RES³T - Rossendorf Expert System for Surface and Sorption Thermodynamics

Results from ³¹P solid-state NMR experiments provide direct evidence for the hydrolysis of phosphate molecules adsorbed on the surface of boehmite (γ-AlOOH). Much of the phosphate surface-excess molecules are in chemical environments that are highly sensitive to solution pH, and the phosphate molecules are held relatively immobile. This chemical environment is believed to be inner-sphere surface complexes. The results of “interrupted-decoupling” ³¹P{¹H} cross-polarization, magic-angle-spinning NMR experiments are used to discriminate protonated surface phosphate species from those that are fully deprotonated. The pH at which surface phosphates become deprotonated lies somewhere between 9 and 11. This transition pH is an NMR observable which can be predicted by surface-complexation models.