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