Competition of Cr(VI) Reduction, H2O2 and H2 Production: A Free Radicals View from Sulfur-Vacancy-Induced ZnIn2S4 Polarization Enhanced Piezo-Photocatalysis

Modulating the generation of free radicals during a catalytic process remains a formidable challenge. To realize the harmless disposal of heavy metal Cr(VI) and efficient hydrogen energy recycling, it is highly imperative to explore high-performance multifunctional catalytic materials. Herein, sulfur-vacancy (Sv) modified ZnIn2S4 (ZIS) is synthesized via a one-step hydrothermal method, aiming to regulate the generated free radicals via piezo-photocatalytic conditions. Sv defects are distributed around indium atoms, which endows ZnIn2S4 with excellent piezo-photocatalytic activity. The Sv-ZIS achieves 100% Cr(VI) removal efficiency within 100 min, which is 1.12-fold and 5.03-fold higher than those under sole light irradiation and single ultrasonication, respectively. It also possesses a H2O2 yield of 158 μmol g–1 h–1 through two-electron ORR (∼80%) and WOR (∼20%) pathways. Moreover, the H2 production rate is 29.5 μmol g–1 h–1. In-depth investigations into defect engineering demonstrate that Sv defects induce the construction of an internal polarized electric field, which greatly accelerates the migration of charge carriers. The proposed catalytic mechanism elucidates that H2O2 production competes with Cr(VI) reduction for electrons, and piezocatalysis can efficiently boost the photocatalytic activity for Cr(VI) reduction, H2O2 and H2 production. This work offers a promising strategy to alleviate environmental contamination and address energy scarcity.