【作者】 丁绍晖；

【导师】 宁平； 鄢亚玲；

【作者基本信息】 昆明理工大学 ， 环境工程， 2008， 硕士

【摘要】 由于室内甲醛污染日益严重,甲醛的治理研究引起诸多学者的关注。用作污染物深度净化的光催化氧化法是近年来的研究热点。在众多光催化剂中,TiO₂以其无毒价廉,催化活性高,氧化能力强,稳定性好而最为常用。而由于自身的局限性使TiO₂光催化降解效率不高,所以本文将采用稀土复合TiO₂制备复合光催化剂,以提高TiO₂的光催化活性。本文采用固相合成法制备了CeO₂与TiO₂的摩尔比从1∶0.8到1∶2.5的系列复合氧化物,利用热差分析仪、X射线衍射仪、紫外-可见光分光光度计、X射线光电子能谱仪、原子荧光光谱仪、FT-IR傅里叶变换红外光谱仪等分析技术对所制备的复合粉体的晶相结构、光谱吸收性能、表面电子结构、表面化学组成及化学状态等进行了分析和表征。采用固相合成法制备出了Ag/CeO₂/TiO₂复合粉体,通过光催化降解甲醛实验对所制备的复合粉体进行了性能表征。实验论证了:1)所制备的复合粉体经800℃热处理后,TiO₂仍呈锐钛矿型,CeO₂的掺杂能有效抑制TiO₂的相变,提高了TiO₂的相变温度;2)在复合粉体中,CeO₂以Ce⁴⁺/Ce³⁺体系共存,TiO₂中也有少量的Ti³⁺,由于Ti与Ce的变价体系产生表面氧空位,使表面吸附氧增加,且CeO₂掺杂后复合粉体表面的羟基浓度增加;3)FT-IR红外光谱表面掺杂后样品表面比纯TiO₂易于吸附水,并含有大量的羟基;4)掺杂CeO₂后TiO₂的吸收带边红移至450 nm左右,增强了催化剂对可见光的吸收,且在TiO₂与CeO₂摩尔比为1∶105时光谱吸收阈值最大;5)适量的Ce掺杂能降低TiO₂的PL光谱强度,在TiO₂与CeO₂摩尔比为1∶1.5时荧光强度最弱,继续增大TiO₂与CeO₂摩尔比时荧光强度反而增大。光催化降解甲醛实验研究表明:1)在普通日光灯下,CeO₂/TiO₂复合粉体对甲醛的降解率为82.4%,是德国Degussa P25的2.3倍,明显优于P25 TiO₂光催化剂;2)普通日光灯下,Ag/CeO₂/TiO₂复合粉体对甲醛的降解率为95.91%,光催化降解6天后,甲醛的浓度为0.02 mg/l,低于国家标准值,其光催化降解效率明显优于CeO₂/TiO₂和德国Degussa P25光催化剂。通过光催化降解甲醛的实验得出最佳的实验参数为:TiO₂与CeO₂的摩尔比为1∶1.5、热处理温度为500℃、保温2.5 h、湿度为53±3%RH左右、甲醛的最佳加入量为0.5 ml（1%）、光催化剂用量为5g。在甲醛光催化降解过程中,温度对光催化降解影响不明显,温度一般在15—40℃本文通过CeO₂及Ag、CeO₂对TiO₂的掺杂改性研究表明,掺杂有利于增强TiO₂对可见光的吸收,提高了TiO₂对太阳光的利用率,掺杂后在可见光下TiO₂对甲醛的光催化降解率明显提高。更多还原

【Abstract】 As the pollution of formaldehyde（HCHO）is worsening in indoor.A number of studies related to the removal of HCHO have been carried out for several decades.In these methods,photocatalytic oxidation has been widely attracted.TiO₂ is close to being an ideal photocatalyst in several respects:nontoxic,low cost,high stability, strong oxidizing.But the photocatalytic degradation is inefficiency because of their own limitation.So this work have used rare earth to compound with TiO₂ in order to improve photocatalytic activity of TiO₂.In this paper,the CeO₂/TiO₂ compound powders with Ti/Ce molar ratios from 1./0.8 to 1/2.5 were prepared by solid state process.The properties of compound powders including crystal structure,the properties of spectral absorption,the electronic structure and chemical state of surface were analyzeded and characterized by means of DSC-TGA,XRD,UV-Vis,XPS,PL,FT-IR etc.the Ag/CeO₂/ TiO₂ compound powders with were prepared by solid state process.The properties of compound powders were analyzeded and characterized by the experiments of photocatalytic degradation in formaldehyde.The results of experiment have proved that:1)The crystal phase of the powders sintered at 800℃were still anatase.This implied that the phase transition of TiO₂ could be inhibited by doping CeO₂,and the phase transition temperature of TiO₂ was improved;2)In the compound powders,as the valence states of Ti or Ce have been changed,the surface oxygen vacancies and adsorption oxygen were increased,and the concentration of hydroxyl of the compound powders were increased;3)The results of FT-IR demonstrated that the surface of CeO₂/TiO₂ compound powders easilier absorbs water than that of pure TiO₂,and contains a large number of hydroxyl;4)The wavelength absorption threshold of TiO₂ doped with CeO₂ was red-shift to 450nm,and enhanced the absorption of visible light;5)Appropriate content of Ce could decline the intensity of PL spectra,as TiO₂ with CeO₂ molar ratio of 1:1.5,the PL spectra intensity is the weakest.But increased the molar ratio of TiO₂ and CeO₂,the PL spectra intensity was increased.The results of photocatalytic degradation of formaldehyde shown:1)The degrading rate of formaldehyde by the CeO2/TiO2 powders was 82.4%.It was 2.3 times than that of P25,which is obviously higher than P25 under the common daylight lamp;2)The degrading rate of formaldehyde by the Ag/CeO2/TiO2 powders was 95.91%.after degradation of six days,the concentration of formaldehyde is 0.02 mg/l,which is below the national standard value,the efficiency is obviously higher than CeO2/TiO2 and P25 under the common daylight lamp.The best parameters obtained by the experiment of photocatalytic degradation of formaldehyde:the molar ration of TiO₂ and CeO₂ was 1:1.5;the sintering temperature was 500℃;the sintering time was 2.5 h,the humidity was about 53±3 %RH,the optimal quantity of formaldehyde was 0.5 ml（1%）,the amount of photocatalyst was 5 g.At the same time,we found that the effect of reaction temperature wasn’t obviously in the process of the photocatalytic degradation.In this work,we generally adopted the temperature about 15-40℃.By investigate the doping effect of CeO₂ and Ag/CeO₂ in TiO₂,the results of this work indicated that the absorption of visible light could be enhanced,and the utilization of sunlight could be improved in TiO₂ doped with CeO₂ and Ag/CeO₂,the degrading rate of formaldehyde could be improved under the visible light更多还原