Novel magnetic polyvinyl alcohol/laponite RD nanocomposite hydrogels for efficient removal of methylene blue

Herein, magnetic nanocomposite hydrogels based on polyvinyl alcohol with enhanced adsorption capacity for methylene blue (MB) is reported. Magnetite nanoparticles were immobilized on negatively charged laponite RD sheets. Magnetic polyvinyl alcohol/laponite RD (mPVALap) nanocomposites were generated in a simple and ecofriendly route through dispersing magnetic clay in PVA solution, followed by the freezing-thawing technique for crosslinking. The resultant physically crosslinked nanocomposites were evaluated for removal of MB from aqueous solutions. Adsorption capability of magnetic PVA nanocomposites for MB was significantly improved by introducing magnetic laponite RD. The effects of contact time, pH, ionic strength, initial concentration of MB, and temperature on the adsorption process were investigated. The effect of contact time revealed the fast adsorption process during 60 min. Although the degree of swelling of hydrogels decreased by increasing magnetic laponite RD, an increased dye adsorption capacity for magnetic nanocomposites was observed. The experimental kinetics data were analyzed using two common kinetic models, pseudo-first-order and pseudosecond-order kinetic models and found that the pseudo-second-order is the best fitting model for the experimental data. The equilibrium isotherm data were analyzed by applying Langmuir and Freundlich isotherm models and better fitting was attained with the Langmuir model. According to the Langmuir model, maximum adsorption capacity of nanocomposite with highest content of magnetic laponite RD was obtained 251 mg/g. In addition to their high adsorption capacities for MB, the removal efficiencies remained more than 93% even after four adsorption-desorption cycles, suggesting the present nanocomposites as a great potential application in the wastewater treatment.