Photocatalytic breaking of C-C bonds in lignin models by combining N-doped carbon nitride and persulfate in micellar aqueous medium

Photocatalysis is thought to be a promising way to obtain aromatic compounds by depolymerizing lignin. However, the development of heterogeneous photocatalysts with high catalytic activity still faces many challenges for the high-value utilization of lignin under mild reaction conditions. Herein, N-doped graphitic carbon nitride (CN) is obtained by using dimethylformamide as a modifier. The conduction band potential of photocatalyst 15DCN (15 mL of dimethylformamide as a modifier) with optimal catalytic performance is reduced to 1.11 eV, which has a stronger reducing ability than CN. Importantly, it can efficiently reduce potassium persulfate (KS) to produce sulfate radicals. By combining 15DCN and KS, the C-C bonds in typical & beta;-1 lignin models are efficiently broken into benzaldehyde and benzoic acid. In addition, the enhanced photogenerated electronhole pairs separation ability and sunlight capture ability also contribute to the high photocatalytic activity. Mechanistic studies revealed that sulfate radicals, superoxide radicals and hydroxyl radicals were generated and triggered C-C bonds breaking. Isotope experiments illustrate that water promotes the photocatalytic reaction and provides the H and O atoms required for C-C bonds cleavage, which is a critical factor for obtaining high photocatalytic efficiency. The photocatalytic reaction mainly follows the single-electron transfer mechanism and the improved C & beta; radical mechanism. This study provides a new photocatalytic strategy for breaking C-C bonds using water as a solvent under mild conditions.