Photocatalysis is a potentially promising approach to harvest aromatic compounds from lignin. However, the development of an active and selective solid photocatalyst is still challenging for lignin transformation under ambient conditions. We herein report a mild photocatalytic oxidative strategy for C–C bond cleavage of lignin β-O-4 and β-1 linkages using a mesoporous graphitic carbon nitride catalyst. Identifications by solid-state NMR techniques and density functional theory (DFT) calculations indicate that π–π stacking interactions are most likely present between the flexible carbon nitride surface and lignin model molecule. Besides, low charge recombination efficiency and high specific surface area (206.5 m2 g–1) of the catalyst also contribute to its high catalytic activity. Mechanistic investigations reveal that photogenerated holes, as the main active species, trigger the oxidation and C–C bond cleavage of lignin models. This study sheds light on the interaction between complex lignin structures and the catalyst surface and provides a new strategy of photocatalytic cleavage of lignin models with heterogeneous photocatalysts.

One of the challenges of depolymerizing lignin to valuable aromatics lies in the selective cleavage of the abundant C−O bonds of β-O-4 linkages. Herein we report a photocatalytic oxidation−hydrogenolysis tandem method for cleaving C−O bonds of β-O-4 alcohols. The Pd/ZnIn 2 S 4 catalyst is used in the aerobic oxidation of α-C−OH of β-O-4 alcohols to α-CO with 455 nm light, and then a TiO 2 − NaOAc system is employed for cleaving C−O bonds neighboring the α-CO bonds through a hydrogenolysis reaction by switching to 365 nm light.Interestingly, the oxidation−hydrogenolysis tandem reaction can be conducted in one pot to offer ketones and phenols (up to 90% selectivity) via a dual light wavelength switching (DLWS) strategy. EPR and metal loading experiments elucidate that Ti 3+ in TiO 2 is formed in situ and is responsible for the photocatalytic hydrogenolysis through electron transfer from Ti 3+ to the β-O-4 ketones.