Zinc porphyrin/g-C3N4 S-scheme photocatalyst for efficient H2O2 production

Constructing heterojunction photocatalyst is a promising strategy to achieve solar-to-chemical energy conversion. Especially, the S-scheme heterojunction has received a great deal of attention because of its superiority of the efficient photogenerated charge carriers’ separation and the strong photoredox capacity. Herein, an S-scheme heterojunction is designed and synthesized through grafting supramolecular Zinc porphyrin (Zn-TCPP) on g-C3N4 (CN) via –CONH- bridging bond for H2O2 production in the O2 atmosphere under a 300 W Xe lamp irradiation using ethanol as a sacrificial agent. As the optimal sample, Zn-TCPP/CN exhibits the highest H2O2 production rate with 532.7 μmol/L within 90 min, which is 3.1 and 9.0 times higher than those of pure CN and Zn-TCPP, respectively. The route of H2O2 production in the photocatalytic process and the mechanism of activity enhancement are revealed by a systematic characterisation. Hence, the results of the radical trapping experiment and rotating disk electrode measurement demonstrate that the two-step single-electron route is the predominant reaction step in the process of H2O2 generation. In-situ irradiated X-ray photoelectron spectroscopy (ISI-XPS) and Kelvin probe force microscopy (KPFM) technology provide strong evidence of the S-scheme charge transfer path between Zn-TCPP and CN, which greatly facilitates the spatial charge separation. Meanwhile, the density functional theory (DFT) calculations reveal that the strong interface interaction between Zn-TCPP and CN can induce the electron delocalization effect, thus restraining charge recombination. This work inspired the design of a high-active metalloporphyrin-based S-scheme heterojunction for energy conversion.