Effective removal of methyl violet dye by montmorillonite-incorporated carboxymethyl cellulose-g-poly(methacrylic acid-co-acrylamide) nanocomposite hydrogel

A novel nanocomposite hydrogel adsorbent, carboxymethyl cellulose-grafted poly(methacrylic acid-co-acrylamide) containing montmorillonite (designated as CMC-g-Poly(MAA-co-AAM)/MMT), was synthesized via free radical polymerization and evaluated for the removal of methyl violet dye from aqueous solutions. Thermogravimetric analysis revealed that the incorporation of a small amount of montmorillonite (2.5 wt. %) into the hydrogel matrix significantly improved the thermal stability of the nanocomposite. Furthermore, experimental results indicated that the presence of MMT nanoparticles enhanced the adsorption efficiency at temperatures above 35°C. The influence of various operational parameters, including pH, temperature, contact time, initial dye concentration, and adsorbent dosage, was systematically investigated. Maximum MV removal was achieved at pH 10, 25 °C, a contact time of 30 min, an initial dye concentration of 10 mg/L, and an adsorbent dose of 1 g/L, yielding removal efficiencies of 97.20 and 98.19% for CMC-g-Poly(MAA-co-AAM)/MMT-2.5 wt. % and CMC-g-Poly(MAA-co-AAM), respectively. Kinetic studies demonstrated that the adsorption process followed a pseudo-first-order model. In addition, isotherm studies revealed that the experimental data were well described by the Freundlich isotherm model. The adsorbents also exhibited good reusability in a KCl/ethanol–water medium, retaining approximately 93% of their initial adsorption capacity after five consecutive adsorption–desorption cycles.