【作者】 吴道新；

【导师】 陈启元；

【作者基本信息】 中南大学 ， 冶金物理化学， 2008， 博士

【摘要】 氢能作为一种绿色新能源,得到越来越多的关注。利用太阳能光催化分解水制取氢气,可望使廉价制备氢气技术成为现实,具有广泛的应用前景。本论文较为详细地综述了光解水领域包括光催化材料的种类、光催化反应体系、可见光分解水等方面的研究进展。针对析氧半反应催化剂的析氧速率偏低,难于与析氢半反应析氢速率匹配的现状,本研究采用施主金属掺杂、稀土金属掺杂以及改善制备方法等多种手段对缺位金红石型TiO₂进行了改性,以Fe³⁺为电子受体,在紫外光（或可见光）辐照下,研究了改性缺位金红石型TiO₂的光解水析氧性能。主要研究结果如下:1.分别用溶胶-凝胶法和低温水解法制得TiO₂,并比较了制备方法对TiO₂光解水析氧活性的影响。结果表明:在紫外光辐照下,Fe³⁺的初始浓度为8.0mmol.L^-1、溶液的pH值为2.0时,锐钛矿型TiO₂析氧活性比金红石型TiO₂的析氧活性差,水解法所制得的金红石型TiO₂的析氧速率达93.2gmol.L^-1.h^-1,比溶胶凝胶法制备的金红石型TiO₂光解水析氧活性高10.6%.在Ar气氛中、煅烧温度为700℃时,超声强化低温水解法制得的缺位金红石型TiO₂在紫外光源下的析氧速率达113.81μmol.L ^-1h^-1在可见光源下的析氧速率达62.1μmol.L（-1）h^-1,分别比未经超声强化处理的缺位金红石型TiO₂的析氧速率提高了6.75%和20.3%.超声波强化能够改善缺位金红石型TiO₂的光解水析氧活性。2.将低温水解法制备的TiO₂前驱物分别在空气、Ar和H₂气氛中,煅烧温度为700℃时制得金红石型TiO₂。结果表明,在Ar和H₂中制备的金红石型TiO₂分解水的析氧速率较高,在紫外光辐照下的析氧速率分别达106.6和103.2μmol.L ^-1.h^-1,与在空气中制备的金红石型TiO₂析氧速率(93.2μmol.L ^-1h^-1)相比分别提高了14.3%和10.8%;在可见光辐照下,催化剂的析氧速率分别达5 1.6和33.8μmol.L ^-1h^-1,与在空气中制备的金红石型TiO₂析氧速率(18.8μmol.L ^-1h^-1)相比分别提高174.5%和79.7%.3.系统研究了（2.0%、）稀土金属La、Nd、Sm、Eu、Gd、Er、Yb掺杂改性对缺位金红石型TiO₂光解水析氧活性的影响。在Fe³⁺的浓度为8.0mmol.L^-1,在紫外光源辐照下,Yb、Eu、Er掺杂能够提高金红石型TiO₂分解水析氧速率,而La、Sm、Nd掺杂对金红石型TiO₂光解水析氧速率影响不显著,Gd掺杂金红石型TiO₂分解水析氧速率降低;在可见光辐照下,掺杂稀土金属后,只有Yb、Eu掺杂能够提高金红石型TiO₂分解水析氧速率,分别提高了31.2%和10.8%,其他稀土金属掺杂后催化剂的析氧速率略有降低。稀土金属的掺杂,导致氧缺位的形成,从而影响金红石型TiO₂的光解水析氧活性。4.将不同的施主金属离子（V、Nb、Ta、W）以不同的掺杂浓度对缺位金红石型TiO₂进行改性。结果表明,V、Nb、Ta、W的掺入能够改善和提高金红石型TiO₂的光解水析氧活性,尤其以V、W的改性效果显著。施主金属V、Nb、Ta、W都存在一个最佳的掺杂浓度,V、Nb、Ta、W最佳的掺杂浓度分别为1.0～2.0%、1.0%、1.0%、2.0%,V、Nb、Ta、W掺杂缺位金红石型TiO₂在紫外光条件下分解水的析氧速率分别为160.0umol.L^-1.h^-1、138.1umol.L^-1.h^-1、130.4umol.L^-1.h^-1、148.8umol.L^-1.h^-1,在可见光条件下分解水的析氧速率分别为105.2umol.L⁽-10.h^-1、80.4umol.L^-1.h^-1、69.6umol.L^-1.h^-1、102.9umol.L^-1.h^-1;在紫外光和可见光辐照条件下,V、Nb、Ta、W掺杂后催化剂的光解水析氧活性与催化剂的光致发光强度的变化趋势基本一致;在可见光条件下,施主金属V、Nb、W对缺位金红石型TiO₂掺杂改性后,改性催化剂的光解水析氧速率均超过文献或者专利报道的结果。5.采用第一性原理的计算方法,计算了施主金属V、Nb、Ta、W掺杂对金红石型TiO₂催化材料的能带结构和态密度的影响。计算结果表明:（1）金红石型TiO₂的带隙为1.9eV。（2）V、Nb、Ta、W的掺杂使得金红石型TiO₂的费米能级进入导带,带隙减小,分别为1.4eV、1.5 eV、1.7eV、1.5 eV,表面势垒变高,空间电荷区变窄,有利于低频光子的激发,光生电子与空穴得到了有效的分离。V、W的掺杂后TiO₂在原来的价带和导带之间出现新的定域能级,使得掺杂金红石型TiO₂更容易激发产生光生电荷。因此,V和W掺杂后的光催化析氧效果高于Nb、Ta掺杂效果。（3）计算的结果验证了V、Nb、Ta、W的掺入能够改善和提高金红石型TiO₂的光解水析氧活性。更多还原

【Abstract】 As a new energy resource,More and more about the hydrogen energy has been attracted.The hydrogen production from water splitting by sunlight has been known as an economic and clean technology and a process with prominent prospect for application.The progress in studies about water photocatalytic splitting was reviewed involving photocatalysts species,photoreaction system and effective visible light harvest for water photolysis.Because of the low rate of oxygen evolution and difficult to match the rate of hydrogen evolution in photocatalytic