Biomass-derived HMF-regulated proton mediation for efficient photocatalytic H2O2 production over Co-N-S modified g-C3N4

Photocatalytic H 2 O 2 synthesis is often promoted by concentrated alcohol (10 vol%) sacrificial agents that consume photogenerated holes and assist electron/proton transfer, together with continuous O 2 purging, which may limit practical sustainability. Integrating renewable and low-cost biomass-derived molecules with photocatalytic oxygen reduction offers a new route for regulating interfacial reactions toward H 2 O 2 synthesis. Here, a Co/N/S co-doped g-C 3 N 4 photocatalyst (Co-N-S/CN) was prepared by hydrothermal-assisted calcination using cobalt phthalocyanine sulfonate and melamine, with 5-hydroxymethylfurfural (HMF) introduced as a biomass-derived reaction additive. With only 0.1 vol% HMF, the optimal Co-N-S/CN photocatalyst achieved an H 2 O 2 production rate of 1834.91 μmol g −1 h −1 under ambient air without external O 2 feeding, representing a 40-fold enhancement over pristine g-C 3 N 4 in pure water. Comprehensive structural and spectroscopic characterization, photoelectrochemical measurements, reactive species identification and quantitative determination, and DFT calculations reveal that Co/N/S co-doping induced defects and electronic redistribution, enhancing light harvesting, charge separation, interfacial electron transfer, and O 2 activation toward H 2 O 2 production via two-electron oxygen reduction pathways. HMF addition increased the H 2 O 2 formation rate and suppressed its decomposition. The accompanying pH decrease, light-induced HMF-derived carbon-centered radical signals, photoluminescence and time-resolved photoluminescence measurements, and favorable HMF adsorption indicate that limited hole-driven HMF oxidation facilitates proton release and interfacial charge transfer. HPLC and TOC analyses showed only minor HMF consumption (3.1%) after the photoreaction of 3 h, supporting its use as a low-dose reaction additive. This work integrates one-step multi-heteroatom co-doping with biomass-assisted reaction regulation for efficient photocatalytic H 2 O 2 synthesis.