Ultrahigh Adsorption Capacity of Acrylic Acid-Grafted Xanthan Gum Hydrogels for Rhodamine B from Aqueous Solution

Rhodamine B (RhB) is considered as a potential source of water pollution because it is harmful to the environment and humans, and thus, it should be removed from the water system. Hydrogels derived from polysaccharides have been received much attention for dye adsorption. In this study, acrylic acid (AAc)-grafted xanthan gum hydrogel (XGH) was synthesized by electron beam irradiation. The effects of AAc concentration and the adsorbed dose on the gel fraction and swelling ratio were studied. The XGH hydrogel structure was characterized by FTIR and SEM analyses. As a result, the sample with 75% gel fraction was selected to investigate the adsorption behaviors toward RhB. The adsorption kinetic data were in good agreement with pseudo-second-order mode. The adsorption isotherms fitted well with the Langmuir equation with an ultrahigh maximum adsorption capacity of 2612.12 to 2777.77 mg/g at 293 to 323 K, which is a significant breakthrough in RhB uptake. Na₂CO₃ and HCl were used to regenerate the RhB-loaded XGH. The removal efficiency was found to be nearly unchanged after five adsorption–desorption cycles. Finally, the selectivity of XGH toward cationic/anionic mixing dyes was investigated.