Preparation and characterization of mercapto functionalized sepiolite and their application for sorption of lead and cadmium

In order to improve the sorption performance of sepiolite for heavy metals, sepiolite was functionalized by nanotexturization in aqueous sepiolite gel and surface grafting in toluene with mercaptopropyltrimethoxysilane. The pristine sepiolite and mercapto functionalized samples were characterized through XRD, FT-IR, SEM, TEM, TG, surface area analysis, solid state 29Si CP/MAS NMR. The chemical bonding took place between the silanol group within sepiolite and the methoxy group of mercaptopropyltrimethoxysilane. The reaction in aqueous gel produced a continuous coating of individual fibers of sepiolite compared with part grafting on the external surface in toluene. After surface modification, the surface areas decreased due to the bulk size of the mercapto ligand, but the crystal structure did not change obviously, and the stretching of mercapto could be detected by FT-IR. The sorption of Pb(II) and Cd(II) on the samples were studied in batch experiments and it was found that the surface modification can obviously increase the sorption capacities for Pb(II) and Cd(II). The mercapto functionalized sepiolite could provide a potential remedy for heavy metal contamination in soils and water.

► Sepiolite was functionalized by nanotexturization in aqueous sepiolite gel and grafting in toluene with mercapto silane.
► 29Si NMR indicated that the chemical bonding took place between Si–OH within sepiolite and the methoxy group of silane.
► Nanotexturization produced a continuous coating on individual fibers compared with part coating in toluene.
► The surface modification can obviously increase the sorption capacities for Pb(II) and Cd(II).