Biofilm hydrogel derived from physical crosslinking (self-assembly) of xanthan gum and chitosan for removing Cd, Ni, and Cu from aqueous solution.

This study aimed to fabricate a series of biodegradable hydrogel films by gelating/physically crosslinking a blend of xanthan gum (XG) and chitosan (CS) in various combinations using a facile, green, and low cost solution casting technique. The adsorption of Cd, Cu and Ni by the XG/CS biofilm in aqueous solution was studied in batch experiments to determine how the pH of the solution, contact time, dosage of adsorbent, initial metal ion concentration and ionic strength affect its adsorption. A highly pH-dependent adsorption process was observed for three metal ions. A maximum amount of Cd, Ni, and Cu ions was adsorbable with 50 mg of the adsorbent at pH 6.0 for an initial metal concentration of 50 mg.L. An empirical pseudo-second-order model seems to fit the kinetic experimental data reasonably well. It was found that the Langmuir model correlated better with equilibrium isotherm when compared with the Freundlich model. For Cd, Ni, and Cu ions at 25 °C, the maximum monolayer adsorption capacity was 152.33, 144.79, and 139.71 mg.g, respectively. Furthermore, the biofilm was capable of regenerating, allowing metal ions to adsorb and desorb for five consecutive cycles. Therefore, the developed biodegradable film offers the potential for remediation of specified metal ions.