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 γ-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 °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 γ-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.