Advances in photocatalytic lignin depolymerization: photocatalytic materials and mechanisms

Lignin, as the only non-petrochemical resource in nature that can provide renewable aromatic-based compounds, has a complex and recalcitrant structure. Photocatalysis has received increasing attention in recent years due to its ability to cleave the C–O and C–C bonds of lignin under mild conditions. Herein, the lignin's composition and structure, lignin photocatalytic depolymerization substrates, multiphase photocatalyst, and photocatalytic selective depolymerization are presented, among which, the focus is on metal oxide, nitride, and sulfide multiphase photocatalysts through heterojunction construction, doping, defect and morphology modulation strategies to improve the performance of photocatalysis. Reaction pathways and reaction mechanisms involved in the photocatalytic process were also further analyzed to facilitate the understanding of the relationship between the photocatalyst composition structure and its performance, to better design high-performance photocatalysts and rational experimental procedures. In addition, certain sulfide photocatalysts can achieve both lignin degradation and H2 generation, to enhance the higher output value of biomass resourcing.