High-Temperature Decomposition of Diisopropyl Methylphosphonate on Alumina: Mechanistic Predictions from Ab Initio Molecular Dynamics

Abstract

The enhanced degradation of organophosphorousbased chemical warfare agents (CWAs) on metal oxide surfaces holds immense promise for neutralization efforts; however, the underlying mechanisms in this process remain poorly understood. For the first time, we utilize large-scale quantum calculations to probe the high-temperature degradation of diisopropyl methylphosphonate (DIMP), a nerve agent simulant. Our Born− Oppenheimer molecular dynamics (BOMD) calculations show that the γ-Al 2 O 3 surface shows immense promise for quickly adsorbing and destroying CWAs. We find that the alumina surface quickly adsorbs DIMP at all temperatures, and subsequent decomposition of DIMP proceeds via a propene elimination. Our BOMD calculations are complemented with metadynamics simulations to produce free energy paths, which show that the activation barrier decreases with temperature and that DIMP readily decomposes on γ-Al 2 O 3 . Our first-principle BOMD and metadynamics simulations provide crucial diagnostics for sarin decomposition models and mechanistic information for examining CWA decomposition reactions on other candidate metal oxide surfaces.

Degradation of Perfluorooctanoic Acid on Aluminum Oxide Surfaces: New Mechanisms from Ab Initio Molecular Dynamics Simulations

“…The PBE exchange-correlation functional with Grimme’s D3 dispersion correction was used in all of our calculations . We used a DZVP basis set for Al and a TZV2P basis set for the C, O, H, and F valence electrons; Goedecker, Teter, and Hutter (GTH) pseudopotentials were used to treat the atomic core electrons. , In previous work, we used a similar basis set to accurately simulate the decomposition of diisopropyl methylphosphonate (a chemical warfare agent simulant) on alumina surfaces . The orbital transformation method was used to converge the SCF cycle with an electronic gradient tolerance value of 1 × 10 –5 au.…”

“…However, due to the inherent complexity of these high-temperature experiments, a detailed understanding of the PFAS degradation mechanisms on these material surfaces is scarce and still in its infancy. , In this work, we present the first ab initio molecular dynamics (AIMD) study for investigating a wide range of temperature-dependent degradation dynamics of perfluorooctanoic acid (PFOA) on various surfaces of γ-Al 2 O 3 . We have chosen to investigate γ-Al 2 O 3 since previous work by us and our experimental collaborators , has shown that γ-Al 2 O 3 has a high degree of surface heterogeneity with Al atoms exhibiting tri-, tetra-, and pentacoordination motifs (depending on the crystallographic plane), which can enhance reactivity. To probe the degradation dynamics of PFOA at a predictive quantum mechanical level, we carried out large-scale AIMD calculations on the (100) and (110) surfaces of γ-Al 2 O 3 (taking into account possible surface defects) over a wide range of temperatures.…”

Strong Emergence Arising from Weak Emergence

“…If these phase transitions can be simulated qualitatively or even quantitatively correctly by micro-to-macro models, then this can be seen as an indicator that likely no hard emergence occurs, even if regular pattern formation and reconfguration take place on the atomic level. Such examples of successful bottom-up bridging between micro and macro can be found, for example, in chemical studies of molecular dynamics and material interactions [38,39].…”

Investigation for Carbonation Mechanism of Tobermorite 9 Å: A Combination of DFT and Ab Initio Molecular Dynamics Study

“…[39] Compared with three mainstream methods, the ab initio molecular dynamics (AIMD) simulation could accurately calculate the transformation process of electronic property and does not depend upon any proposed empirical force field parameters [40] on the atomic scale. The dispersion force correction AIMD approach was used by Biswas et al [41] to investigate the high-temperature degradation of diisopropyl methylphosphonate (DIMP). They discovered that DIMP was promptly adsorbed on the alumina surface at all temperatures.…”

“…The dispersion force correction AIMD approach was used by Biswas et al. [ 41 ] to investigate the high‐temperature degradation of diisopropyl methylphosphonate (DIMP). They discovered that DIMP was promptly adsorbed on the alumina surface at all temperatures.…”