Interaction of organophosphorous compounds with TiO2 and WO3 surfaces probed by vibrational spectroscopy

The interaction of organophosphorous compounds with TiO2 and WO3 high surface area powders has been studied by thin film infrared spectroscopy. Room temperature adsorption of dimethyl methyl phosphonate (DMMP), dimethyl hydrogen phosphonate (DMHP), and trimethyl methyl phosphonate (TMP) is through hydrogen bonding of the PO functional group to the hydroxyl groups of the metal oxide surface. At higher reaction temperatures, these hydrogen bonded organophosphorous compounds dissociate and form covalently attached species. Above 200°C, the methoxy groups desorb from the surface while the methyl groups remain stable. Above 300°C, a stable phosphate surface complex is formed. The presence of the phosphate complex may be responsible for poisoning effects observed during DMMP gas exposure of chemiresistive sensors operating in this temperature range.