Structure and Performance of Bentonite-Enhanced Superabsorbent Gels for Water Absorption and Methylene Blue Adsorption

To address the limitations of conventional superabsorbent polymers in complex aqueous environments, a novel ternary composite gel (BT-SAP) based on xanthan gum, poly(acrylic acid-co-acrylamide), and bentonite was synthesized via a facile one-pot polymerization. Characterization confirmed the formation of a stable organic–inorganic hybrid three-dimensional network. The gel demonstrated outstanding comprehensive performance: a maximum water absorption capacity of 378.6 g/g; good adaptability to various pH levels, salt ions, and real water bodies; and rapid absorption kinetics and reusable potential over multiple cycles. Simultaneously, it exhibited a high adsorption capacity of 181.3 mg/g for methylene blue. The adsorption isotherm followed the Freundlich model, indicating adsorption on a heterogeneous surface. Kinetic studies revealed that the process was best described by the pseudo-second-order model, suggesting chemisorption as the rate-controlling step. XPS analysis further elucidated that the adsorption primarily occurred through the synergistic effect of electrostatic attraction from carboxyl groups and hydrogen bonding from amide/hydroxyl groups within the gel. This work provides a new strategy for developing smart materials integrating efficient water absorption and dye removal functionalities.