Alkali-Mediated Engineering of Intralayer Nitrogen Defects and Interlayer Spacing in Carbon Nitride for Enhanced Charge Transfer in Photocatalytic Lignin Depolymerization

The urgent necessity for sustainable lignin valorization drives the development of photocatalytic depolymerization. This study introduces an alkali-mediated strategy to engineer intralayer nitrogen defects and interlayer spacing in carbon nitride. KOH-synthesized g-C3Nx (K-C3Nx) delivers the best performance due to balanced alkalinity and ionic radius. Comprehensive characterizations confirm that KOH generates abundant nitrogen defects and expanded interlayer spacing, synergistically narrowing the band gap and suppressing carrier recombination. These advantages endow K-C3Nx with prolonged carrier lifetime and efficient visible light harvesting, achieving 64.0% conversion of 2-phenoxy-1-phenylethanol to benzaldehyde (51.2%) and phenyl formate (34.8%) via Cα-Cβ cleavage. K-C3Nx also enables selective scission of Cα-Cβ in various lignin model compounds and extracted methanosolv lignin. Mechanistic studies reveal that photogenerated electrons reduce O2 to •O2-, which combine with H+ and •Cβ to form a six-membered transition state, facilitating Cα-Cβ cleavage. This work establishes a dual-parameter engineering approach for synthesizing carbon nitride, enabling sustainable lignin depolymerization into aromatic monomers.