Ultrafast photoreduction of Cr(VI) by enhanced adsorption and internal electric field induced via S-scheme In₂S₃/Sn₃O₄ heterostructures with robust interface

Hexavalent chromium (Cr(VI)) in wastewater has been considered as a serious threat to human health and ecosystem. However, the rapid and efficient reduction of Cr(VI) to nontoxic Cr(III) on photocatalysts still remains a challenge, mainly suppressed by the high recombination rate of photogenerated carriers and weak adsorption ability of Cr(VI). Herein, an ultrafast photoreduction process of Cr(VI) is proposed on S-scheme In₂S₃/Sn₃O₄ heterojunctions (x-I-S) with robust interface. The results demonstrate that the robust interface would provide more accessible active sites, and the internal electric fields are modulated by S-scheme charge transfer, which greatly promote the separation of electron-hole pairs during the photoreduction process. In addition, the validated positive charges on In₂S₃/Sn₃O₄ surface contribute to the adsorption of Cr(VI), directly leading to the improvement of photoreduction activity of Cr(VI). The optimized photocatalyst (55-I-S) exhibits a stunning Cr(Ⅵ) reduction rate of 1.07 min⁻¹ after visible light irradiation for only 2.5 min, which is 15.3 and 6.7 times higher than that of pristine Sn₃O₄ (0.07 min⁻¹) and In₂S₃ (0.16 min⁻¹), respectively. This work provides creative inspiration for further improvement of heterojunction complexes in photocatalytic treatment of Cr(VI).