Mechanistic insights into the photocatalytic valorization of lignin models via C-O/C-C cleavage or C-C/C-N coupling

Serving as an earth-abundant, aromatic structure-rich but underutil-ized lignocellulosic component, the effective conversion of lignin into high-value-added chemicals is considered a major countermea-sure for an energy-efficient and low-carbon future. Encouraged by the unique reaction pattern induced by photo-generated charge car-riers or reactive species, the environmentally benign and low-energy dissipative photocatalytic technology emerges as a marvelous strat-egy for lignin valorization and has received increasing attention and extensive research. By focusing on the mechanistic perspectives, this review provides a comprehensive summary of the state-of-the-art developments in (1) the photocatalytic depolymerization of lignin models by precisely breaking targeted C -O and/or C -C bonds to obtain aromatic monomers and (2) the upgradation of lignin-derived aromatics via C -C or C -N bonds coupling into high-value-added coupling compounds. We then present the opportunities for photoca-talytic conversion of native lignin, as well as the future challenges for achieving a photocatalytic system with profitability and sustainability.