Photocatalytic Property of Mixture of SnS2 and TiO2 Powders

Applied Catalysis B:Environmental26(2000)207–215Effects of calcination on the photocatalytic properties of nanosized TiO2powders prepared by TiCl4hydrolysisQinghong Zhang,Lian Gao∗,Jingkun GuoThe State Key Laboratory of High Performance Ceramics and Superfine Microstructure,Shanghai Institute of Ceramics,Chinese Academy of Sciences,Dingxi Road1295,Shanghai200050,PR ChinaReceived17November1999;received in revised form31January2000;accepted31January2000AbstractThe ultrafine nanosized TiO2photocatalysts in the anatase,rutile,and both phases were prepared by the hydrolysis of TiCl4solution.The resulting materials have been characterized by HREM,XRD,BET and UV–VIS absorption spectroscopy. The photoactivity,effective degradation,and the selectivity for complete mineralization of these catalysts were tested in the photocatalytic degradation of phenol.For this reaction,the quantum-sized catalyst particles(4nm)in the anatase phase shows the highest selectivity,the concentrations of p-benzoquinone and hydroquinol as the photocatalytic products were at very low level.However,the selectivity of the quantum-sized crystallites in the rutile phase was not improved in comparison with that of catalysts which bandgap corresponding bulk rutile.HREM micrographs show the quantum-sized catalysts were crystallized partially or many defects occurred on their crystal planes,they are responsible for their relative low photoactivity.Calcination is an effective treatment to increase the photoactivity of nanosized TiO2photocatalysts resulting from the improvement of crystallinity.Mixtures of both phases exhibit higher photoactivity as well as effective degradation in comparison with pure anatase or rutile catalysts.To the best of our knowledge,we arefirst to report that the quantum-sized TiO2crystallite exhibit high selectivity for complete mineralization in the photocatalytic degradation of phenol solution.©2000Elsevier Science B.V.All rights reserved.Keywords:Photocatalyst;Titania;Nanocrystalline;Anatase;Rutile;Water purification;Phenol degradation1.IntroductionTitanium dioxide,in both the anatase and the ru-tile crystallographic forms,has long been known to possess photocatalytic activity.Illumination of semi-conductors with illumination of energies greater than the band-gap energy promotes electrons from the va-lence band to the conduction band,leaving behind positive holes.When TiO2is illuminated with light ∗Corresponding author.Tel.:+86-21-62512990;fax:+86-21-62513903.E-mail address:liangaoc@(L.Gao)ofλ<390nm,it generates electron/hole pairs for this purpose so one employs titania as photocatalysts.The valence band potential is positive enough to generate hydroxyl radicals at the surface and the conduction band potential is negative enough to reduce molecular O2.The hydroxyl radical is a powerful oxidising agent and attacks organic pollutants present at or near the surface of the TiO2resulting usually in their complete oxidation to CO2.The mechanisms of photocatalysis are discussed in recent reviews by Hoffmann et al.[1], and Fox and Dulay[2].One of the major limitations in photocatalysis is the relatively low value of the overall quantum effi-0926-3373/00/$–see front matter©2000Elsevier Science B.V.All rights reserved. PII:S0926-3373(00)00122-3208Q.Zhang et al./Applied Catalysis B:Environmental26(2000)207–215ciencies,combined with the necessity of using near ultra-violet radiation.Some success in enhancing the efficiencies of photocatalysts has been achieved through the ultrafine TiO2crystallites instead of bulk TiO2materials,while crystallite size is less than 10nm,the quantum size effect is observed in the gaseous phtocatalytic hydrogenation of CH3CCH with H2O[3].However,there are little studies on pho-tocatalytic activity of ultrafine(less than10nm)TiO2 crystallites in aqueous suspensions systems.Phenol and its derivatives are widely distributed contami-nants of natural waters,and wastewater often contain these compounds in high concentrations.Of these compounds,phenol is hard to be degraded[4],so we employed the photodegradation of phenol as model reaction to investigate the photocatalytic activity and selectivity of nanosized TiO2crystallites.The overall catalytic performance has been sug-gested to be dependent on quite a number of parame-ters including