Synthesis and characterization of ultrasound assisted graphene oxide-magnetite hybrid, and investigation of its adsorption properties for Sr(II) and Co(II) ions

Magnetite nanoparticles with a size distribution of 15-21 nm were synthesized and decorated onto surface of graphene oxide by ultrasound assisted precipitation. Size and size distribution of the obtained M-GO hybrid were appreciably finer than the hybrids prepared by stirring method. M-GO is a superparamagnetic material with saturation magnetization of 31 emu g(-1). The Langevin equation was successfully applied for estimation of size of Fe3O4 nanoparticles in M-GO hybrid, with maximum error of 17.5%. The study put forward a formation mechanism for M-GO, based on instrumental analyses. Adsorption isotherms of Sr2+ and Co2+ ions, which were fitted by Langmuir monolayer model, displayed two-fold higher capacity for Co2+ ions, presumably due to its similarity to Fe2+ (of Fe3O4 component). Uptake of both Co2+ and Sr2+ ions were endothermic, and spontaneous, however the former proceeded through inner-shell complex formation, while the latter took place via ion exchange mechanism. Rate of adsorption of Co2+ was faster, but for both ions, chemical reaction was the rate determining step. Sorption of Sr2+ and Co2+ ions greatly increased at pHs above 5, where (1) surface zeta potential changed its sign, and (2) deprotonating reactions at the surface became complete. (C) 2015 Elsevier B.V. All rights reserved.