Chemical trigger toward phase separation in the aqueous Al(III) system revealed

Area of Science:

• Inorganic Chemistry
• Materials Science
• Solution Chemistry

Background:

• Aluminum (Al) hydrolysis, condensation, and nucleation are critical in synthesizing Al-based materials and dictate their chemical properties.
• Experimental data on the solution chemistry of nucleation remains limited, hindering precise control over material formation.

Purpose of the Study:

• To investigate the fundamental chemistry of nucleation in Al(III) systems from solution.
• To identify the initial precursors and mechanisms driving the formation of Al-based nanosolids.

Main Methods:

• Advanced titration assays to monitor solution chemistry.
• High-resolution transmission electron microscopy (HR-TEM) for structural analysis.
• 27Al-nuclear magnetic resonance (NMR) spectroscopy for detailed chemical speciation.

Main Results:

• Identified dynamic solute prenucleation clusters (PNCs) as fundamental precursors to nanosolid formation.
• Demonstrated that chemical transformations within PNCs, including olation and oxolation, are triggered by the formation of tetrahedral AlO4 units.
• Observed phase separation at low supersaturation, independent of Keggin-Al13 ion formation in early stages.

Conclusions:

• The prenucleation cluster (PNC) pathway is crucial for the formation of Al(III) (oxy)(hydr)oxides.
• Understanding PNC chemistry provides novel strategies for controlling the entire crystallization process of Al-based materials.