particle size,surface area,the ratio be-tween the anatase and the rutile crystal phases,light intensity,and the materials to be degraded.For most photocatalytic reaction systems it is generally accepted that anatase demonstrated a higher activity than rutile. However,the role of other parameters on photocat-alytic activity is still unclear.Calcination is a common treatment that can be used to increase the photocatalytic activities,although it is far from clear how it affects the physicochemical parameters that control the photoactivity.The litera-ture on the use of powders produced by hydrolysis of TiCl4productions for photocatalysis is very limited. Recently,Fotou et al.studied the photodestruction of phenol using pure and Si-doped TiO2produced by flame synthesis,which exhibits a higher activity than commercial TiO2powders[5];Porter et al.also stud-ied the effect of calcination on the microstructural characteristics and photoactivity of a commercial pho-tocatalyst Degussa P-25[6].However,the effects of calcination on the microstructure characteristics and the photoactivity of the ultrafine(<10nm)titania powders were not studied.In the present study,we prepared the anatase and ru-tile crystallographic forms in which crystalline size is less than5nm.Calcination temperature significantly effects the photocatalytic activity:when photocatalysts are calcined at the temperatures in the range from673 to823K,both anatase and rutile exhibit higher photo-activity.To the best of our knowledge,we arefirstto report that the ultrafine(<5nm)TiO2crystallitesexhibit the high selectivity for the complete mineral-ization in the photocatalytic degradation of phenol.2.Experimental2.1.Preparation of the catalystsThe nanocrystalline titania catalysts reported in thisstudy(see Table1)have been prepared by TiCl4hy-drolysis.Titanium tetrachloride(98%TiCl4)was usedas a main starting material without any further purifi-cation,the appreciated amount TiCl4was dissolved indistilled water in an ice-water bath.The concentrationof titanium was adjusted to3M.This aqueous solutionwas then mixed with(NH4)2SO4solution or distilledwater(for preparation of anatase or mixture,respec-tively)in a temperature-controlled bath.The mixturewas stirred at high speed while the amount of TiCl4solution necessary for the desired[H2O]:[Ti]molarratio was added dropwise.Maintaining at the hydroly-sis temperature(70◦C)for1h,the mixed solution wastreated with2.5M dilute NH4OH until the pH valuewas7.For preparation of rutile crystallites,the TiCl4solution was diluted with0.5M HCl solution(0◦C)and was not treated with NH4OH solution.Then,themixed solution was placed into a constant temperature(70◦C)bath maintaining for5h.Subsequently,the pre-cipitated titanium oxide(TiO2·nH2O)was separated from the solution by using centrifugation and repeat-edly washed with distilled water to make TiO2·nH2O that was free of chloride ions.The hydrous oxides weredried at110◦C under vacuum and ground tofine pow-der.In some cases,the TiO2powders were calcined at400,600,or700◦C for2h.The process and syntheticconditions have been described in detail elsewhere[7].2.2.Catalyst characterizationPowder X-ray diffraction(XRD)was used for crys-tal phase identification and estimation of the anataseto rutile ratio and the crystallite size of each phasepresent.The XRD intensities of the anatase(101)peakat2θ=25.4◦and the rutile(110)peak at27.5◦wereanalyzed.The percentage of rutile in the samples canbe estimated from the respective integrated XRD peakintensities using the following equation[8]:Q.Zhang et al./Applied Catalysis B:Environmental26(2000)207–215209 Table1Summary of the properties and calcination conditions of TiO2Sample a Calcination BET area Rutile by Crystallite size Crystallite size Photoactivity temperature(K)(m2/g)XRD(%)of anatase(nm)of rutile(nm)by TOC(%) A110383289.90 4.038.0A400673183.60 6.850.5A60087371.4014.140.2A70097335.91334.358.238.7RA110383271.463 5.9 4.456.7RA40067377.55810.714.261.2RA60087334.57221.531.239.4RA70097320.58527.750.028.5R110383167.61007.247.1R40067332.710018.549.4R60087312.210040.840.1R700973 5.0100–15.6a A—anatase,R—rutile,the digits following A,RA,and R denote the calcining temperature(◦C).