Organic ligands containing the thiol (-SH) metal-chelating functionality were either grafted to the external surface silanol groups of sepiolite or introduced in the interlayers of montmorillonite, and the resulting functionalized clays were characterized and assayed as adsorbents for Hg(II), Pb(II), and Zn(II) ions from solution. Sepiolite was functionalized by covalently grafting 3-mercaptopro-pyltrimethoxysilane (MPS) to the surface tSi-OH groups of the clay, whereas montmorillonite was functionalized by replacement of the interlayer inorganic cation (Na + ) by 2-mercaptoethylammonium (MEA) cations. These clayorganic ligand systems were selected to minimize the congestion of the internal porosity of the clays, which has recently been shown to be the main obstacle to heavy metal adsorption by functionalized clays. Infrared spectroscopy and elemental analyses demonstrated the presence of the organic ligands in the modified clays. X-ray diffraction analysis indicated the organic cations (MEA) occupied the interlayers of montmorillonite. N 2 specific surface area measurements suggested that much of the surface area of montmorillonite and sepiolite remained accessible upon functionalization and that the organic ligand kept the montmorillonite interlayers open. The functionalized clays adsorbed most of the Hg(II) ions present in solution up to saturation and were also good adsorbents of Pb(II) at low metal ion concentrations (i.e., <0.02 mM). They were, however, less effective toward Pb(II) and Zn(II) at high metal ion concentrations. The presence of NaNO 3 or Ca(NO 3 ) 2 as background electrolytes at concentrations ranging from 0.001 to 0.1 M did not alter the great adsorption capacity of functionalized sepiolite for Hg(II). The results show that clay functionalization can be optimized by matching clay structure with a suitable reactive (i.e., fibrous clay with a graftable ligand or expandable clay with an exchangeable cationic ligand) and minimizing the gallery volume taken up by the organic ligand, thus improving the performance of the functionalized clay as adsorbent of heavy metals from solution.

The risk of ground water contamination resulting from rapid leaching of highly soluble pesticides can be minimized through the application of the pesticide adsorbed on a matrix or carrier, which limits the amount of pesticide immediately available for undesirable losses. The use of natural materials for this purpose is of special interest in terms of economy and sustainability. In this work the adsorption of the herbicide hexazinone by two montmorillonites saturated with various inorganic and organic cations was determined and the ability of the two clays displaying the highest adsorption capacities [Fe(3+)-saturated Wyoming montmorillonite, (Fe-SW) and hexadecyltrimethylammonium-saturated Arizona montmorillonite (HDTMA-SA)] to act as carriers for slow release of hexazinone and to reduce herbicide leaching losses was evaluated. Hexazinone formulations based on Fe-SW and HDTMA-SA displayed slow release properties in water and soil/water suspensions, reduced herbicide leaching in soil columns, and maintained herbicidal activity, as compared with the currently available commercial hexazinone formulation (wettable powder). Loosely bound hexazinone-HDTMASA formulations, which led to the slowest breakthrough of hexazinone in soil columns along with the greatest amounts of herbicide released from the clay particles, displayed the most interesting characteristics for their use as slow release formulations and to prevent ground water contamination.

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