Development of a poly (acrylonitrile- <i>co</i> -styrene- <i>co</i> -styrene sulfonate) hydrogel for cationic dye removal: Preparation, characterization, and adsorption study

The development of effective, reusable adsorbent materials is urgently needed to address the growing problem of water contamination by chemical pollutants. In this study, a sulfonated terpolymer hydrogel was produced via radical polymerization and evaluated as an effective adsorbent for removing cationic dyes. The prepared terpolymer hydrogel was characterized by several techniques, and its adsorption performance was studied and compared with that of polyacrylonitrile (PAN). The adsorption process was best described by the Langmuir model, as indicated by equilibrium studies, which showed a maximum adsorption capacity of 1118.7 mg∙g -1 . According to the kinetic analysis, the pseudo-second order model was the most fitting, and equilibrium was reached within 5-30 min. Spontaneous and endothermic adsorption were confirmed by the thermodynamic parameters (ΔG° = -12.34 to -9.53 kJ∙mol -1 , ΔH° = 73.76 kJ∙mol -1 , ΔS° = 205.32 Jmol -1 K -1 ). Fourier transform infrared (FTIR) validated the participation of functional groups via electrostatic attraction, dipole-ion interactions, and π–π stacking. Tests for reusability showed remarkable consistency, with efficiency remaining above 99% even after six cycles. These findings demonstrate that the sulfonated terpolymer hydrogel is a highly promising adsorbent for the practical treatment of wastewater containing harmful cationic dyes because it is rapid, effective, and reusable.