Adsorption of Th(IV) ions from aqueous solutions by ZnO functionalized graphene oxide

Graphene oxide (GO) and zinc oxide (ZnO) were synthesized via the Tour' and sol-gel methods, respectively. Adsorption potentials of Th(IV) ions were investigated with the functionalization of GO with ZnO nanoparticles (GO-ZnO) and compared with the GO. Studies concerning factors affecting the adsorption process, kinetics, adsorption iso-therms, and thermodynamic properties were carried out. In this study, the optimum pH for the adsorption of Th(IV) ions is 3.0, and quickly reaching equilibrium is an indication of the high efficacy of the sorbent. A pseudo-second order adsorption model fits the kinetic data well. Experimental results were compared with Langmuir, Freundlich, and Dubinin-Radushkevich isotherm models. These results show that the Langmuir model fits the data well. Measured thermodynamic parameters, Gibbs free energy change (?G degrees), enthalpy change (?H degrees), and entropy change (?S degrees) indicate that the adsorption of Th(IV) on GO-ZnO is spontaneous and endothermic in nature. According to the linear fit in the Langmuir isotherm model, the maximum adsorption ca-pacity of GO and GO-ZnO at 298 K occurs at 109.89 mg/g and 243.90 mg/g, respectively. The results show that decoration with ZnO nanoparticles is a good method to improve the adsorption capacity of GO for Th(IV) removal.