【作者】 钟俊波；

【导师】 陈耀强；

【作者基本信息】 四川大学 ， 物理化学， 2007， 博士

【摘要】 近年来,由挥发性有机物所带来的空气污染问题日趋严重。在众多的治理技术中,TiO₂光催化降解有机污染物作为一种理想的环境治理技术而倍受关注。芳烃特别是苯,作为室内挥发性有机物的代表之一,结构稳定,不容易被氧化降解。以TiO₂为催化剂,利用光催化氧化降解处理室内空气中的苯是一个很有效的方法,但是二氧化钛的失活却是一个相当严峻的问题。因此,延长光催化剂的使用寿命同时提高它的催化活性,成为亟待解决的问题。本文在以发光材料、储氧材料为载体和用硅烷偶联剂对二氧化钛进行修饰的基础上,设计和制备了具有寿命长、催化活性高的光催化剂,以气相苯为模拟污染物,考察了光催化效果。主要研究内容及结果如下:1.用溶胶-凝胶法、水热沉淀法、钛酸四丁酯水解法制备了TiO₂。溶胶-凝胶法工艺简单,便于操作。溶胶-凝胶法制备的TiO₂粉体具有最小的粒径和最高的比表面,500℃焙烧2 h TiO₂粉体为锐钛型,600℃时向金红石型转化。表征结果表明溶胶-凝胶法制备的TiO₂粉体对可见光有较强的响应, Ti2p结合能（eV）最低。溶胶-凝胶法制备的TiO₂具有最高的光催化活性,对气相苯的降解率最高,但催化剂使用寿命较短,因此有必要延长光催化剂的使用寿命同时提高它的活性。2.在研究的实验条件下,苯在0.2g TiO₂上的气相光催化降解符合Langmuir-Hinshelwood动力学模型,光催化反应速率常数k和Langmuir吸附常数K分别为0.0064mgL^-1min^-1和4.6719 Lmg^-1。苯气相光催化氧化的中间产物包括:（1）乙酸乙酯（2）3-环氧乙基甲醇（3）2,6-二叔丁基-4,4-二甲基环己-2,5-二烯酮（4）2,6-二叔丁基环己-2,5-二烯^-1,4-二酮（5）2,6-二叔丁基-4-甲基苯酚（6）间二苯乙酸丁酯。2,6-二叔丁基-4,4-二甲基环己-2,5-二烯酮、2,6-二叔丁基环己-2,5-二烯^-1,4-二酮、2,6-二叔丁基-4-甲基苯酚和间二苯乙酸丁酯中至少有一种中间产物造成了催化剂失活。苯的光催化氧化在不同条件下遵循不同的反应历程。3.以发光材料Sr2CeO4作为载体,制备了二氧化钛负载量为0.5wt%、1.0wt%、1.5wt%、2.0wt%、4.0wt%的光催化剂,考察了不同负载量的TiO₂降解初始浓度为1.0mg/l苯的降解性能,结果表明1.0wt%为最佳负载量。TiO₂/Sr2CeO4（1.0wt%）和纯TiO₂光催化降解性能比较表明,负载型催化剂的活性提高了0.74倍,寿命延长了1.00倍。苯的最高转化率达到了65.0%。研究了光源,水蒸气以及铁离子掺杂对苯光催化降解的影响。结果表明用日光灯作光源时苯的转化率很低,只有15.3%,而用紫外灯作光源时转化率明显提高了近3倍;适量水蒸气的添加和铁离子的掺杂对苯的光催化降解均有促进影响。水的最佳添加量是50mg/L;铁离子的最佳掺杂摩尔比为1.0%。4. XRD表征显示负载的TiO₂的晶型主要是锐钛矿型;紫外-可见漫反射结果表明,负载型催化剂与纯TiO₂在紫外光区漫反射几乎没有变化,在可见光区负载型光催化剂漫反射减弱,明显提高了对可见光的吸收;XPS表征表明负载型催化剂的Ti（2p）结合能向低能端偏移了0.7eV,这表明TiO₂与Sr2CeO4之间发生了强烈的相互作用,TiO₂化学微环境的改变可能导致了负载型催化剂光催化活性的提高。该实验条件下,苯在TiO₂/Sr2CeO4的气相光催化降解符合Langmuir-Hinshelwood动力学模型,光催化反应速率常数k和Langmuir吸附常数K分别为0.0064mgL^-1min^-1和9.2078Lmg^-1。采用红外对失活催化剂的表面进行了研究,结果表明催化剂表面出现了羰基与羟基等的振动峰,运用色谱-质谱对萃取的表面物种进行了测试,苯气相光催化氧化的中间产物包括:（1）乙酸乙酯（2）3-环氧乙基甲醇（3）2,6-二叔丁基-4,4-二甲基环己-2,5-二烯酮（4）2,6-二叔丁基环己-2,5-二烯-1,4-二酮（5）2,6-二叔丁基-4-甲基苯酚。2,6-二叔丁基-4,4-二甲基环己-2,5-二烯酮、2,6-二叔丁基环己-2,5-二烯-1,4-二酮和2,6-二叔丁基-4-甲基苯酚中至少有一种中间产物造成了催化剂失活。苯的光催化氧化在不同条件下遵循不同的反应历程。Sr2CeO4的存在抑制了电子-空穴的复合,电子转移以及对可见的响应提高了TiO₂/Sr2CeO4的光催化活性。5.红外表征表明TiO₂已被硅烷偶联剂成功改性（记为M-TiO₂）,甲基丙烯酸甲酯已成功包覆了TiO₂（记为P-TiO₂）。XPS表征显示在M-TiO₂表面存在Ti、O、C和Si元素,但在P-TiO₂表面只检测到了Ti、O、C三种元素。对P-TiO₂而言只检测到了Ti2p3/2,但是两种催化剂的Ti2p3/2结合能都向低能端偏移了0.7eV。M-TiO₂的紫外-可见漫反射谱图和纯TiO₂的紫外-可见漫反射谱图相比没有明显差异,但P-TiO₂对紫外-可见光的响应表现出红移,且在可见光区有吸收。6. M-TiO₂和P-TiO₂都显示出比TiO₂高一倍以上的光催化活性,催化剂使用寿命延长了一倍。但M-TiO₂很不稳定,存在自身光催化降解问题。P-TiO₂显示出较强的稳定性,未发现自身光催化降解问题。硅烷偶联剂在光催化反应中的作用被推断为羰基吸引光生电子,抑制了电子-空穴对的复合,提高了光催化活性。7.对于CexZr1-xO2负载的样品,随着锆含量的增加,TiO₂/CexZr1-xO2比表面逐渐降低,带隙能先降低后升高,Ti2p3/2结合能位移是先增加后减小,其中TiO₂/Ce0.5Zr0.5O2具有最高的光催化活性。随着Mn含量的增加,TiO₂/Ce0.5-xZr0.5-xMn2xOy催化剂比表面降低,对紫外-可见光的响应增强且表现出红移,TiO₂/Ce0.475Zr0.475Mn0.05Oy的Ti2p3/2结合能向低能端偏移程度最大,TiO₂/Ce0.475Zr0.475Mn0.05Oy具有最高的光催化活性。随着La含量的增加,TiO₂/Ce0.5-xZr0.5-xLa2xOy催化剂比表面降低,晶粒粒径逐渐增大,对紫外-可见光的响应表现出红移,TiO₂/Ce0.425Zr0.425La0.15Oy的Ti2p3/2结合能向低能端偏移程度最大,TiO₂/Ce0.425Zr0.425La0.15Oy具有最高的光催化活性。随着Y含量的增加,TiO₂/Ce0.5-xZr0.5-xY2xOy催化剂比表面没有显著变化,对紫外-可见光的响应表现出红移,TiO₂/Ce0.5Zr0.5O₂、TiO₂/Ce0.475Zr0.475Y0.05Oy和TiO₂/Ce0.45Zr0.45Y0.10Oy的Ti2p3/2结合能偏移程度最大,偏移值达到0.6eV,TiO₂/Ce0.45Zr0.45Y0.10Oy具有最高的光催化活性。对TiO₂/CeO₂-ZrO₂催化剂中CeO₂-ZrO₂的作用进行了推断,可能是电子转移、TiO₂/CeO₂-ZrO₂在紫外区增强了吸收以及Ti2p和O （1s）结合能向低能端偏移等综合作用的结果。更多还原

