Band Engineering of Lignin Nanoparticle/Graphene Quantum Dots Heterojunction for In Situ Photocatalytic Hydrogen Peroxide Synthesis

Lignin, Earth’s most abundant renewable aromatic polymer, displays intrinsic photoactivity that enables strategies for high-value utilization. In this work, lignin nanoparticle/graphene quantum dot composites (EL-GQDs) were synthesized via surface modification for efficient H2O2 production, achieving 116.4 μM of H2O2 within 1 h at a photocatalyst dosage of 10 mg. Directional electron transport driven by π–π stacking interactions within the heterogeneous EL-GQDs structure facilitates efficient charge carrier migration. Mechanistic investigations demonstrate that GQD incorporation substantially lowers the electron migration impedance at the EL-GQDs surface by restructuring the electronic configuration of lignin nanoparticles, while concurrently extending the photoresponse threshold to 436 nm. Combined experimental and computational approaches reveal two key molecular features: the β-O-4 ether bond hinders HOMO–LUMO orbital overlap, whereas the hydroxyl group at the Cα position enhances the electron-accepting capacity of the LUMO orbital. Notably, oxygen photoreduction constitutes the dominant pathway for H2O2 generation in EL-GQDs. The concurrent water oxidation reaction delays electron–hole recombination by scavenging holes. Radical quenching experiments further confirm the involvement of superoxide radical intermediates during EL-GQDs catalysis, elucidating the specific mechanism of H2O2 synthesis and establishing design principles for practical implementation.