This is an important point since the general applicability of Two previously published surface complexation models of phea model, most likely, depends upon how good the agreement nylphosphonate on aged g-Al 2 O 3 and boehmite (g-AlOOH), reis between the thermodynamic model and the actual molecuspectively, have been examined by means of FTIR and FT-Raman lar processes, as indicated in a previous study (4). Consespectroscopy. The spectral features of adsorbed phenylphosphoquently, a proposed surface complexation model should, nate were studied as a function of pH and total phenylphosphonate when possible, be tested against spectroscopic data.
concentration. No evidence for a phase transformation into a
In two recent papers the adsorption of phenylphosphonate three-dimensional aluminum phenylphosphonate phase was on aged g-Al 2 O 3 (aged denotes a g-Al 2 O 3 which has been found. This suggested that phenylphosphonate is sorbed as surface preequilibrated in aqueous suspension for at least 1 month; complexes under the conditions used in this study. Both the infrared and the Raman data showed that the surface-bound phenyl-see Materials and Methods) and boehmite (g-AlOOH), rephosphonate ions undergo protonation reactions as pH is varied. spectively, was studied (5, 6). These systems are of great These results together with the fact that the ligand has only two applied interest within the field of surface modified materidonor atoms for complexation and protonation led to the concluals. The potentiometric and adsorption data presented and the sion that a monodentate coordination to the surface is most likely proposed surface complexation models also revealed several in both systems. Overall, the spectroscopic results were in good results of more fundamental importance. Both systems could qualitative agreement with the thermodynamic surface complexbe satisfactorily explained by the existence of two domiation models. ᭧ 1997 Academic Press nating monomeric surface complexes. There were no indi-Key Words: water-aluminum (hydr)oxide interface; phenylcations of a phase transformation into a three-dimensional phosphonate ions; FTIR spectroscopy; FT-Raman spectroscopy.
Al-phenylphosphonate phase, as has been observed under certain experimental conditions in the orthophosphate/aged g-Al 2 O 3 system (7). The adsorbed phenylphosphonate ions were also shown to display proton-active properties; at low