By using Fourier transform infrared spectroscopy (FTIR) we have witnessed the sequential steps of surface diffusion, weak chemical bonding, and decomposition of dimethyl methylphosphonate (DMMP) on TiO2 powder. At temperature lower than ∼160 K, DMMP condenses as an ice layer on the outer surface of the TiO2 sample. In the temperature range 160− 200 K, diffusion into the TiO2 interior occurs and hydrogen bonding of DMMP to isolated TiOH groups is observed. In addition, bonding to Lewis acid sites occurs. Above 214 K, cleavage of P−OCH3 groups takes place, with the production of Ti−OCH3 surface species and this is accompanied by the consumption of surface hydroxyl groups. A reduction of P−O bond order then occurs as adsorbed phosphonate species are formed.

The photooxidation of dimethyl methylphosphonate (DMMP) on powdered TiO 2 has been studied using UV irradiation in the range 2.1 eV to 5.0 eV. It has been found that the P-CH 3 and the P-OCH 3 moieties are destroyed together by photooxidation, producing adsorbed CO and CO 2 as well as formate ions and water. By working at 200 K the photooxidation process has been studied alone, whereas at room temperature both hydrolysis and photooxidation will occur together. An adsorbed PO 3 species is the final phosphorus-containing photooxidation product. High coverages of DMMP are not photooxidized due to site blockage for O 2 adsorption on the TiO 2 surface.