Acetamide- or Formamide-Assisted In Situ Approach to Carbon-Rich or Nitrogen-Deficient Graphitic Carbon Nitride for Notably Enhanced Visible-Light Photocatalytic Redox Performance

Acetamide- or formamide-assisted in situ strategy is designed to synthesize carbon atom self-doped g-C3N4 (AHCN(x)) or nitrogen vacancy-modified g-C3N4 (FHCNx). Different from the direct copolymerization route that suffers from the problem of mismatched physical properties of acetamide (or formamide) with urea, the synthesis of AHCN(x) (or FHCNx) starts from a crucial preorganization step of acetamide (or formamide) with urea via freeze drying-hydrothermal treatment so that the chemical structures as well as C-doping level in AHCN(x) and N-vacancy concentration in FHCNx can be precisely regulated. By using various structural characterization methods, well-defined AHCN(x) and FHCNx structures are proposed. At the optimal C-doping level in AHCN(x) or N-vacancy concentration in FHCNx, both AHCN(x) and FHCNx exhibit remarkably improved visible-light photocatalytic performance in oxidation of emerging organic pollutants (acetaminophen and methylparaben) and reduction of proton to H-2 in comparison of unmodified g-C3N4. Combination of the experimental results with theoretical calculations, it is confirmed that AHCN(x) and FHCNx show different charge separation and transfer mechanisms, while the enhanced visible-light harvesting capacity and the localized charge distributions on HOMO and LUMO are responsible for this excellent photocatalytic redox performance of AHCN(x) and FHCNx.