Ag-Cu2O composite films with enhanced photocatalytic activities for methylene blue degradation: Analysis of the mechanism and the degradation pathways

Abstract As refractory organic pollutants, dyes have caused widespread concern about their pollution of water environments. The development of visible light responsive catalysts with high catalytic activity is of great significance for the removal of organic pollutants using sunlight as a light source. Ag-Cu2O composite film was prepared by the electrochemical deposition and a redox reaction. The influence of Ag on the microstructure and performance of the Cu2O was investigated by physical and chemical characterization. Results show that compared with the single-layer Cu2O film, the Ag-Cu2O composite film shows good visible light absorption performance. The carrier concentration, photocurrent and open-circuit voltage are all increased, and the photogenerated electron and hole transfer and separation efficiency are effectively improved. Degradation experiments show that the Ag-Cu2O exhibits good photocatalytic performance, and that the degradation rate of methylene blue reaches over 95.1%. The enhanced photocatalytic activity of Cu2O is primarily due to the efficient separation and transfer system of the photogenerated charge from Cu2O to Ag and the increased visible-light absorption ability; thus the composite film exhibits a synergistic effect. Experiments for detecting the active substances show that hydroxyl radical and hole play a leading role in methylene blue degradation. Methylene blue begins to be degraded under the action of the photogenerated holes and hydroxyl radicals. Based on the analysis of experimental data and combined with the theoretical calculation, two possible degradation pathways of methylene blue are proposed. This work presents a new idea for studying the mechanism and pathway of the degradation of methylene blue with an Ag-Cu2O and provides a new opportunity for the use of semiconductor photocatalytic oxidation technology to remove organic dyes in wastewater