FOURIER-TRANSFORM INFRARED PHOTOACOUSTIC-SPECTROSCOPY STUDY OF THE ADSORPTION OF ORGANOPHOSPHORUS COMPOUNDS ON HEAT-TREATED MAGNESIUM-OXIDE

A series of magnesium oxide samples of varying surface area were prepared and heat treated (thermally activated) at 500 or 700-degrees-C. Dimethyl methylphosphonate (DMMP), trimethyl phosphate (TMP), and triethyl phosphate (TEP) were allowed to adsorb on the MgO samples both in a vacuum environment and in a helium stream. Analyses of the powdered samples were carried out by Fourier transform infrared photoacoustic spectroscopy. These studies revealed that adsorption occurred on all samples in proportion to surface area. Physisorbed organophosphorus molecules were easily removed by evacuation or under helium flow. However, substantial amounts strongly chemisorbed through the oxygen atom of the P = O bond. Even at room temperature and up to 190-degrees-C the chemisorbed compounds began to decompose, but decomposition products remained adsorbed. At 500-degrees-C complete decomposition took place releasing mainly formic acid plus some methanol. The phosphorus moiety remained immobilized as a [CH3OPCH3] residue.