)generation of the alka-line titanate nanotubes;(b)substitution of alkali ions with protons; and(c)heat dehydration reactions in air(Hafez,2009and Wang et al.,2008).The hydrothermal method is amenable to the prepa-ration of TiO2nanotubes with different crystallite phases such as the anatase,brookite,monoclinic and rutile phases(Wang et al.,2008).C.L.Wong et al./Journal of Environmental Management92(2011)1669e16801671Kasuga et al.(1998)carried out preliminary studies on titania nanotube formation using crystalline TiO 2nanoparticles as pre-cursors.The crystalline TiO 2nanoparticles were reacted with highly concentrated NaOH solution to form titania nanotubes by the hydrothermal ing this simple technique,titania nano-tubes were produced with uniform diameter (8e 10nm),speci fic surface area (380e 400m 2/g)and length (50e 200nm)(Okour et al.,2009;Yu et al.,2007a ).Titania nanotubes produced in this manner were initially considered anatase phase products.When some of the Ti e O e Ti bonds were interrupted by the addition of NaOH solutions,some Ti þions were exchanged with Na þions to form Ti e O e Na bonds (Chen and Mao,2007).In this situation,the anatase phase existed in a metastable condition that had resulted from the “soft-chemical reaction ”at low temperature.The presence of Na þions in fluenced the subsequent photocatalytic activity of the titania nanotubes (Sreekantan and Lai,2010).Kasuga and his workers subsequently introduced an acid washing treatment step following the hydrothermal process to form tri-titanate nanotubes (Kasuga et al.,1999).The purpose of the acid treatment was toremove the Na þions from the samples and to form new Ti e O e Ti bonds that would improve photocatalytic activity of the titania nanotubes (Kasuga et al.,1999).When the samples were treated with hydrochloric acid,the electrostatic repulsions disappeared immediately (Kasuga et al.,1999).The charged components were only gradually removed upon further washing with deionized water (Kasuga et al.,1999).The Na þions were displaced by H þions to form Ti e OH bonds in the washing process (Chen and Mao,2007).Next,the dehydration of Ti e OH bonds produced Ti e O e Ti bonds or Ti e O .H e O e Ti hydrogen bonds (Chen and Mao,2007and Kasuga et al.,1999).The bond distance between one Ti and another on the photocatalyst surface conse-quently decreased,facilitating the sheet folding process (Chen and Mao,2007and Kasuga et al.,1999).The electrostatic repulsion from Ti e O e Na bonds enabled a joint at the ends of the sheets to form the tube structure (Chen and Mao,2007and Kasuga et al.,1999).Kasuga et al.concluded that washing with acid and with deionized water were two principal crucial steps to produce high activity of titania nanotubes (Chen et al.,2002).The simple formation mechanism for titania nanotubes is shown in Fig.1.Yuan and Su (2004)proposed a mechanism for the fabrication of titanate nanotubes that was roughly similar to Kasuga ’s.They postulated that the crystalline structure of TiO 2was represented as TiO 6octahedral and that the crystalline structure of TiO 2shared vertices and edges to form in the three-dimensional structure.Ti e O e Ti bonds were broken by a cauterization process to produce the layered titanates.The titanate sheets were then peeled off intonanosheets and subsequently folded into nanotubes.The Na þions were exchanged and eliminated after washing with acid and then with deionized water.The major difference between Yuan and Su ’s titanate nanotubes and Kasuga ’s nanotubes was the dif ficulty in rolling up the former product completely.There were several tri-titanate layers produced simultaneously in the hydrothermal process to form three-dimensional nanosheets,resulting in the nanosheet edges being bent at the end of the hydrothermal process.Some researchers contend that the hydrothermal treatment is signi ficantly the more important step as compared with the washing process in the mechanism of nanotubes formation.For eters and lengths of a few hundred nanometers by the hydro-thermal process using NaOH (10M)at 130 C,but without HCl washings.Wang et al.(Poudel et al.,2005)reported that the acid washing procedure was not necessary for the formation of titania nanotubes,essentially contradicting the assumptions of Kasuga et al.The foregoing notwithstanding,there are other researchers who are of the view that the acid washing practice is requisite for the titanate precursor sheets rolling into nanotubes (Liu et al.,2009).For instance,in 2007,Li and his workers (Liu et al.,2009)found that some partially curled nanofoils were formed after brie fly washing with nitric acid and water.The nanofoils were transformed to nanotubes only after a more thorough washing with a large quantity of nitric acid and water (Liu et al.,2009).Yao et al.