χ=1+0.8I AI R−1(1)whereχis the weight fraction of rutile in the powder, and I A and I R are the X-ray intensities of the anatase and the rutile peaks,respectively.The crystallite size can be determined from the broadening of corresponding X-ray spectral peaks by Scherrer formula.L=Kλ(βcosθ)(2)where L is the crystallite size,λis the wavelength of the X-ray radiation(Cu K␣=0.15418nm),K is usually taken as0.89,andβis the line width at half-maximum height,after subtraction of equipment broadening. XRD patterns were obtained at room temperature with a diffractometer using Cu K␣radiation.Trans-mission electron microscopy(TEM)observations were carried out using a JEOL−2010electron micro-scope.The Brunauer-Emmett-Teller(BET)surface area was determined using a Micromeritics ASAP 2010nitrogen adsorption apparatus.The absorption spectra of the solid catalysts were performed on Perkin–Elmer Lambda20spectrophotometer.2.3.Degradation experimentsThe phenol was used as supplied.Photocatalytic experiments were carried out by adding the required quantity of TiO2powder into450ml Pyrex photore-actor containing400ml of1.06mM(100mg/l)phe-nol solution.The cooling water in a quartz cylindri-cal jacket round the lamp was used to keep the re-action temperature constant(20◦C).The mixture was sonicated before illumination.The stirred suspensions were illuminated by means of300W medium pressure Hg lamp withoutfilter,its strongest emission light is with wavelength of365nm.The concentration of the catalyst was0.4g/l.The pH of the solution was not adjusted and when phenol dissolved in distilled wa-ter,the pH value was equal to6.56.Neither oxidant such as H2O2,S2O82−nor hole or electron scavenges was added into reaction suspensions.The reactor was opened to air,no oxygen or air was bubbled into re-action suspension,and oxygen available was the at-mospheric oxygen dissolved in water.Samples were taken out at regular time intervals and the analysis of concentration of phenol as well as photocatalytic prod-ucts was performed by means of Shimadzu UV-1601 spectrophotometer.The total organic carbon(TOC)content of the sam-ples,measured with Dohrmann DC-190(Rosemount Analytical)by the nondispersive infrared absorption method described elsewhere[9].3.Results and discussion3.1.CharacterizationCalcination is a common treatment that can be used to improve the crystalliny of TiO2powders.When210Q.Zhang et al./Applied Catalysis B:Environmental26(2000)207–215Fig.1.XRD patterns of TiO2photocatalysts dried at(A)110◦C and(B)calcined at400◦C.(A):a:R110;b:RA110,c:A110, d:Amorphous;(B):a:R400;b:RA400,c:A400,d:Amorphous transformed to anatase after calcined at400◦C.TiO2powders are calcined at higher temperatures,the transformations such as amorphous to anatase,anatase to rutile may occur.The amorphous-anatase transfor-mation was complete in the temperature range from 350to450◦C[10],the anatase-rutile transformation has been reported to occur in different temperature ranges from600to1100◦C[11],depending on the preparation conditions for anatase.Fig.1shows XRD patterns for synthesized powders dried at110◦C un-der vacuum as well as for powders calcined at400◦C.The XRD peaks of powder A110were weak in com-parison with those of the others calcined at higher temperatures,which suggested that amorphous parts remained in the powder.There are some literatures which reported a simple method to estimate the con-tents of amorphous parts in the TiO2powders[12,13]. The contents of the amorphous part in the powder A110and A400were estimated to be39.3and10.5%, respectively,by comparing the peak areas of XRD with those of powder A600.The amorphous titania was made according to the reference[7],and its XRD patterns are also presented in Fig.1d.We couldfind that the amorphous titania transformed to anatase after calcination at400◦C.The contents of the amor-phous parts in RA110and R110were estimated using RA600and R600as a reference,respectively.The content of amorphous parts is8%in the RA110,how-ever,no amorphous parts were detected in the powder R110.The crystallite size was estimated by Scherrer formula,this is a generally accepted method to es-timate the mean particle size.The XRD patterns of amorphous titania are plat curve,this is in agreement with literature[10],so the effect of amorphous parts on the broadening of nanosized TiO2XRD patterns is be negligible.The particle size estimated by XRD broadening is good agreement with the observation by HREM.The particle size is uniform as shown in Fig.2. The XRD