Theory of carbon doping of titanium dioxide
Theory of carbon doping of titanium dioxide
复制标题
DOI：
10.1021/cm051921h
复制
发表时间：
2005-12-27
影响因子：
8.6
通讯作者：
Selloni, A
中科院分区：
文献类型：
--
作者：
Di Valentin, C;Pacchioni, G;Selloni, A
近期的实验研究已确定，碳掺杂显著提高了二氧化钛在可见光区域的光催化活性。利用广义梯度近似下的密度泛函理论（DFT）计算，我们研究了锐钛矿和金红石两种二氧化钛多晶型中碳杂质的各种结构模型，并分析了电子能带结构的相关变化。我们根据形成能（其为氧化学势的函数，氧化学势决定了体系是处于氧化还是还原环境）比较了所有这些不同种类物质的稳定性。在低碳浓度下，我们发现，在贫氧条件下，取代（氧）碳和氧空位更有利；而在富氧条件下，间隙和取代（钛）的碳原子更受青睐。较高的碳浓度因多掺杂效应而出现意想不到的稳定情况，这可解释为物种间的氧化还原过程。碳杂质导致带隙有适度变化，但在禁带中引入了几个局域占据态，这可能是实验中观察到的吸收边向可见光红移的原因。我们的研究结果还表明，碳掺杂可能有利于块状二氧化钛中氧空位的形成。
Recent experimental studies have determined that carbon doping dramatically improves the photocatalytic activity of TiO2 in the visible-light region. Using density functional theory (DFT) calculations within the generalized gradient corrected approximation, we investigate various structural models of carbon impurities in both the anatase and rutile polymorphs of TiO2 and analyze the associated modifications of the electronic band structure. We compare the stability of all these diverse species on the basis of their energy of formation as a function of the oxygen chemical potential, which determines whether the system is in an oxidizing or reducing environment. At low carbon concentrations, we find that, under oxygen-poor conditions, substitutional (to oxygen) carbon and oxygen vacancies are favored, whereas, under oxygen-rich conditions, interstitial and substitutional (to Ti) C atoms are preferred. Higher carbon concentrations undergo an unexpected stabilization caused by multicloping effects, interpreted as inter-species redox processes. Carbon impurities result in modest variations of the band gap but induce several localized occupied states in the (lap, which may account for the experimentally observed red shift of the absorption edge toward the visible. Our results also indicate that carbon doping may favor the formation of oxygen vacancies in bulk TiO2.