splitting water system,modified rutile TiO₂ with oxygen vacancies was synthesised using donor metal doped,rare-earth doped and improving preparation method.With Fe³⁺ as electron acceptor under UV irradiation and visible radiation,the photocatalytic activities for oxygen evolution using modified rutile TiO₂ with oxygen vacancies were studied.Work has been done as follows:1.TiO₂ was prepared by sol-gel method and low-temperature ultrasonical hydrolysis method.The influence of preparation method on the activity of TiO₂ splitting water for oxygen evolution was studied.The results show that the photoactivity of anatase TiO₂ was poorer than that of rutile TiO₂.Under the ultraviolet irradiation,when the initial concentration of Fe³⁺ was 8.0 mmol·L^-1 and the pH value of the solution was 2.0,the maximun speed of O₂ evolution for rutile TiO₂ prepared by hydrolysis method was 93.2μmol·L^-1·h^-1.The oxygen evolution ratio of rutile TiO₂ prepared by hydrolysis method is 10.6%higher than that of rutile TiO₂ prepared by a sol-gel method.The oxygen production rate under ultraviolet irradiation and visible light irradiation was 113.8μmol·L^-1·h^-1 and 62.1μmol·L^-1·h^-1 when rutile TiO₂ with oxygen vacancies prepared by ultrasonical hydrolysis method and calcined at 700℃under Ar atmosphere,respectively.Ultrasonical treatment can improve the photocatalytic activity of TiO₂.2.The water photocatalytic splitting activity of rutile TiO₂ prepared by hydrolysis method under air,Ar and H₂ atmosphere The results show that rutile TiO₂ has higher photocatalytic activity for water splitting prepared under Ar and H₂ atmosphere than that prepared under air atmosphere.The oxygen production rates under ultraviolet irradiation were 106.6 and 103.2μmol·L^-1·h^-1 when TiO₂ was prepared under Ar and H2 atmosphere as photocatalyst,respectively.And the oxygen production ratios compared to the rate of futile TiO₂ prepared under air atmosphere(93.2μmol·L^-1·h^-1).The oxygen production rates under visible light irradiation were 51.6 and 33.8μmol·L^-1·h^-1 when TiO₂ was prepared under Ar and H₂ atmosphere as photocatalyst,respectively,compared to the rate of futile TiO₂ prepared under air atmosphere(18.8μmol·L^-1·h^-1).3.The effects of rare earth metal（2.0%）La,Nd,Sm,Eu,Gd,Er, Yb doping rutile TiO₂ on the photocatalytic activity of splitting water with oxygen evolution were investigated systematically.The results shows that under UV-light irradiation,Yb,Eu or Er doping rutile TiO₂ can improve the photocatalytic activity of rutile TiO₂,and La,Sm,Nd doping can not infuence the photocatalytic activity of rutile TiO₂ obviously,and Gd rutile TiO₂ doping can reduce the