results of all powders are summarized in Table1.3.2.Analysis of productsThe purpose of this research is to investigate the photoactivity and selectivity of nanosized TiO2for degradation of phenol in aqueous solutions.In all the experiments,medium pressure Hg lamp was used for irradiation of the aqueous solutions.The concentration of phenol,hydroquinol and p-benzoquinone in var-ious stages was determined using UV spectroscopy. As nanosized TiO2particles absorb the light which wavelength is less than its light band-gap and scatters both ultraviolet and visible light,although centrifuga-tion was applied to separate TiO2particles from the solution at rate6000rpm,some colloidal TiO2still re-mained in the supernatant.Adjusted the pH value of phenol solution being greater than10,the absorption peaks of phenol shift to longer wavelength and the in-tensity of absorption also increases.From Fig.3,weQ.Zhang et al./Applied Catalysis B:Environmental 26(2000)207–215211Fig.2.High resolution transmission electron micrograph (HREM)of (A)A110,(B)R110,(C)RA110and (D)RA400.take the solution acidified with 1drop of 0.5mol/l HCl to 10ml solution as reference solution and basified with 1drop of 10mol/l NaOH to 10ml solution for de-termination of the concentration of phenol at λ=234.5and 287.5nm.However,when the solution wastreatedFig. 3.Absorption spectra of (a)aqueous phenol solu-tion (pH =12.30)using the same concentration phenol solu-tion (pH =2.85)as reference,and (b)aqueous phenol solution (pH =2.85)versus water (pH =2.85).C phenol =1.6×10−4mol/l.with 10mol/l NaOH,one of the photocatalytic prod-ucts —p -benzoquinone shows a strong negative ab-sorbance in the range from 221to 258nm versus its acidified solution.We determined the concentration of phenol at wavelength λ=287.5nm quantitatively and its concentration was rectified to eliminate error result-ing from the absorbance difference between acidified and basified solution of the photocatalytic products.After centrifugation twice at the rate 6000rpm,the concentrations of p -benzoquinone and hydroquinol are determined quantitatively at λ=244nm and λ=295nm (the sample is acidified with a drop of 0.5mol/l HCl to 10ml solution)using distilled water as reference so-lution,respectively.Fig.4gave the absorption spectra of phenol,p -benzoquinone,and hydroquinol in acidi-fied solution (pH =2.85).3.3.Effect of crystallinity on the photodegradation of phenolTable 1shows the photodegradation of phenol with nanosized TiO 2catalysts prepared by the hydrolysis212Q.Zhang et al./Applied Catalysis B:Environmental26(2000)207–215Fig. 4.Absorption spectra of(a)aqueous phenol solution (pH=2.85)(b)aqueous p-benzoquinone solution(pH=2.85), and(c)aqueous hydroquinol solution(pH=2.85)using wa-ter(pH=2.85)as reference solution.C phenol=1.6×10−4mol/l, C p-benzoquinone=C hydroquinol=1.2×10−4mol/l.of TiCl4solution.Surface areas of these catalysts var-ied from35.9to289.9m2/g,5.0–167.6m2/g and20.5 to271.4m2/g for anatase,rutile,and mixtures of both the phases in the rangeχ=0.58∼0.85,respectively. The photoactivities(P)of these catalysts were calcu-lated from the results of TOC analysis.Samples cal-cined at673and873K showed that the highest activ-ity R110and RA110are also found to be highly active when compared to A110in the phenol degradation reaction.The photocatalytic activity of samples cal-cined at973K is lower than that of samples calcined at lower temperatures.This trend is significant espe-cially for rutile and mixture since the fast growth of its grains and remarkable decrease of its specific surface area.The mixtures of anatase and rutile are found to be more active than anatase crystallites or rutile crys-tallites at the same calcination temperatures.During the photocatalysis of p-coumaric acid,the most effi-cient catalyst is a mixture containing30%rutile and 70%anatase rather than pure anatase,which is pre-pared by the hydrolysis of tetraisopropyl orthotitanate [14].They concluded that the presence of mesopores of radii in the range6–25Åin this mixture was re-sponsible for the effective adsorption of the pollutant on the catalyst that resulted in relative high photoac-tivity.From their HREM micrograph of30%rutile and70%anatase,it indicated that rutile crystallized perfectly.However,the micrographs of other catalysts were not provided,we can notfind more information about the effect