Statistical Modeling and Taguchi optimization of malachite green dye adsorption onto SiO2 Nano-reinforced hydrogel network

A novel hydrogel was prepared by the free-radical co -polymerization of sodium alginate with acrylamide and crotonic acid, and the optimal feed concentrations of the reactants were determined statistically using the Taguchi method. A composite hydrogel was then obtained by incorporating SiO₂ nanoparticles into the polymeric network in order to increase the number of active surface sites and to improve the dye-removal rate. The hydrogel and its nanocomposite were characterized using TGA, TEM, FE-SEM–EDX, XRD, BET–BJH, and FTIR analyses. The materials were used to remove malachite green dye from aqueous solution. The maximum adsorption capacity reached 589.55 mg/g at 35 °C for an initial dye concentration of 600 ppm. The adsorption kinetics were best described by a pseudo-second-order model, while the equilibrium data were better fitted by the Langmuir and Temkin isotherm models. Thermodynamic analysis at 5, 15, 25 and 35 °C indicated that the adsorption is spontaneous and endothermic, and the values of ΔS, ΔH and ΔG are reported. The removal efficiency increased with both temperature and pH, and the composite retained a high adsorption performance even after four regeneration cycles using a NaOH wash step.