Environmental applications of ordered mesoporous materials: Organosilicas with multifunctional ligands for adsorption of mercury ions.

摘要

Ordered mesoporous silicas with multifunctional surface and/or bridging organic groups were synthesized, thoroughly characterized, and tested as adsorbents for the removal of mercury ions from aqueous solutions. The major parts of the dissertation present three different strategies for the synthesis of organic-inorganic mesoporous materials with the desired structural and interfacial properties for adsorption of heavy metal ions.; The first strategy involves the post-synthesis modification of ordered mesoporous silicas (OMS), such as MCM-41, MCM-48, and SBA-15 with multifunctional metal-chelating ligands; namely, 1-benzoyl-3-propylthiourea and 2,5-dimercapto-1,3,4-thiadiazole. Chemically modified OMS were synthesized by reacting the template-free (calcined or extracted) OMS with the appropriate organosilanes, bearing metal-chelating organic groups, and by reacting the template-containing OMS with organosilanes, causing a simultaneous template removal and attachment of the desired organic ligands. The attachment of these multifunctional ligands, which are able to attract two or more mercury(II) ions per ligand, afforded the OMS-based adsorbents high selectivity toward mercury ions and much higher adsorption capacity (as opposed to that obtained for adsorbents with monofunctional ligands). In addition, the regeneration of the adsorbents studied was possible under mild conditions.; The second strategy employs a direct incorporation of multifunctional organic groups into the siloxane bridges of the OMS framework, instead of oxygen atoms. Novel periodic mesoporous organosilicas (PMO), which have a large heterocyclic multifunctional bridging group, tris[3-(trimethoxysilyl)propyl]isocyanurate, high surface area, large pore volume and a remarkable affinity toward mercury metal ions, were prepared by the co-condensation synthesis. Further research in this direction involved the co-condensation of tris[3-(trimethoxysilyl)propyl]isocyanurate with (3-mercaptopropyl)-trimethoxysilane and tetraethylorthosilicate to obtain bifunctional PMO with chemically-modified framework and additional surface functionality, assuring a high adsorption capacity of this PMO adsorbent for mercury ions.; The third strategy focuses on the incorporation of mixed multifunctional bridging and surface groups into the PMO framework, such as tris[3-(trimethoxysilyl)-propyl]isocyanurate, bis[3-(triethoxysilyl)propyl]tetrasulfide, and (3-mercaptopropyl)-trimethoxysilane. Various techniques such as elemental analysis, nitrogen adsorption, high resolution thermogravimetry, transmission electron microscopy, and powder X-ray diffraction were employed to monitor the synthesis of ordered mesoporous organosilicas, as well as to characterize their surface and structural properties.