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

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

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O_(2)进而产生更多的H_(2)O_(2)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。

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 O_(2) by ZnO and can produce more H_(2)O_(2) and·HO.The defect coexistence of V_(Zn) and V_(O) both improve the photocatalytic performance of ZnO.