N,Cd TiO2光催化活性的实验与理论研究

 采用热分解法制备了N, Cd共掺杂纳米TiO₂光催化剂，通过XRD、XPS和UV-DRS等对样品进行了分析表征，并以甲基橙为目标降解物考察了其光催化性能。实验表明产物N, Cd TiO₂为锐钛矿型，颗粒约为10~15 nm，N取代了TiO₂晶格中的O原子，而Cd以游离态分布在TiO₂表面；其光吸收发生明显红移；光催化活性提高，N、Cd在提高TiO₂的光催化活性方面具有协同作用。采用第一性原理方法，对其电子结构和光学性质进行了理论计算。结果发现在N,Cd TiO₂的带隙中出现了N2p和Cd5s的杂质能级，价带的电子可以吸收较小的能量跃迁到杂质能级上，接着二次激发跃迁到导带上，电子跃迁变得容易，吸收波长向可见光区移动。计算结果很好地解释了实验现象。

Photocatalytic Activity and Electronic Structural Analysis of N, Cd-codoped Anatase TiO2 :A Combined Experimental and Theoretical Study

N, Cd codoped TiO₂ was synthesized by thermolysis method. The products were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV visible diffuse reflectance spectra (DRS) analyses, respectively. The photocatalytic activities of samples were studied on the degradation of methyl orange (MO). The results showed that photacatalysts possessed an anatase crystalline framework with particle sizes of 10~15 nm. N atom was incorporated into the TiO₂ crystal lattice, while Cd atoms existed on the crystal surface. Doping resulted in the observation of optical absorption edges shifting to the red light. It indicated a strong N Cd synergistic interaction appeared to play a decisive role in driving the excellent photoactivity performance of N,Cd codoped TiO₂. First principles density functional theory (DFT) calculations were performed to explore the effect of dopants on electronic and optical properties of N, Cd TiO₂. There were impurities states between the valence band and the conduction band, which came from N2p and Cd5s, respectively. The electron on the valence band could transit to the impurity states, and then were migrated secondly to the conduction band in the light irradiation. So the electronic excitation in N, Cd TiO₂ became easier compared to pure TiO₂, and the absorption edge shifted to the visible light region. It could account for the experimentally observed optical absorption edge of N, Cd TiO₂ shifting toward the lower energies.