Heavy metal retention by organoclays:: Synthesis, applications, and retention mechanism

Organoclays with thiol functionalities pending in the interlayer space were prepared by a single-template sol-gel synthesis. With magnesium nitrate, aluminum acetylacetonate, and mercaptopropyltrimethoxysilane involved, the reaction was established at room temperature. Characterizations were carried out using X-ray diffraction (XRD), X-ray fluorescence, IR, Raman, and solid-state Si-29 and C-13 NMR spectroscopies. XRD patterns exhibit broad peaks characteristics of badly organized solids. The comparison of the experimental basal distance with the theoretical one indicated that organic groups are not perpendicular to the sheets. IR spectra presented the structural bands of the framework while Raman spectroscopy was necessary to confirm the presence of the thiol function. The silicon NMR spectra showed that silanes were fully hydrolyzed but weakly condensated (presence of T1 sites). Comparison between magic-angle spinning (MAS) and cross-polarization MAS C-13 NMR spectra revealed rigid and mobile chains. To evaluate the retention capacity of these materials, tests on the chelating of heavy metal cations were performed. These hybrids offer a high retention capacity for mercury and copper (similar to 100%). On the basis of different characterizations, a retention mechanism is proposed.