Dimethyl methylphosphonate adsorption and decomposition on MoO₂ as studied by ambient pressure x-ray photoelectron spectroscopy and DFT calculations

Abstract

Organophosphonates range in their toxicity and are used as pesticides, herbicides, and chemical warfare agents (CWAs). Few laboratories are equipped to handle the most toxic molecules, thus simulants such as dimethyl methylphosphonate (DMMP), are used as a first step in studying adsorption and reactivity on materials. Benchmarked by combined experimental and theoretical studies of simulants, calculations offer an opportunity to understand how molecular interactions with a surface changes upon using a CWA. However, most calculations of DMMP and CWAs on surfaces are limited to adsorption studies on clusters of atoms, which may differ markedly from the behavior on bulk solid-state materials with extended surfaces. We have benchmarked our solid-state periodic calculations of DMMP adsorption and reactivity on MoO with ambient pressure x-ray photoelectron spectroscopy studies (APXPS). DMMP is found to interact strongly with a MoO film, a model system for the MoO component in the ASZM-TEDA© gas filtration material. Density functional theory modeling of several adsorption and decomposition mechanisms assist the assignment of APXPS peaks. Our results show that some of the adsorbed DMMP decomposes, with all the products remaining on the surface. The rigorous calculations benchmarked with experiments pave a path to reliable and predictive theoretical studies of CWA interactions with surfaces.

Adsorption and Decomposition of Sarin on Dry and Wet Cu2O(111) and CuO(111) Surfaces: Insight from First-Principles Calculations

“…32 Joint experiment-theory studies indicate that oxygen vacancies, surface hydroxylation, and different oxidation states of MoO 3 and MoO 2 might influence adsorption and decomposition of DMMP. 33,34 Generally, the surface adsorption prefers low-coordination metal sites with the high accessibility, which serve as Lewis acid sites to facilitate the initial binding of GB and its simulant on the surface of metal oxides. In addition, oxygen atoms in the lattice participate in the surface adsorption and decomposition and promote the fission of P−X (X = F, CH 3 , OC 3 H 7 ) and C−O bonds.…”

Thermal Decomposition of Dimethyl Methylphosphonate on Size-Selected Clusters: A Comparative Study between Copper Metal and Cupric Oxide Clusters

“…The adsorption and decomposition chemistries of DMMP have been studied on an extensive library of metal oxide surfaces, such as Al 2 O 3 , 9−12 SiO 2 , 13−15 TiO 2 , 16−23 CeO 2 , 24−26 WO 3 , 19,27 MoO 2 , 28 MoO 3 , 29−31 Fe 2 O 3 , 12,16,24 CuO, 32 Cu 2 O, 33 and so on. On most of these metal oxide surfaces, DMMP first adsorbs via its phosphoryl oxygen (PO) at the coordinatively unsaturated metal ion sites or on surface hydroxyls at relatively low temperature (typically below room temperature).…”

“…On most of these metal oxide surfaces, DMMP first adsorbs via its phosphoryl oxygen (PO) at the coordinatively unsaturated metal ion sites or on surface hydroxyls at relatively low temperature (typically below room temperature). 4,14,16,19,23,28 The PO bond can convert to a bridging O−P−O moiety at near room temperature. 23,26 Adsorbed DMMP can then undergo stepwise elimination of methoxy groups upon heating.…”

Degradation of Fatal Toxic Nerve Agents on Dry TiO2

“…Therefore, metal oxides are usually used as components of filter materials. Over the last three decades, numerous experimental and theoretical studies were carried out to study atomistic interactions of organophosphorus CWAs and their model compounds with metal oxides. − These studies show that the interaction of simulant compounds with metal oxide surfaces depends on many factors, including a chemical composition, oxidation state of metal atoms, surface structure, and the presence of surface defects, water, and contaminants. Some metal oxides readily adsorb and decompose toxic agents, , whereas other oxides can effectively interact with toxins only in the presence of surface defects or surface hydroxyls. , Metal–organic frameworks − were proposed as potential filter materials because of their catalytic properties.…”