(Poudel et al.,2005)observed the formation of titania nanotubes after acid washing.Sun and Li (Poudel et al.,2005)observed that the washing step was the main step to the formation of both titania and sodium titanate nanotubes.There are also researchers who think that regardless of whether the titanate nanotubes are washed or unwashed,they are capable of removing organic or inorganic pollutants ef ficiently.Thus,Nawin et al.(2009)stated that the presence of Na had little bearing on the ef ficiency of the rate at which the pollutants decomposed,as this was in fluenced more by the rate of nanotube sedimentation,available surface area and tubular structure.Wang et al.(2002)carried out an in-depth probe of the titania nanotube formation mechanism.They observed that the three-dimensional titanium dioxide structures (anatase phase),whichFig.1.Formation mechanism of TiO 2nanotubes using hydrothermal method (Chen and Mao,2007and Kasuga et al.,1999).C.L.Wong et al./Journal of Environmental Management 92(2011)1669e 16801672werefirst reacted with sodium hydroxide aqueous solution,were transformed into2-dimensional layered structures.These lamellar structures then scrolled or wrapped to form titania nanotubes.In their opinion,the two-dimensional lamellar structure was essential in the formation of titania nanotubes.A formation of titania nanotubes was proposed by Wang et al. (Chen and Mao,2007).During the hydrothermal reaction with NaOH,the Ti e O e Ti bonds were broken.The free octahedral shapes shared edges between the Ti ions to form hydroxyl bridges,then, a zigzag structure was formed.Thus,the crystalline sheets rolled up in order to saturate these dangling bonds from the surface.This lowered the total energy and hence TiO2nanotubes were formed.There have been recent debates over the crystal structures of TiO2e based nanotubes,possible forms of which can be summa-rized as follows:(a)anatase/rutile/brookite TiO2,(b)lepidocro-cite H x Ti2Àx/4[]x/4O4(x w0.7,[]:vacancy),(c)H2Ti3O7/Na2Ti3O7/ Na x H2Àx Ti3O7and(d)H2Ti4O9(Guo et al.,2008;Ou and Lo,2007 and Qamar et al.,2008).Some researchers were of the opinion that anatase TiO2powder formed nanotubes more readily as compared with the rutile TiO2powder due to better surface energy of the former.In this connection,Wang et al.(Poudel et al.,2005) reported that the crystallinity of nanotubes was slightly better using the anatase TiO2phase as precursor.On the other hand,Chen et al.showed that nanotubes were obtained regardless of the size and the structure of the precursor or the starting materials(Papa et al.,2009).Ma et al.(Idakiev et al.,2005)contended that the nanotubes were formed from lepidocrocite H x Ti2Àx/4[]x/4O4(x w0.7,[]:vacancy) sheets rather than the other structures.When the duration of sonication was increased,the reactants formed rolled structures that transformed to rod-like structures.The growth of the length of rod-like structures was increased during the hydrothermal treatment. The sodium ions could then be washed off by the hydrochloric acid solution.Yoshikazu et al.(Poudel et al.,2005)reported that the nanotubes were hydrated hydrogen titanate(H2Ti3O7∙n H2O(n<3)).Du et al. (Poudel et al.,2005)found that the nanotube crystalline phase was not TiO2anatase but H2Ti3O7(a monoclinic system)and that the tubes had multi-wall morphology with interlayer spacing of 0.75e0.78nm.Kukovecz et al.(2005)tried to roll the tri-titanate nanosheets directly from the assumed Na2Ti3O7intermediate in their experiment.However,since sodium tri-titanate was quite stable under the reaction conditions(10M NaOH,130 C),it was not destroyed by NaOH,and nanotube formation did not occur.With the same alkaline hydrothermal treatment,the researchers then used the assumed Na2Ti3O7intermediates as seeding materials to convert anatase TiO2into titania nanotubes.In this instance,the yield of titania nanotubes was almost100%.Fluctuation in the local concentrations of the intermediates might have initiated the formation of nanoloops from the anatase starting materials,and these served as the seeds for titania nanotube formation.Peng et al.(Idakiev et al.,2005and Ou and Lo,2007)were of the view that H2Ti3O7was produced in the hydrothermal treatment. They proposed the two most likely mechanisms in tri-titanate nanotubes formation.In the initial stage of the hydrothermal process,the reaction between titanium dioxide and concentrated sodium hydroxide solution produced a highly disordered inter-mediate,which contained Ti,O and Na.In thefirst proposed mechanism,single sheets of the tri-titanate(Ti3O7)2Àstarted to grow at a slow rate within the disordered intermediate phase.The slow growth was mainly due to the high concentration of NaOH that was present.As the tri-titanite sheets grew two-dimensionally, they rolled up into nanotubes.In the process,however,some H2Ti3O7plates failed to wrap up successfully,resulting in the edges of H2Ti3O7plates having a tendency to twist.In the second proposed mechanism,the lepidocrocite Na2Ti3O7was postulated to assume the form of disorder-phase nanocrystals that was not stable in the boiling water.With the excessive of Naþcations intercalating in the interlayer spaces,single layers of tri-titanate were either flaked off to form nanocrystals or they were curled like wood shavings into nanotubes.Yang et al.