photocatalytic activity of rutile TiO₂.Under the visible-light irradiation only Yb and Eu rutile TiO₂ doping can improve the photocatalytic activity of rutile TiO₂. The rare earth metal doping rutile TiO₂ can cause oxygen vacancies,which can influence the photocatalytic activity of rutile TiO₂.4.The donor metals（V,Nb,Ta and W） were firstly used to modify rutile TiO₂ with oxygen vacancies.The results show that TiO₂ doped with V,Nb,Ta and W exhibites higher photocatalytic activity of splitting water for oxygen evolution.TiO₂ doped with V and W exhibites the highest photocatalytic activity of oxygen evolution.When the photocatalytic activity of rutile TiO₂ splitting water for oxygen evolution can be enhanced,there was an optimum doping concentration.The optimum doping concentration of V,Nb,Ta and W were 1.0～2.0%,1.0%,1.0%, 2.0%,respectively.The oxygen production rate of rutile TiO₂ with oxygen vacancies doped with V,Nb,Ta and W under ultraviolet irradiation were 160.0μmol·L^-1·h^-1,138.1μmol·L^-1·h^-1,130.4μmol·L^-1·h^-1 and 148.8μmol·L^-1·h^-1;and the oxygen production rate of rutile TiO₂ with oxygen vacancies were 105.2μmol·L^-1·h^-1,80.4μmol·L^-1·h^-1, 69.6μmol·L^-1·h^-1 and 102.9μmol·L^-1·h^-1,respectively.The trend of photocatalytic activity of V,Nb,Ta and W-doped TiO₂ splitting water for oxygen evolution was consistent with its photoluminescence strength. The oxygen production rates of rutile TiO₂ doped with donor elements V, Nb,and W under visible light irradiation were higher than that reported in the literatures.5.Rutile TiO₂ doped with the donor metals（V,Nb,Ta and W） have been analyzed by the first principles calculations with the density functional theory.The results show that:（1）The band gap of futile TiO₂ was 1.9eV.（2）The fermi energy level of rutile TiO₂ moved to the conduction bands when doping content of V,Nb,Ta and W was elevated.The band gap decreased,the surface barrier raised,space charge district narrowed.The E_g of rutile TiO₂ was reduced and photoproduced electrons and holes were easily excited with lower energy compare with the undoped rutile TiO₂,which was advantage to the excitation of low-frequency photons and the separation of photoproduced electrons and holes.New levels between the conduction and valence bands occured when TiO₂ was doped with V and W.Thus,the doped TiO₂ can easily excited photoproduced charges.The photocatalytic effects of oxygen evolution as TiO₂ doped with V and W were better than that doped with Nb and Ta.（3）The calculation results indicate that the photocatalytic activity of splitting water for oxygen evolution can improved after TiO₂ was doped with V,Nb,Ta and W,respectiely.更多还原