Heavy metal adsorbents mercapto and amino functionalized palygorskite: Preparation and characterization

Palygorskite was functionalized by mercapto and amino groups respectively in the high-speed shear process based on the rheological properties to enhance its sorption amounts and selectivity for heavy metals. The mercapto and amino functionalized samples were characterized through solid-state 29Si CP/MAS NMR, TEM, SEM, TG, XRD, surface area analysis and zeta potentials. The surface modification took place in the high-speed shear process between the silanol groups of palygorskite and organosilanes. The reaction produced a continuous coating of individual fibers of palygorskite. The crystal structure of palygorskite did not change significantly after surface modification. The isoelectric points shifted to lower pH values and the surface areas decreased due to the bulk size of the functional ligands. The sorption of Pb2+, Cd2+ and Cu2+ on the samples was studied in batch experiments and it was found that the surface modification could obviously increase the sorption capacities for Pb2+, Cd2+ and Cu2+. The mercapto and amino functionalized palygorskite could provide a potential remedy for heavy metal contamination in aqueous environment.