We report the synthesis and characterization of a new class of organic/inorganic hybrid polymers composed of covalently-bound 1,3,5-benzenetricarboxamide linkers and anionic polyoxovanadate clusters with varying counter-cations. These materials form gels within seconds upon contact with polar aprotic organic liquids and catalyze the degradation of odorants and toxic molecules under mild conditions including aerobic oxidation of thiols, hydrogen peroxide-catalyzed oxidation of sulfides, and hydrolysis of organophosphate chemical warfare agent analogues.

The Zr-containing polyoxometalates (POMs), including (Et2NH2)8{[α-PW11O39Zr­(μ–OH)­(H2O)]2}·7H2O (1), effectively catalyze the hydrolysis of nerve agent simulants at near-neutral pH. Analogous Zr-containing heterogeneous systems are much-studied and effective nerve-agent hydrolysis catalysts, but due to their heterogeneous nature, it is very challenging to know the exact structure of the catalytic sites during turnover and to clarify at the molecular level the elementary mechanistic processes. Here, under homogeneous conditions, hydrolysis rates of the nerve-agent simulant methyl paraoxon catalyzed by 1 are examined as a function of pH, ionic strength, catalyst, and substrate concentrations. In addition, the specific effect of three commonly used buffers is examined, revealing that acetate functions as a co-catalyst, phosphate inhibits hydrolytic activity, and 2-(N-morpholino)­ethanesulfonic acid (MES) has no effect on the hydrolysis rate. Spectroscopic (31P nuclear magnetic resonance) and computational studies demonstrate how each of these buffers interacts with the catalyst and offer explanations of their impacts on the hydrolysis rates. The impact of the nerve-agent hydrolysis product, methyl phosphonic acid, is also examined, and it is shown to inhibit hydrolysis. These results will aid in the design of future Zr-based hydrolysis catalysts.

Development of technologies for protection against chemical warfare agents (CWAs) is critically important. Recently, polyoxometalates have attracted attention as potential catalysts for nerve-agent decomposition. Improvement of their effectiveness in real operating conditions requires an atomic-level understanding of CWA decomposition at the gas–solid interface. We investigated decomposition of the nerve agent Sarin and its simulant, dimethyl chlorophosphate (DMCP), by zirconium polytungstate. Using a multimodal approach, we showed that upon DMCP and Sarin exposure the dimeric tungstate undergoes monomerization, making coordinatively unsaturated Zr­(IV) centers available, which activate nucleophilic hydrolysis. Further, DMCP is shown to be a good model system of reduced toxicity for studies of CWA deactivation at the gas–solid interface.

The threat of chemical warfare agents (CWAs), assured by their ease of synthesis and effectiveness as a terrorizing weapon, will persist long after the once-tremendous stockpiles in the U.S. and elsewhere are finally destroyed. As such, soldier and civilian protection, battlefield decontamination, and environmental remediation from CWAs remain top national security priorities. New chemical approaches for the fast and complete destruction of CWAs have been an active field of research for many decades, and new technologies have generated immense interest. In particular, our research team and others have shown metal–organic frameworks (MOFs) and polyoxometalates (POMs) to be active for sequestering CWAs and even catalyzing the rapid hydrolysis of agents. In this Forum Article, we highlight recent advancements made in the understanding and evaluation of POMs and Zr-based MOFs as CWA decontamination materials. Specifically, our aim is to bridge the gap between controlled, solution-phase laboratory studies and real-world or battlefield-like conditions by examining agent–material interactions at the gas–solid interface utilizing a multimodal experimental and computational approach. Herein, we report our progress in addressing the following research goals: (1) elucidating molecular-level mechanisms of the adsorption, diffusion, and reaction of CWA and CWA simulants within a series of Zr-based MOFs, such as UiO-66, MOF-808, and NU-1000, and POMs, including Cs8Nb6O19 and (Et2NH2)8[(α-PW11O39Zr­(μ-OH)­(H2O))2]·7H2O, (2) probing the effects that common ambient gases, such as CO2, SO2, and NO2, have on the efficacy of the MOF and POM materials for CWA destruction, and (3) using CWA simulant results to develop hypotheses for live agent chemistry. Key hypotheses are then tested with targeted live agent studies. Overall, our collaborative effort has provided insight into the fundamental aspects of agent–material interactions and revealed strategies for new catalyst development.

Fast and earth-abundant-element polyoxometalates (POMs) have been heavily studied recently as water oxidation catalysts (WOCs) in homogeneous solution. However, POM WOCs can be quite unstable when supported on electrode or photoelectrode surfaces under applied potential. This article reports for the first time that a nanoscale oxide coating (AlO) applied by the atomic layer deposition (ALD) aids immobilization and greatly stabilizes this now large family of molecular WOCs when on electrode surfaces. In this study, [{Ru(OH)(HO)}(γ-SiWO)] (RuSi) is supported on hematite photoelectrodes and then protected by ALD AlO; this ternary system was characterized before and after photoelectrocatalytic water oxidation by Fourier transform infrared, X-ray photoelectron spectroscopy, energy-dispersive X-ray, and voltammetry. All these studies indicate that RuSi remains intact with AlO ALD protection, but not without. The thickness of the AlO layer significantly affects the catalytic performance of the system: a 4 nm thick AlO layer provides optimal performance with nearly 100% faradaic efficiency for oxygen generation under visible-light illumination. AlO layers thicker than 6.5 nm appear to completely bury the RuSi catalyst, removing all of the catalytic activity, whereas thinner layers are insufficient to maintain a long-term attachment of the catalytic POM.