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

Synergistic modulation of photogenerated electrons and holes of g‐C 3 N 4 especially achieved by simply modifying bimetallic species is highly desired for efficient photocatalytic CO 2 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‐C 3 N 4 nanosheets via OH and NH 2 in COS as the coordination sites. Optimized Ni and Mn comodified photocatalyst obtained by regulating bimetallic molar ratio exceptionally exhibits 22‐times CO 2 conversion rate under solar‐light irradiation and ≈20‐times quantum efficiency at 405 nm light compared with pristine g‐C 3 N 4 . 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 CO 2 activation and hole‐capture along with catalytic H 2 O 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‐C 3 N 4 ‐based photocatalysts for solar‐fuel production is proposed.