Browsing by Author "Caruso, RA"
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- ItemEffective gel for gold nanoparticle formation, support and metal oxide templating(Royal Society of Chemistry, 2007-08-07) Wang, XD; Egan, CE; Zhou, MF; Prince, KE; Mitchell, DRG; Caruso, RAGold nanoparticles were synthesized using agarose as a reducing agent, which gelled to support the gold nanoparticles, then readily functioned as a template to produce a porous, evenly-distributed Au/TiO2 nano-hybrid. © 2007, Royal Society of Chemistry
- ItemGold nanoparticle incorporation into porous titania networks using an agarose gel templating technique for photocatalytic applications(American Chemical Society, 2008-05-20) Wang, XD; Mitchell, DRG; Prince, KE; Atanacio, AJ; Caruso, RAPorous titania networks containing gold nanoparticles have been synthesized and tested in photocatalytic applications. The porous structure was controlled using a templating technique, while a range of gold concentrations and a variety of routes were investigated to incorporate the gold nanoparticles. The influence of these parameters on the final structure (surface area and pore size), the gold crystal size, distribution, and content, and the photocatalytic activity of the porous materials were investigated. UV−vis diffuse reflectance spectra of the Au/TiO2 materials showed strong absorbance at approximately 580 nm, indicating the successful incorporation of the gold species. X-ray diffraction analysis ascertained that the titania materials were crystalline (anatase phase) with gold peaks observed only when the gold content was greater than 0.25 wt %. Gold distribution and content in the materials were measured using secondary ion mass spectrometry and inductively coupled plasma mass spectrometry. From transmission electron microscopy analysis, the gold particle size and distribution varied with both the material preparation method and the concentration of gold used in the synthesis. Photocatalytic activity was dependent on the gold particle size and gold quantity. The highest photocatalytic activity under UV light irradiation as monitored by the photodecomposition of methylene blue was obtained for the Au/TiO2 sample containing 2.0 wt % gold prepared by the deposition of gold onto prefabricated porous TiO2.© 2008 American Chemical Society
- ItemOne-pot preparation and uranyl adsorption properties of hierarchically porous zirconium titanium oxide beads using phase separation processes to vary macropore morphology(American Chemical Society, 2010-11-16) Drisko, GL; Kimling, MC; Scales, N; Ide, A; Sizgek, E; Caruso, RA; Luca, VA 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 Society
- ItemPhotocatalytic application of porous Au/TiO2 nano-hybrids prepared by a templating technique(International Conference on the Photochemical Conversion and Storage of Solar Energy, 2008-07-30) Wang, XD; Mitchell, DRG; Prince, KE; Caruso, RAGold doping or deposition in TiO2 can effectively improve the photocatalytic performance of the titania by either modifying the bandgap and thereby inducing photoactivity under visible light or decreasing the recombination of excited electron and hole. Templating techniques can produce materials with designed morphology and porosity. The objective of this project was to couple controlled porosity allowing faster molecule diffusion through the porous channels with gold deposition to further increase the photocatalytic activity of TiO2. Templating and sol-gel techniques were combined to synthesise Au/TiO2 nano-hybrids with improved photocatalytic activity. The porous structures directed by the agarose gel template were examined by SEM. X-ray diffraction analysis ascertained the materials to be anatase phase, and the gold peaks were observed when the gold content was over 0.25 wt%. TEM further confirmed the highly porous structure of the composites (Figure 1). The gold particle sizes, influenced by both the synthesis methods and initial gold content, ranged from ~ 2 to 40 nm. The gold distribution and content were identified by means of secondary ion mass spectrometer and inductively coupled plasma mass spectrometry, respectively. Finally, the catalytic performance of the Au/TiO2 was assessed by photodecomposition of methylene blue under UV light. The influence of parameters such as synthesis methods, material properties and photocatalytic test conditions (e.g., pH, catalyst and dye concentration) on the photocatalytic efficiency was also investigated. The photocatalytic efficiency improved by a maximum 40% for the Au/TiO2 sample with a gold particle size of 2 nm and 2 wt % gold content.
