The grafting of 3-aminopropyltriethoxysilane (APTES) onto the internal aluminol groups of two kaolinite minerals from Georgia and from Cameroon was achieved by utilizing their corresponding dimethyl sulfoxide (DMSO) intercalation compounds as intermediates. The modified clays were characterized by powder X-ray diffraction, thermal gravimetric analysis coupled with mass spectrometry, Fourier transform infrared, and solid-state MAS NMR. These techniques demonstrated the effectiveness of the interlamellar grafting process. An expansion of the interlayer distance from 11.2 to 15.9-16.4 Å on going from the precursors to the nanohybrid materials was observed. The study of the thermal behavior of the organoclays showed the release under heating of grafted APTES fragments, typical of the decomposition products of carbon, hydrogen, and nitrogen bearing organic matter. The hydroxyl stretching vibration zone (3700-3600 cm -1 ) of the starting clays and of the DMSO intercalated precursors was intensively perturbed in the final materials. New bands were observed, indicating strong interactions between APTES and the kaolinite interlayer surfaces. Solid-state 29 Si CP-MAS NMR spectra of silylated kaolinite showed T 2 and T 3 signals corresponding to the linkage of APTES moieties. This was confirmed by the relative intensities of the signals in the quantitative 13 C CP-MAS NMR spectra of the nanohybrid materials. Concomitant silylation and ethoxylation of the interlayer aluminol surface were obtained to give a mixed alkoxy-organosilyl kaolinite derivative. The silylation was roughly equally distributed between bidentate and tridentate fixations, with a minor amount of monodentate material. A remarkable feature of the new materials was their response to the [Ru(CN) 6 ] 4-electrochemical probe in acidic medium when the functionalized clays were coated on a platinum electrode. This is due to the protonated amine groups that act as anion exchange sites. These preliminary results open the way to further development of kaolinite-based electrochemical sensors.

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Naturally occurring smectite clays have been expanded by a surfactant (cetyltrimethylammonium) and a cosurfactant (dodecylamine), which were then used in combination with the sol-gel process to prepare porous clay heterostructures (PCHs). A variety of thiol-functionalized PCHs have been obtained in one step by surfactant-directed co-condensation of tetraethoxysilane (TEOS) and 3-mercaptopropyltrimethoxysilane (MPTMS) in various molar ratios (ranging from 0 to 35% MPTMS) in the interlayer region of the clay. These materials have been characterized by several physicochemical techniques. They featured large specific surface areas and pore volumes (after template removal), due to the presence of regular mesopore channels between the clay sheets, but the mesostructural order and porosity were found to decrease upon rising the functionalization level. Hg(II) binding to these materials was then analyzed to get insight in the accessibility to the active centers and to characterize mass transfer rates to the binding sites. The experiments have been carried out at two distinct pH values (2 and 4) to point out the influence of speciation on these processes. Full accessibility was always observed at pH 4 where Hg(II) was adsorbed under a neutral form, giving rise to very high sorption capacities (up to about 600 mg g -1 ). The rate of access to the binding sites was usually faster in the more ordered materials, but some limitations were observed at pH 2 due to unfavorable electrostatic interactions. Finally, hydrodynamic electrochemistry has been applied to demonstrate that mesostructuration of the interlayer region of the clay has positive impact in terms of enhancing diffusion rates through PCH thin films in comparison to nonmodified clay coatings. The layered structure of the materials creates their direct arrangement as mechanically stable layers onto electrode surfaces, contrary to other powdered mesoporous materials which require the use of a polymeric binder.