Synthesis and characterization of xanthan gum-grafted poly(acrylic acid) (XG-g-PAA) hydrogel as supersorbent for the remediation of textile dyes form aqueous media; kinetic, isotherm and thermodynamic insights

Abstract The uncontrolled discharge of textile dyes such as Pollen Yellow G (PY-G) and Nile Blue A (NB-A) into aquatic systems poses serious environmental and health risks due to their toxicity, persistence, and resistance to biodegradation. In this study, xanthan gum-grafted poly(acrylic acid) (XG-g-PAA) hydrogel was successfully synthesized and evaluated as an efficient adsorbent for dye removal using batch adsorption experiments. The hydrogel was characterized by SEM, EDX, FTIR, TGA, and BET/BJH analyses, confirming a rough, highly porous, and sponge-like morphology with abundant active sites and good thermal stability up to 250 °C, which are favorable for adsorption applications. Under optimized conditions of contact time 60 min, adsorbent dose 0.01 g, initial dye concentration 250 mg/L, temperature 298 K, and pH 6 (PY-G) and 8 (NB-A), the adsorption process exhibited excellent performance. Kinetic analysis showed that the adsorption followed the pseudo-second-order model with R2 > 0.99, indicating chemisorption as the dominant mechanism, while equilibrium data were best fitted to the Langmuir isotherm, yielding maximum adsorption capacities of 327 mg/g for PY-G and 636 mg/g for NB-A. Thermodynamic parameters further supported the adsorption behavior, where Δ H ° values of 9.396 and 6.450 kJ/mol and Δ S ° values of 31.32 and 40.53 J/mol. K were obtained for PY-G and NB-A, respectively, while Δ G ° values decreased from (−220.06 to −1,032.7 J/mol) for PY-G dye and from (−5,422.41 to −7,043.31 J/mol) for NB-A with increasing temperature (293–333 K), confirming that the adsorption process is spontaneous, endothermic, and entropy-driven, consistent with previously reported xanthan-based hydrogel systems showing high adsorption capacities and Langmuir behavior. Furthermore, the hydrogel demonstrated good reusability with only a slight reduction in efficiency after multiple adsorption–desorption cycles. Overall, the results indicate that XG-g-PAA hydrogel is a highly effective, recyclable, and eco-friendly adsorbent for the removal of hazardous dyes from wastewater.