Mn₃ O₄ /N-Doped Graphite Catalysts from Wastewater for the Degradation of Methylene Blue

The accelerating research interest in graphene involving the use of Hummers method has generated non-negligible amount of wastewater containing residual graphite as well as Mn²⁺ . In this paper, we report the first example of using this wastewater as precursor to prepare Mn₃ O₄ /N-doped graphite (NG) composites through a facile solvothermal process. The mass fraction of Mn₃ O₄ in the composites was manipulated by adding various amounts of extra Mn²⁺ . The conversion of Mn²⁺ to Mn₃ O₄ nanoparticles and the N atoms doping were achieved by adding hydrazine hydrate and ammonia into the system. The as-obtained Mn₃ O₄ /NG composites were well characterized by SEM, TEM, EDS, Raman, XPS, TGA, XRD and N₂ adsorption-desorption experiments and showed excellent catalytic performances as well as stability in the degradation of a model organic pollutant methylene blue (MB). Theoretical simulation was also carried out to illustrate the structural features of the Mn₃ O₄ /NG composite. This work presents a novel idea of designing functional materials from waste precursors.