Titania Nanomaterials for Sarin Decomposition: Understanding Fundamentals

Abstract

While TiO2-based materials have been attracting growing interest in combating chemical warfare agents (CWAs), their usefulness and details of chemical mechanisms remain unknown. In this study, we explored the potential of TiO2 nanomaterials as filter materials to degrade sarin (GB), one of the deadliest nerve agents. We performed joint experimental and theoretical studies of the breakdown of sarin gas on three different TiO2 nanomaterials: P25 TiO2, pure anatase TiO2 nanopowder, and mesoporous anatase TiO2. Infrared and X-ray photoelectron spectroscopic measurements of TiO2 nanomaterials upon GB dosing demonstrate that GB readily decomposes on TiO2. The photoelectron spectra indicate the formation of metal fluoride on the surface, implying a mechanism for GB dissociation that involves P–F bond cleavage. Our results reveal that the as-synthesized mesoporous anatase TiO2 exhibits the highest activity toward GB decomposition despite it having the same crystalline structure and a similar surface area as the anatase TiO2 nanopowder. With density functional theory (DFT) calculations, we explore possible causes for the high reactivity of mesoporous TiO2. We modeled sarin decomposition mechanisms on anatase (101) surfaces and considered the effect of frequent defects in materials, such as oxygen vacancies, steps, water, and hydroxyl groups. Calculations show that GB decomposition through P–F bond breaking on the (101) anatase surface can be promoted by a stepped structure and hydroxylation due to both a lower activation energy barrier and lower energy of the final products. Our experiments corroborate that water/hydroxylation facilitates the dissociation of sarin on mesoporous TiO2. Our study suggests that mesoporous TiO2 is an attractive candidate material for use in gas masks and other protective equipment.

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