Synergetic Subnano Ni‐ and Mn‐Oxo Clusters Anchored by Chitosan Oligomers on 2D g‐C3N4 Boost Photocatalytic CO2 Reduction

Abstract

Synergistic modulation of photogenerated electrons and holes of g‐C3N4 especially achieved by simply modifying bimetallic species is highly desired for efficient photocatalytic CO2 reduction. Herein, ultrasmall subnano Ni‐ and Mn‐oxo clusters (average diameter of ≈0.8 nm) are uniformly anchored on tailored chitosan oligomer (COS)‐functionalized ultrathin g‐C3N4 nanosheets via OH and NH2 in COS as the coordination sites. Optimized Ni and Mn comodified photocatalyst obtained by regulating bimetallic molar ratio exceptionally exhibits 22‐times CO2 conversion rate under solar‐light irradiation and ≈20‐times quantum efficiency at 405 nm light compared with pristine g‐C3N4. By electron paramagnetic resonance, surface photovoltage spectroscopy, fluorescence spectra, photoluminescence spectra, and electrochemical curves, it is evidenced the enhanced photoactivities originate from the synergetic effect between Ni‐ and Mn‐oxo species, capable of photoelectron‐capture along with catalytic CO2 activation and hole‐capture along with catalytic H2O activation, respectively. More importantly, due to the carrier‐modulating capability difference, it is verified only a matching Ni:Mn molar ratio leads to the best charge separation then photoactivity as supported by the transient‐state photoluminescence spectra. A new avenue to rationally modulate photogenerated charge carriers for fabricating efficient g‐C3N4‐based photocatalysts for solar‐fuel production is proposed.