Overlooked roles of high-valence Sn in SnS₂ loaded on gC₃N₄ for enhanced photocatalytic H₂O₂ production: Mechanism, DFT, and techno-economic analysis study

Solar-driven photocatalysis with charge-transfer modulation is a green approach for enhancing the oxygen reduction reaction (ORR) to generate hydrogen peroxide (H₂O₂). In this study, we introduced a novel method for synthesizing high-valence Sn^δ+ in SnS₂, combined with gC₃N₄ to create gC₃N₄/SnS₂. Density functional theory (DFT) calculations exhibited that the interface between SnS₂ and gC₃N₄ creates interband states through strong hybridization, revealing that photoexcited electrons flowed from C in gC₃N₄ to S in SnS₂, forming a Z-scheme heterojunction. The optimal gC₃N₄/SnS₂-2 (2% SnS₂ loaded) achieved a high H₂O₂ production rate of 7.186 mmol g⁻¹ h⁻¹ and an apparent quantum efficiency (AQE) of 33.8% at 405 nm with isopropanol (IPA), converting 88.8% IPA to acetone in 2 h. The gC₃N₄/SnS₂ composite improved the charge transfer resistance and elongated the non-radiative electron decay time. Notably, SnS₂ doping of gC₃N₄ decreased the antibonding orbital occupancy and lowered the energy barrier for O₂ and OOH* adsorption. In situ surface-enhanced Raman spectroscopy (SERS) analysis confirmed the generation of OOH* on gC₃N₄/SnS₂ during light irradiation. A techno-economic analysis (TEA) was conducted to evaluate the economic viability of photocatalytic H₂O₂ production, revealing that it was not economically feasible owing to challenges in the separation process. This study provides unique perspectives on the approaches to inducing a high valence state of Sn^δ+ for enhancing photocatalytic H₂O₂ generation and the challenge of commercializing H₂O₂ production via photocatalysis.