Sacrificial agent-free photocatalytic H2O2 evolution via two-electron oxygen reduction using a ternary α-Fe2O3/CQD@g-C3N4 photocatalyst with broad-spectrum response

Abstract

Ultrathin g-C₃N₄ nanosheets have been fabricated via a two-step calcination regulated by melamine precursors at a high heating rate (30 °C min⁻¹). The resulting g-C₃N₄ nanosheets were further employed as carriers for the growth of carbon quantum dots (CQDs) and (110) exposed α-Fe₂O₃ through the PVP-enabled adsorption effects by a solvothermal process. It was discovered that the so fabricated ternary photocatalyst α-Fe₂O₃/CQD@g-C₃N₄ presented a broad-spectrum absorption range (up to 800 nm) and particularly enhanced active sites of photogenerated electrons for highly efficient photocatalytic oxygen reduction toward H₂O₂ evolution in pure water. A H₂O₂ production rate of 1.16 μM min⁻¹ could be expected for the developed photocatalyst under visible light irradiation, which is about 19 times faster than that of pure ultrathin g-C₃N₄. Herein, the loaded Fe₂O₃ could transform the H₂O₂ evolution from two-step single-electron reduction into one-step two-electron one, as verified by the various active species experiments and rotating ring-disk electrode tests. This work presents a new perspective in designing ultrathin g-C₃N₄ through a simple method of precursor-regulated calcination, which features more outstanding advantages than the conventional exfoliation of bulk g-C₃N₄ towards ultrathin g-C₃N₄. More importantly, it provides an optimized photocatalytic reaction route of two-electron oxygen reduction for efficient H₂O₂ production in pure water under visible light irradiation, without the need for noble metals or organic sacrificial agents.