Adsorption characteristics and behavior of a graphene oxide–Al₁₃ composite for cadmium ion removal from aqueous solutions

Graphene oxide–Al₁₃ (GO–Al₁₃) composites were synthesized by a hydrolysis method on the basis of graphite oxide and were characterized by XRD, FT-IR and SEM. The adsorption of Cd²⁺ onto the GO–Al₁₃ composite was investigated as a function of pH, temperature and adsorbent dose. Langmuir and Freundlich models were employed to describe the adsorption equilibrium. The adsorption kinetic was investigated by the pseudo-first-order, pseudo-second-order and the intraparticle diffusion models. The results showed that the GO–Al₁₃ composite has excellent adsorption capacity, and the Cd²⁺ removal rate could reach 98.92% at the optimum conditions. The adsorption isotherm fitted the Langmuir model well and the adsorption process was found to fit the pseudo-second-order rate equation. Also, the thermodynamic parameters including free energy (ΔG^⊖), enthalpy (ΔH^⊖) and entropy (ΔS^⊖) of adsorption were calculated. These experimental data suggested that the adsorption of Cd²⁺ on GO–Al₁₃ composite was an endothermic and spontaneous process.