Preparation of corn stover hydrothermal carbon sphere-CdS/g-C3N4 composite and evaluation of its performance in the photocatalytic co-reduction of CO2 and decomposition of water for hydrogen production

In this paper, a composite photocatalyst based on g-C3N4/CdS/corn straw hydrothermal carbon spheres was prepared by one-pot thermal synthesis method and applied for photocatalytic reduction of CO2 and hydrogen production. The morphology and structure of CdS/g-C3N4/ corn straw hydrothermal carbon spheres were characterized, which confirmed that the corn straw hydrothermal carbon spheres were successfully loaded into the heterojunction of g-C3N4 and CdS nanosheets. Through the study of photoelectric characteristics and DFT simulation, it was found that the energy band of g-C3N4/CdS/corn straw hydrothermal carbon spheres composite is reduced by 2.04 eV compared with that of pure g-C3N4 and CdS, and the photogenerated carrier transfer rate is accelerated. The Z-scheme heterostructure between g-C3N4 and CdS and the graphitized hydrothermal carbon spheres increase the surface active sites of the composite, leading to the generation of synergistic photocatalytic reaction. The photocatalytic experiment showed that g-C3N4/CdS/corn straw hydrothermal carbon spheres composite exhibited synergistic photocatalytic performance, while pure g-C3N4 and CdS did not. When the mass ratio of g-C3N4/CdS/corn straw hydrothermal carbon spheres was 1:0.1:0.5, the synergistic reaction efficiency was the highest, and the H2 yield was 250 μ mol·h−1·g−1, CO yield was 100 μ mol·h−1·g−1, and CH4 yield was 25 μ mol·h−1·g−1. By calculating the Gibbs free energy of the photocatalytic reaction and determining the possible mechanism of the synergistic reaction of g-C3N4/CdS/corn straw hydrothermal carbon spheres, it was inferred that the key step in the reaction was generation of CO.