Eco-friendly Chitosan Condensation Adduct Resins for Removal of Toxic Silver Ions from Aqueous Medium

Abstract

A simple and economical method for modifying chitosan based on non-catalytic direct condensation reaction between chitosan and phenolic acids “Gallic and Caffeic acids” has been developed to produce condensation adduct resins RI and RII. The resins structure and morphology were confirmed by physical and chemical tools such as FTIR, SEM, EDX, XRD elemental analysis, TGA, water regain, dissociation in acidic medium, and point of zero charge. The new resins were evaluated as silver ions adsorbents. Factors affecting adsorption, as well as kinetics, equilibrium, and thermal properties of adsorption, were studied using conventional equations. The new resins showed more efficient removal of toxic silver ions from the aqueous medium than parent chitosan polymer. The maximum adsorption capacity amounted to 67.5, 300, and 278 mg/g with removal efficiency reaching 22.5%, 100%, and 92.66% for chitosan, RI, and RII; respectively at pH 6.5 and initial silver concentration 300 mg/L. The new resins showed spontaneous chemisorption toward silver ions with exothermic nature for RI, and endothermic nature for RII. The new condensation adduct resins showed good re-use ability reaching 83% and 67% for RI and RII; respectively, by using 0.01 M nitric acid solution.