Covalent bonding of MnO2 onto graphene aerogel forwards: Efficiently catalytic degradation of organic wastewater

Graphene/alpha-MnO2 nanocrystals hybrid aerogel (GMA) was designed for catalytic ozonation of rhodamine B (RhB) solution in this study. A novel method was proposed to synthesize this hybrid aerogel in an isopropanol-water system, in contrast to the conventional reaction of potassium permanganate with graphene aerogel, which destroyed the desired structure of graphene. Characterization of the synthesized GMA was carried out by XRD, SEM, TEM, Raman, and BET. It was found that GMA had a porous structure and the needle-like alpha-MnO2 nanocrystals were doped in the graphene aerogel uniformly. Based on the FTIR and XPS analysis, the alpha-MnO2 was found to covalently bond with graphene aerogel. The removal efficiency of both RhB and COD was found to be in the following order of Blank < GA < SMA (silica wool with nano MnO2 deposited on it)< GMA(I) < GMA(II) < GMA(III). The degradation rate constant (kappa) of RhB ozonation catalyzed by GMA was determined to be 1.2-2.3 times higher as compared with that by UV/Ozone. The enhanced catalytic activity of GMA could be attributed to the high dispersibility of the alpha-MnO2 nanocrystals on graphene and the abundant mesopores (r < 40 nm) in GMA. The higher electron cloud density of the Mn atoms, when supported by graphene aerogel, promoted the generation of HO center dot radicals, thereby resulting in better decomposition performance of GMA than UV/Ozone systems.