Molten salt assistance and heterostructure construction strategy for effectively enhancing H2O2 photosynthesis over modified g-C3N4/h-BN

Graphitic carbon nitride (g-C 3 N 4 , CN) is promising in boosting H 2 O 2 photosynthesis at present, but facing huge challenges due to the limitations of common CN (e.g. small specific surface area, low absorption coefficient, and fast recombination of photoinduced carriers). To overcome these drawbacks, herein, the novel type-II heterojunctions are successfully constructed from hexagonal boron nitride (h-BN, abbreviated as BN), melamine, and KCl with the one-pot calcination method. The molten salt effect of KCl and the hard template effect of BN optimize the interlayer spacing, porosity and structural uniformity of CN, thus optimizing the adsorption and photocatalytic properties. Moreover, the constructed heterostructure between BN and modified CN further favors the photoinduced charge transfer. Hence, the resulting composites afford exciting photocatalytic H 2 O 2 synthesis performance. Particularly, catalyzed by MCN/BN-2, the H 2 O 2 production rate is separately 1515.05 μmol g −1  h −1 and 3382.17 μmol g −1  h −1 irradiated by visible light and the simulated solar light, which are significantly higher than those over MCN, BN, and most of CN-based materials previously reported. The results of band potential analyses, relevant radical scavenging experiments, as well as electron paramagnetic resonance measurements verify that the photocatalytic H 2 O 2 production over MCN/BN-2 by using 10 vol% EtOH solution is predominantly through the two-step single-electron oxygen reduction reaction (ORR) process. Also, the one-step two-electron ORR involves in H 2 O 2 formation. This work not only develops a novel broad-spectrum responsive metal-free photocatalyst, but also enriches the deep understanding of the roles played by molten salt engineering and heterostructure in photocatalysis.