Synthesis and Characterization of Nickel Manganese Oxysulfide (NiMnOS) Catalyst for Reduction of Methylene Blue Dye in Aqueous Solution

Abstract

Environmentally toxic organic dyes discharged from industries as wastes are a great public concern due to their harsh effect on humans and aquatic organisms even at low concentrations. As a result, effective removal and/or reduction of these toxic substances is very critical. Bimetal oxysulfide catalysts have been widely used for reduction of organic dyes due to their facile preparation technique and effective catalytic performance. However, toxic hydrazine is used as a reducing agent during the preparation process. In this study, noble metal free flower-like nickel manganese oxysulfide (NiMnOS) catalysts were produced via a facile and environmentally friendly approach. The NiMnOS catalysts were synthesized by varying Ni: Mn molar ratios (Ni: Mn = 25:75, 50:50, 75:25 and assigned as NiMnOS 25, NiMnOS-50, and NiMnOS-75, respectively) at low synthesis temperature of 90 °C in a water bath. The bare NiOS and MnOS were also prepared with the same technique for comparison. The prepared samples were characterized using X-ray Diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), Scanning electron microscope (SEM), Energy dispersive X-ray spectroscopy (EDS), Fourier transforms infrared spectroscopy (FTIR), and UV–Vis spectroscopy to determine phase purity, chemical binding, and ionization state, the morphology and composition of the particles, functional groups, and optical property of samples, respectively. The catalytic activity of the samples was investigated through the reduction of methylene blue (MB) dye in the presence of NaBH4 in an aqueous solution. The NiMnOS-25 catalyst exhibited excellent performance and reduced 98.46% of 10 ppm methylene blue (MB) solution 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 solution, respectively, within 7 min. The catalytic reduction activity could be mainly attributed to the synergistic effect between the two metals (Ni and Mn), more exposed active sites, and the optimum amount of Mn in the NiMnOS sample. The recyclability of catalyst was performed for four runs and good stability and durability were obtained. Finally, a possible mechanism for methylene blue (MB) dye reduction reaction was proposed. Therefore, NiMnOS could be a good candidate for the reduction of organic dyes in environmental remediation.Environmentally Toxic Organic Dyes Discharged From Industries As Wastes Are A Great Public Concern Due To Their Harsh Effect On Humans And Aquatic Organisms Even At Low Concentrations. As A Result, Effective Removal And/Or Reduction Of These Toxic Substances Is Very Critical. Bimetal Oxysulfide Catalysts Have Been Widely Used For Reduction Of Organic Dyes Due To Their Facile Preparation Technique And Effective Catalytic Performance. However, Toxic Hydrazine Is Used As A Reducing Agent During The Preparation Process. In This Study, Noble Metal Free Flower-Like Nickel Manganese Oxysulfide (Nimnos) Catalysts Were ProducedVia A Facile And Environmentally Friendly Approach. The Nimnos Catalysts Were Synthesized By Varying Ni: Mn Molar Ratios (Ni: Mn = 25:75, 50:50, 75:25 And Assigned As Nimnos 25, Nimnos-50, And Nimnos-75, Respectively) At Low Synthesis Temperature Of 90 ??C In A Water Bath. The Bare Nios And Mnos Were Also Prepared With The Same Technique For Comparison. The Prepared Samples Were Characterized Using X-Ray Diffractometer (Xrd),X-Ray Photoelectron Spectroscopy (Xps), Scanning Electron Microscope (Sem), Energy Dispersive X-Ray Spectroscopy (Eds), Fourier Transforms Infrared Spectroscopy (Ftir), And Uv?�?Vis Spectroscopy To Determine Phase Purity, Chemical Binding, And Ionization State, The Morphology And Composition Of The Particles, Functional Groups, And Optical Property Of Samples, Respectively. The Catalytic Activity Of The Samples Was Investigated Through The Reduction Of Methylene Blue (Mb) Dye In The Presence Of Nabh4 In An Aqueous Solution. The Nimnos-25 Catalyst Exhibited Excellent Performance And Reduced 98.46% Of 10 Ppm Methylene Blue (Mb) Solution 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 Solution, Respectively, Within 7 Min. The Catalytic Reduction Activity Could Be Mainly Attributed To The Synergistic Effect Between The Two Metals (Ni And Mn), More Exposed Active Sites, And The Optimum Amount Of Mn In The Nimnos Sample. The Recyclability Of Catalyst Was Performed For Four Runs And Good Stability And Durability Were Obtained. Finally, A Possible Mechanism For Methylene Blue (Mb) Dye Reduction Reaction Was Proposed. Therefore, Nimnos Could Be A Good Candidate For The Reduction Of Organic Dyes In Environmental Remediation.