of morphology on the photocatalytic activity.As we know,the defects in the semiconduc-tors may be the recombination centre of photogener-ated holes and electrons,additionally,crystallinity is another important factor affecting the photocatalytic activity since the amorphous solid in the catalysts is isolate which resulting in its poor activity.To investi-gate the effect of crystallinity on the photoactivity of nanosized TiO2crystallites,we observed the morphol-ogy of some photocatalysts by means of HREM.Fig.2 gives HREM micrographs of A110,R110,RA110 and RA400.The surface area of A110was as high as289.9m2/g and its primary particle size asfine as 4.0nm,we expect it shows quantum-size effect and exhibits the highest photocatalytic activity than oth-ers.However,for the phenol degradation,its activity is lower than A400,and A600,although the surface areas of those catalysts are lower and their primary particle size is larger.A700is a mixture of both phases (χ=0.13),it shows better photoactivity than those in the pure anatase phase do.Literatures have reported the enhanced effect of rutile occurrence on the photo-catalytic activity in the p-coumaric acid[14]and the phenol[15]degradation,but the mechanism of this enhanced effect is still unclear.The lower activity of A110may due to its poor crystallinity,the content of amorphous parts in sample A110is39.3%,which is responsible for its relative low photocatalytic activity. The inserted ED patterns as well as HREM micro-graph show it crystallized partially.Nanosized TiO2 crystallized perfectly at the elevated temperature,for example,compared to RA110,RA400is in good crys-tallinity and has little defects on its crystal planes.The crystallinity of R110is better than those of A110 although more defects are found on its crystal planes.3.4.Selectivity of nanosized TiO2The products of the photodegradation of phenol are complex,many intermediates and compounds may occur during this reaction process[16–18].As shown in Table1,the overall degradation rate is quite differ-ent for these catalysts.Palmisano et al.reported that derivatives of phenol occurred in the phenol degra-dation by means of FT-IR technique,but the con-centration of these products were not determined quantitatively[16].Our interest is the concentration of p-benzoquinone and hydroquinol of the photocatalytic products.In the photocatalytic reaction of phenol,weQ.Zhang et al./Applied Catalysis B:Environmental 26(2000)207–215213expect that phenol can be degraded to small inorganic molecules such as carbon dioxide and water,which are safe for our environment.Thus,the selectivity of TiO 2catalysts for complete mineralization in the phenol degradation reaction is an important factor to be considered to design and evaluate catalysts.The selectivity (S)of these catalysts was calculated by the following equation:S =1+C q +C hC 0−C p×100%(3)where C 0is the initial molar concentration of phe-nol,C p ,C q and C h are the molar concentration of phenol,p -benzoquinone and hydroquinol in the reaction suspensions after illumination for 4h,respec-tively.D t is total degradation percentage of phenol,D t =(C 0−C p )/C 0×100%,Table 2shows D t and the selectivity of the photocatalytic reaction when dif-ferent TiO 2powders are used as the photocatalysts.A110shows the highest selectivity for complete min-eralization in the phenol degradation,the selectivities of catalysts in the anatase phase decrease in the order of A110>A400>A600>A700.According their UV–VIS absorption spectra of these catalysts,the op-tical bandgaps decrease in the same order.We attribute the higher selectivity of A110to its quantum-size effect,which is in good agreement with the results of UV–VIS absorption spectra.A700is a mixture of both the phases (χ=0.13),it shows lower selectivity thanTable 2Selectivity and effective degradation of nanosized TiO 2photocatalysts for the phenol degradationConversion to p -benzoquinone (%)Conversion to hydroquinol (%)D t (%)S (%)D e (%)A1100.31 1.3438.195.636.4A400 1.3 6.259.387.351.1A600 1.5 6.647.783.040.1A700 2.612.861.474.942.3RA110 1.17.965.986.356.9RA400 1.98.978.384.966.5RA600 2.913.257.271.841.1RA700 3.317.258.264.637.6R110 3.919.486.373.163.1R400 4.119.586.172.662.5R600 4.119.681.771.058.1R7005.427.363.448.430.7Without TiO 29.545.3aaWithout TiO 2,the TOC of phenol solution decreased 2%after illumination