Surface reaction kinetics of dimethyl methylphosphonate (DMMP) on zirconium hydroxide using attenuated total reflection infrared (ATR-FTIR) spectroscopy*

Amorphous zirconium hydroxide (ZH) attracts growing attention due to its high activity for decomposing toxic chemicals, especially chemical warfare agents (CWA). We synthesize zirconium hydroxide films using cathodic electrodeposition and investigate their surface chemistry to a CWA simulant, dimethyl methylphosphonate (DMMP), using attenuated total reflection infrared spectroscopy (ATR).
The ATR data show the accumulation of surface-bound decomposition products, including methoxy and phosphonate derivatives. Time-dependent IR absorption spectra reveal the adsorption, decomposition, and desorption kinetics. Growth of the IR absorption intensities for surface reaction products is evaluated with various adsorption and diffusion kinetic models. Thermodynamic parameters are derived from the adsorption isotherm. The dependence of the kinetic and thermodynamic parameters on reaction temperature will be discussed.
Calcination of amorphous zirconium hydroxide produces crystalline zirconia via a transition to amorphous zirconia. Reduced chemical activity upon calcination correlates with decreased surface area and loss of hydroxyl groups, as confirmed by XPS and ATR data.