Rational Design of S-Scheme CeO2/Bi2MoO6 Microsphere Heterojunction for Efficient Photocatalytic CO2 Reduction

In the pursuit of efficient photocatalytic carbon dioxide (CO 2 ) conversion, the use of artificial semiconductors powered by solar energy offers great potential for simulating natural carbon cycling. However, the efficiency of photocatalytic CO 2 conversion remains suboptimal, primarily due to inadequate separation of photogenerated charges, which hinders the performance of semiconductor-based CO 2 reduction. Consequently, recent research efforts have focused on identifying ideal materials for CO 2 photocatalytic conversion. Among the candidate materials, the structure of Bi 2 MoO 6 consists of alternating layers of (Bi 2 O 2 ) 2+ and perovskite-like (MoO 4 ) 2− layers with shared oxygen atoms between them. This inherent charge distribution within Bi 2 MoO 6 creates an inhomogeneous electric field, facilitating the efficient separation of photogenerated charge carriers. The morphology and structure of a catalyst significantly influence the rate of recombination of photogenerated charge carriers. Research has shown that ultrathin Bi 2 MoO 6 nanosheets , compared to other 2D and 3D structures of Bi 2 MoO 6 materials, possess longer fluorescence lifetimes , providing more opportunities for the separation of photogenerated charge carriers. However, Bi 2 MoO 6 still exhibits relatively low catalytic efficiency due to its insufficiently negative conduction band position (ranging between −0.2 and −0.4 V). To address this limitation, a viable strategy is to load a semiconductor with a more negatively positioned conduction band onto Bi 2 MoO 6 , creating an S-scheme heterojunction . In this study, Bi 2 MoO 6 nanosheets were synthesized through a hydrothermal method , and simultaneously, CeO 2 nanoparticles were grown on their surfaces, forming an S-scheme heterojunction modified with Ce 3+ /Ce 4+ ion bridges. Time-resolved photoluminescence (TRPL) and photoelectrochemical tests demonstrated the enhanced charge separation effect of this heterojunction. In situ X-ray photoelectron spectroscopy ( In situ XPS) analysis and theoretical calculations further confirmed that photogenerated electrons follow an S-scheme mechanism, transferring from Bi 2 MoO 6 to CeO 2 . Experimental results revealed that the photocatalytic CO 2 reduction efficiencies of CeO 2 /Bi 2 MoO 6 , Bi 2 MoO 6 , and CeO 2 were 65.3, 14.8, and 1.2 μmol∙g −1 ∙h −1 , respectively. Compared to pure Bi 2 MoO 6 , the catalytic efficiency of the CeO 2 /Bi 2 MoO 6 composite catalyst for CO 2 photocatalytic reduction to CO improved by a factor of 3.12. This enhancement in photocatalytic CO 2 conversion performance can be attributed to the synergistic interaction between the S-scheme heterojunction and Ce 3+ /Ce 4+ ion bridging, resulting in enhanced light absorption , efficient charge separation, and redox capabilities of the composite catalyst. This study offers valuable insights into the rational design and construction of novel S-scheme heterojunction photocatalysts . The S-scheme heterojunction of CeO 2 /Bi 2 MoO 6 synergistically enhances the photocatalytic CO 2 reduction through Ce 3+ /Ce 4+ ion bridging.