Equilibrium and kinetics studies for the adsorption of Ni²⁺ and Fe³⁺ ions from aqueous solution by graphene oxide

In this study, the adsorption of Ni²⁺ and Fe³⁺ metal ions from aqueous solutions onto graphene oxide (GO) have been explored. The effects of various experimental factors such as pH of the solution, initial metal ion concentration and temperature were evaluated. The kinetic, equilibrium and thermodynamic studies were also investigated. The adsorption rate data were analyzed using the pseudo-first-order kinetic model, the pseudo-second-order kinetic model and the intraparticle diffusion model. Kinetic studies indicate that the adsorption of both ions follows the pseudo-second-order kinetics. The isotherms of adsorption data were analyzed by adsorption isotherm models such as Langmuir and Freundlich. Equilibrium data fitted well with the Langmuir model. The maximum adsorption capacities of Ni²⁺ and Fe³⁺ onto GO were 35.6 and 27.3 mg g⁻¹, respectively. In addition, various thermodynamic parameters, such as enthalpy (ΔHO), entropy (ΔSO) and Gibbs free energy (ΔGO), were calculated.