On-Surface Polymerization of In-Plane Highly Ordered Carbon Nitride Nanosheets toward Photocatalytic Mineralization of Mercaptan Gas

2D carbon nitride nanosheets have attracted ever-increasing interest in photocatalysis due to their unique structural advantages. However, the nanosheets synthesized by the traditional methods, such as post oxidation and liquid exfoliation, have suffered from in-plane disorder with abundant structural defects, which seriously counteracts their structural benefits for photocatalysis. Herein, it is demonstrated that polymer carbon nitride nanosheets with in-plane highly ordered structure (PCNNs-IHO) can be successfully prepared by on-surface polymerization of melamine on NaCl crystal surface at elevated temperatures. The NaCl crystals with relative high surface energy not only facilitate the adsorption and activation of melamine to undergo condensation reaction, but also function as unique substrates to orientate the assembly of 2D nanosheet structure. In addition, NaCl also acts as a reactant to provide Na⁺ doping into carbon nitride matrix, affording PCNNs-IHO with robust structural base sites. Benefiting from this structural basicity, PCNNs-IHO exhibits superior photocatalytic performance toward CH₃ SH mineralization under visible light irradiation.