Browsing by Author "Cao, L"

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    Pore 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, RA
    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 Society
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    Synthesis 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, RA
    Monodisperse 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