Adsorption Mechanism of Xanthan Gum Based Hydrogel Adsorbent for the Removal of Cationic Methylene Blue from Aqueous Solutions

In this study a poly(2-(N-morpholinoethyl methacrylate) (Xg-PMEMA) hydrogel grafted with xanthan gum was prepared and used as a potential adsorbent to remove dyes from wastewater. Methylene blue (MB), a cationic dye, was chosen as a model to mimic dye-contaminated water because it is widely used in the textile industry. The micro-porous adsorbent was characterized by FT-IR, FESEM, and zero point of charge (pHzpc) analyses. Adsorption parameters, such as solution pH, adsorbent dosage, contact time, and initial dye concentration, that affect the removal of MB from aqueous solutions were studied. The pH of the solution was found to have a significant effect on adsorption, with maximum removal occurring at a pH of 11.0. The pHzpc of the hydrogel adsorbent Xg-PMEMA was determined to be 7.8. The adsorption process followed the Freundlich isotherm model and the pseudo-second-order kinetic model, suggesting that the multilayer adsorption of MB occurred by a chemisorption mechanism on the heterogeneous surfaces of Xg-PMEMA. In addition, Xg-PMEMA exhibited good reusability after four successive adsorption/desorption cycles, indicating that the material could be used as an effective adsorbent for the removal of cationic dyes from wastewater.