Environmental Effects on Zirconium Hydroxide Nanoparticles and Chemical Warfare Agent Decomposition: Implications of Atmospheric Water and Carbon Dioxide

Abstract

Zirconium hydroxide (Zr(OH)₄) has excellent sorption properties and wide-ranging reactivity toward numerous types of chemical warfare agents (CWAs) and toxic industrial chemicals. Under pristine laboratory conditions, the effectiveness of Zr(OH)₄ has been attributed to a combination of diverse surface hydroxyl species and defects; however, atmospheric components (e.g., CO₂, H₂O, etc.) and trace contaminants can form adsorbates with potentially detrimental impact to the chemical reactivity of Zr(OH)₄. Here, we report the hydrolysis of a CWA simulant, dimethyl methylphosphonate (DMMP) on Zr(OH)₄ determined by gas chromatography-mass spectrometry and in situ attenuated total reflectance Fourier transform infrared spectroscopy under ambient conditions. DMMP dosing on Zr(OH)₄ formed methyl methylphosphonate and methoxy degradation products on free bridging and terminal hydroxyl sites of Zr(OH)₄ under all evaluated environmental conditions. CO₂ dosing on Zr(OH)₄ formed adsorbed (bi)carbonates and interfacial carbonate complexes with relative stability dependent on CO₂ and H₂O partial pressures. High concentrations of CO₂ reduced DMMP decomposition kinetics by occupying Zr(OH)₄ active sites with carbonaceous adsorbates. Elevated humidity promoted hydrolysis of adsorbed DMMP on Zr(OH)₄ to produce methanol and regenerated free hydroxyl species. Hydrolysis of DMMP by Zr(OH)₄ occurred under all conditions evaluated, demonstrating promise for chemical decontamination under diverse, real-world conditions.