【Abstract】 Air pollution by Volatile organic counds （VOCs） has drawn considerable attention in recent years. Among the technologies developed for the treatment of VOCs, the photocatalytic oxidation process is considered to be a promising technology. Aromatic hydrocarbons, especially benzene, are typical pollutants emitted from numerous urban and industrial sources and difficult to degrade due to their stability. VOCs removal from air by photocatalytic oxidation techniques has been paid much more attention to in recently. However, the deactivation of the titanium dioxide catalyst during gas-solid photocatalytic oxidation of air contaminated by VOCs is a serious issue.The decomposition of VOCs has been difficult because of the low conversion and the common deactivation of photocatalyst. Therefore it is crucial to prolong the lifetime of photocatalyst and enhance its photoactivity. In this thesis, a series of novel photocatalysts by modifying TiO₂ with silane coupling agent and loading of TiO₂ onto the fluorescent material Sr2CeO4 and CeO2-ZrO2 were synthesized, and their activity with benzene as the model gas in a batch reactor was investigated. The main contents and results in this thesis can be summarized as follow:1. Nanosized titanium dioxide powder was prepared by Sol– Gel methods, Hydrothermal methods and Hydrolysis methods from tetrabutyl titanate. Sol-Gel method itself is simple and can be easily manipulated .TiO₂ prepared by Sol-Gel method possesses the smallest particle size and the highest specific surface area. TiO₂ is anatase after annealing at 500℃for 2h and is rutile after annealing at 600℃for 2h.The results show that TiO₂ prepared by Sol-Gel method can be excited by visible light, binding energy of Ti2p is the lowest and the conversion of benzene is the highest on TiO₂ prepared by Sol-Gel method, but the lifetime of the catalyst is short. Therefore it is crucial to prolong the lifetime of photocatalyst and enhance its photocatalytic activity.2.Photocatalytic degradation of benzene on pure TiO₂ matches Langmuir-Hinshelwood （L-H） kinetic model,the value of k and K over 0.2g pure TiO₂ are 0.0064mgL-1min-1 and 4.6719 Lmg-1 respectively.The intermediates of photocatalytic oxidation of benzene over TiO₂ are : （1） butylated hydroxytoluene （2） （3-methyl-oxiran-2-yl）-methanol （3） ethyl acetate （4） dibutyl phthalate （5）2,6-bis（1,1-dimethylethyl）-4,4-dimethylycyclohe（6）2,5-cyclohexadiene-1,4,dione,2,6-bis（1,1-dim）. It is plausible that at least one of these less-reactive intermediates causes the deactivation of the photocatalyst. The gas-phase photocatalytic oxidation of benzene has different reaction mechanisms under different reaction conditions.3.The photoactivity of different TiO₂ loadings on Sr2CeO4 was investigated. The results show that the highest efficiency of 65.0% is obtained when the TiO₂ loading amount is 1.0%, the photocatalytic activity of TiO₂/Sr2CeO4 is 1.74 times of that of TiO₂ and the lifetime of TiO₂/Sr2CeO4 is 2.0 times of that of TiO₂.The effect of light source, water and Fe3+ doped into TiO₂ on conversion of benzene were investigated. The conversion of benzene under visible light is only 15.3%,the optimum water in the reactor is 50mg/L and the concertration of Fe3+ doped into TiO₂ is 1.0%（atom）4. The characterization results of XRD indicate that TiO₂ loaded on Sr2CeO4 is anatase at 773K firing temperature. TiO₂/Sr2CeO4 absorbs much more visible light than TiO₂ in the visible light region. The XPS spectrum show that the binding energy value of Ti2p3/2 transfers to a lower value,so it is obvious that there is stronger interaction between Sr2CeO4 and TiO₂, which may promote the catalytic activity of TiO₂. Photocatalytic degradation of benzene on 20g TiO₂/Sr2CeO4 matches Langmuir-Hinshelwood （L-H） kinetic model, the value of k and K are 0.0064mgl-1min-1 and 9.2078lmg-1 respectively. The chemical species adsorbed on the surface of deactivated photocatalyst were scanned by a FT-IR spectroscopy, the results show there are C=O bonding and OH bonding on the surface. Qualitative analysis of the chemical species adsorbed on the surface of deactivated TiO₂/Sr2CeO4 catalyst samples was carried on the 6890N GC-5973 MS. The detected compounds included: （1）2,6-bis（1,1-dimethylethyl）-4,4-dimethylycyclohe（2）ethyl acetate （3）2,5-cyclohexadiene-1,4,dione,2,6-bis（1,1-dim） （4） butylated hydroxytoluene （5）（3-methyl-oxiran-2-yl）-methanol. It is plausible that at least one of these less-reactive intermediates causes the deactivation of the photocatalyst. The gas-phase photocatalytic oxidation of benzene has different reaction mechanisms under different reaction conditions.The presence of Sr2CeO4 can prolong the life of electron-hole pairs and inhibit the recombination of electron-hole pairs. The synergy of electron transfer and the stronger absorption in the region 400–850 nm promotes the catalytic activity of TiO₂/Sr2CeO4.5.The FT-IR characterization result indicates that the pure TiO₂ has been