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UVM Theses and Dissertations

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Format:
Print
Author:
Livingston, Stephanie R.
Dept./Program:
Chemistry
Degree:
PhD
Abstract:
The U.S. Army is obligated by an international treaty to destroy its stockpiles of chemical warfare agents (CWAs) and is seeking alternative destruction methods to the most commonly used technique, incineration. In addition to destroying known stockpiles of CWAs, in the event of a military or terrorist attack involving chemical weapons, it is necessary to rapidly and nondestructively decontaminate surfaces or objects exposed to the chemicals. This dissertation describes work on the development of catalysts supported on mesoporous silica for the degradation of CWA analogues. Chapter 1 provides an introduction to CWAs and current methods for their destruction, background information on the synthesis and properties of mesoporous silica, and an overview of the techniques used to characterized mesoporous silica. The synthesis and characterization of vanadium doped acid-prepared mesoporous spheres (V-APMS) with vanadium loadings of 1 -40 wt% are described in Chapter 2.
APMS with vanadium loadings exceeding 2 wt% contained V₂O₅ crystallites, whereas APMS with vanadium loadings up to 2 wt% contained well-dispersed VO₄ species. Chapter 3 describes the application of these materials as catalysts for the oxidation of the mustard gas anologue 2-chloroethyl ethyl sulfide (CEES). V-APMS catalyzed oxidation of CEES was found to proceed through different mechanisms, depending on whether the vanadium oxide species existed as isolated VO₄ species or crystalline V₂O₅, and samples containing isolated VO₄ species were more effective catalysts. V-APMS was also found to catalyze the aerobic oxidation of aldehydes to acids through the generation of the corresponding peracid, and the oxidation of CEES by peracids produced from the oxidation of aldehydes with O₂ is reported in Chapter 4. The VAPMS catalyzed oxidation of aldehydes to acids was shown to proceed through a free radical mechanism, and V-APMS was found to catalyze the both the oxidation of aldehydes to acids and the oxidation of CEES by peracids.
Chapters 5 and 6 describe preliminary work towards the development of a solid decontaminant composed of enzymes encapsulated within the pores APMS that could be released by a specific triggering agent. A method for loading substrates within the pores of APMS, coating the loaded particles with a polymer, and releasing the molecules under specific conditions is presented in Chapter 5 using the dye Rhodamine B (RhB) as a model substrate. RhB-Ioaded APMS was covered with the polymers poly(allylamine) or polyethyleneimine bound to the silica through a disulfide bond that could be cleaved by the reducing agent dithiothreitol, allowing the dye to be released from the silica. The adsorption, release, and activity of the enzyme glucose oxidase (GOX) adsorbed on APMS with pore diameters ranging from 36 -117 A is described in Chapter 6. As the pore diameter of the silica increased, the amount of adsorbed GOX increased because a greater number of the pores were large enough to allow the enzyme to diffuse into the pores. The GOX activity decreased after adsorption on APMS, and the activity of adsorbed GOX was lower for samples with smaller pores and samples with high GOX loadings due to decreased access to the adsorbed enzymes.