Coupling monoclinic Pb2(CrO4)O with Mn3O4 quantum dots as oxygen vacancies-rich S-scheme photocatalysts for visible-light-driven photocatalytic CO2 reduction with H2O

Abstract

Simulating natural photosynthesis to convert CO2 and H2O into fuels achieving overall reaction is a promising solution for addressing environmental problems and energy crises. Constructing an S-scheme catalyst of two or more catalytic sites with rapid electron transfer and strong redox capability may be an effective strategy for coupling photocatalytic CO2 reduction and H2O oxidation. Here, an oxygen vacancies-rich S-scheme semiconductor photocatalyst composed of monoclinic lead chromate oxide (Pb2(CrO4)O) coupled with Mn3O4 quantum dots (QDs) (Pb2(CrO4)O@Mn3O4QDs) are synthesized and tested for photoconversion of CO2 with H2O under visible light. Through the integration of Pb2(CrO4)O with Mn3O4QDs, the photocatalytic C1-evolution rate on Pb2(CrO4)O@Mn3O4QDs is radically increased by 6.0 and 8.1 times, which is much faster than that of pristine Pb2(CrO4)O and Mn3O4. The origin of the greatly raised activity is revealed by advanced characterizations, and in situ X-ray photoelectron spectroscopy (XPS) confirms the electron transport pathway in Pb2(CrO4)O@Mn3O4QDs with light illumination, unveiling the efficient spatial separation/transfer of charge carriers in oxygen vacancies-rich Pb2(CrO4)O@Mn3O4QDs S-scheme heterojunction. Consequently, powerful photoelectrons and holes accumulate in the Mn3O4 conduction band and Pb2(CrO4)O valence band, respectively, exhibiting prolonged long lifetimes and facilitating their involvement in CO2 photoreduction and H2O photooxidation through altering the interfacial charge dynamics.