第一性原理研究Ag掺杂及缺陷共存对ZnO光催化性质的影响

运用第一性原理研究了Ag掺杂及缺陷共存对ZnO光电性质的影响。计算结果表明富O条件有利于Ag的掺杂,贫O条件不利于Ag的掺杂。Ag掺杂浓度较低时有利于模型的稳定,其在富O或贫O条件下都以Ag_Zn为主要掺杂方式。当Ag掺杂浓度较高时,富O条件下以Ag_Zn-Ag_Zn为主要掺杂方式,贫O条件下Ag_Zn-Ag_i是较为有利的掺杂方式。富O条件下Ag掺杂较难引入V_Zn和O_i共存缺陷。贫O条件下优先出现的模型为V_O,V_O在一定程度上会促进Ag的掺杂。Ag掺杂降低了ZnO的带隙宽度,掺杂浓度越大模型带隙宽度越窄。V_Zn、V_O和O_i缺陷共存不同程度地增加了Ag掺杂模型的带隙宽度。Ag掺杂及V_Zn和O_i缺陷共存均使ZnO吸收边红移至可见光区,扩展了ZnO对太阳光的吸收范围,而Ag_Zn-V_O在可见光范围内依然是透明。在低能区紫外-可见光范围内,Ag_Zn-Ag_Zn表现出更高的光吸收率,但是相应形成能也高于Ag_Zn。V_Zn的引入提高了Ag_Zn-V_Zn和Ag_Zn-Ag_Zn-V_Zn对低能区紫外-可见光的吸收,V_O的引入有利于ZnO表面吸附更多的O₂进而产生更多的H₂O₂和·HO强氧化性物质,即V_Zn和V_O缺陷共存都有利于ZnO光催化性能的提高。

First-Principles Study on the Effects of Ag Doping and Defect Coexistence on the Photocatalytic Properties of ZnO

The effects of Ag doping and defect coexistence on the photoelectric properties of ZnO were studied by first-principles method. The calculation results indicate that O-rich condition is beneficial to Ag doping, while O-poor condition has an inhibitory effect. When Ag doping concentration is lower, Ag_Zn is dominant doping model under O-rich or O-poor conditions, and the model is more stable. When Ag doping concentration is higher, Ag_Zn-Ag_Zn is dominant doping model under O-rich condition, and that is Ag_Zn-Ag_i under O-poor condition. Under O-rich condition, it is difficult to introduce the coexistence defect of V_Zn and O_i by Ag doping. V_O is a preferred model under O-poor condition, and it can promote Ag doping to a certain extent. Ag doping reduces the band gap of ZnO. The higher of doping concentration is, the narrower of band gap will be. The defect coexistence of V_Zn, V_O and O_i increase the band gap of Ag doped models. Ag doping and the defect coexistence of V_Zn, O_i all red shift the absorption edge of ZnO to the visible region, which expands the absorption range of ZnO to sunlight. Ag_Zn-V_O is transparent in the visible region. In the low energy region, Ag_Zn-Ag_Zn shows higher optical absorptivity, but the corresponding formation energy is also higher than that of Ag_Zn. V_Zn improves the optical absorptivity of Ag_Zn-V_Zn and Ag_Zn-Ag_Zn-V_Zn in the low energy region. V_O is beneficial to the adsorption of O₂ by ZnO and can produce more H₂O₂ and ·HO. The defect coexistence of V_Zn and V_O both improve the photocatalytic performance of ZnO.