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

Abstract

Herein, by decorating NH₂-MIL-125 (NM) with NiTiLDH (NTL), NM_xNTL_y is designed for the CO₂ photoreduction reaction in only water media. The optimal NM₃NTL₁ presents electronic yields of 65.74 μmol 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 NM_xNTL_y 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 O₂ might not completely desorb, which should explain for O₂ readings below the theoretical values. This study provides new heterojunction photocatalyst designs and insights into the enhancement mechanism of the photocatalytic response.