Mn/O co-doped Bi2S3 bimetal oxysulfide catalyst for highly efficient reduction of organic and hexavalent chromium pollutants in the dark

Mn and O co-doped Bi2S3 (labeled as BiMnOS) catalyst was synthesized using different amounts of Mn precursor (MnCl2.4H2O) by a simple and feasible method and characterized by various techniques. The doped Mn and O improve the energy band structure and morphology, reduce the charge transfer resistance, increase the electrochemically active surface sites, and the heterovalent Mn3+/Mn2+ states in Mn/O-Bi2S3 enhances the electron lifetime and facilitates fast electron transfer, which accelerates the pollutants reduction reaction. The BiMnOS-3 at n(Mn): n(Bi): n(C2H5NS) = 4: 1: 4 has the best-reducing properties. 10 mg BiMnOS-3 ultimately reduced the 20 ppm 100 mL 4-aminophenol (4-NP) solution in the presence of NaBH4 within 14 min, and the reduction rate constant of 0.3514 min-1 was 12.5 times that of BiOS and 11.7 times that of MnOS. The reduction reactions of methyl orange (MO), methylene blue (MB), Rhodamine B (RhB), and Cr (VI) were also completed within 8, 10, 28, and 24 min, respectively. The catalytic activity of BiMnOS-3 remained above 90.6% after 6 repeated tests for the reduction of 4-NP, which showed good cycling stability. Therefore, this study verified that the suitable ratio of the metal precursors plays a vital role in designing novel, efficient, and synergistically defect-attired bimetal oxysulfide catalysts.