Spectroscopically Resolved Binding Sites for the Adsorption of Sarin Gas in a Metal–Organic Framework: Insights beyond Lewis Acidity

Abstract

Here we report molecular level details regarding the adsorption of sarin (GB) gas in a prototypical zirconium-based metal–organic framework (MOF, UiO-66). By combining predictive modeling and experimental spectroscopic techniques, we unambiguously identify several unique bindings sites within the MOF, using the PO stretch frequency of GB as a probe. Remarkable agreement between predicted and experimental IR spectrum is demonstrated. As previously hypothesized, the undercoordinated Lewis acid metal site is the most favorable binding site. Yet multiple sites participate in the adsorption process; specifically, the Zr-chelated hydroxyl groups form hydrogen bonds with the GB molecule, and GB weakly interacts with fully coordinated metals. Importantly, this work highlights that subtle orientational effects of bound GB are observable via shifts in characteristic vibrational modes; this finding has large implications for degradation rates and opens a new route for future materials design.

Battling Chemical Weapons with Zirconium Hydroxide Nanoparticle Sorbent: Impact of Environmental Contaminants on Sarin Sequestration and Decomposition

“…However, no evidence of adsorbed molecular GB was observed by ex situ XPS analysis, suggesting that either any intact GB observed with DRIFTS desorbs from the surface under high vacuum or decomposes before XPS data can be collected. 56 These data suggest that contaminated ZH surfaces potentially retain more adsorbed GB compared to clean ZH.…”

“…SO 2 -predosed ZH samples also show a small band near 1272 cm –1 that is likely “liquid-like” multilayers of GB, suggesting that GB accumulates on the ZH surface with prolonged exposure. However, no evidence of adsorbed molecular GB was observed by ex situ XPS analysis, suggesting that either any intact GB observed with DRIFTS desorbs from the surface under high vacuum or decomposes before XPS data can be collected . These data suggest that contaminated ZH surfaces potentially retain more adsorbed GB compared to clean ZH.…”

Degradation of Fatal Toxic Nerve Agents on Dry TiO2

“…Experimental GB adsorption studies on TiO 2 were performed in a high vacuum chamber with a base pressure at 3 × 10 –9 Torr. A more detailed description of the vacuum chamber is provided elsewhere. , The TiO 2 nanoparticles were pressed into a 0.004″ thick W-grid and attached to the sample mount via stainless steel clamps connected to copper rods. The copper rods were attached to a power supply allowing for resistive heating of the sample up to ∼1000 K at a resolution of ±0.1 K. Before introducing GB vapor into the vacuum chamber, the sample was heated up to 450 K for 30 min in order to remove H 2 O, hydrocarbon impurities, and as many isolated OH sites as possible from the TiO 2 sample.…”

Determining Diffusion Coefficients of Chemical Warfare Agents in Metal–Organic Frameworks

“…Computational studies have contributed to understanding the degradation and adsorption of CWAs and their simulants in MOFs. Harvey et al , and Liu et al . used periodic density functional theory (DFT) to provide theoretical insights into catalytic degradation of CWAs and simulants in MOFs.…”