(Idakiev et al.,2005and Ou and Lo,2007)stated that titanium dioxide particle swelling was indicative of Na2Ti2O4(OH)2 formation.After the addition of concentrated NaOH solution,the shorter Ti e O bonds split and swelled.The linear portions(one-dimensional)connected to each other in the presence of OÀe Naþe OÀbonds to produce planar fragments(two-dimensional).Titania nanotubes would then be formed by the formation of covalent bonds within the end groups.Seo et al.(2009)studied the formation mechanism of titania nanotubes by the hydrothermal process at a higher temperature of 230 C TiO2wasfirstly reacted with NaOH solution to form Na2Ti2O5$H2O.Next,the hydrochloric acid washing step was carried out to remove Naþions and to form the exfoliated sheets that then curled up to produce more uniform nanotube structures.At the present time,the formation mechanism is still ambiguous despite efforts that have been made to come up with an acceptable and verifiable explanation(Bavykin et al.,2006and Ribbens et al., 2008).Even though a complete understanding has yet to be ach-ieved,it is generally accepted that titanium dioxide(amorphous, anatase,brookite and rutile)under alkaline circumstances are converted to intermediates(single layer and multi-layered titanate nanosheets)that roll or curl into nanotubular structure(Bavykin et al.,2006).The putative driving force that is responsible for the rolling or curving nanotubular structure has been suggested by some groups(Bavykin et al.,2006).Table1shows the major steps of titania nanotube formation proposed by various researchers.4.Factors influencing the formation of titania nanotubesThere are several considerations affecting the formation of titania nanotubes(Fig.2).These include(a)the starting materials (commercial,self-prepared,amorphous,crystalline,anatase,rutile and brookite),(b)sonication pretreatment,(c)hydrothermal temperature,(d)treatment time and(e)post-treatments(washing, calcinations)(Morgan et al.,2008and Wang et al.,2008).The characteristics and morphology of titania nanotubes such as the specific surface area,crystal structure and others are dependent on the hydrothermal conditions selected.4.1.Effect of the starting materialsThe hydrothermal synthesis of titania nanotubes can start with different titania powders such as rutile or anatase TiO2,Degussa TiO2(P25)nanoparticles,layered titanate Na2Ti3O7,Ti metal, TiOSO4,molecular Ti IV alkoxide,doped anatase TiO2,or SiO2e TiO2 mixture(Wang et al.,2008).Alternatively,titania sol can also be utilized as the starting reactant in the hydrothermal process.It has been observed that the structural properties of the nanostructured TiO2products are markedly dependent on different starting TiO2 materials.Basically,nanotubes with outer diameters between10 and20nm can be obtained by the hydrothermal method when starting with titania powder of relative large particle size,such as rutile TiO2,Degussa TiO2(P25),and SiO2e TiO2mixture(Wang et al., 2008).Saponjic et al.(2005)used different starting materials to produce titania nanotubes using hydrothermal method,which are Degussa TiO2P25nanoparticles,TiO2colloids,and molecular Ti IV alkoxide.Titania nanotubes obtained from those starting materialsC.L.Wong et al./Journal of Environmental Management92(2011)1669e16801673。

专利名称：PREPARATION OF PHOTOCATALYST 发明人：SUZUKI KENICHIRO,SATOSHIGEYUKI,YAMASHITA KATSUJI申请号：JP19565690申请日：19900724公开号：JPH0483537A公开日：19920317专利内容由知识产权出版社提供摘要：PURPOSE:To obtain a photocatalyst having a large specific surface area and enhanced in close adhesiveness and dispersibility by dissolving an organometallic compound containing the metal in a metal oxide of a carrier and a drying suppressing agent in a solvent and impregnating the carrier with the resulting solution to bake the same. CONSTITUTION:An organometallic compound such as alkoxide containing a metal such as titanium in a metal oxide of a carrier such as titanium oxide and a drying suppressing agent such as amide or glycol are dissolved in a solvent such as hexane. The carrier being a substrate on which a photocatalyst is formed is dipped in the resulting solution and subsequently baked in an oxidative atmosphere. The photocatalyst thus obtained has a large surface area and is enhanced in the close adhesiveness with the carrier and dispersability.申请人：TOYOTA CENTRAL RES & DEV LAB INC更多信息请下载全文后查看。