The chemisorption of organophosphorus compounds at an Al(1 1 1) surface

The reactive chemisorption of three organophosphorus compounds have been investigated at clean and oxidised Al(1 1 1) surfaces using X-ray photoelectron spectroscopy (XPS). Phosphoric acid, trimethyl ester (or trimethylphosphate, TMP, OP(OCH3)3), and methyl phosphonic acid and dimethyl ester (or dimethylmethylphosphate, DMMP, OP(CH3)(OCH3)2,) were adsorbed from the gas phase, but this approach proved unsuccessful for methyl phosphonic acid (MPA, OP(CH3)(OH)2) due to decomposition in the gas phase. MPA was therefore adsorbed from either an aqueous or an ether solution placed onto the aluminium sample in a helium atmosphere. Core binding energies for the POCH3, PCH3, PO and PO groups are reported and the decomposition pathways for the three compounds discussed. The PCH3 bond is stable at both clean and oxidised aluminium surfaces up to temperatures of 570 K, whereas the POCH3 bond can be broken even at room temperature. Decomposition of all three molecules requires clean aluminium sites and is hindered by high concentrations of adsorbed species.