Synergetic piezo-photocatalysis of g-C3N4/PCN-224 core-shell heterojunctions for ultrahigh H2O2 generation

Hydrogen peroxide (H2O2) is a high-value-added chemical for multitudinous industrial applications. Being compared with traditional anthraquinone processes, it is an eco-friendly and promising strategy to accomplish catalytic reduction of molecular oxygen for H2O2 production with the aid of mechanical and solar energy. It was the first attempt to combine a porphyrin-based metal-organic framework (PCN-224) and piezoelectric semiconductor (g-C3N4) to fabricate heterostructures (abbreviated as CP-x) with core-shell structure for piezo-photocatalytic H2O2 production. The introduction of PCN-224 not only widened light absorption range and accelerated electron transfer, but also facilitated the hydrogenation and generation of OOH*, which was more prone to direct two-electron O2 reduction. Furthermore, benefitting from the synergism of the piezo-photocatalysis, an exceptional piezo-photocatalytic H2O2 evolution rate of 5.97 mmol g–1 h–1 with solar-to-chemical conversion (SCC) efficiency of 0.14% was achieved by the optimum CP-5 heterojunction. This achievement significantly surpassed the previously reported g-C3N4-based and MOF-based materials. The use of rainwater as proton sources also allowed an impressive H2O2 generation rate (2.78 mmol g–1 h–1), thereby this outcome was of great significance to the rainwater utilization. This work contributed an in-depth understanding of piezo-photocatalytic O2 reduction and provided an alternative way for the development of porphyrinic MOFs heterojunctions for synthesis of H2O2.