LAUSR

Abstract Herein, the synthesis, characterization, and water treatment application of reduced graphene oxide-manganese oxide-black cumin hybrid composite, rGO-MnO2/BC, has been reported. The rGO-MnO2/BC was synthesized by incorporating MnO2 particles into reduced graphene oxide functionalized with functional groups of black cumin seeds. The prepared rGO-MnO2/BC was highly amorphous, having large numbers of functional sites, and was evaluated for adsorptive removal of arsenic and methylene blue from their respective aqueous solutions. Adsorption capacities of rGO-MnO2/BC for methylene blue and arsenite were evaluated in batch manner under optimum conditions. 1.0 g/L dosage of rGO-MnO2/BC could remove approximately 99 % of methylene blue and arsenite from initial concentration of 10.0 and 1.0 mg/L, respectively, after 75 min at 7.0 pH, and 27 °C temperature. The sorption data was evaluated to propose the adsorption mechanism by fitting into isotherm and kinetic models. The process of methylene blue and arsenite sorption was proved to be exothermic and feasible based on thermodynamic parameters. The Freundlich isotherm was most suitable for arsenite sorption and both Langmuir and Freundlich isotherms were suitable for methylene blue sorption data. The sorption kinetics followed pseudo-second order relationship for both adsorbates. The exploration of thermodynamics, isotherms, and kinetics parameters revealed physicochemical sorption mechanisms for both adsorbates onto rGO-MnO2/BC surface. The Langmuir sorption capacity of rGO-MnO2/BC for methylene blue and arsenite were found to be 232.5 and 14.7  mg/g, respectively, at 27 °C. The rGO-MnO2/BC is easy to prepare and is low-cost material, and showed high adsorption capacity as compared to the other reported adsorbents. Therefore, the application of rGO-MnO2/BC will be beneficial for upcoming research on water treatment technologies.