Ultrasonic-assisted synthesis of polyacrylamide/bentonite hydrogel nanocomposite for the sequestration of lead and cadmium from aqueous phase: Equilibrium, kinetics and thermodynamic studies.

Clay-hydrogel nanocomposites are suitable material for mitigating the pollution/environmental impact because of their high adsorption capacity. In this study, the synthesis of polyacrylamide/bentonite hydrogel nanocomposite was assisted by ultrasound through successful incorporation of nanobentonite as filler and cross-linker into polyacrylamide framework. The adsorbent was characterized by FTIR, XRD, BET, SEM-EDX, and TEM in order to observe structural changes and sorption interactions. The effect of adsorbent dose, contact time, initial metal ion concentration and pH on the sequestration of Pb and Cd was analyzed. The adsorbent removed more than 95% Pb and Cd within first 20 min, which corresponds to relatively high pseudo-first order rate constant, k (0.240 for Pb and 0.253 1/min for Cd) and pseudo-second order rate constant, k (0.031 for Pb and 0.033 g/mg/min for Cd). The isotherm and kinetics modeling data were best described by Freundlich isotherm over the entire concentration range and pseudo-second order rate equation, respectively. The thermodynamic studies implied spontaneous and endothermic nature of adsorption process. The maximum adsorption capacity (138.33 for Pb and 200.41 mg/g for Cd) determined using Langmuir model along with a good regeneration potential depicts that polyacrylamide/bentonite hydrogel nanocomposite could be used effectively for Pb and Cd uptake from aqueous solution.