for 4h.D t —total degradation of phenol,S —selectivity for deep oxidation of phenol,D e —effective degradation of phenol.those in the anatase phase,but which are comparable to those in the rutile phase.Both RA110and RA400shows high selectivity as well as high photocatalytic activity in the degradation reaction,their UV–VIS absorption spectra are in similar shape as those in the anatase phase.Although the blue shift of the absorp-tion edge in R110is about 10nm,its selectivity is similar to R400and R600.R700and RA700exhibit the lowest selectivity for deep oxidation,this may be attributed to larger particle size and lower specific surface area.We conclude that the redox potentials are responsible for the difference of selectivity in these catalysts.The catalysts with band-gap more than 3.2eV exhibit high selectivity,quantum-size effect is observed for R110,its band-gap is 3.08eV but still less than 3.2eV ,its selectivity for complete mineral-ization is low.Additionally,both RA110and RA400show high selectivity,their UV–VIS spectra indicate that their bandgaps are higher than those of rutile cat-alysts.Here,we employ a term effective degradation (D e )to describe and evaluate our catalysts,D e was calculated as described in Eq.(4):D e =S ×D t ×100%(4)D e of RA400is the highest in these catalysts since its higher band-gap and better crystallinity which re-sulting in higher selectivity and photoactivity,respec-tively.The values of D t and calculated D e are listed in Table 2.214Q.Zhang et al./Applied Catalysis B:Environmental26(2000)207–215For samples with higher selectivity for deep oxi-dation of phenol,the calculated value of D e matched the photoactivity determined by TOC analysis(listed in Table1).However,the photoactivity determined by TOC analysis of samples those had lower selec-tivity(R700and RA700)are somewhat lower than the calculated value of D e,indicated some interme-diates other than p-benzoquinone and hydroquinol existed,and they can not be degraded completely resulting from their low photoactivity.These inter-mediates included maleic and fumaric acids[19,20], these organic diacids are not detected for photocat-alysts with high selectivity for deep oxidation be-cause of a rapid mineralization to CO2of both the compounds.3.5.Quantum-size effect of these catalystsUV–VIS spectroscopy has been utilized to char-acterize the bulk structure of crystalline and amor-phous titania.TiO2is a semiconductor oxide with easily measured optical band-gap.UV–VIS diffuse reflectance spectroscopy is used to probe the band structure,or molecular energy levels,in the materials since UV–VIS light excitation creates photogenerated electrons and holes.The UV–VIS absorption band edge is a strong function of titania cluster size for di-ameter less than10nm,which can be attributed to the well-known quantum-size effect for semiconductors [3].Normalized absorption spectra derived from UV–VIS diffuse reflectance data are presented for these catalysts in Fig.5.The position of the absorption edge for R400and R600corresponds to its known bandgap energy of3.0eV(410nm),the absorption edge of R110is blue-shifted by about10nm in com-parison with R400and R600,the quantum-size effect is notable for this catalyst.The onset of the UV–VIS absorption edge for the anatase samples overlaps the spectrum of A600,and also their UV–VIS spectra are not so steep as rutile samples,but the blue shift of absorption is also observed in comparison with A700. The absorption spectra of mixtures in both phases show the absorption edge of RA110was blue-shifted, moreover,both RA110and RA400absorb visible light with the wavelengthλ<450nm andλ<500nm, respectively.From the HREM micrographs,we found some particles were in close juxtaposition.Wemixed Fig.5.Absorption spectra of TiO2catalysts(a)in the anatase phase,(b)in the rutile,and(c)mixtures of anatase and rutile at various temperatures measured by the UV–VIS diffuse reflectance method.A110with R110mechanically at the ratioχ=0.60, the mixture did not absorb the visible light.There-fore,we assume that the close juxtaposition at crystal plane level of both phases may be responsible for the absorbance in the visible range.4.ConclusionsThe photoactivities,selectivity,and effective degra-dation of nanosized TiO2catalysts have been testedQ.Zhang et al./Applied Catalysis B:Environmental26(2000)207–215215using