Efficient Removal of Pb(II) from Aqueous Solution by Modified Montmorillonite/Carbon Composite: Equilibrium, Kinetics, and Thermodynamics

In the present study, a new type of montmorillonite/carbon (MMT/C) adsorbent has been prepared by a one-pot hydrothermal carbonization process. The MMT/C composite was further modified to obtain functionalized MMT/C, i.e., hydroxylated MMT/C, carboxylated MMT/C, and aminated MMT/C. The prepared MMT/C-based sorbents were systematically characterized by X-ray diffraction (XRD), specific surface area, zeta potential, and scanning electron microscopy (SEM). Their adsorption capacity was evaluated by the removal of aqueous Pb(II) ions, following the order carboxylated MMT/C > hydroxylated MMT/C > aminated MMT/C > MMT/C. Moreover, the influential factors for Pb(II) removal by carboxylated MMT/C composites, such as pH, temperature, and initial concentration, were thoroughly explored. The adsorption capacity increases significantly when the pH increases from 2.0 to 5.0 but with minor change beyond. The maximum adsorption capacities of MMT/C–COOH toward Pb(II) are 247.85 mg g –1 . The complexation of surface groups such as −COOH on MMT/C–COOH might be responsible for Pb(II) sorption. The adsorption kinetic follows a pseudo-second-order model, and thermodynamic analysis implies an endothermic and spontaneous chemisorption process. The overall results suggest that the obtained composites are promising as an adsorbent for effective removal of Pb(II) from water.