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

Our development of high surface-area mesoporous expressions of ceria (CeO 2 ) is motivated by recent studies identifying CeO 2 as one of the most reactive oxides for adsorbing and degrading toxic organophosphorus compounds, including chemical warfare simulants. We synthesize nanostructured CeO 2 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 spectroscopically characterize the degradation of dimethyl methylphosphonate (DMMP) at the aerogel surface. The CeO 2 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 CeO 2 aerogel surfaces. Whereas the Cl-fouled CeO 2 surface weakly and reversibly binds DMMP, the rinsed, OH-rich surface irreversibly binds DMMP and rapidly generates hydrolysis products. Exciting the CeO 2 bandgap with UV light (390–400 nm) accelerates DMMP degradation and generates a higher proportion of mineralized PO x products than the dark reaction. Our work marks the first-ever report of photodegradation of a chemical warfare simulant at CeO 2 as well as the first report of mineralized PO x formation at CeO 2 at room temperature. The high surface-area CeO 2 aerogels exhibit higher capacity than non-networked, nanoparticulate CeO 2, thus highlighting the potential applicability of nanocrystalline CeO 2 aerogels for protection against organophosphorus compounds.