Mesoporous Nyssa sylvatica Gum-Based Hydrogel: Statistical Optimization and Evaluation for Dye Removal, Antibacterial Activity, and Phytotoxicity

This study reports the synthesis of an Nyssa sylvatica gum-based hydrogel [NS-g-poly(AA)] via free-radical polymerization for the treatment of malachite green (MG)-contaminated wastewater. The novelty of this study lies in the use of Nyssa sylvatica gum as a sustainable biopolymer backbone for hydrogel synthesis and the optimization of NS-g-poly(AA) using an RSM-CCD model to maximize swelling capacity. The statistical optimization resulted in a maximum swelling of 1125%. The synthesized hydrogel was characterized using FE-SEM, XRD, 1 H NMR, BET, FTIR, and TGA. BET results confirmed a mesoporous structure with an average pore diameter of 6.55 nm and surface area of 1.183 m2 g −1 . The adsorption performance of the prepared hydrogel was evaluated under varying conditions, including contact time, pH, adsorbent dose, initial dye concentration, and temperature. Optimal adsorption conditions were determined to be a contact time of 150 min, pH 7, an adsorbent dose of 60 mg L −1 , an initial dye concentration of 100 mg L −1 , and a temperature of 303.15 K. Under these conditions, the hydrogel exhibited a maximum removal of 98.39% and a maximum adsorption capacity of 512.82 mg g −1 . Kinetic studies revealed that the adsorption process follows a pseudo-second-order model, suggesting a chemisorption mechanism, while the equilibrium data were best described by the Langmuir isotherm, indicating monolayer adsorption of MG dye molecules on the NS-g-poly(AA) hydrogel. Thermodynamic studies confirmed that the adsorption process was spontaneous, exothermic, and thermodynamically favorable at lower temperatures. Based on experimental findings, the adsorption mechanism was mainly governed by electrostatic interactions, hydrogen bonding, and pore diffusion. Regeneration studies demonstrated that the hydrogel retained 80.60% of its adsorption efficiency after five adsorption-desorption cycles. In addition to adsorption, the prepared hydrogel exhibited antibacterial activity against both Gram-positive and Gram-negative bacteria, with the highest inhibition zone (27.33 mm) observed against Escherichia coli. Phytotoxicity assessment showed 100% seed germination in treated water, comparable to that in distilled water, indicating environmental safety. These results suggest that the synthesized hydrogel demonstrates strong potential as a sustainable, multifunctional material for wastewater applications involving dye removal, microbial control, and ecological safety.