Green H2O2 synthesis via melamine-foam supported S-scheme Cd0.5Zn0.5In2S4/S-doped carbon nitride heterojunction: Synergistic interfacial charge transfer and local photothermal effect

Abstract

Green photocatalytic synthesis of hydrogen peroxide (H₂O₂) represents a promising alternative to the energy-intensive anthraquinone process, yet it is hindered by rapid carrier recombination and insufficient redox capacity in sacrificial-agent-free systems. This work reports a melamine-foam (MF) supported sulfur (S)-doped carbon nitride (SCN)/S vacancy-modified Cd_0.5Zn_0.5In₂S₄ (CZIS) S-scheme heterojunction (CZIS/SCN/MF) via an in situ chemical bath-hydrothermal method for sacrificial-agent-free H₂O₂ photosynthesis. The S-scheme charge transfer mechanism was confirmed by in situ irradiated X-ray photoelectron spectroscopy, free-radical trapping electron paramagnetic resonance, femtosecond transient absorption spectra and theoretical calculations. Specifically, the sulfur doping could modulate the local charge distribution of the carbon nitride framework to reinforce the interfacial built-in electric field for the CZIS/SCN S-scheme heterojunction. Meanwhile, the calcination-induced S-vacancies in CZIS could serve as photoelectron traps, promoting charge separation, and reserving photoinduced holes for H₂O oxidation, thereby achieving sacrificial-agent-free H₂O₂ synthesis. Coupled with the photothermal effect of MF's three-dimensional porous framework, the CZIS/SCN/MF catalyst with optimized S-doping density and SCN dosage delivers an H₂O₂ production rate of 3.46 ​mmol ​g⁻¹ h⁻¹ in pure water, surpassing most of the sacrificial-agent-free systems. This study proposes a novel strategy for synergistic interfacial charge regulation and energy conversion enhancement in sacrificial-agent-free photocatalytic systems.