SnS₂-In₂S₃ p-n heterostructures with enhanced Cr⁶⁺ reduction under visible-light irradiation

We present one-pot hydrothemal syntheis of SnS₂-In₂S₃ p-n heterostructures for photocatalytic reduction of Cr⁶⁺ to Cr³⁺. The conduction bands of In₂S₃ and SnS₂ serve as the photogenerated electron donors and acceptors, respectively, forming a p-n junction band alignment improving the photogenerated charge separation efficiency. Through a detailed investigation of photocurrent spectra, photoluminescence spectra and electrochemical impedance, the heterojunction formation is shown to enhance the photogenerated charge separation and transport properties. In addition, the analysis of 5,5-Dimethyl-1-pyrroline N-oxide (DMPO) spin trapping electron spin resonance (ESR) spectra and band structure further testify the p-n junction of the composite catalyst that could accelerate the electron transport and change the pathway of photocatalytic process toward Cr⁶⁺ reduction. Furthermore, SnS₂-In₂S₃ heterojunction photocatalyst achieved 3 times and 67 times higher efficiency than pure In₂S₃ and SnS₂ photocatalysts under visible light toward Cr⁶⁺ reduction. Moreover, the SnS₂-In₂S₃ p-n heterojunction photocatalyst demonstrates Cr⁶⁺ removal in a weak alkaline solution, breaking through the challenge of Cr⁶⁺ reduction in an alkaline environment.