Optimization of Polyacrylamide/Sodium Alginate/Nanocellulose Hydrogel Composite Fabrication toward Malachite Green Removal

Textile dye wastewater harms ecosystems; toxic malachite green (MG) demands urgent removal. The polyacrylamide (PAM)/sodium alginate (SA)/cellulose nanocrystal (CNC) hydrogel with an interpenetrating polymer network (IPN) structure was synthesized. Through systematic optimization of key preparation parameters, the hydrogel achieved the best mechanical properties under the optimal conditions of 3 wt % CNC content, mol L–1 CaCl2 concentration, and 50 °C polymerization temperature, with a tensile strength of 264 kPa and an elongation at break as high as 1496%. In deionized water and 1 mol L–1 NaCl solution, the swelling ratios of PAM/SA/CNC were 847.58% and 1161.31%, respectively. Adsorption experiments showed that the PAM/SA/CNC hydrogel exhibited a maximum MG adsorption capacity of 1185.15 mg g–1 at 45 °C. Kinetic and isotherm analyses indicated that the adsorption process followed a pseudo-first-order kinetic model and a Langmuir isotherm model. ΔG0 of the adsorption process is −3.8 kJ mol–1, which confirms the spontaneity of the adsorption process. Notably, the hydrogel maintained over 50% removal efficiency after four adsorption–desorption cycles. The adsorption process was driven by electrostatic attraction, hydrogen bonding, and physical entrapment. The IPN hydrogel with high mechanical strength and adsorption capacity has great potential in environmental remediation and offers valuable insights for the design of next-generation adsorbents.