- ItemPore size and volume effects on the incorporation of polymer into macro- and mesoporous zirconium titanium oxide membranes(American Chemical Society, 2009-12) Drisko, GL; Cao, L; Kimling, MC; Harrisson, S; Luca, V; Caruso, RAMacro- and mesoporous hybrid materials have applications in the fields of drug delivery, catalysis, biosensing, and separations. The pore size requirements must be well-understood to maximize the performance (e.g., load capacity and accessibility) of such materials. Hybrid materials were prepared by coating five distinct macroporous commercial membranes with zirconium titanium oxide through sol−gel chemistry. Calcination of these templated materials produced oxide membranes which had a suite of macropore and mesopore architectures, pore volumes, and surface areas. These differences in physical properties were used to conduct a fundamental study on the relationship between the pore size and volume and the polymer incorporation. Metal oxide membranes were postsynthetically modified with poly(ethyleneimine) (PEI) ranging in molecular weight from 1300 to 1000000 Da (1.2−11 nm in hydrodynamic diameter). The incorporation of the polymer from a 9 wt % solution at pH 10 was highly dependent on the pore size and pore volume. As the surface area increased, loading capacity decreased, indicating that much of the increased internal surface, due to small pore diameters (≤8 nm), was inaccessible to the macromolecules. Exclusion of PEI from small mesopores was apparent even for the lowest molecular weight polymer. A high maximum loading of 1.25 mg m−2 of 600000−1000000 Da PEI was achieved in the metal oxide with the largest minimum mesopore diameter. Thus, mesopore diameter and pore volume must be considered when designing a mesoporous solid support. © 2009, American Chemical Society
- ItemSize matters: incorporation of poly(acrylic acid) and small molecules into hierarchically porous metal oxides prepared with and without templates(American Chemical Society, 2010-09-07) Drisko, GL; Imperia, P; de los Reyes, M; Luca, V; Caruso, RATemplate synthesis of metal oxides can create materials with highly controlled and reproducible pore structures that can be optimized for particular applications. Zirconium titanium oxides (25:75 mol %) with three different pore structures were synthesized in order to relate polymer loading capacity to macropore architecture. Sol−gel chemistry was used to prepare the materials in conjunction with (i) agarose gel templating, (ii) no template, and (iii) stearic acid templating. The three materials possessed high surface areas (212−316 m2 g−1). Surface modification was performed postsynthetically using propionic acid (a monomer), glutaric acid (a dimer), and three molecular weights of poly(acrylic acid) (2000, 100000, and 250000 g mol−1). Higher loading (mg g−1) was observed for the polymers than for the small molecules. Following surface modification, a perceptible decrease in surface area and mesopore volume was noted, but both mesoporosity and macroporosity were retained. The pore architecture had a strong bearing on the quantity and rate of polymer incorporation into metal oxides. The templated pellet with hierarchical porosity outperformed the nontemplated powder and the mesoporous monolith (in both loading capacity and surface coverage). The materials were subjected to irradiation with 60Co γ-rays to determine the radiolytic stability of the inorganic support and the hybrid material containing the monomer, dimer, and polymer. The polymer and the metal oxide substrate demonstrated notable radiolytic stability. © 2010, American Chemical Society
