Fabrication of GO–MnO₂ nanocomposite using hydrothermal process for cationic and anionic dyes adsorption: Kinetics, isotherm, and reusability

The presence of anionic and cationic dyes in wastewater has highlighted a great necessity to develop new and effective approaches for their simultaneous removal. Herein, graphene oxide-manganese dioxide (GO-MnO₂) nanocomposite was synthesized using a hydrothermal method to reduce pollution load of wastewater. In this stidy, synthesized material was utilized as adsorbent for the removal of cationic methylene blue (MB) and anionic methyl orange (MO) dyes from aqueous solution that act as model organic pollutants. The morphology, chemical structure, thermal stability, and other properties of the synthesized adsorbent were characterized using Field emmision scanning electron microscopy, Powder X-ray differaction, Raman spectroscopy, Fourier transform infrared spectra, Energy dispersive spectroscopy, Thermogravimetric analysis, and Brunauer-Emmett-Teller surface area techniques. The kinetics results showed the removal efficiency of 50.48% and 85.35% within the starting 5 min for both MO and MB, respectively, and fitted well to a pseudo-second-order kinetics model. The isotherms adsorption results fitted well to the Langmuir isotherm model, confirming the monolayer adsorption and give maximum adsorption capacities 149.253 and 178.253 mg/g for MO and MB, respectively. GO-MnO₂ showed a good reusability and gave > 90% removal efficiencies after seven continuous cycles. Lastly, the simultaneous adsorption performance of the adsorbent for both dyes ggave 100% removal efficiency. All these results give a direct visual impression of the fast kinetics efficiency and high adsorption capacity for real wastewater treatment application.