31P and 27Al NMR studies of aqueous (2-hydroxyethyl) trimethylammonium solutions containing aluminum and phosphorus

Phosphorus-31 and aluminum-27 nuclear magnetic resonance techniques have been used to characterize the distribution of soluble aluminophosphate species in aqueous solutions of (2-hydroxyethyl) trimethylammonium chloride (2-HETMACl), phosphoric acid, and aluminum sulfate. Soluble aluminophosphate cations obtain from reactions of hexaaqua aluminum cations [A1(H2O)6]3+, with phosphate ligands (i.e., H3PO4, H2PO4–, and acid dimers H6P2O8 and H5P2O7–). 31P NMR and 27Al NMR spectroscopies are very powerful techniques for characterization of the species present in the solution. A number of solutions containing different mole ratio of Al/P were prepared. The assignment of the peaks to aluminate connectivities is attempted, clarifying earlier works and producing information on the equilibrium between various aluminum-containing species (different aluminophosphate complexes). At least seven separated resonances were observed by 31P NMR spectroscopy indicating presence of different complexes in aluminum phosphate solutions.