【作者】 童海霞；

【导师】 陈启元；

【作者基本信息】 中南大学 ， 化学工程， 2008， 博士

【摘要】 针对“双床”光解水析氧过程中光生电子与空穴对分离效率低,导致光解水析氧速率偏低,难于与析氢速率匹配的现状,本研究采用半导体掺杂、半导体复合以及还原气氛处理等多种手段对金红石型TiO₂进行了改性,得到了一系列改性TiO₂析氧用光催化剂,研究了紫外光（或可见光）辐照下,改性TiO₂的光解水析氧性能。首次制备了WO₃复合铌掺杂TiO₂析氧用光催化剂,并考察了WO₃复合浓度对WO₃-TiO₂/Nb₂O₅光催化性能的影响;制备了WO₃、V₂O₅和Fe₂O₃复合的金红石型TiO₂光催化剂,首次考察了不同催化剂复合和同一催化剂不同复合浓度对金红石型TiO₂催化剂光解水析氧性能的影响,探讨了光催化剂的光致发光性能与其析氧活性之间的关系;首次制备了含氧缺位的金红石型TiO₂光催化剂,考察了氧缺位浓度对金红石型TiO₂光催化剂析氧性能的影响,采用量子化学计算方法,研究了含氧缺位金红石型TiO₂的能带结构;首次制备了含氧缺位的2%WO₃-TiO₂光催化剂,考察了氧缺位浓度对2%WO₃-TiO₂催化剂光解水析氧性能的影响。主要研究结果如下:1)WO₃的复合能提高TiO₂/Nb₂O₅的光催化活性,当WO₃复合浓度为2%时,WO₃-TiO₂/Nb₂O₅的光催化活性最高,达到152μmol·l^-1·h^-1,此时WO₃在TiO₂/Nb₂O₅表面刚好达到单层复合。另外,当WO₃复合浓度为2%,Fe³⁺浓度为16·10^-3mol·L^-1,二次处理温度为873K时,WO₃-TiO₂/Nb₂O₅光催化剂光解水析氧速率约为191.7μmol·l^-1·h^-1。光能转化材料器件化简化了光催化反应装置,能适当延长TiO₂光催化剂的使用寿命,简化实验装置,具有较为广阔的前景。2)LRS表明WO₃在TiO₂表面的单层复合浓度为2%,当达到单层复合时,析氧速率最大,在紫外光辐照下2%WO₃-TiO₂催化剂光解水的析氧速率约为420μmol·L^-1·h^-1。根据其透射光谱,采用外推法求出WO₃能隙约为2.78eV。LRS表明V2_O5在TiO₂表面的单层复合浓度约为8%,8%V₂O₅-TiO₂催化剂在紫外光辐照下分解水析氧速率约为110μmol·L^-1·h^-1,在可见光辐照下分解水的析氧速率约为80μmol·L^-1·h^-1。根据其透射光谱,采用外推法求出V₂O₅的能隙约为2.14eV,推导出金红石型TiO₂能隙约为3.08eV。无论是在紫外光还还是在可见光照射下,Fe₂O₃-TiO₂光催化剂都不能分解水析出氧气。光催化剂的FL测试结果显示:光催化剂的光致发光性能并非影响催化剂光催化活性的决定性因素。3)在Ti³⁺含量极少,只有极少量羟基（OH）存在的情况下,适量的氧缺位能显著提高金红石型TiO₂光解水的析氧活性,其最大析氧速率达222μmol·L^-1·h^-1。量子化学计算结果显示:氧缺位能降低半导体带隙能,在带隙中引入中间能级。4)含氧缺位的2.0%WO₃-TiO₂光催化剂的最大析氧速率约为803μmol·L^-1·h^-1。基本与“双床”光解水析氢速率相匹配。更多还原

【Abstract】 In this study, because of the low separation efficiency of photo-electrons and holes that leads to the low rate of oxygen evolution and difficult to match the rate of hydrogen evolution in the "Double-Bed" splitting water system, modified rutile TiO₂ was synthesised by being treated using semiconductor doping, semiconductor compounding and reducing atmosphere. The photocatalytic-activities for oxygen evolution were firstly compared in the "Double-Bed" splitting water system using rutile TiO₂ catalysts compounded different semiconductors or the same semiconductor with different compounding concentration. Rutile TiO₂ and 2% WO₃-TiO₂ were treated by reducing atmosphere and the photocatalytic activity of TiO₂ and 2% WO₃-TiO₂ with oxygen vacancies were firstly investigated in the "Double-Bed" splitting water system. Quantum chemistry calculations for different oxygen vacancies content of TiO₂ were carried out and the results can reasonablely explain experimental results.WO₃ compounding can improve the rate of O₂ evolution of the photodecomposition of water. It reaches to 151.8μmol·L^-1·h^-1 when the concentration of compounding WO₃ is 2% which is the concentration of monolayer for WO₃ on the surface of TiO₂/Nb₂O₅. Besides, the concentration of the electron acceptor Fe³⁺ and the second calcination temperature also can effect the rate of O² evolution. When the concentration of Fe³⁺ is 16·10^-3mol·L^-1 and the second calcination temperature is 600℃the maximum rate of O₂ evolution of 2%WO₃-TiO₂/Nb₂O₅ photocatalyst is 191.7μmol·L^-1·h^-1.From the result of LRS, the concentration of monolayered WO₃ on the surface of TiO₂ is 2 mol%. The rate of O₂ evolution for TiO₂ compounded with WO₃ as photocatalyst is larger than that of the TiO₂ within 12 hours. With the increase of the quantity of loaded WO₃, the rate of O₂ evolution also increases. It reaches to the maximum rate of 420μmol·L^-1·h^-1 with the UV-light irradiation when the concentration of loaded WO₃ is 2%. When the concentration of compounding WO₃ is above 2.67%, the rate of O₂ evolution decreased gradually. There is no response to visible light for WO₃-TiO₂. According to its transmitted spectrum, the band gap energy of WO₃ is about 2.78eV by extrapolation. The concentration of monolayer for V₂O₅ on the surface of TiO₂ is 8%. The maximum rate of O₂ evolution is 110μmol·L^-1·h^-1 when the concentration of compounding V₂O₅ is 8% with the UV-light irradiation and 80μmol·L^-1·h^-1 with the visible light irradiation. According to its transmitted spectrum, the band gap energy of V₂O₅ is about 2.14eV by extrapolation and 3.08eV for rutile TiO₂. As for Fe₂O₃- TiO₂, there is no gas evolution with the UV-light or visible light irradiation. The FL spectrum and the rate of O₂ evolution show that the photocatalytic activity of the catalyst is influenceed by several factors and the FL intensity is not the pacing one.Appropriate oxygen vacancies could obviously improve the photocatalytic activity of rutile TiO₂ with minute quantity Ti³⁺ and hydroxyl group （OH）. The maximum rate for O₂ evolution of rutile TiO₂ with oxygen vacancies was 222μmol·L^-1·h^-1. The theoretical calculation shows that oxygen vacancies can reduce the band-gap energy of rutile TiO₂ and introduce middle energy level in its forbidden band.The maximum rate for O₂ evolution of 2.0%WO₃-TiO₂ with oxygen vacancies is 803μmol·L^-1·h^-1 which matches the H₂ evolution speed in "Double-Bed" water splitting.更多还原