Deepa Khushalani

Facile synthesis of hollow silica microspheres

Hollow silica microspheres were synthesised at room temperature from a vortexed mixture of water and droplets of tetraethoxysilane (TEOS) containing 10xa0mol% aminopropyltriethoxysilane: droplets stabilized with the surfactant cetyltrimethylammonium bromide produced silica shells, 30.6xa0µm in mean diameter, whereas replacing the Br− counterion with [Co(B9C2H11)2]− gave an approximately hundred-fold decrease in the size of the hollow spheres. Organo-functionalized hollow microspheres containing a covalently linked dye moiety were prepared by replacing 5xa0mol% of TEOS with dinitrophenylaminotriethoxysilane in the reaction mixture, and encapsulation of TEOS-soluble additives within the silica shells was demonstrated by incorporating porphyrin molecules and particles into the ethoxysilane droplets.

Interfacial synthesis of hollow microspheres of mesostructured silica

Hollow microspheres with ordered mesoporous walls are synthesised under ambient conditions by a simple procedure involving dilution and neutralisation of an aqueous tetraethoxysilane/cetyltrimethylammonium bromide reaction mixture.

Glycometallate surfactants Part 2: non-aqueous synthesis of mesoporous titanium, zirconium and niobium oxides

Cetyltrimethylammonium glycotitanate(IV), glycozirconate(IV) and glyconiobate(V), CTA n 1,2 n[M(OCH n 2 nCH n 2 n) n 3 n] where M=Ti(IV), Zr(IV), Nb(V), have been synthesized under non-aqueous conditions by reacting Na n 1,2 n[M(OCH n 2 nCH n 2 n) n 3 n] with CTACl in ethylene glycol. The glycometallates all have a structure based upon an octahedral metal center containing three chelated glycolate ligands. In ethylene glycol all of the CTA n 1,2 n[M(OCH n 2 nCH n 2 n) n 3 n] moieties are found to self-assemble into a lamellar mesophase with a structure based upon bilayers of cationic CTA n + n that are charge-balanced by [M(OCH n 2 nCH n 2 n) n 3 n] n 2– n counter-anions. Hydrolysis of the lamellar glycometallate mesophase in ethylene glycol leads to well-ordered hexagonal phases of mesoporous zirconia and niobia but partially ordered for mesoporous titania. In all cases it is found that the extent of condensation-polymerization of the transition metal oxide in the as-synthesized mesoporous materials is insufficient to sustain the integrity of the structure after the surfactant template is removed by a thermal treatment. Structure re-enforcement of the metal oxide framework can however be achieved by silanation post-treatment of the dehydrated mesoporous metal oxide with Si n 2 nH n 6 n at 100u2006°C. All of the mesoporous transition metal oxides that emerge from this procedure are found to be extensively polymerized and stable to the removal of surfactant. Moreover, they all contain silica in the structure at levels that are tunable over a much wider range as compared to that previously reported in the literature. The method described in this paper is a novel approach to the synthesis of stable high surface area mesoporous transition metal oxides with an adjustable level of silica incorporation into the structure.

Glycometallate surfactants. Part 1: non-aqueous synthesis of mesoporous silica

A novel two step procedure for the synthesis of hexagonal mesoporous silica has been developed. The first non-aqueous step involves the use of ethylene glycol both as solvent and chelating alkoxide. In this step a cetyltrimethylammonium glycosilicate(IV), CTA n 2 n[Si n 2 n(OCH n 2 nCH n 2 n) n 5 n], building-block is synthesized under non-aqueous conditions by solubilizing SiO n 2 n with NaOH in ethylene glycol in the presence of CTACl. Alternatively, CTA n 2 n[Si n 2 n(OCH n 2 nCH n 2 n) n 5 n] can be formed by reacting sodium glycosilicate(IV), Na n 2 n[Si n 2 n(OCH n 2 nCH n 2 n) n 5 n], with CTACl under non-aqueous conditions in ethylene glycol. The glycosilicate(IV) is a structurally well defined dimeric anion based on trigonal-bipyramidal silicon(IV) containing two bidentate and one bridging monodentate glycolate ligand. In ethylene glycol the glycosilicate(IV) surfactant CTA n 2 n[Si n 2 n(OCH n 2 nCH n 2 n) n 5 n] self-assembles into a lamellar mesophase containing bilayers of cationic CTA n + n that are charge-balanced by [Si n 2 n(OCH n 2 nCH n 2 n) n 5 n] n 2– n counter-anions. In the second step of the preparation, controlled hydrolysis of the lamellar glycosilicate(IV) phase with water leads to a well ordered hexagonal mesoporous silica in which the extent of condensation-polymerization of the silica is insufficient to sustain the integrity of the structure when the CTA n + n cation is removed from the channels. Structure re-enforcement can however be achieved by various post-treatments of the vacuum dehydrated mesoporous silica that enable the creation of stable silica-based mesoporous materials with a wide range of elemental compositions. In this paper a post-treatment with Si n 2 nH n 6 n at 100u2006°C was employed to produce extensively polymerized hexagonal mesoporous silica that is stable to removal of the surfactant. The method described in this paper is a novel approach to the synthesis of stable and structurally well defined mesoporous silica-based materials with a wide range of elemental compositions.