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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 isotherms, 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 (ΔG°), enthalpy change (ΔH°), and entropy change (ΔS°) 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 capacity 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.

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Graphene oxide (GO) and reduced graphene oxide (rGO) are efficient and low-cost adsorbent carbon-based materials for removing Pb(II) ions from wastewater. This study focuses on the synthesizing GO and rGO by green methods with Tour approach and reduction with L-ascorbic acid, respectively and were characterized by X-ray diffraction, Fourier transform infra-red spectroscopy, Raman spectroscopy and scanning electron microscopy with energy dispersive X-ray spectroscopy. The prepared GO and rGO were used to adsorb Pb(II) ions from aqueous solutions. From the adsorption isotherms, the maximum adsorption capacities of Pb(II) ions on GO and rGO calculated from the Langmuir (117.6 mg/g) and Dubinin–Radushkevich isotherms (138.5 mg/g), respectively, higher than reported studies in the literature. By thermodynamic investigation, it was found that the adsorption of Pb(II) ions on GO and rGO was spontaneous and exothermic.