Sorption of Cd2+ on mercapto and amino functionalized palygorskite

Mercapto and amino functionalized palygorskite samples were prepared by nanotexturization method, respectively, and applied for the sorption of Cd2+ from aqueous solution to investigate the sorption mechanism and assess the application potential for the remediation of Cd polluted water and soils. The samples before and after sorption were characterized through XRD, FTIR, Si-29 CP/MAS NMR and XPS. The sorption thermodynamics, kinetics and mechanisms of Cd2+ sorption on mercapto and amino functionalized palygorskite were studied. Langmuir isotherm was proved to describe the sorption data better and pseudo second order kinetic model could fit the sorption kinetic processes well. Functionalization increased the sorption amounts significantly compared to pristine palygorskite. The positive enthalpy change confirmed that the sorption process was endothermic. The positive entropy changes revealed that sorption of Cd2+ was driven by entropy changes. Combined the results of analyses of the diffraction peaks by XRD, vibration modes of functional groups by FTIR, chemical shifts by Si-29 CP/MAS NMR and binding energies of key elements by XPS, the sorption mechanisms were complexation with mercapto or amino groups, and surface precipitation of CdCO3. (C) 2014 Elsevier B.V. All rights reserved.