modified by silane coupling agent （labeled as M-TiO₂） and pure TiO₂ has been successfully encapsulated by methylmethacrylate（labeled as P-TiO₂）. The XPS spectrum show that there are Ti,O,C and Si elements on the surface of the M-TiO₂, there are Ti,O,C elements on the surface of the P-TiO₂.Only Ti2p3/2 was detected on the surface of the P-TiO₂, but both Ti2p3/2 of two catalysts shift to a lower value. Uv-Vis diffuse reflective spectra between M-TiO₂ and TiO₂ have no obvious difference, compared to the UV-vis diffuse reflective spectra of pure TiO₂, spectra of P-TiO₂ appears red-shift and has strong absorption in visible light.6.The photocatalytic activity of M-TiO₂ and P- TiO₂ is more than1.0 times of that of TiO₂ and the lifetime of M-TiO₂ and P- TiO₂ is 2.0 times of that of TiO₂. M-TiO₂ is not stable and can be degraded, while P-TiO₂ is stable.The ester group on theγ-MPS molecule can prolong the life of electron-hole pairs and inhibit the recombination of electron-hole pairs, which promotes the catalytic activity of TiO₂.7.The BET surface areas of TiO₂/CexZr1-xO₂ decrease, the band gap and Ti2p3/2 decrease and then increase as the Zr amount increasing. TiO₂/Ce0.5Zr0.5O₂ has the highest photocatalytic activity. The BET surface areas of TiO₂/Ce0.5-xZr0.5-xMn2xOy decrease, the UV-vis diffuse reflective spectra of TiO₂/Ce0.5-xZr0.5-xMn2xOy appears red-shift and the degree of response to the light increases as the Mn amount increasing. The binding energy value of Ti2p3/2 of TiO₂/Ce0.475Zr0.475Mn0.05Oy transfers to the lowest value, TiO₂/Ce0.475Zr0.475Mn0.05Oy has the highest photocatalytic activity.The BET surface areas of TiO₂/Ce0.5-xZr0.5-xLa2xOy decrease, the particle sizes of TiO₂/Ce0.5-xZr0.5-xLa2xOy increase as the La amount increasing. The Uv-Vis diffuse reflective spectra of TiO₂/Ce0.5-xZr0.5-xLa2xOy appears red-shift, the binding energy value of Ti2p3/2 of TiO₂/Ce0.5-xZr0.5-xLa2xOy transfers to the lowest value, TiO₂/Ce0.5-xZr0.5-xLa2xOy has the highest photocatalytic activity.There is no obvious difference among the BET surface areas of TiO₂/Ce0.5-xZr0.5-xY2xOy as the Y amount increasing. The UV-vis diffuse reflective spectra of TiO₂/Ce0.5-xZr0.5-xY2xOy appear red-shift. The binding energy values of Ti2p3/2 of TiO₂/Ce0.5Zr0.5O₂、 TiO₂/Ce0.475Zr0.475Y0.05Oy and TiO₂/Ce0.45Zr0.45Y0.10Oy transfer to the lowest value, TiO₂/Ce0.45Zr0.45Y0.10Oy has the highest photocatalytic activity.The role of CeO₂-ZrO₂ in the photocatalytic reaction has been speculated. The synergy of electron transfer, the stronger absorption in violet regions and shift of binding energy of Ti2p and O （1s） promote the photocatalytic activity of TiO₂/CeO₂-ZrO₂.更多还原