Morphology of colloidal metal pyrophosphate salts

We report the preparation and characterization of colloidal particles of several pyrophosphate metal salts, including, for the first time, salts containing multiple metals. These materials are compared in order to determine the influence of the composition and experimental conditions on particle morphology. From this we make two observations: first, the metal ion valence determines the degree of crystallinity of the material. While trivalent metal ions lead to amorphous precipitates, divalent ones result in crystalline nanoparticles. Furthermore, the nature of the metal ion has a significant influence on the morphology of the crystalline particles as we find clear shape preference for each metal ion. Second, methods such as autoclave treatment and surfactant addition can be used to further change particle morphology. Finally we mixed iron(III) with divalent metals during preparation and find that this only has a significant effect on the resulting particles if the Fe-III : M-II ratio is 1 : 5 or higher in M-II content.