Adsorption of methyl violet dye from wastewater using poly(methacrylic acid-co-acrylamide)/bentonite nanocomposite hydrogels

In this study, nanocomposite hydrogels of poly(methacrylic acid-co-acrylamide) (Poly(MAA-co-AAm)) containing different weight percent bentonite clay nanoparticles (0, 5, 10, and 15 wt. %) were used to remove methyl violet (MV) dye. FTIR, SEM, TGA, and XRD were used to analyze the properties of adsorbents. Results showed that bentonite nanoparticles were successfully distributed in the hydrogel system. Bentonite nanoparticles at 10 wt. % gave the maximum MV dye adsorption efficiency. The highest adsorption was obtained at a pH of 5, an adsorbent dosage of 1.5 g/L, a temperature of 25 °C, a contact time of 60 min, and a pollutant concentration of 10 mg/L. In thermodynamics studies, a negative values of Gibbs free energy (ΔG°) indicating that the adsorption process was spontaneous. In addition, Poly(MAA-co-AAm) hydrogels and Poly(MAA-co-AAm)/bentonite nanocomposite hydrogels gave the adsorption enthalpy (ΔH°) of –61.24 and –36.14 kJ/mol witch shows that the adsorption process is exothermic in the temperature range 25–45 °C using both adsorbents. Langmuir isotherm model was successfully applied in describing the equilibrium behavior of the adsorption process. The kinetic study showed that the pseudo-second-order model was more successful in describing the kinetic behavior of the adsorption process than pseudo-first-order and Elovich models. Poly(methacrylic acid-co-acrylamide) and poly(methacrylic acid-co-acrylamide)/bentonite adsorbents gave the α parameter values of 0.4276 and 22.15 mg.(g.min)−1, respectively indicating the high adsorption capacity of these adsorbents.