Facile Synthesis of Mn₃O₄–Reduced Graphene Oxide Hybrids for Catalytic Decomposition of Aqueous Organics

Abstract

Mn3O4-reduced graphene oxide (rGO) hybrids were synthesized, and their catalytic performance in heterogeneous activation of peroxymonosulfate (PMS) to oxidize a target pollutant, Orange II, in aqueous solutions was investigated. The surface morphology and structure of the Mn3O4-rGO hybrids were characterized by field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), powder X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA). Through an in situ chemical deposition and reduction, Mn3O4-rGO hybrids with Mn3O4 nanoparticles at an average size of 29.2 nm were produced. The catalytic activity in Orange II oxidative decomposition was evaluated in view of the effects of various processes, pH, PMS concentration, Orange II concentration, and temperature. The combination of Mn3O4 nanoparticles with graphene sheets leads to a much higher catalytic activity than that of pure Mn3O4 or rGO. Graphene was found to play an important role in Mn3O4 dispersion and decomposition of Orange II. Typically, 30 mg/L of Orange II could be completely oxidized in 120 min at 25 °C and 0.05 g/L of Mn3O4-rGO hybrids, showing a promising application of the catalyst in the oxidative degradation of aqueous organic pollutants. The efficiency of Orange II decomposition increased with increasing temperature (25-55 °C), pH (4.0-11.0), and PMS dosage (0.25-1.5 g/L), but it decreased with increasing initial Orange II concentration (30-90 mg/L). Mn3O4-rGO hybrids exhibited stable performance without losing activity after four successive runs.