pH-controlled Pt valence states modulation over Pt/g-C3N4 for highly active photocatalytic CO2 methanation at room-temperature

Pt-2 + - and Pt4+-loaded g-C3N4 (Pt/CN) catalysts were synthesized for the reduction of CO2 to CH4 at room temperature (25 degrees C) by adjusting the solution pH during the photodeposition process. Acidic conditions (pH = 4) favored the formation of Pt2+, while Pt4(+) was the predominant species under alkaline conditions (pH =10) in the Pt/CN photocatalyst. A strong electronic metal-support interaction between Pt and N atom was constructed, enhancing charge transfer from N to Pt. Pt2+ exhibited superior electron-trapping capabilities. The influence of Pt species on the bandgap of Pt/CN photocatalyst was minimal, but the positions of the conduction band and valence band changed significantly. An increased presence of Pt2+ resulted in a more negative valence band position and improved separation efficiency of photogenerated carriers, which enhances the reactivity of photocatalytic CO2-to-CH4 reduction process. Furthermore, the amount of Pt loading played a crucial role in the photocatalytic performance for CO2 methanation. Consequently, the as-prepared 3 %-Pt/CN-4 photocatalyst (3 wt% Pt content, pH = 4) demonstrated the highest photocatalytic activity for CO2-to-CH4 conversion, achieving a rate of 11.69 mu mol.g(-1).h(-1) under xenon lamp AM1.5 G light irradiation at 25 degrees C.