Mesoporous zirconium titanium oxides. Part 3. Synthesis and adsorption properties of unfunctionalized and phosphonate-functionalized hierarchical polyacrylonitrile-f-127-templated beads.

A method is presented for the preparation of zirconium titanate mixed oxides in bead form having hierarchical pore structure. This method entailed the use of both preformed polyacrylonitrile (PAN) polymer beads and surfactants as templates. The templates were removed by calcination at temperatures below about 500°C, resulting in mixed oxide beads with trimodal pore size distributions and interconnected pores. The pore size distributions as determined using nitrogen adsorption−desorption showed clear maxima at 4.5 and 45 nm length scales and also clear evidence of microporosity. The macroporous framework morphology was a replica of the PAN beads with radial structure. The mesoporous framework possessed wormhole-like pores with pore size of about 6 nm that was consistent with the F-127 triblock copolymer template used. The mixed oxide beads exhibited surface areas of 215 and 185 m2/g after calcination at 500 and 600°C. Thermal stability up to 650°C is unprecedented for bulk systems. The adsorption properties were characterized using uranyl as the target cation and the mass transport in the beads with the present hierarchical architectures has been shown to be exceptional. The beads were functionalized with 4-amino,1-hydroxy,1,1-bis-phosphonic acid (HABDP) and amino-tris-methylene phosphonic acid (ATMP) and the adsorption properties for the extraction of uranyl sulfate complexes from acidic solution examined. Of the two molecules investigated, ATMP functionalization resulted in the best extraction efficiency with equilibrium uptake of about 90% of uranium available in solution between pH 1 and 2. The beads could potentially be utilized as catalysts, catalyst supports, adsorbents, and separation materials. © 2009, American Chemical Societ

Template synthesis and adsorption properties of hierarchically porous zirconium titanium oxides.

Hierarchical morphologies in metal oxides are advantageous for many applications, including controlled drug release, photocatalysis, catalysis, synthetic biomaterials, and adsorption and separation technologies. In this study, agarose gel has been used as a template to prepare zirconium titanium mixed oxide pellets with bimodal porosity. Sol−gel chemistry conducted within the agarose gel produced "coral-like" interconnected networks of oxide nanoparticles with controllable quantities of zirconium and titanium. The materials were characterized using N2 sorption, extended X-ray absorption fine structure, X-ray diffraction, TEM, SEM, zeta potential, and thermogravimetric analysis (to measure surface hydroxyl group density). The oxides were then tested for the adsorption of vanadyl and vanadate to determine which Zr mole fraction exhibited the highest capacity and fastest kinetics. The material containing 25 mol % Zr exhibited the highest surface area (322 ± 8 m2/g) of the compositions investigated and also displayed a superior adsorption rate and capacity. Vanadate adsorption occurred with faster kinetics than did vanadyl adsorption. A comparative study demonstrated that the macro/meso pore structure had improved transport properties over a monomodal mesopore structure of similar Zr/Ti composition. The faster vanadate adsorption kinetics is attributed to enhanced surface accessibility in a hierarchical material. © 2009, American Chemical Societ

Drying of a liquid droplet suspended in its own vapour

We consider the spray drying of colloidal solutions or sols, a process that leads to the production of nanoporous powders, which are of importance in numerous manufacturing applications. An initial model of this process is formulated by considering the evaporation of a liquid droplet suspended in its own vapour. Mass, momentum, and energy balances are given for the liquid and vapour phases of the problem. Perturbation analysis shows that the system is effectively isobaric, and it is shown that surface tension may be neglected. The subsequent moving boundary problem is solved numerically and the results of this process are presented

A study of reverse bias in a dye sensitised photoelectrochemical device

A dye-sensitized nanocrystalline solar subjected to reverse bias of 800 m V showed no measurable loss in performance. However, at 2000 m V, a dramatic and irreversible reduction in the cells performance is observed. Raman spectroscopy experiments suggested that no desorption of the photosensitising dye occurred. Spectroelectrochemical experiments revealed that an irreversible loss of intensity in the metal to ligand charge transfer band at 540 nm occurred. In practical terms, these results indicate that cells which are incorrectly connected to an array of cells or a system failure where potentials greater than 1500 m V are present, may be irreversibly damaged. © 2002 Elsevier Science B.V. All rights reserved

One-pot preparation and uranyl adsorption properties of hierarchically porous zirconium titanium oxide beads using phase separation processes to vary macropore morphology.

A simple and engineering friendly one-step process has been used to prepare zirconium titanium mixed oxide beads with porosity on multiple length scales. In this facile synthesis, the bead diameter and the macroporosity can be conveniently controlled through minor alterations in the synthesis conditions. The precursor solution consisted of poly(acrylonitrile) dissolved in dimethyl sulfoxide to which was added block copolymer Pluronic F127 and metal alkoxides. The millimeter-sized spheres were fabricated with differing macropore dimensions and morphology through dropwise addition of the precursor solution into a gelation bath consisting of water (H2O beads) or liquid nitrogen (LN2 beads). The inorganic beads obtained after calcination (550°C in air) had surface areas of 140 and 128 m2 g−1, respectively, and had varied pore architectures. The H2O-derived beads had much larger macropores (5.7 μm) and smaller mesopores (6.3 nm) compared with the LN2-derived beads (0.8 μm and 24 nm, respectively). Pluronic F127 was an important addition to the precursor solution, as it resulted in increased surface area, pore volume, and compressive yield point. From nonambient XRD analysis, it was concluded that the zirconium and titanium were homogeneously mixed within the oxide. The beads were analyzed for surface accessibility and adsorption rate by monitoring the uptake of uranyl species from solution. The macropore diameter and morphology greatly impacted surface accessibility. Beads with larger macropores reached adsorption equilibrium much faster than the beads with a more tortuous macropore network. © 2010, American Chemical Societ

One-Pot Synthesis of Hierarchically Structured Ceramic Monoliths with Adjustable Porosity

Hierarchically porous oxides are used in a variety of applications within the energy sector (e.g., fuel cells, batteries), biology (e.g., scaffolds, biocatalysis), separations, and catalysis. This article describes a reproducible one-step method for the preparation of metal oxides with controllable hierarchical pore architectures. The preparation is demonstrated for a wide range of materials, specifically silica, titania, zirconia, aluminum titanium oxide, titanium zirconium oxide, and yttrium zirconium oxide monoliths. The samples were prepared by exploiting the polymerization and phase separation of furfuryl alcohol to produce a colloidal dispersion of poly(furfuryl alcohol) particles. The gelation in the sol-gel process occurred after the in situ formation of the template. The removal of the polymer template led to the formation of macropores, whereas inclusion of an amphiphilic block copolymer (Pluronic F127) assisted mesopore formation, either by templating or by stabilizing the inorganic building blocks. The macropore and mesopore morphology could be altered by varying the synthesis conditions. This control over the pore structure was demonstrated in the silica, titania, and titanium zirconium oxide materials.Fil: Drisko, Glenna L.. University of Melbourne; AustraliaFil: Zelcer, Andrés. Comisión Nacional de Energía Atómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Luca, Vittorio. Comisión Nacional de Energía Atómica; ArgentinaFil: Caruso, Rachel A.. University of Melbourne; AustraliaFil: Soler Illia, Galo Juan de Avila Arturo. Comisión Nacional de Energía Atómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin