Mechanochemically Engineered poly(heptazine Imide): Synergizing Carbon Vacancies and Built-In Electric Fields for Photocatalytic Lignin C–C Bond Cleavage

The performance of photocatalysts for cleaving lignin C-C bonds is often constrained by insufficient active sites and severe recombination of photogenerated carriers. Herein, a facile sulfuric acid-assisted ball milling strategy was employed to simultaneously introduce carbon vacancies and construct a built-in electric field within poly(heptazine imide) (PHI), thereby overcoming these inherent limitations. Experimental characterization and density functional theory (DFT) calculations revealed that the introduced vacancies serve as electron-trapping centers and active adsorption sites, while solvent modulation optimizes surface electron density. This synergistic regulation significantly enhances charge carrier separation and light absorption. Consequently, the optimized photocatalyst (PHI-S-450r) exhibited exceptional performance, achieving 99.27% conversion of a lignin model compound (pp-ol) with a total product yield of 190.68%, alongside the effective depolymerization of authentic enzymatic lignin. This work provides a sustainable mechanochemical strategy for designing high-efficiency photocatalysts for biomass valorization.