Microwave-assisted hydrothermal synthesis of Mn3O4/reduced graphene oxide composites for efficiently catalytic reduction of 4-nitrophenol in wastewater

We designed a microwave-assisted hydrothermal method to synthesize Mn3O4/reduced graphene oxide (Mn3O4/RGO) composites for catalytic reduction of 4-nitrophenol (4-NP), in which Mn3O4 nanoparticles were uniformly anchored on the surface of RGO. The catalytic activity for 4-NP reduction was directly dependent on the RGO-to-Mn3O4 mass ratio and the amount of the catalyst. With RGO-to-Mn3O4 ratio of 3/1 (G3M1), significantly enhanced activity of the Mn3O4/RGO composites was achieved in comparison to their individual components, which could be attributed to the synergistic effect between Mn3O4 and RGO. As the amount of G3M1 was 19 mu g/ml, the normalized rate constant reached 556/s/g, which could be compatible to some noble metal catalysts. Considering 4-NP as a serious pollutant in industrial wastewater, the effects of various inorganic and organic compounds were further tested. It was found that these compounds had an inessential impact on the catalytic activity. Also, the composites could be conveniently handled for filtering and catalyzing and recycling with an excellent catalytic stability even in stimulated wastewater, which was of practical value for achieving regioselective oxidation into useful products. (C) 2018 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.