Bentonite/Sesbania Gum Hydrogel for Effective Removal of Cationic Dyes: Network Structure Construction and the Role of Multiple Hydroxyl and Carboxyl Adsorption Sites

Effective hydrogel adsorbents are widely used in toxic dyes removal, but weak toughness and inferior adsorption performance limit their actual application. Herein, a dual-functionalized epoxy and amino groups hyperbranched polysiloxane (HPSi) cross-linker was initially developed, bentonite (BT) was incorporated with sesbania gum (SG), acrylic acid/acrylamide (AA/AAm) was utilized as monomers to synthesize hydrogel adsorbent H-SG/BT(AA/AAm) for the adsorption of methylene blue (MB) and malachite green (MG). Various characterization techniques, adsorption parameters test and mechanism analysis demonstrated that HPSi and BT endowed H-SG/BT(AA/AAm) with enhanced mechanical strength (tentative extensibility of 2645% and elastic recovery was over 90%). The hydroxyl of BT and SG was completely insert into the hydrogel then significantly enhanced the swelling and adsorption capacity. H-SG/BT(AA/AAm) exposed a promising adsorption capacity towards MB and MG with maximum adsorption capacity of 1226 mg/g and 783 mg/g. Kinetic and isotherm studies indicated that the adsorption of MB and MG onto H-SG/BT (AA/AAm) closely followed the pseudo-second-order kinetic model and Langmuir isotherm. The adsorption efficiency of H-SG/BT (AA/AAm) for MB and MG could still reach 80% after five adsorption–desorption cycles. Clearly, H-SG/BT(AA/AAm) composites can be effectively utilized as an eco-friendly adsorbent for dyes adsorption in aqueous environments.