掺铁氧化锌可见光催化特性的实验研究及其能带结构的第一性原理计算

Due to its wide band gap (3.37 eV), undoped ZnO exhibits negligible visible-light driven photocatalytic activity since it can only absorb the ultraviolet photons in the sunlight. With the merits of abundance in mineral resources and non toxicity of its most natural oxides, transition metal Fe has similar ionic radius when compared to the ionic radius of Zn in ZnO. In this project, Fe-doped ZnO nanoparticles with the dopant concentration in the range of 0.00-0.05 are to be synthesized via the sol-gel route in order to incorporate the 3d levels of Fe into the bandgap of ZnO. The visible-light driven photocatalytic activity of Fe-doped ZnO nanoparticles can be enhanced of by extending the absorption of ZnO to the visible spectral region as well as by suppressing the electron-hole recombination in ZnO. Fe-doped ZnO nanoparticles with highest visible-light driven photocatalytic activity will be obtained by optimizing the dopant concentration of Fe ions in ZnO. The band structures, density of states, and imaginary dielectric function of Fe-doped ZnO are to be calculated by employing first-principles density functional theory in the frame work of meta general gradient approximation (meta GGA). In combination of the theoretical calculation and experimental data, the dopant concentration dependent electronic structures of Fe-doped ZnO will be investigated, the relationship between the visible light driven photocatalytic activity of Fe-doped ZnO and the defect levels of the dopant will be established. The mechanisms of visible-light driven photocatalytic activity will be discussed for Fe-doped ZnO. The results of this project will be helpful in developing highly efficient visible-light active photocatalysts to make our environment clean.

宽禁带ZnO只能吸收太阳光中的紫外光，未掺杂ZnO的可见光催化活性可以忽略不计。鉴于铁与锌的离子半径比较匹配以及铁的常见氧化物储量丰富、无毒的特点，本项目采用溶胶凝胶法制备掺铁ZnO纳米颗粒，掺铁浓度在0.00和0.05之间，目的在于将铁的3d杂质能级引入ZnO禁带中，不仅抑制光生空穴电子对的复合，而且将ZnO的吸收光谱拓展至可见光区以提高ZnO的可见光催化活性，获得最佳的掺铁浓度使掺铁ZnO的可见光催化活性最高。改变掺铁浓度，采用含动能密度的广义梯度近似，基于密度泛函的第一性原理计算掺铁ZnO的能带结构、态密度和介电常数虚部。通过理论计算与实验测试比对分析，系统研究掺铁浓度对ZnO能带结构的调节作用，建立掺铁ZnO可见光催化活性与铁杂质能级之间的内在关系，揭示铁掺杂提高ZnO可见光催化的过程和机理，从而为治理有机污染提供了一种新思路。

宽禁带ZnO的可见光催化活性可以忽略不计，如何赋予氧化锌可见光催化特性是光催化领域里的一个重要课题。本项目制备了掺铁氧化锌纳米颗粒，掺铁浓度在0.00和10 mol %之间，一方面从实验上研究了掺铁浓度对氧化锌纳米颗粒的可见光吸收和可见光催化活性的影响，另一方面采用含动能密度的广义梯度近似，基于密度泛函的第一性原理计算掺铁ZnO的能带结构、态密度。实验结果表明：当掺铁浓度为4 mol%时，氧化锌的可见光吸收能力最大，氧化锌的可见光催化活性最高。理论计算结果表明：铁离子能将杂质能级引入氧化锌的带隙中，其中一个杂质能级位于价带以上1.0 eV左右，掺铁浓度能有限度地调节此杂质能级的位置。通过比对上述理论计算和实验结果，我们确认了杂质能级EV+1.0 eV对掺铁氧化锌的可见光吸收和光催化起着决定性的作用。从这个杂质能级往导带的电子跃迁产生了峰位在520 nm左右的可见光吸收，从而使氧化锌具有可见光催化活性，从根本上阐明了铁掺杂为什么能提高ZnO的可见光催化活性。本项目要产生一些学术研究成果，共发表学术论文12篇，其中SCI 2区论文5篇，SCI 3区论文5篇，SCI 4区论文1篇，EI论文1篇。培养了3名硕士研究生毕业。项目投入经费22万元，支出经费12.4403万元，结余经费9.5597万元。该笔结余经费计划用于该项目的后续研究。