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- All Subjects: Porous
- Creators: Petuskey, William
Description
Nanoporous crystalline oxides with high porosity and large surface areas are promising in catalysis, clean energy technologies and environmental applications all which require efficient chemical reactions at solid-solid, solid-liquid, and/or solid-gas interfaces. Achieving the balance between open porosity and structural stability is an ongoing challenge when synthesizing such porous materials. Increasing porosity while maintaining an open porous network usually comes at the cost of fragility, as seen for example in ultra low density, highly random porous aerogels. It has become increasingly important to develop synthetic techniques that produce materials with these desired properties while utilizing low cost precursors and increasing their structural strength. Based on non-alkoxide sol-gel chemistry, two novel synthetic methods for nanoporous metal oxides have been developed. The first is a high temperature combustion method that utilizes biorenewable oil, affording gamma alumina (Al2O3) with a surface area over 300 cm3/g and porosity over 80% and controllable pore sizes (average pore width 8 to 20 nm). The calcined crystalline products exhibit an aerogel-like textural mesoporosity. To demonstrate the versatility of the new method, it was used to synthesize highly porous amorphous silica (SiO2) which exhibited increased mechanical robustness while achieving a surface area of 960 m2/g and porosity of 85%. The second method utilizes sequential gelation of inorganic and organic precursors forming an interpenetrating inorganic/organic gel network. The method affords yttria-stabilized zirconia with surface area over 90 cm3/g and porosity over 60% and controllable pore sizes (average pore width 6 to 12 nm). X-ray diffraction, gas sorption analysis, Raman spectroscopy, nuclear magnetic resonance spectroscopy and electron microscopy were all used to characterize the structure, morphology, and the chemical structure of the newly afforded materials. Both novel methods produce products that show superior pore properties and robustness compared to equivalent commercially available and currently reported materials.
ContributorsLadd, Danielle (Author) / Seo, Don (Thesis advisor) / Häussermann, Ulrich (Committee member) / Petuskey, William (Committee member) / Arizona State University (Publisher)
Created2012
Description
New sol-gel routes were developed to fabricate transparent conducting oxide coatings for energy applications. Sol-gel synthesis was chosen because the metal oxide products have high surface area and porosity. Titanium sol-gel chemistry was the main focus of the studies, and the synthesis of macroporous antimony-doped tin oxide was also explored. The surface chemistry and band characteristics of anatase TiO2 show promise for solar energy purposes as photoelectrodes in DSSCs and as photocatalysts to degrade organic dyes and to split water. Modifying the band structure by increasing the conduction band edge energy is specifically of interest for reducing protons in water. To this end, a new sol-gel method was developed for incorporating Zr-dopant in nanoporous anatase TiO2. The products follow Vegard’s law up to 20 atom%, exhibiting surface area of 79 m2/g and pore volume of 0.20 cm3/g with average pore diameter of 10.3 nm; the conduction band edge energy increased by 0.22 eV and the band gap increased by 0.1 eV.
In pursuit of a greener sol-gel route for TiO2 materials, a solution of TiOSO4 in water was explored. Success in obtaining a gel came by utilizing hydrogen peroxide as a ligand that suppressed precipitation reactions. Through modifying this sol-gel chemistry to obtain a solid acid, the new material hydrogen titanium phosphate sulfate, H1-xTi2(PO4)3-x(SO4)x, (0 < x < 0.5) was synthesized and characterized for the first time. From the reported synthetic route, this compound took the form of macroscopic agglomerates of nanoporous aggregates of nanoparticles around 20 nm and the product calcined at 600 °C exhibited surface area of 78 m2/g, pore volume of 0.22 cm3/g and an average pore width of 11 nm. This solid acid exhibits complete selectivity for the non-oxidative dehydrogenation of methanol to formaldehyde and hydrogen gas, with >50% conversion at 300 °C.
Finally, hierarchically meso-macroporous antimony doped tin oxide was synthesized with regular macropore size around 210 nm, determined by statistical dye trajectory tracking, and also with larger pores up to micrometers in size. The structure consisted of nanoparticles around 4 nm in size, with textural mesopores around 20 nm in diameter.
In pursuit of a greener sol-gel route for TiO2 materials, a solution of TiOSO4 in water was explored. Success in obtaining a gel came by utilizing hydrogen peroxide as a ligand that suppressed precipitation reactions. Through modifying this sol-gel chemistry to obtain a solid acid, the new material hydrogen titanium phosphate sulfate, H1-xTi2(PO4)3-x(SO4)x, (0 < x < 0.5) was synthesized and characterized for the first time. From the reported synthetic route, this compound took the form of macroscopic agglomerates of nanoporous aggregates of nanoparticles around 20 nm and the product calcined at 600 °C exhibited surface area of 78 m2/g, pore volume of 0.22 cm3/g and an average pore width of 11 nm. This solid acid exhibits complete selectivity for the non-oxidative dehydrogenation of methanol to formaldehyde and hydrogen gas, with >50% conversion at 300 °C.
Finally, hierarchically meso-macroporous antimony doped tin oxide was synthesized with regular macropore size around 210 nm, determined by statistical dye trajectory tracking, and also with larger pores up to micrometers in size. The structure consisted of nanoparticles around 4 nm in size, with textural mesopores around 20 nm in diameter.
ContributorsMieritz, Daniel (Author) / Seo, Dong-Kyun (Thesis advisor) / Petuskey, William (Committee member) / Herckes, Pierre (Committee member) / Arizona State University (Publisher)
Created2016