Fe-Ni-Doped Graphene Oxide for Uranium Removal—Kinetics and Equilibrium Studies

Abstract

In this study, graphene oxide (GO) was prepared using modified Hummer’s method and doped with Fe-Ni nanoparticles. Morphological characterization of the Fe-Ni nanoparticles showed flake-like structure correlating to taenite phase, while Raman spectroscopy suggested that graphene oxide was multi-layered. Batch adsorption experiments were performed to determine the effect of solution pH, initial uranium (VI) concentration, adsorbent dosage, contact time, and specific anions (SO42− and NO32−) on the adsorption of U (VI). Solution pH had significant effect on U (VI) sorption on Fe-Ni/GO, with maximum removal of 98.4% at pH 4, while it was 98% at pH 8 for GO. Sorption kinetics revealed fast adsorption within 15 min. The kinetic and equilibrium data was evaluated using pseudo-first-order, pseudo-second-order, Elovich, Langmuir, Freundlich, and Temkin models. The mechanism of U (VI) sorption appeared to be a combination of chemisorption and possible pore diffusion of the U (VI) moieties to the porous structure of GO and Fe-Ni/GO. Overall, Fe-Ni/GO was a better adsorbent than GO with higher sorption capacities. U (VI) sorption on GO and Fe-Ni/GO followed pseudo-second-order reaction kinetics (R2 > 0.99). Good fit to Langmuir isotherm model (R2 > 0.98) suggested favorable monolayer adsorption, with a maximum U (VI) adsorption capacity on Fe-Ni/GO to be 25.64 mg/g. Moderate to insignificant effect of specific anions even at high concentrations on U (VI) removal capacities makes Fe-Ni/GO an excellent candidate.