Removal of malachite green dye from aqueous solutions using xanthan gum-grafted-poly(acrylamide-co-itaconic acid-co-acrylic acid)/TiO₂ nanocomposite hydrogel: kinetic, isotherm, and thermodynamic studies

Water pollution by synthetic dyes represents a serious environmental challenge, requiring efficient and sustainable treatment methods. This study develops a novel nanocomposite hydrogel based on xanthan gum grafted with poly(acrylamide-co-itaconic acid-co-acrylic acid) and reinforced with titanium dioxide nanoparticles (XG-g-P(AAm-IA-AAc)/TiO₂) for malachite green (MG) removal. The material was synthesized via free radical graft copolymerization and characterized by FT-IR, XRD, FE-SEM, TGA, and BET analyses, confirming successful grafting and anatase TiO₂ incorporation. Surface area increased markedly from 0.22 to 8.19 m² g⁻¹ after TiO₂ addition. Batch adsorption experiments achieved 99% MG removal under optimal conditions (0.05 g/10 mL, pH 8, 180 min, 200 mg L⁻¹, 25 °C), with a maximum capacity of 39.23 mg g⁻¹. Adsorption followed pseudo-second-order kinetics (R² = 0.9997) and fitted the Freundlich isotherm (R² = 0.9286), indicating multilayer adsorption on heterogeneous surfaces. Thermodynamic parameters revealed a spontaneous and endothermic process. The adsorbent showed good reusability, retaining 76.1% capacity after six cycles and over 90% stability after six months. Overall, this eco-friendly nanocomposite is a promising candidate for industrial wastewater treatment. Novel XG-g-P(AAm-IA-AAc)/TiO₂ nanocomposite hydrogel was synthesized via free radical graft copolymerization for malachite green removal. TiO₂ incorporation enhanced BET surface area by 37-fold (0.22 → 8.19 m²/g) and improved thermal stability. Maximum adsorption capacity of 39.23 mg g⁻¹ with 99% removal efficiency achieved under optimized conditions. Adsorption followed pseudo-second-order kinetics and Freundlich isotherm, indicating surface-controlled adsorption on heterogeneous surfaces. Excellent reusability (76.1% retention after 6 cycles) and storage stability (> 90% retention over 6 months) demonstrated.