Supercritical synthesis of a magnetite-reduced graphene oxide hybrid with enhanced adsorption properties toward cobalt & strontium ions

Abstract

The current study presents a supercritical synthesis of magnetite-reduced graphene oxide (M-RGO) in methanol media, in which Fe₃O₄ nanoparticles are simultaneously formed, surface modified and decorated on the surface of the reduced graphene oxide. Simulations using density functional theory, which were performed using the M06-2x/cc-pVDZ level of theory, indicate that upon adsorption of a Fe₃O₄ cluster on the graphene, the overall charge on the graphene surface becomes about −0.0236e, indicating charge transfer from the Fe₃O₄ cluster to the graphene surface. Instrumental and chemical analyses exhibited the formation of strong bonds between Fe₃O₄ and graphene, through C–O–Fe and C–Fe bridges. Based on this data the study puts forward a formation mechanism for M-RGO. The adsorption behavior of the M-RGO towards Co²⁺ and Sr²⁺ ions demonstrated an appreciably higher uptake capacity than that of magnetite-graphene oxide (M-GO), a zero zeta potential point at pH ≈ 2, endothermic and spontaneous adsorption, and fast kinetics that was controlled by the chemical reaction between the ions and the surface active sites of the Fe₃O₄ nanoparticles. The material also showed good reusability, quick elution by 0.5 mol dm⁻³ HCl, and most importantly, simple separation from the solution using a magnet. Overall, the M-RGO appears to be a promising alternative for the current magnetite-graphene oxide hybrids in the adsorption of heavy metal ions.