Effect of precursor and surfactant nature on geometrical characteristics of mesoporous silicas

Bimodal mesoporous silicas and materials MCM-41 type were synthesized with the use as a template cationic surfactants distinguished by a length of the alkyl chain. Fumed silica, tetraethyl orthosilicate as well as of mixture these compounds were applied as a silicate precursor. Obtained samples have been characterized by the powder X-ray diffraction technique and adsorption measurements. Specific surface area, pore diameter, pore size distribution was determined from nitrogen ad(de)sorption isotherms at 77 K for the silicas prepared. The products with bimodal pore distribution have not ordered structure and contain macropores and mesopores, whose sizes are typical for MCM-41 materials. Effect of surfactant and precursor nature on the geometrical features of the ordered structure of MCM-41 type and bimodal porous materials was studied

Composition and Nano-Periodic Structure of Compounds Formed by the Reaction of Molybdenum and Tungsten Heteropolyanions with Cationic Surfactants

Keggin heteropolyanions (HPAns) of structure [PMo 12 O 40 ] 3– and [PW 12 O 40 ] 3– have been allowed to react in acidic media at room temperature with some cationic surfactants of the quaternary ammonium or primary amine type to yield meso-structured insoluble salts with the general formulae Am 3 [PM 12 O 40 ], Etn 3 [PM 12 O 40 ] 2 , Etn 3 [PM 12 O 40 ] 2 •nEtnCl 2 or Am n H 7-n [PM 11 O 39 ]•xH 2 O, where Am and Etn are, respectively, mono- and di-cationic surfactant species, M is Mo or W and n can vary in the range 0 to ∼3. All of the materials obtained possessed nano-periodic structures whose maximum d 100 parameters ranged from 26 Å to 36 Å, exhibiting lamellar, tetragonal, hexagonal or cubic meso structures depending on the synthesis conditions employed and the nature of the surfactant and HPAns used. The values of the highest d 100 parameter obtained for the substances prepared were generally in line with the length of the hydrophobic tail in the surfactant molecule but less dependent on the nature of the metal (Mo or W) when the latter was incorporated in a Keggin anion. However, the structure of the materials was considerably influenced by the pH value of the reaction medium and the P/M ratio when transformation of the Keggin anions into lacunary or other anions was possible

Synthesis and Characterization of Ti—MCM-41-Type Mesoporous Molecular Sieves with High Titanium Contents

By employing a sodium silicate + titanium tetrabutoxide + trimethylmyristylammonium bromide system, it has been possible to obtain mesoporous titanosilicate Ti–MCM-41-type molecular sieves containing systematically varying titanium contents. The samples obtained possessed a high BET specific surface area and exhibited the perfect hexagonal mesoporous structure characteristic for MCM-41 materials even when the titanium fraction present was as great as 20 mol%. It has been shown that most of the titanium can be expelled from the structure when the materials are treated with sulphuric acid solution. However, such treatment does not destroy their inherent hexagonal structure, thereby suggesting that the titanium is preferentially localized in the mesopore surface layer. The structure/sorption properties of the materials were investigated by X-ray diffraction methods and by the adsorption of n-hexane and water vapour. A possible mechanism for the formation of such MCM-41-type molecular sieves is proposed which suggests that the use of organometallic ethers M(OR) n , accompanied by ether solubilization with organic micellar templates, leads to the preferential localization of M in the mesopore surface

Adsorptive Properties of Template-Containing Silica-Based MCM-41 and MCM-50 Materials

Template-containing silica-based MCM-41 and MCM-50 materials have been shown to have microporous adsorbent properties, with the characteristic adsorption energy in such micropores being strongly dependent on the molecular mass of the adsorptives employed. The total adsorption volume was found to decrease as the molar volume of the adsorptive increased. A model explaining the peculiarities of the adsorptive properties of the template-containing materials is proposed

First complexes of diphenylphosphorylalkanones with titanium tetrafluoride

The reaction of TiF4 with a twofold excess of Ph2P(O)CH2C(O)Me (L) (one of the simplest and, very likely, most practically interesting representatives of a new class of organophosphorus ligands - diorganylphosphorylalkanones) in CH2Cl2 has been studied. © 2015 Pleiades Publishing, Ltd

First complexes of diphenylphosphorylalkanones with titanium tetrafluoride

The reaction of TiF4 with a twofold excess of Ph2P(O)CH2C(O)Me (L) (one of the simplest and, very likely, most practically interesting representatives of a new class of organophosphorus ligands - diorganylphosphorylalkanones) in CH2Cl2 has been studied. © 2015 Pleiades Publishing, Ltd