Conformal Nanoscale Zirconium Hydroxide Films for Decomposing Chemical Warfare Agents

Abstract

Amorphous zirconium hydroxide (ZH) has attracted recent attention for its high decomposition reactivity with chemical warfare agents (CWA). Conformal, 50 nm thick amorphous ZH films were produced on arbitrarily shaped metallic substrates by cathodic electrodeposition from ZrOCl2 in aqueous solution, with nanoscale control of the film thickness. The films had a root-mean-square (rms) roughness of ∼6–8 nm, ∼2.4 nm nanoscale pores, and a high specific surface area of 132 m2 g–1. These rapidly grown, cost-effective, and scalable films may be more suitable for some in situ decontamination needs than post-event application of powders prepared by conventional wet-synthesis methods. The morphology and chemical properties of the electrodeposited films were characterized with scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis mass spectrometry (TGA-MS), and nitrogen-sorption porosimetry. The decomposition activity of ZH toward dimethyl methylphosphonate (DMMP), a CWA simulant, was probed with gas chromatography–mass spectrometry (GC-MS) and in situ attenuated total reflection infrared spectroscopy (ATR) by monitoring the evolution of gas-phase methanol and the coverage of surface-bound methoxy and phosphonate species during and after DMMP dosing. We compared the chemical activity of electrochemically synthesized ZH (EZ), commercial ZH (CZ) and ZrO2 nanopowders, and calcined EZ at 100–500 °C. The ATR, XPS, and XRD results indicate that calcination to 500 °C decreased DMMP decomposition due to the loss of hydroxyls and conversion to crystalline ZrO2 and that EZ and CZ had virtually identical surface reactions. This study provides a framework for characterizing the evolution of complex reactions during the transition from amorphous-to-crystalline material.