VIBRATION SPECTROSCOPY STUDY OF PHENYLPHOSPHONATE AT THE WATER-ALUMINUM (HYDR)OXIDE INTERFACE

Two previously published surface complexation models of phenylphosphon ate on aged gamma-Al2O3 and boehmite (gamma-AlOOH), respectively, have been examined by means of FTIR and FT-Raman spectroscopy. The spectra l features of adsorbed phenylphosphonate were studied as a function of pH and total phenylphosphonate concentration. No evidence for a phase transformation into a three-dimensional aluminum phenylphosphonate ph ase was found. This suggested that phenylphosphonate is sorbed as surf ace complexes under the conditions used in this study. Both the infrar ed and the Raman data showed that the surface-bound phenylphosphonate ions undergo protonation reactions as pH is varied. These results toge ther with the fact that the ligand has only two donor atoms for comple xation and protonation led to the conclusion that a monodentate coordi nation to the surface is most likely in both systems. Overall, the spe ctroscopic results were in good qualitative agreement with the thermod ynamic surface complexation models. (C) 1997 Academic Press.