A novel S-scheme heterojunction constructed by Ti-based hydrotalcite decorating MOFs for boosting CO2-to-CO photoreduction and mechanism insights

Herein, by decorating NH2-MIL-125 (NM) with NiTiLDH (NTL), NMxNTLy is designed for the CO2 photoreduction reaction in only water media. The optimal NM3NTL1 presents electronic yields of 65.74 mu mol g(-1) h(-1) with a CO selectivity of 96.2%. Supported by in situ irradiated X-ray photoelectron spectroscopy (ISIXPS) and Kelvin probe force microscopy (KPFM), the designed NMxNTLy forms the S-scheme electron transfer mode with an interfacial electric field from NTL to NM, facilitating the migration of e(-)/h(+) pairs. NTL serves as an electron acceptor responsible for anchoring CO2, while NM is rich in holes for H2O oxidization, driven by coulombic forces under irradiation. Revealed by in situ DRIFTS, CO production follows the CO2- and *COOH mechanisms. Significantly, we observed the reoxidation of CO from isotope labeling experiments, which could be inhibited on a S-scheme heterojunction with a spatially separated oxidation/reduction reaction. TPD coupled mass spectrometry (TPD-MS) suggests that the produced O-2 might not completely desorb, which should explain for O-2 readings below the theoretical values. This study provides new heterojunction photocatalyst designs and insights into the enhancement mechanism of the photocatalytic response.

Automated summary

Here, a new photocatalyst for CO2 photoreduction reaction in water media is designed by decorating NH2-MIL-125 with NiTiLDH. The optimized photocatalyst exhibits high electron yields and CO selectivity with an S-scheme electron transfer mode. The electron acceptor NTL plays a crucial role in electron transfer and CO2 fixation, while NM facilitates H2O oxidation. Furthermore, the study provides valuable insights into the reaction mechanism and the enhancement mechanism of the CO2 photoreduction reaction.