New materials for the rapid decomposition of chemical warfare agents (CWAs) are in high demand for protecting military and civilian populations from these weapons of mass destruction. The need for novel sorbents and decontamination catalysts has gained great urgency as terrorists groups demonstrate the ability to synthesize and deploy agents in chemical attacks. Although many new materials, such as metal-organic frameworks (MOFs), have been proposed to use as CWA filtration media, their eventual transition requires a detailed understanding of the atomic-scale reaction mechanisms. Zr-based MOFs were recently shown to be among the fastest catalysts of nerve-agent hydrolysis reaction in solution. We show the results of a detailed study of the adsorption and decomposition of a nerve-agent simulant, dimethyl methylphosphonate (DMMP), on UiO-66, UiO-67, MOF-808 and NU-1000 MOFs (that have different pore sizes and connectivities) using synchrotron-based X-ray powder diffraction, X-ray absorption and infrared spectroscopies, which reveals key aspects of the reaction mechanism.[1] This study describes the implementation of a newly developed experimental setup for delivering vaporized DMMP to a reaction cell containing a MOF sample. The diffraction measurements indicate that all four MOFs adsorb DMMP (introduced at atmospheric pressures through a flow of helium or in air) within the pore space. In addition, the combination of X-ray absorption and infrared spectra suggests direct coordination of DMMP to the Zr 6 cores of all MOFs and its subsequent decomposition to phosphonate products. Further, we show that DMMP is actively adsorbed from air with good selectivity, even in the presence of humidity or other ambient gases, demonstrating that Zr 6-based MOFs may serve as effective sorbents for CWAs under ambient conditions. These experimental probes into the mechanism of adsorption and decomposition of chemical warfare agent simulants on Zr-based MOFs open new opportunities for rational design of new and superior decontamination materials.

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Here we discuss the removal of nitrogen dioxide, an important toxic industrial chemical and pollutant, from air using the MOF UiO-66-NH2 . The amine group is found to substantially aid in the removal, resulting in unprecedented removal capacities upwards of 1.4 g of NO2  /g of MOF. Furthermore, whereas NO2 typically generates substantial quantities of NO on sorbents, the amount generated by UiO-66-NH2 is significantly reduced. Of particular significance is the formation of a diazonium ion on the aromatic ring of the MOF, and the potential reduction of NO2 to molecular nitrogen.

Adsorption of formate on oxide surfaces plays a role in water-gas shift (WGS) and other reactions related to H(2) production and CO(2) utilization. CeO(2) is of particular interest because its reducibility affects the redox of organic molecules. In this work, the adsorption and thermal evolution of formic acid and formate on highly ordered films of fully oxidized CeO(2)(111) and highly reduced CeO(x)(111) surfaces have been studied using reflection absorption infrared spectroscopy (RAIRS) under ultra-high vacuum conditions, and the experimental results are combined with density functional theory (DFT) calculations to probe the identity, symmetry, and bonding of the surface intermediates. Disordered ice, ordered alpha-polymorph and molecular formic acid bonded through the carbonyl are observed at low temperatures. By 250 K, desorption and deprotonation lead to formate coexisting with hydroxyl on CeO(2)(111), identified to be a bridging bidentate formate species that is coordinated to Ce cations in nearly C(2v) symmetry and interacting strongly with neighboring H. Changes in the spectra at higher temperatures are consistent with additional tilting of the formate, resulting in C(s)(2) or lower symmetry. This change in bonding is caused primarily by interaction with oxygen vacancies introduced by water desorption at 300 K. On reduced CeO(x), multiple low-symmetry formate states exist likewise due to interactions with oxygen vacancies. Isotopic studies demonstrate that the formyl hydrogen does not contribute to H incorporated in hydroxyl on the surface, and that both formate oxygen atoms may exchange with lattice oxygen at 400 K. The combined experimental and theoretical results thus provide important insights on the surface reaction pathways of formic acid on ceria.

The fundamental interactions of a series of chemical warfare agent (CWA) simulants on amorphous silica particulates have been investigated with transmission infrared spectroscopy and temperature-programmed desorption (TPD). The simulants methyl dichlorophosphate (MDCP), dimethyl cholorophosphate (DMCP), trimethyl phosphate (TMP), dimethyl methylphosphonate (DMMP), and diisopropyl methylphosphonate (DIMP) were chosen to help develop a comprehensive understanding for how the structure and functionality of CWA surrogate compounds affect uptake and hydrogen-bond strengths at the gas− surface interface. Each simulant was found to adsorb molecularly to silica through the formation of strong hydrogen bonds primarily between isolated surface silanol groups and the oxygen atom of the PO moiety in the adsorbate. The TPD data revealed that the activation energy for desorption of a single simulant molecule from amorphous silica varied slightly with coverage. In the limit of zero coverage and the absence of significant surface defects, the activation energies for desorption were found to follow the trend MDCP < DMCP < TMP < DMMP < DIMP. This trend demonstrates the critical role of electron-withdrawing substituents in determining the adsorption energies through hydrogen-bonding interactions. The infrared spectra for each adsorbed species, recorded during uptake, showed a significant shift in the frequency of the ν(SiO−H) mode as the hydrogen bonds formed. A clear linear relationship between the desorption energy and the shift of the surface ν(SiO−H) mode across this series of adsorbates demonstrates that the Badger−Bauer relationship, established origninally for solute−solvent interactions, effectively extends to gas−surface interactions. High-level electronic structure calculations, including extrapolation to the complete basis set limit, reproduce the experimental energies of all simulants with high levels of accuracy and have been employed to provide insight into the molecular-level details of adsorption geometries for the simulants and to predict the interaction energies for the CWA isopropyl methylphosphonofluoridate (sarin).