Unraveling the Synergistic Mechanism of Boosted Photocatalytic H₂O₂ Production over Cyano-g-C₃N₄/In₂S₃/Ppy Heterostructure and Enhanced Photocatalysis-Self-Fenton Degradation Performance

In this work, cyano contained g-C₃N₄ comodified by In₂S₃ and polypyrrole (C≡N─CN/IS/Ppy) materials are synthesized for the photocatalytic production of H₂O₂ and photocatalysis-self-Fenton reaction for highly efficient degradation of metronidazole. The results from UV–vis spectrophotometry, surface photovoltage, and Kelvin probe measurements reveal the promoted transport and separation efficiency of photoinduced charges after the introduction of In₂S₃ and Ppy in the heterojunction. The existence of a built-in electric field accelerates the photoinduced charge separation and preserves the stronger oxidation ability of holes at the valence band of C≡N─CN. Linear sweep voltammetry measurements, zeta potential analyzations, nitroblue tetrazolium determination, and other measurements show that Ppy improves the conversion ratio of ^•O₂⁻ to H₂O₂ and the utilization ratio of ^•O₂⁻, as well as suppresses decomposition of H₂O₂. Accordingly, the H₂O₂ evolution rate produced via a two-step single-electron reduction reaction reaches almost 895 µmol L⁻¹ h⁻¹, a value 80% and 7.2-fold higher than those obtained with C≡N─CN/IS and C≡N─CN, respectively. The metronidazole removal rate obtained via photocatalysis-self-Fenton reaction attains 83.7% within 120 minutes, a value much higher than that recorded by the traditional Fenton method. Overall, the proposed synthesis materials and route look promising for the H₂O₂ production and organic pollutants degradation.