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

Size matters: incorporation of poly(acrylic acid) and small molecules into hierarchically porous metal oxides prepared with and without templates

Template 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 Societ

Pore size and volume effects on the incorporation of polymer into macro- and mesoporous zirconium titanium oxide membranes.

Macro- 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 Societ

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

Gold-silica quantum rattles for multimodal imaging and therapy

Gold quantum dots exhibit distinctive optical and magnetic behaviors compared with larger gold nanoparticles. However, their unfavorable interaction with living systems and lack of stability in aqueous solvents has so far prevented their adoption in biology and medicine. Here, a simple synthetic pathway integrates gold quantum dots within a mesoporous silica shell, alongside larger gold nanoparticles within the shell’s central cavity. This “quantum rattle” structure is stable in aqueous solutions, does not elicit cell toxicity, preserves the attractive near-infrared photonics and paramagnetism of gold quantum dots, and enhances the drug-carrier performance of the silica shell. In vivo, the quantum rattles reduced tumor burden in a single course of photothermal therapy while coupling three complementary imaging modalities: near-infrared fluorescence, photoacoustic, and magnetic resonance imaging. The incorporation of gold within the quantum rattles significantly enhanced the drug-carrier performance of the silica shell. This innovative material design based on the mutually beneficial interaction of gold and silica introduces the use of gold quantum dots for imaging and therapeutic applications