Adsorption and Decomposition of Dimethyl Methylphosphonate on TiO₂

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 TiO 2 powder. At temperature lower than ∼160 K, DMMP condenses as an ice layer on the outer surface of the TiO 2 sample. In the temperature range 160− 200 K, diffusion into the TiO 2 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−OCH 3 groups takes place, with the production of Ti−OCH 3 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.