Showing papers by "Vadim G. Kessler published in 2010"

Biomimetic synthesis of hierarchically porous nanostructured metal oxide microparticles--potential scaffolds for drug delivery and catalysis.

Abstract: Hierarchically porous hybrid microparticles, strikingly reminscent in their structure of the silica skeletons of single-cell algae, diatoms, but composed of titanium dioxide, and the chemically bound amphiphilic amino acids or small proteins can be prepared by a simple one-step biomimetic procedure, using hydrolysis of titanium alkoxides modified by these ligands. The growth of the hierarchical structure results from the conditions mimicking the growth of skeletons in real diatoms—the self-assembly of hydrolysis-generated titanium dioxide nanoparticles, templated by the microemulsion, originating from mixing the hydrocarbon solvent and water on action of amino acids as surfactants. The obtained microsize nanoparticle aggregates possess remarkable chemical and thermal stability and are promising substrates for applications in drug delivery and catalysis. They can be provided with pronounced surface chirality through application of chiral modifying ligands. They display also high selectivity in sorption of ...

Simple and efficient synthesis of a Nd:LaAlO3 NIR nanophosphor from rare earth alkoxo-monoaluminates Ln2Al2(O(i)Pr)12((i)PrOH)2 single source precursors by Bradley reaction.

Abstract: Nanoparticles of a Nd-doped LaAlO(3) perovskite can be obtained rapidly and with quantitative yield using the Bradley (ether elimination) treatment of a mixture of individual Ln(2)Al(2)(O(i)Pr)(12)((i)PrOH)(2), Ln = La, Nd, in acetophenone. The initially produced particles are poorly crystalline, but their crystallinity improves strongly on heating to 800 degrees C, which leads also to a controllable aggregation. The prepared nanoparticles are rather solution stable and can easily be surface-modified, which opens prospects for their use as phosphors in bioimaging applications. The precursors, bimetallic isopropoxides of rare earth elements and aluminum with a 1:1 composition, Ln(2)Al(2)(O(i)Pr)(12)((i)PrOH)(2), can be prepared with high yields via direct dissolution of metallic lanthanoids in a solution of aluminum isopropoxide in a toluene-isopropanol medium or through a short time reflux of "Ln(O(i)Pr)(3)" with 1 equiv of Al(O(i)Pr)(3) in toluene. In spite of good volatility and their proper composition, the Ln(2)Al(2)(O(i)Pr)(12)((i)PrOH)(2), Ln = La, Nd, do not act as single-source precursors in MOCVD, because of their quantitative transformation into LnAl(3)(O(i)Pr)(12) together with Ln(5)O(O(i)Pr)(13) on evaporation. These molecules are, however, present intact in solution according to variable temperature NMR studies, which permits application of them successfully as single source precursors in the synthesis of Ln:LaAlO(3) perovskite nanopowders with compositions thoroughly controlled through the conditions of the synthesis. Luminescent properties of the Nd:LaAlO(3) were examined and discussed in detail. The thermal population of the (4)F(5/2) and (2)H(9/2) states was found as a consequence of the grain size effect causing difficulties in heat dissipation. Moreover, luminescence behavior of the powder annealed at a lowest temperature shows well-defined short-range order.

Highly symmetric organic ligand-capped Lindqvist structures derived from 3d-elements.

Abstract: Interaction of M(acac)(2) with Ti(OEt)(4) associated with hydrolysis or thermolysis provides with high yields, through the decomposition of the initially formed M(2)Ti(2)(acac)(4)(OEt)(8), M = Ni (1), Co (2), poorly soluble Lindqvist-type products with the formula M(5)TiO(acac)(6)(OEt)(6), M = Ni (3), Co (4), Mg (5). The compounds 3-5 are isostructural and display a perfect statistical disorder between the OEt groups and 1/2 of the beta-diketonate, acac, ligand. The metal atoms constitute a regular octahedron, centered by the oxo-oxygen atom. There is only one symmetrically independent metal site, which imposes it to contain 1/6 of titanium and 5/6 of the divalent metal atom. The oxygen atoms on the surface of the octahedron are doubly bridging and are located above the twelve edges of the octahedron, as is usual for the Lindqvist-type structures. The coordination of the metal atoms is completed by a single terminal oxygen atom. The complexes 3-5 are volatile with decomposition, releasing only homometallic products into the gas phase in the case of 3 and 4, but with a considerable contribution of molecular evaporation in the case of 5. The intermediates 1 and 2 belong to the tetramolybdate, M(4)O(16), structure type. Highly soluble 1 and 2 can be considered as attractive molecular precursors for the incorporation of 3 and 4 into porous matrices for the preparation of combustion catalysts. Application of the same synthetic approach to n-propoxide complexes offers in a Co-Ti system a derivative with a different composition and resolved metal and ligand disorder, Co(4)Ti(2)O(acac)(4)(O(n)Pr)(10) (6), which, however, still follows the Lindquist type and displays high (tetragonal) symmetry for both the molecule and the crystal structure.

A new concept for titanium oxo-alkoxo-carboxylates’ encapsulated biocompatible time temperature food indicators based on arising, not fading color

Abstract: New insight into the factors determining formation and stability of oxo-alkoxide carboxylates of titanium permits to design biocompatible systems for encapsulation of binary food quality inorganic dyes, such as Preussian blue, in a temperature-sensitive shell. The shells are formed spontaneously on hydrolysis of carboxylic acid-modified titanium alkoxides on the surface of water droplets containing the dye components. The complete dye is then prepared through mixing of pre-frozen encapsulated droplets which can be activated by heating to room temperature and also influenced by the storage time. The stable shells are obtained from longer chain carboxylates providing the micellar self-assembly derived constructions with increased colloid stability. The factors influencing the formation of individual crystalline oxo-alkoxide carboxylates—a process competing with the micellar self-assembly and decreasing the stability of the oxo-alkoxide carboxylate shells are discussed with the starting point in the molecular structures of the known compounds and also the new complexes Ti6O6(OAc)6(OiPr)6 · C6H14 (1) and Ti12O12(OAc)6(OnPr)18 (2).

A cost-effective method for monitoring airborne particulate matter using tabletop SEM-EDS

Abstract: Inhalable airborne Particulate Matter (PM) has been linked to adverse effects in the airways and cardiovascular system in humans leading indirectly to hospitalization and possibly premature death. The need to monitor these on a local level has recently been realized with the emergence of low cost tabletop Scanning Electron Microscopes (SEM) with high magnification possibilities offering a quick and easy way of analyzing PM down to 300 nanometres in size. The ease of use of these instruments makes them suitable for an untrained person to routinely monitor elemental constituents of individual particles and possibly linking them to inherent health risks. In this study particles from outdoor air were collected onto Polyamide filters and analyzed using tabletop SEM utilizing Energy Dispersive Spectroscopy (EDS) to determine and identify their chemical composition. 341 particles were successfully characterized and classified in relation to their chemical identity and origin. The regional differences in the samples could be related to the location of sample collection proving that tabletop SEMs offers a possibility of air quality monitoring in relation to the particle impurities.