- ItemSynthesis of monodisperse mesoporous titania beads with controllable diameter, high surface areas, and variable pore diameters (14−23 nm)(American Chemical Society, 2010-03-31) Chen, DH; Cao, L; Huang, FZ; Imperia, P; Cheng, YB; Caruso, RAMonodisperse mesoporous anatase titania beads with high surface areas and tunable pore size and grain diameter have been prepared through a combined sol−gel and solvothermal process in the presence of hexadecylamine (HDA) as a structure-directing agent. The monodispersity of the resultant titania beads, along with the spherical shape, can be controlled by varying the amount of structure-directing agent involved in the sol−gel process. The diameter of the titania beads is tunable from 320 to 1150 nm by altering the hydrolysis and condensation rates of the titanium alkoxide. The crystallite size, specific surface area (from 89 to 120 m2/g), and pore size distribution (from 14 to 23 nm) of the resultant materials can be varied through a mild solvothermal treatment in the presence of varied amounts of ammonia. On the basis of the results of small-angle XRD, high-resolution SEM/TEM, and gas sorption characterization, a mechanism for the formation of the monodisperse precursor beads has been proposed to illustrate the role of HDA in determining the morphology and monodispersity during the sol−gel synthesis. The approach presented in this study demonstrates that simultaneous control of the physical properties, including specific surface area, mesoporosity, crystallinity, morphology, and monodispersity, of the titania materials can be achieved by a facile sol−gel synthesis and solvothermal process. © 2010, American Chemical Society
- ItemTemplate synthesis and adsorption properties of hierarchically porous zirconium titanium oxides(American Chemical Society, 2009-05-05) Drisko, GL; Luca, V; Sizgek, E; Scales, N; Caruso, RAHierarchical 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 Society
- ItemUnderstanding solvothermal crystallization of mesoporous anatase beads by in situ synchrotron PXRD and SAXS(American Chemical Society, 2014-07-07) Xia, F; Chen, DH; Scarlett, NVY; Madsen, IC; Lau, D; Leoni, M; Ilavsky, J; Brand, HEA; Caruso, RASubmicrometer-sized mesoporous anatase (TiO2) beads have shown high efficiency as electrodes for dye-sensitized solar cells and are recoverable photocatalysts for the degradation of organic pollutants. The detailed mechanism for crystallization of the amorphous TiO2/hexadecylamine (HDA) hybrid beads occurring during the solvothermal process needs to be understood so that reaction parameters can be rationally refined for optimizing the synthesis. In this work, the solvothermal crystallization was monitored by in situ synchrotron powder X-ray diffraction (PXRD) and synchrotron small-angle X-ray scattering (SAXS) techniques. In situ PXRD provided crystallization curves, as well as the time evolution of anatase crystallite mean size and size distribution, and in situ SAXS provided complementary information regarding the evolution of the internal bead structure and the formation of pores during the course of the solvothermal process. By exploring the effects of temperature (140-180 °C), bead diameter (300 and 1150 nm), bead internal structure, and solvent composition (ethanol and ammonia concentrations) on this process, the crystallization was observed to progress 3-dimensionally throughout the entire bead due to solvent entrance after an initial fast partial dissolution of HDA from the nonporous precursor bead. On the basis of the kinetic and size evolution results, a 4-step crystallization process was proposed: (1) an induction period for precursor partial dissolution and anatase nucleation; (2) continued precursor dissolution accompanied by anatase nucleation and crystal growth; (3) continued precursor dissolution accompanied by only anatase crystal growth; and (4) complete crystallization with no significant Ostwald ripening. © 2014 American Chemical Society.
- ItemZn-doped TiO2 electrodes in dye-sensitized solar cells for enhanced photocurrent(Royal Society of Chemistry, 2012-07-20) Huang, FZ; Li, Q; Thorogood, GJ; Cheng, YB; Caruso, RAPorous nanocrystalline Zn/TiO2 materials were synthesized employing agarose gel as a template, achieving a maximum Zn-doping concentration of around 2 at.%. Low Zn-doping concentrations (e.g. <1 at.%) improved the photocurrent of the dye-sensitized solar cell when these materials were applied as the working electrode, as n-type doping favors electron transportation. Compared to the efficiency of the undoped sample, 6.7%, the 0.5 at.% sample showed a much higher efficiency of 7.6%. Further doping decreases the performance of the device as it introduces deficiencies that act as electron–hole recombination centers. © 2012 The Royal Society of Chemistry