Comparative investigation on defect-engineered Bi₂S_3-xSe_x for boosting photocatalytic Cr(VI) reduction and in-situ H₂O₂ generation: Mechanistic and kinetic studies

Heterogeneous photocatalysis has been demonstrated as a highly effective approach in addressing the difficulties encountered by conventional technologies in environmental remediation. Herein, for the first time, a novel hierarchical photocatalyst of selenium-doped Bi₂S₃ (Bi₂S_3-xSe_x) was successfully synthesized through a one-spot hydrothermal route followed by a vacancy engineering process (V-Bi₂S_3-xSe_x). The photocatalytic reduction of Cr(VI) and in-situ generation of hydrogen peroxide (H₂O₂) under simulated solar-light irradiation were performed to evaluate the catalytic activity of the as-prepared samples. The catalytic activity of as-prepared samples was evaluated toward the photocatalytic reduction of Cr(VI) and in-situ generation of H₂O₂ under simulated solar-light irradiation. Notably, V-Bi₂S_3-xSe_x (V-BSSe-5, as optimum sample) exhibited a photo-reduction of Cr(VI) at a rate of 97.04% during 150 min, which was 1.53- and 1.39-fold higher than those of pure Bi₂S₃ and Bi₂Se₃, respectively. Interestingly, the V-Bi₂S_3-xSe_x photocatalyst not only harvested more incident light in the UV–vis and near-infrared (NIR) regions but also supplied many active sites, improving the promotion of photo-generated charge-carriers, inhibiting charge recombination, and thus enhancing the photocatalytic activity. In addition, V-BSSe-5 showed greater photocatalytic efficiency for H₂O₂ generation, which was 15.69, 10.07, and 1.79 times higher than those of Bi₂S₃, Bi₂Se₃, and BSSe-5, respectively. The charge-carrier migration pathway and possible photocatalytic mechanisms were systematically discussed by assisting the electron spin resonance and ultraviolet photoelectron spectroscopy analyses. The findings of this study demonstrate that doping and defect engineering strategies have the potential to be a significant advancement in the development of visible- and NIR-light responsiveness photocatalysts, thereby providing a solution to current environmental and energy challenges.