A facile synthesis of poly (methyl methacrylate) grafted alginate@Cys-bentonite copolymer hybrid nanocomposite for sequestration of heavy metals

A novel PMMA-g-Alg@Cys-Bentonite (BAPM) nanocomposite was synthesized by in situ chemical oxidative polymerization of methyl methacrylate in a colloidal solution of Alg@Cys-Bent. The material was well characterized by XRD, FT-IR, TGA, SEM and TEM and further explored for the removal of Pb (II) and Cd (II) ions from aqueous solution. Batch adsorption system was applied to optimize the various adsorption parameters such as effect of time (180 min), pH (5 for Pb (II), 4 for Cd (II)), adsorbent dose (0.05 g), initial metal ion concentration (100 mg L-1) and temperature (45 degrees C). The experimental data obtained was used to study the Langmuir, Freundlich, Sips and Temkin isotherms. Based on correlation coefficient values, the equilibrium data followed the isotherm models in the order Langmuir> Temkin> Sips> Freundlich. The maximum monolayer adsorption capacity was found 60.24 mg g(-1) for Pb (II) and 48.78 mg g(-1) for Cd (II). A comparative study was done between linear and non-linear fitting of isotherm models and results obtained are in good agreement. With a higher R-2 and low chi(2) value, pseudo second order was found to be best described kinetic data suggesting the chemical adsorption to be rate determining step. The thermodynamic studies reveal that adsorption process is spontaneous and endothermic in nature. The mechanism involved in the removal of heavy metals was electrostatic adsorption coupled reduction which is also evident from EDX analysis.