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

Abstract

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.