Effects of Prepared Gadolinium Oxide-Doped Chitosan/PVA Hydrogels on Congo Red Removal in Water

Chitosan/polyvinyl alcohol/Gd 2 O 3 (Ch-PVA-Gd) hydrogels were produced by freeze–thaw method for the adsorption of Congo red (CR) dye. The adsorbent was characterized using FT-IR, XRD, SEM–EDX, BET, and Zetasizer instruments. On the adsorption, the effects of the Gd 2 O 3 doping ratio, pH, starting concentration, and adsorbent quantity were studied. The adsorption experiments removed more than 99% of Congo red. The Langmuir and Freundlich isotherm models were compared, and the Langmuir isotherm was found to be the most compatible. The maximum adsorption was calculated to be 312.5 mg/g using the Langmuir isotherm. The pseudo-second-order kinetic model was found to be the best fit for adsorption kinetics.