The quantitative contribution of interfacial coexisting Mn and O vacancies to MnO2 photocatalytic degradation of phenol

Abstract

Vacancy engineering is an important means to improve the catalytic performance of photocatalysts. Both V_Mn and V_O can promote photocatalytic and thermocatalytic reactions of MnO₂ catalysts. From the point of view of reducing energy consumption, photocatalysis has incomparable advantages over thermocatalysis. Meanwhile, in-depth investigation of the relative contribution of V_Mn and V_O on the photocatalytic reaction was not concluded yet. In this paper, V_Mn-1 and V_Mn-2 (with different levels of manganese vacancies (V_Mn)) and V_Mn,O (with both V_Mn and oxygen vacancies (V_O)) were synthesized to investigate the relative contributions of V_Mn and V_O in the photocatalytic process by MnO₂. The catalysts were characterized by EDS, ICP, and XPS to explore their structures and the concentrations of V_Mn and V_O. The contributions to phenol degradation were calculated to be 487 321.43 (mg L⁻¹) phenol per mol V_Mn and 125 917.16 (mg L⁻¹) phenol per mol V_O for 2 h irradiation under 400 mW cm⁻² visible light. Density-functional theory (DFT) calculations were performed to explain the different contributions of V_Mn and V_O. The higher contribution of V_Mn is attributed to its induced formation of a continuous band gap on the (001) crystal surface, which is favourable for visible light absorption and carrier transport. This study provides theoretical guidance and research direction for the design of efficient photocatalysts using vacancy engineering.