Hydrolyzed Al(III)-clusters. II: Speciation transformation and stability of Al13 aggregates

Pure nano-Al13 and aggregates at various concentrations were prepared to examine their stability and potential role in coagulation processes and natural systems. Alkalinity titration experiments showed that the hydrolysis of Al13 solutions exhibits significant difference from that of the normal Al(III) solutions. The transition OH/Al ratio (pH points) shifts from normal 2.5 to higher values (∼2.9). No significant structural rearrangement takes place during Al13 aggregation. The aggregates exhibit stability during short aging up to 1 month. The Alb species obtained by Ferron assay in the initial aging period no longer corresponds to Al13. The aggregates disappear quickly in 27Al-NMR detection with increasing B value (OH/Al ratio) maintaining efficient Ferron reactivity. This shows that the Alb in Ferron assay corresponds with Al13 only under certain conditions.

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► The speciation of Al13 aggregates exhibits quite stable nature.
► The Al13 aggregates might maintain the Keggin-Al13 structure for more than one month.
► Aggregates disappear quickly in 27Al-NMR detection with increasing OH/Al ratio while maintain efficient Ferron reactivity.
► The Alb in Ferron assay corresponds with Al13 only under certain conditions.