The role of magnetite/graphene oxide nano-composite as a high-efficiency adsorbent for removal of phenazopyridine residues from water samples, an experimental/theoretical investigation

Presence of phenazopyridine residues in water resources can be harmful to human body, hence it is very important to remove them from aqueous media. In this study, a magnetic nano-composite adsorbent, i.e. reduced graphene-iron oxide (rGO-Fe3O4) was synthesized and used for removal of phenazopyridine residues from wastewater samples. Experimental parameters influencing adsorption process were optimized, and results showed a sorption capacity of 14.064 mg g(-1) at pH=6.0 for phenazopyridine. Under the best experimental condition, rGO-Fe3O4 nanocomposite showed an efficiency of 91.4% for removal of phenazopyridine in aqueous solution. Adsorption of phenazopyridine on flat and parallel oxygen and iron-terminated rGO-Fe3O4 surfaces was studied by density functional theory calculations. It was found that, in case of both oxygen and iron-terminated rGO-Fe3O4 surfaces, phenazopyridine prefers to interact with aromatic ring and amino flat to oxygen-terminated rGO-Fe3O4 surface, as opposed to iron-terminated sites due to enhanced charge migration at the interface. Negative adsorption energy revealed that formation of phenazopyridine@rGO-Fe3O4 is an exothermic process, confirming stability of these species. (C) 2019 Elsevier B.V. All rights reserved.