Synthesis and application of recyclable magnetic freeze-dried graphene oxide nanocomposite as a high capacity adsorbent for cationic dye adsorption

In this study, magnetic graphene oxide freeze-dried (MGO-FD) nanocomposite was synthesized using a simple hydrothermal method. It was applied for removal of RhB (a cationic dye) from aqueous solutions. In order to find the optimum conditions, the effects of some parameters such as content of GO-FD in nanocomposite, adsorbent value, pH, and contact time on the adsorption efficiency were investigated. Pseudo-first-order and pseudo-second-order kinetics models, Langmuir and Freundlich isotherm models, and thermodynamics of adsorption were also studied. It was found that adsorption kinetics was best described by the pseudo-second-order model and adsorption equilibrium data were well fitted to the Langmuir isotherm model with the maximum monolayer adsorption capacity of 126.58 mg/g. The estimated values of thermodynamics parameters such as ΔG°, ΔH°, and ΔS° indicated that the sorption process has an endothermic and spontaneous nature. The values of ΔG° approved that the adsorption of RhB on MGO-FD is physisorption. The synthesized adsorbent with a high surface area (720.09 m2/g) and suitable adsorption capacity (113.92 m2/g) presents a high efficiency adsorbent in removal of cationic dyes from water. Reusability of MGO-FD was also evaluated and results showed that the adsorption capability of the adsorbent is not significantly changed after eight cycles and can be used as economical adsorbent for cationic dyes.