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

Vacancy engineering is an important means to improve the catalytic performance of photocatalysts. Both V-Mn and VO 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 VO on the photocatalytic reaction was not concluded yet. In this paper, VMn-1 and V-Mn-2 (with different levels of manganese vacancies (V-Mn)) and V-Mn,V-O (with both V-Mn and oxygen vacancies (VO)) were synthesized to investigate the relative contributions of V-Mn and VO 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 VO. 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 VO 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 VO. 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.