Z-Scheme Cu2O/Bi/BiVO4 Nanocomposite Photocatalysts: Synthesis, Characterization, and Application for CO2 Photoreduction

The rational design and facile fabrication of visible-light responsive photocatalysts with excellent photocatalytic performance and photostability are still a great challenge for photocatalytic CO2 reduction into solar fuels. Herein, novel Z-scheme composite photocatalysts composed of monoclinic or tetragonal BiVO4 (m-BiVO4 or t-BiVO4) nanochains, metallic Bi nanoparticles, and Cu2O nanosheets (Cu2O/Bi/BiVO4) were successfully constructed by using a facile solvothermal method combined with a subsequent hydrothermal process. The characterization results revealed that the crystal phase of BiVO4 and the content of Cu2O and metallic Bi in Cu2O/Bi/BiVO4 can be easily manipulated by tuning the reaction conditions. Photoreduction experiments demonstrated that the Cu2O content and crystal phase of BiVO4 had a great influence on the photocatalytic activity of Cu2O/Bi/BiVO4. The optimized Cu2O/Bi/m-BiVO4 exhibited significantly improved CH4/CO evolution rates of 1.8/8.4 μmol/(g·h) under visible-light irradiation, being much higher than those of Bi/m-BiVO4 [0.32/1.9 μmol/(g·h)] and Cu2O [0.12/1.0 μmol/(g·h)]. Moreover, Cu2O/Bi/m-BiVO4 also displayed much higher photocatalytic activity as compared to Cu2O/Bi/t-BiVO4 with a similar Cu2O content. The enhanced photocatalytic performance of Cu2O/Bi/m-BiVO4 was predominantly ascribed to the large surface area, enhanced harvesting capability of visible light, abundant oxygen vacancies, and improved charge separation efficiency as a result of the Z-scheme heterojunctions. In addition, a possible charge-transfer mechanism for Cu2O/Bi/m-BiVO4 with enhanced photocatalytic activity was also proposed.