Synthesis of a novel MnO2@carbon nanotubes-graphene hybrid catalyst (MnO2@CNT-G) for catalytic oxidation of basic red 18 dye (BR18)

In this paper, a hierarchical graphene-based MnO2 coated carbon nanotubes as a hybrid catalyst (MnO2@CNT-G) was fabricated from gamma-MnO2@CNT. Effect of calcination temperature on its surface features and catalytic activity was investigated and characterized by field-emission scanning electron microscope (FE-SEM) combined with energy dispersive spectroscopy (EDS), high-resolution transmission electron microscope (HR-TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Brunauer-Emmett-Teller surface area (BET). FE-SEM and EDS analyses showed the formation of nanoflakes from MnO2@CNT supported on graphene nanosheets with decreasing in the weight percentage of Mn species from 20.3% to 9.00% and 8.20% upon calcination at 400 and 600 degrees C, respectively. Also with increasing temperature, a considerable decrease in the total porosity was taken place. The catalytic performance of the prepared hybrid was examined through catalytic wet peroxide oxidation method for studying the removal of a basic red 18 (BR18) dye from aqueous solution by varying the temperature and initial dye concentration at the optimum pH. The catalytic performance of prepared MnO2@CNT-G hybrid was compared with that of gamma-MnO2@CNT and found that MnO2@CNT-G hybrid had superior catalytic activity. Therefore, the combination of MnO2 with graphene beside the highest surface area in MnO2@CNT-G could accelerate the decomposition of a RB18 dye in short time. Reusability studies showed that the prepared hybrid had high very good decolorization performance through three consecutive catalytic wet peroxide processes within 30 min. (C) 2017 Published by Elsevier Ltd.