Cu/Ag单掺及Cu-Ag共掺对ZnO光催化性能影响的第一性原理研究

运用第一性原理方法研究了Cu/Ag单掺及Cu-Ag共掺对ZnO稳定性、电子结构和光学性质的影响。CuZn2和CuZn1-CuZn3的形成能接近0.0 eV,CuZn1-CuZn2的形成能为负值,表明Cu较易掺杂且掺杂时有聚集的趋势。AgZn2的形成能为2.5 eV,AgZn1-AgZn2和AgZn1-AgZn3的形成能高于4.5 eV,说明高浓度的Ag掺杂在实际合成中不易出现。CuZn1-AgZn2和CuZn1-AgZn3的形成能与AgZn2的相近。CuZn2、CuZn1-CuZn2和CuZn1-CuZn3模型的Cu3d与O2p轨道有较大程度的杂化,价带顶端主要由Cu3d轨道占据。AgZn2、AgZn1-AgZn2和AgZn1-AgZn3模型的Ag4d与O2p轨道杂化较弱,价带顶端主要由O2p轨道占据。CuZn1-AgZn2和CuZn1-AgZn3模型的Cu3d与O2p轨道虽有杂化,但价带顶端主要由O2p轨道占据。Cu或Ag原子掺杂使Zn4s轨道在导带区显著向下移动,降低了模型的带隙宽度,它们对ZnO电子结构的影响主要集中在带隙附近。Cu-Ag共掺修饰ZnO电子结构的能力介于Cu和Ag单掺之间。上述掺杂模型吸收边都发生了红移,实现了ZnO对可见光的吸收,同时对3.10~3.90 eV范围内紫外光的吸收均高于纯ZnO,有效提高了ZnO的光催化效率。结合形成能分析可知,在不同类型掺杂下最有利的光催化模型分别为CuZn1-CuZn2、AgZn2和CuZn1-AgZn2。

First-principles Study on the Photocatalytic Activity of Cu/Ag Doped and Cu-Ag Codoped ZnO

The stability,electronic structure and optical properties of ZnO with Cu/Ag doped and Cu-Ag codoped were studied by first-principles method.Formation energies of CuZn2 and CuZn1-CuZn3 are close to 0.0 eV,and negative for CuZn1-CuZn2,which indicates that Cu doped is effortless and tends to gather.The value for AgZn2 is 2.5 eV,and higher than 4.5 eV for AgZn1-AgZn2 and AgZn1-AgZn3.It’s difficult for Ag doping with higher concentration.Formation energies of CuZn1-AgZn2 and CuZn1-AgZn3 are close to that of AgZn2.The Cu3d and O2p states have obvious hybridization in models of CuZn2,CuZn1-CuZn2 and CuZn1-CuZn3,the top of valence band is mainly occupied by Cu3d states.The hybridization between Ag4d and O2p states for AgZn2,AgZn1-AgZn2 and AgZn1-AgZn3 models is weaker,the top of valence band is mainly occupied by O2p states.For CuZn1-AgZn2 and CuZn1-AgZn3 models,although Cu3d states hybridize with O2p states,the top of valence band is mainly occupied by O2p states.Cu/Ag doped and Cu-Ag codoped lead Zn4s states downward significantly,which reduces the band gap of above models.They influence the electronic structure of ZnO near the band gap mainly.The modified ability of Cu-Ag codoped to ZnO electronic structure is between Cu/Ag doped ZnO.The absorption edges of above models have obvious red-shift,which realizes the visible light absorption for ZnO.The ultraviolet light absorption also is higher than pure ZnO in the range of 3.10-3.90 eV.Cu/Ag doped and Cu-Ag codoped improves the photocatalytic activity of ZnO.According to formation energy analysis,the models with higher photocatalysis under different doping are CuZn1-CuZn2,AgZn2 and CuZn1-AgZn2.