Photocatalytic efficient cleavage of C-C bond in lignin model using water as solvent

Photocatalytic lignin C-C bond (LCCD) cleavage is one possible strategy to promote high-value utilization of lignin. However, it still confronts many difficulties due to the stability of the lignin structure and the high activation energy of LCCD. Herein, a graphitic carbon nitride photocatalyst with the introduction of cyano groups and K+ ions (6MCN) is synthesized. Compared with pure carbon nitride (PCN), 6MCN exhibits superior photogenerated carrier separation ability, excellent sunlight capture ability, and greater oxidation capability. Under simulated sunlight, 6MCN significantly improves the photocatalytic efficiency of LCCD breakage in β-1 lignin models and aromatic vicinal diols (ACD), compared with earlier literature. The improved Cβ radical mechanism and single-electron transfer (SET) pathway are the primary mechanisms in the photocatalytic reaction. Hydroxyl radicals, superoxide radicals, and photogenerated holes are all involved in the photocatalytic cleavage of LCCD. However, hydroxyl radicals, as the most important active radicals, not only trigger the SET mechanism and Cβ radical mechanism but also provide the O and H atoms required for photocatalytic fracture of LCCD, which is very critical to obtain excellent photocatalytic efficiency. This work offers new insights into the photocatalytic breakage of LCCD in β-1 lignin models and ACD through the development of high-performance photocatalysts and the control of radical types.