Synthesis and characterization of a bimetal nickel manganese oxysulfide (NiMnOS) catalyst for the reduction of methylene blue dye

Noble metal-free nickel manganese oxysulfide (NiMnOS) catalysts were successfully prepared via a facile and eco-friendly approach at a low synthesis temperature of 90 °C in a water bath. The catalysts were synthesized by varying Ni: Mn molar ratios such as 25:75, 50:50, 75:25 and abbreviated as NiMnOS-25, NiMnOS-50, and NiMnOS-75, respectively. The bare NiOS and MnOS were also prepared for comparison purposes. The characterizations of the prepared samples were conducted with different techniques, and the catalytic activity was investigated through the reduction of methylene blue (MB) dye in the presence of NaBH₄ in an aqueous solution. Among the prepared catalysts, NiMnOS-25 exhibited excellent performance and reduced 98.46% of MB within 5 min. However, NiOS, NiMnOS-50, NiMnOS-75, and MnOS were reduced 9.6%, 98.41%, 97.04%, and 6.40% of MB dye, respectively, within 7 min. The catalytic reduction activity could be mainly attributed to the synergistic effects of the metals (Ni and Mn), more exposed active sites. Therefore, the bimetal NiMnOS catalyst could be a promising candidate for the reduction of organic dyes in wastewater treatment technologies.