Synergistic effect of zeolite/chitosan in the removal of fluoride from aqueous solution

Today, fluoride represents one of the most often found, and resilient, pollutants threatening the health of millions of people around the globe. The use of biosorbents is an interesting alternative technique for the removal of fluorine-ions. Chitosan is a natural biopolymer with surface groups capable of removing fluorine; however, their lack of mechanical stability restricts its application. In the present work, we proposed that such limitations can be overcame by forming a composite with zeolite (ZCC). A proper zeolite-to-chitosan ration must be kept to prevent a collapse of the material's capacity. Two ZCCs at ratios of 1:1 and 1:3 were formed and tested for the removal of fluoride from aqueous solution. The composites were characterized by Electron Microscopy, FT-IR, N₂ physisorption, and potentiometric titration techniques. During fluoride adsorption studies, the effects of pH and temperature were analysed and thermodynamic parameters for adsorption were calculated. The results demonstrated that there is a chemical interaction between the zeolite and chitosan components leading to a superior adsorption performance than if there was a simple physical mixture of the precursors. Maximum adsorption capacities were reached using the composite material with the lowest chitosan content due to reduced constriction of the zeolite pores and a better dispersion of overall the adsorption sites. Both pH and temperature had a significant, and negative, impact on the adsorption; these effects were discussed. The present work represents an advance in the development of functional biocomposites for the removal of pollutants from aqueous solutions.