Dark and UV-Enhanced Degradation of Dimethyl Methylphosphonate on Mesoporous CeO2 Aerogels

Our development of high surface-area mesoporous expressions of ceria (CeO2) is motivated by recent studies identifying CeO2 as one of the most reactive oxides for adsorbing and degrading toxic organophosphorus compounds, including chemical warfare simulants. We synthesize nanostructured CeO2 aerogels using a facile, scalable, and template-free sol-gel method to amplify the number of available and accessible surface sites for organophosphorus adsorption/degradation and then spectroscopi-cally characterize the degradation of dimethyl methylphosphonate (DMMP) at the aerogel surface. The CeO2 aerogels retain high concentrations of surface-sited residual Cl from the chloride sol- gel precursors, which block DMMP binding sites and hinder the formation of surface hydroxyls (OH). We demonstrate that a simple alkaline soak removes surface-fouling Cl and creates a more OH-rich surface, thus unleashing the hydrolytic activity of the amplified CeO2 aerogel surfaces. Whereas the Cl-fouled CeO2 surface weakly and reversibly binds DMMP, the rinsed, OH-rich surface irreversibly binds DMMP and rapidly generates hydrolysis products. Exciting the CeO2 bandgap with UV light (390-400 nm) accelerates DMMP degradation and generates a higher proportion of mineralized POx products than the dark reaction. Our work marks the first-ever report of photodegradation of a chemical warfare simulant at CeO2 as well as the first report of mineralized POx formation at CeO2 at room temperature. The high surface-area CeO2 aerogels exhibit higher capacity than non-networked, nanoparticulate CeO2, thus highlighting the potential applicability of nanocrystalline CeO2 aerogels for protection against organophosphorus compounds.