Photocatalytic reduction of Cr(vi) on a series of defective MnmIn2S3+m (m = 1–5, integer)

Abstract

A series of defective Mn_mIn₂S_3+m (m = 1–5, integer) microflowers were successfully synthesized via a facile hydrothermal method and characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). These solid solution photocatalysts have similar cubic phase crystal structures. The results of electron paramagnetic resonance (EPR) spectra showed that the concentration of sulfur vacancy (V_S) increased with the increase in Mn/In atomic ratio. The photocatalytic performance of the prepared Mn_mIn₂S_3+m was evaluated by the reduction of Cr(VI) in aqueous solution under simulated sunlight, in which Mn₄In₂S₇ showed the highest photocatalytic activity. 40 ppm K₂Cr₂O₇(VI) was almost completely reduced to Cr(III) within 60 minutes. Additionally, the photocatalytic mechanism was investigated and it was demonstrated that the appropriate concentration of V_S could accelerate the carrier separation and transfer of Mn₄In₂S₇, so as to improve the photocatalysis efficiency. This work will expand the application of solid solution photocatalysts in the future.