Synergistic effect of Cu impurity and oxygen vacancies on the photocatalytic performance of monoclinic ZrO2

Abstract

Crystallographic and electronic properties of copper doped monoclinic ZrO₂ (m-ZrO₂) is investigated utilizing density functional theory calculations. Formation energies of the Cu impurity in the investigated doping sites in m‑ZrO₂ suggest that Cu substitution for Zr (Cu_Zr) is generally more favorable under oxygen-rich conditions. Substitution of Cu for O becomes significant under oxygen-lean conditions. However, the formation energy obtained for Cu substituting O, is relatively high and positive (1.63 eV) demonstrating the difficulty of formation. Cu substituting for Zr in m‑ZrO₂ with different oxygen vacancy (V_O) positions relative to the Cu impurity is simulated. The structural calculation shows that V_O occupies a site near the Cu impurity. The cumulative impact of Cu and V_O on structural and optical properties of the host m‑ZrO₂ is investigated. In comparison to pure ZrO₂, the band gap of Cu-doped ZrO₂ with oxygen vacancies is reduced by 30%. The energy band gap reduction relates to the creation of spin-polarized gap states. This band gap reduction reduces the band gap of the doped system to the energy range in the visible region and thus increases its ability for absorption. The obtained results indicate that Cu-doped m‑ZrO_2−x serves as an effective route for the light absorption and is efficiency is of a visible-light photocatalyst.