Interactions and Binding Energies of Dimethyl Methylphosphonate and Dimethyl Chlorophosphate with Amorphous Silica

The fundamental interactions of dimethyl methylphosphonate (DMMP) and dimethyl chlorophosphate (DMCP) on amorphous silica nanoparticles have been investigated with transmission infrared spectroscopy and temperature-programmed desorption (TPD). DMMP and DMCP both adsorb molecularly to silica through the formation of hydrogen bonds between isolated silanols and the phosphoryl oxygen of the adsorbate. The magnitude of the shift of the v(OH) mode upon simulant adsorption is correlated to the adsorption strength. The activation energies for desorption for a single DMMP or DMCP molecule from amorphous silica varied with coverage. In the limit of zero coverage, after the effects of defects were excluded, the activation energies were 54.5 +/- 0.3 and 48.4 +/- 1.0 kJ/mol for DMMP and DMCP, respectively.