Removal of Cu2+ from aqueous solution by adsorption onto mercapto functionalized palygorskite

•Freundlich isotherm and second order kinetics fit sorption processes well.•The sorption mechanisms were investigated by XRD, FTIR, 29Si CP/MAS NMR and XPS.•The sorption mechanisms involved surface complexation and surface precipitation.

In order to enhance sorption capacity of palygorskite for heavy metals, mercapto functionalized palygorskite (MPAL) were prepared and utilized for the sorption of Cu2+ from aqueous solution. Sorption kinetic and thermodynamic experiments were conducted to assess the sorption behavior and application potentials for the remediation of heavy-meta-polluted soil. Sorption mechanisms were investigated by XRD, FT-IR, 29Si CP/MAS NMR, SEM-EDS and XPS in detail. The maximum sorption amount of Cu2+ on MPAL was approximately 30 mg/g, which was 10 times more than pristine palygorskite. Freundlich isotherm describes the sorption data better than other isotherms, and pseudo second order kinetic model fit the sorption kinetic processes well. The positive enthalpy change confirmed that the sorption process of MPAL was endothermic and the positive entropy changes revealed that sorption of Cu2+ was driven by entropy changes. Further characterization analyses and the “Hard and Soft Acids and Bases theory” for mechenism research exhibited the complexation existence of Cu2+ with mercapto groups. The good performance demonstrated that MPAL has great potential application values in removal of heavy metals both from aqueous and soils.

Graphical abstractIn order to enhance sorption capacity of palygorskite for heavy metals, mercapto functionalized palygorskite (MPAL) were prepared and utilized for the sorption of Cu2+ from aqueous solution. Sorption kinetic and thermodynamic experiments were conducted to assess the sorption behavior and application potentials for the remediation of heavy-meta-polluted soil. Sorption mechanisms were investigated by XRD, FT-IR, 29Si CP/MAS NMR, SEM-EDS and XPS in detail. The maximum sorption amount of Cu2+ on MPAL was approximately 30 mg/g, which was 10 times than pristine palygorskite. Freundlich isotherm describes the sorption data better than other isotherms, and pseudo second order kinetic model fit the sorption kinetic processes well. The positive enthalpy change confirmed that the sorption process of MPAL was endothermic and the positive entropy changes revealed that sorption of Cu2+ was driven by entropy changes. Further mechanisms research exhibited that Cu2+ reacted with surface hydroxyl groups to form surface complexation in pristine palygorskiteSur-OH + Cu2+ → Sur-OCu+ + H+2Sur-OH + Cu2+ → Sur-OCuO-Sur + 2H+;While for mercapto functionalized palygorskite, according to the characterization analyses and “Hard and Soft Acids and Bases theory”, the complexation of Cu2+ with mercapto groups existed2Sur-SH + 0.5O2 → Sur-SS-Sur + H2OSur-SH + Cu2+ → Sur-SCu+ + H+2Sur-SH + Cu2+ → Sur-SCuS-Sur + 2H+.The positive enthalpy change confirmed that the sorption process was endothermic and the positive entropy changes revealed that sorption of Cu2+ was driven by entropy changes. In conclusion, the good performance demonstrated that MPAL has great potential application values in removal of heavy metals both from aqueous and soils.Figure optionsDownload full-size imageDownload as PowerPoint slide