Application of Response Surface Methodology (RSM) in optimisation of fluoride removal by magnetic chitosan/graphene oxide composite: kinetics and isotherm study

Abstract

ABSTRACT The presence of fluoride ions is considered a threat to public health and the environment due to health challenges. Graphene, as an adsorbent with a porous structure and high surface area, has been used on a large scale to effectively remove organic and inorganic contaminants from aqueous media. Therefore, the present study aimed to use magnetic chitosan/graphene oxide (MCGO) composite in fluoride adsorption and study adsorption isotherms and kinetics. At first, a magnetic chitosan/graphene oxide compound was synthesised and its characteristics were determined by SEM, XRD and FTIR. Then, fluoride adsorption process experiments were performed by studying the effect of pH, contact time, adsorbent mass, and fluoride initial concentration. TheLangmuir, Freundlich, Temkin, and Dubinin and Radushkevich isotherm models were also studied to describe the equilibrium of the adsorbate between the solid and fluid phases, and the pseudo-first-order, pseudo-second-order, Intraparticle diffusion, and Elovich kinetic models were analyzed to investigate the adsorption behaviour. To evaluate the effect of each parameter, R software based on Response Surface Methodology (RSM) was used. All experiments were repeated three times and the average was considered as presented as the final results. The results showed that the maximum fluoride adsorption was at pH5. The equilibrium time was reported at 136 minutes and the maximum removal percentage obtained 91% in optimal conditions. Investigation of the isotherm and kinetics showed that the results of fluoride adsorption process were correlated with Langmuir isotherm model (R2 > 0.99) and Elovich kinetic model (R2 > 0.989), respectively. It can be concluded that theMCGOcomposite is an effective adsorbent for fluoride removal from water resources.