【作者】 郭美丽；

【导师】 杜九林；

【作者基本信息】 天津大学 ， 材料物理与化学， 2013， 博士

【摘要】 锐钛矿型二氧化钛（TiO2）是一种非常理想的半导体光催化剂，由于具有催化活性高、稳定性好、对人体无毒、成本低等优点被广泛用于环境保护和能源再生等领域。然而它的禁带宽度较大(3.2eV)，只有波长小于387nm的紫外光才能使TiO2产生光催化作用。而占太阳光能约43%的可见光得不到充分利用。为了有效的利用太阳能，本文采用基于密度泛函理论的第一性原理研究了几种离子掺杂在改进TiO2可见光响应方面的作用。首先，研究了N-B共掺杂TiO2的几何结构、电子结构和光学特性。选取了三种不同的掺杂结构，即N s B i （N替位O，B填隙）、N s B s （N、B双替位O）和N i Bi（N、B双填隙）共掺结构。采用GGA方法对几何结构进行优化，然后采用GGA+U的方法对N-B共掺的TiO2的电子结构和光学特性进行了计算，我们发现三种共掺结构都能产生带隙态，但是只有N s Bi共掺结构能产生可见光吸收，而且可见光吸收与掺杂原子之间的距离有关系，当N和B原子之间的距离较近时，可见光吸收强度很弱，随着距离的增大，吸收强度明显增强。结合电子态密度与介电函数虚部的结果，我们可以得出此可见光学跃迁归因于N的2p态到Ti的3d态之间的跃迁。其次，采用同样的方法研究了C-N共掺TiO2的电子结构和光学特性。采用GGA和GGA+U方法分别计算了纯TiO2的能带结构，结果表明GGA+U能有效的改进TiO2的带隙。与纯的TiO2相比，C、N单掺杂和C-N共掺后的带隙均减小，而且共掺所导致的带隙减小程度要大于单掺杂的情况。从光学特性看，三种掺杂体系的带边均发生了红移，并且在450-800nm范围内出现了吸收，C-N共掺TiO2的吸收强度要优于C和N单掺杂的情况，也就是说C和N共掺杂的时候出现了协同效应。根据计算结果，我们可以得出C-N共掺TiO2的可见光学跃迁归因于N和C杂化的2p态到Ti的3d态之间的跃迁。最后，我们采用GGA的方法计算了Cu、Ag和Au掺杂TiO2的电子结构和光学特性。Cu，Ag和Au掺杂后会在TiO2禁带中不同位置处产生带隙态，三种元素掺杂后都能使带隙缩小，而且都能产生可见光吸收。Cu和Ag掺杂产生的可见光吸收很强，而Au掺杂导致的可见光吸收很弱。根据三种元素掺杂后的能带结构，我们给出了可见光学跃迁机理。Cu掺杂后产生的吸收与Cu3d-Ti3d跃迁是对应的。Ag掺杂产生的可见光吸收与Ag的4d态到导带的跃迁相对应。而Au掺杂后产生的可见光吸收，与价带顶端和Au的5d带隙态之间的跃迁对应。更多还原

【Abstract】 Anatase TiO2has several excellent properties, such as nontoxic, relativelyinexpensive, physical and chemical stability, and high photocatalytic activity.Therefore, TiO2is considered as a kind of ideal semiconductor photocatalyst, and iswidely applied in environmental protection and renewable energy. Unfortunately,anatase TiO2has a wide band gap (about3.2eV), which only responds to UV lightirradiation accounting for only a small fraction of solar light, while visible lightoccupying most fraction of solar light can’t be utilized. In order to use solar energyeffectively, we studied the visible light response of several kinds of ions doped TiO2based on the density functional theory.First, we studied the geometry, electronic structures, and optical properties of N-Bcodoped TiO2. Three codoped structures were chosen, including N s B i, N s Bs, andN i Bi(s means substitution and i means interstitial). Geometry optimization wasperformed by GGA method. Further, we calculated the electronic structures andoptical properties of N-B codoped TiO2using GGA+U method. It was shown that theband gap states were observed in the three codoped structures, however, the visibleoptical absorption only appeared in N s B i structure. In addition, the N s Bistructure wassensitive to the distance of dopants, and a decrease of the distance between N and Batoms induces a decrease of the absorption. The visible optical transition in N s Bistructure was attributed to the N2p-Ti3d transition.Second, we investigated the electronic structures and optical properties of C-doped,N-doped, and C-N codoped TiO2. Band structure of pure TiO2was calculated usingGGA and GGA+U methods, and the results showed that the band gap of pure TiO2could be corrected effectively. It was shown that the band gaps of C-doped, N-doped,and C-N codoped TiO2were reduced compared with pure TiO2. Optical propertiesresults showed that the band edges of the three doped systems shifted to the longwaveregion, and the optical absorptions were all observed in450-800nm. Moreover, theabsorption intensity of C-N codoped TiO2was larger than that of C-doped andN-doped TiO2, which mean that C and N have a synergy in the C-N codoped TiO2.According to the calculated results, we concluded that the visible optical transition inthe C-N codoped TiO2was attributed to the transition of N and C2p-Ti3d states. Finally, we investigated the electronic structures and optical properties of Cu, Ag,and Au-doped TiO2. Cu doping could produce some electronic states near the top ofvalence band of TiO2, and Ag and Au doping also produced band gap states. Theincorporation of the three dopants could reduce the band gap of TiO2, and also,produced visible optical absorption. The visible absorption intensities of Cu andAg-doped TiO2were larger than that of Au-doped TiO2. We gave the visible opticaltransition mechanisms of three doped systems. For the Cu-doped TiO2, the visibleoptical transition corresponded to the Cu3d-Ti3d states transition. The Ag dopingcaused the visible optical transition between middle Ag4d and Ti3d states, while theAu doping caused the visible optical transition between O2p and middle Au5d states.更多还原