Efficient and fast removal of Pb2+ and Cd2+ from an aqueous solution using a chitosan/Mg-Al-layered double hydroxide nanocomposite.

A new nanocomposite based on chitosan (CS) and Mg-Al-layered double hydroxide (Mg-Al-LDH) was prepared using an emulsion-crosslinking method. CS was immobilized within the Mg-Al-LDH matrix to form the CS-LDH after crosslinking by epichlorohydrin. The characterization of XPS, SEM, TEM, FTIR, and BET analysis showed that the CS-LDH had a high specific surface area and contained many different functional groups. The adsorption capacity of the CS-LDH was evaluated by adsorbing Pb2+ and Cd2+ as representative heavy metals. Batch adsorption method was used to investigate the effects of the amount of adsorbent, pH of the initial solution, and contact time. We also examined the adsorption kinetics, isotherms, and mechanisms. The capacity of the CS-LDH for Pb2+ and Cd2+ adsorption was higher than that of CS and the Mg-Al-LDH, and the isothermal data followed the Langmuir isotherm model. The adsorption equilibrium was quickly achieved and the kinetic data obeyed the pseudo-second-order kinetic model. The adsorption process was almost not affected by solution pH above 3. The CS-LDH and heavy metals interacted via the following mechanisms: precipitation, surface complexation, and isomorphic substitution.