the photocatalytic degradation of aqueous phe-nol solution as a model reaction.The quantum-sized crystallites in the anatase phase shows the highest selectivity for complete mineralization but lower pho-toactivity than others do since it crystallized partially. The quantum-sized crystallites in the ruitle phase (7.2nm)exhibit higher photoactivity and lower se-lectivity for complete mineralization than Q-sized catalysts in the anatase phase do.Poor crystallinity and defects on crystal planes are responsible for rela-tively low photoactivity of these Q-sized crystallites. By means of calcination at elevated temperature,the improved crystallinity has a beneficial effect on the increasing of photocatalytic activity,in all cases,the photoactivity of catalysts calcined at400◦C is higher than those of catalysts dried at110◦C.After calcina-tion at600◦C,the photoactivities of these catalysts decrease significantly,since semiconductors in larger size result in the recombination of photogenerated holes and electrons at higher rate.Additionally,mix-tures of both the phases exhibit higher photoactivity as well as effective degradation in comparison with pure anatase or rutile catalysts,which absorption spectra are different from the mixture of anatase and rutile mixed mechanically:they absorb visible light with wavelengthλ<500nm. 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不同溶剂对钨酸铋形貌及可见光催化性能的影响张鸿羽;王爱军;袁耀【摘要】以水、乙醇、乙二醇与丙三醇的纯溶液和水与三种醇的混合溶液为溶剂,通过溶剂热法合成了Bi2WO6催化剂,并对其形貌及可见光催化性能进行研究,结果表明:相比纯溶剂,混合溶剂合成的Bi2WO6结构复杂、形貌规则,且粒径较大、分散性好;此外,随着溶剂分子中羟基数目的增加,Bi2WO6呈现出结晶度降低,晶体粒径和纳米片尺寸减小的规律;最后,乙二醇和水混合溶剂制备的花球状Bi2WO6光催化活性良好,且容易沉淀分离,易于回收,具有实际应用价值.%Bi2WO6 was synthesized by solvothermal method,using four pure solutions(H2O,C2H5OH, (CH2OH)2 and C3H8O3)and three alcohol-water solutions as solvents.Research on the morphology and visible-light photocatalytic properties of Bi2WO6 suggested that Bi2WO6 synthesized by alcohol-water solutions had more complex structure and regular morphology with larger size and better dispersion compared with Bi2WO6 synthesized by pure solvents.In addition, with the increase of hydroxyl groups, the crystallinity of Bi2WO6 went worse and the size of crystal and nanosheet decreased.Furthermore, the follow-spherical Bi2WO6 prepared by the mixture of ethylene glycol and water had better visible-light photocatalytic activity, it was of better value to apply to reality because it can be subsided and recycled easily.【期刊名称】《广州化工》【年(卷),期】2017(045)009【总页数】4页(P81-84)【关键词】溶剂热法;钨酸铋;形貌;可见光催化性能【作者】张鸿羽;王爱军;袁耀【作者单位】中国石油大学(北京)理学院,中国石油大学(北京)油气光学探测技术北京市重点实验室,北京 102249;中国石油大学(北京)理学院,中国石油大学(北京)油气光学探测技术北京市重点实验室,北京 102249;中国石油大学(北京)理学院,中国石油大学(北京)油气光学探测技术北京市重点实验室,北京 102249【正文语种】中文【中图分类】O643.3TiO2在光催化领域有着广泛应用，但TiO2基光催化材料的禁带宽度为3.2 V，只有420 nm 以下的紫外光可以利用[1]。

光电催化反应的英文## Photocatalytic reactions.Photocatalytic reactions are a type of chemical reaction that is initiated by the absorption of light. The absorbed light energy excites an electron in the photocatalyst, which then reacts with a substrate molecule to form a new product. Photocatalytic reactions are used in a variety of applications, including water purification,air pollution control, and solar energy conversion.The basic mechanism of a photocatalytic reaction is as follows:1. Light absorption: A photon of light is absorbed by the photocatalyst, exciting an electron from the valence band to the conduction band.2. Charge separation: The excited electron is separated from the hole that is created in the valence band.3. Redox reactions: The separated electron and holereact with substrate molecules to form new products.The efficiency of a photocatalytic reaction depends ona number of factors, including the following:The wavelength of light used.The intensity of light.The concentration of the photocatalyst.The concentration of the substrate.The temperature of the reaction.The pH of the reaction.Photocatalytic reactions can be used to accomplish a wide variety of chemical reactions, including the following:Water purification: Photocatalytic reactions can be used to remove organic contaminants from water.Air pollution control: Photocatalytic reactions can be used to remove nitrogen oxides and other pollutants fromthe air.Solar energy conversion: Photocatalytic reactions can be used to convert solar energy into electrical energy.Photocatalytic reactions are a promising technology for a variety of applications. They are efficient, environmentally friendly, and can be used to accomplish a wide variety of chemical reactions.### 中文回答：光电催化反应是一种由光吸收引发的化学反应。

