Achieving high CH4 selectivity in CO2 photoreduction via S-type MoO3/g-C3N4 heterojunction with Pt co-catalyst†

A Pt-assisted MoO₃/g-C₃N₄ photocatalyst (Pt/5MoO₃/g-C₃N₄) was designed and synthesized for the selective photocatalytic reduction of CO₂ to CH₄. The structure, morphology, and chemical states of the catalyst were systematically analyzed using XRD, XPS, SEM, and TEM. The formation of an S-type heterojunction between MoO₃ and g-C₃N₄ effectively promoted charge separation and migration, enhancing photocatalytic efficiency. Pt, as a co-catalyst, facilitated charge transfer, reduced recombination, and improved CH₄ selectivity. The Pt/5MoO₃/g-C₃N₄ catalyst achieved a CH₄ production rate of 34.9 μmol g⁻¹ h⁻¹, 2.2 times higher than that of g-C₃N₄, with 100% CH₄ selectivity. In situ FTIR and XPS analyses confirmed that Pt⁰ acted as the primary catalytic site, while MoO₃ contributed to CO₂ adsorption and intermediate stabilization. Photoelectrochemical tests further demonstrated the synergistic effect of the S-type heterojunction and Pt co-catalyst, leading to enhanced charge separation and reduced interfacial charge transfer resistance. Moreover, Pt/5MoO₃/g-C₃N₄ exhibited excellent stability and recyclability. This study highlights the effectiveness of S-type heterojunction engineering and Pt co-catalysts in improving photocatalytic CO₂ reduction efficiency and selectivity.