Date of Award

Summer 8-4-2015

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Advisor

Carl P. Tripp

Abstract

The overall goal of this work was to develop methods for the surface modification of particulate materials. In one case, we explored the use of supercritical CO2 (sc‑CO2) as a vehicle for tuning the pore size in a mesoporous silica. In the second case, we developed a method to coat magnetic particles with commercially available titania powder.

An in situ FTIR thin film technique was used to follow the reaction, during the Atomic Layer Deposition (ALD) of SiO2 layers. When using sc‑CO2 as a solvent, the reaction of two silica precursors, tetraethyl orthosilicate (TEOS) and SiCl4 followed different pathways to react with the Si‑OH group on the silica surface. The ALD reaction with SiCl4 and an amine catalyst (triethylamine) proceeded rapidly but the HCl produced as a byproduct of this reaction was corrosive to the stainless steel components in the sc-CO2 delivery system. A 2-step ALD with TEOS was found to produce the best growth. The application of this 2-step process resulted in the MCM-41 pore size being reduced from 2.82 nm to 2.61 nm after one cycle, but with higher cycles the rate of pore size reduction was lower. It was found that the water remained in the pores after the second step which led to the polymerization of TEOS and restricted access to the inner pore regions.

In our second method, the photocatalytic properties of magnetic iron(II,III) oxide particles coated with different wt% of commercially available P25 powder using a simple wet impregnation method were measured. However, the photocatalytic activity for these particles at all P25 loadings was lower than those obtained for pure P25. Precoating the magnetic particles with a SiO2 sol‑gel layer prevented the electron hole migration and oxidation of magnetite to hematite, but also led to a weakly bound P25 layer. This was overcome by adding a second TiO2 sol‑gel on top of the SiO2 coated magnetic particles for anchoring the P25 particles to the surface without significant loss of surface area. The photocatalytic degradation of terephthalic acid and phenol for P25 coated magnetic particles was found to be equivalent to that of the P25.

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