纳米二氧化钛在沥青路面中的综合应用赵路;钱国平【摘要】In the asphalt pavement application, titanium dioxide nanoparticles as a catalyst be used to degrade automobile exhaust, and improve the mechanical properties and durability of asphalt pavement in a certain extent. This paper summarizes the application of nanometer titanium dioxide in asphalt and asphalt mixture in the above two aspects, and prospect the development of nano titanium dioxide in the direction of the two study.% 纳米二氧化钛可以很好地催化降解汽车尾气，并在一定程度上改善沥青路面的力学性能和耐久性。

本文从以上两方面归纳了纳米二氧化钛在沥青和沥青混合料中的中的应用，最后对纳米二氧化钛在这两个研究方向的发展进行了展望。

【期刊名称】《价值工程》【年(卷),期】2013(000)008【总页数】3页(P144-146)【关键词】纳米二氧化钛;沥青改性;催化降解;汽车尾气【作者】赵路;钱国平【作者单位】长沙理工大学，长沙 410004;长沙理工大学，长沙 410004【正文语种】中文【中图分类】U410 引言随着科技的高速发展，汽车保有量呈不断增长的趋势，大量汽车排放出的尾气导致生态环境不断恶化，如何改善人类赖以生存的环境已经成为亟待解决的难题。

光催化降解污染物由于其新颖性、能源消耗少、环境友好等特点逐渐成为处理工业污染的一项新课题。

化工进展Chemical Industry and Engineering Progress2024 年第 43 卷第 4 期粉体光催化全水分解技术研究进展吴晨赫1，刘彧旻1，杨昕旻1，崔记伟1，姜韶堃2，叶金花1，刘乐全1（1 天津大学材料科学与工程学院，天津300072；2 邯郸净化设备研究所，河北 邯郸 056000）摘要：光催化全水分解制氢可以直接将太阳能转变为绿色氢能，该技术具有过程简单、成本低等优势，受到广泛关注的同时展现出了良好的应用前景。

半导体光催化剂的性能是光催化全水分解技术发展的核心因素，目前该领域主要围绕光催化反应的三个基本步骤对其性能进行提升：光吸收、载流子分离与迁移以及表面反应。

本文从光催化基本原理出发，围绕以上三方面概述了应对相应挑战的有效策略与近年来的研究进展，在此基础上总结了设计、制备高效光催化全水分解材料的重要方法，分析了当前影响该水分解制氢技术工业化应用的难点，指出该领域的核心问题是开发高效的窄带隙光催化材料，同时未来需着重解决逆反应严重、催化剂稳定性不足以及大规模实施过程中的氢氧混合气体分离等技术问题。

关键词：太阳能；光催化；全水分解；制氢；催化剂；可再生能源中图分类号：TQ116.2 文献标志码：A 文章编号：1000-6613（2024）04-1810-13Particulate photocatalysts for light-driven overall water splittingWU Chenhe 1，LIU Yumin 1，YANG Xinmin 1，CUI Jiwei 1，JIANG Shaokun 2，YE Jinhua 1，LIU Lequan 1(1 School of Materials Science and Engineering, Tianjin University, Tianjin 300072, China; 2 Purification EquipmentResearch Institute of Handan, Handan 056000, Hebei, China)Abstract: Photocatalytic overall water splitting (POWS) is a simple and cost-effective approach to directly transforming solar energy into green hydrogen, which attracts great attention and demonstrates a bright prospect. The performance of photocatalyst is recognized as the key factor in the development of POWS. The strategies for improving the performance mainly focus on the three fundamental steps of photocatalysis, i.e., light absorption, carrier separation and migration and surface reaction. This paper reviews the recent achievements from the perspectives of valid strategies in coping with the challenges in these steps. Based on this, we summarize the important strategies of designing and preparing efficient photocatalysts for POWS and analyze the remaining obstacles to the industrial application of POWS. It is pointed out that the main challenge at present is to develop efficient narrow-gap photocatalysts. Meanwhile, the problems of serious backward reaction, the instability of the materials, and the technological problems like the separation of H 2-O 2 mixture during large-scale operations should also be addressed in the future.Keywords: solar energy; photocatalysis; overall water splitting; hydrogen production; catalyst; renewable energy综述与专论DOI ：10.16085/j.issn.1000-6613.2023-0603收稿日期：2023-04-14；修改稿日期：2023-05-28。

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.。

光电催化反应的英文English:Photocatalytic reactions involve the use of light to activate a substance, typically a semiconductor material, to accelerate a chemical reaction. In these reactions, photons (light particles) are absorbed by the photocatalyst, generating electron-hole pairs which drive redox reactions on the catalyst surface. This process allows for the conversion of sunlight into chemical energy, making photocatalysis a sustainable and environmentally friendly way to drive various chemical processes. Some common applications of photocatalytic reactions include water splitting for hydrogen production, carbon dioxide reduction for fuel synthesis, and pollutant degradation for environmental remediation. Researchers continue to explore and optimize the efficiency of photocatalytic systems by developing novel materials, enhancing light absorption, and improving charge separation mechanisms. Overall, photocatalytic reactions represent a promising technology for green chemistry and renewable energy applications.中文翻译:光催化反应涉及利用光激活物质，通常是半导体材料，加速化学反应。