Tailoring sulfur-doped and nitrogen-defective carbon nitride nanosheets for efficient photo-controlled radical polymerizations

Despite the challenges that remain, the synergistic adjustment of various microstructures and photochemical parameters of graphitic carbon nitride (g-C₃N₄) in photocatalytic reactions holds promises for improving catalytic efficiency and reducing energy consumption. Herein, sulfur-doped and nitrogen-defective g-C₃N₄ (n-SC₃N_x) nanosheets were designed and elaborately synthesized. The resultant n-SC₃N_x possessed a precisely defined 2D layer structure with extensive porosity and incremental specific surface area. Enhanced photoinduced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization of vinyl monomers with low dispersity, excellent temporal control and high chain-end fidelity was achieved under mild blue light irradiation in a nondegassed system. Owing to their ultrathin nanostructures with nitrogen defects and sulfur dopants, n-SC₃N_x was capable of catalyzing RAFT polymerization in aqueous solutions at significantly accelerated rates, which were nearly 8 times faster compared to bulk g-C₃N₄. The ease of separation and efficient reusability in subsequent polymerizations was enabled by the heterogeneous nature of n-SC₃N_x. The appeal of this approach was illustrated by the fact that utilizing a reusable and metal-free photocatalyst in aqueous environments allowed for the synthesis of polymers with molecular weight up to 300 kg mol⁻¹ and a dispersity of 1.32.