Adsorption Mechanism of Bentonite with Dispersed Chitosan for Cadmium Ions

Chitosan was dispersed on bentonite for the preparation of a Cd 2+ adsorbent. The adsorption process followed a Freundlich isotherm, and the experimental adsorption capacity was determined. For understanding the adsorption mechanism, the pristine and Cd‐doped adsorbents were analyzed by Fourier transform infrared and X‐ray photoelectron spectroscopy. A red shift of the band corresponding to amino groups was observed, while the Cd 3d binding energy declined. Furthermore, density functional theory calculation results indicated that Cd 2+ bonded with amino and hydroxyl groups in chitosan. The zeta potential of the adsorbent was lower than that of the support bentonite, improving the electrostatic affinity for Cd 2+ . The synergy between electrostatic and coordination interactions contributed to the adsorption capacity.