Control of nucleation and crystallization of Al(III)(oxy)(hydr)oxides: An avenue toward advanced materials

• Applicant: Professor Dr. Denis Gebauer
• Subject Area: Solid State and Surface Chemistry, Material Synthesis ; Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
• Term: from 2021 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 455689363

The chemistry of aluminium attracts enormous attention due to the importance of new sustainable energy sources, organometallic hybrid networks, advanced vaccine formulations, environmental wastewater treatments, the acidification of soils and aquatic systems upon climate change, and many more. Possibly the most important aspect concerns its detrimental effects on human health, the scientific explanation of which is elusive. In all these contexts, the aqueous formation of Al(III) (oxy)(hydr)oxides (AlOx) seems to play a central role. However, the physical-chemical conditions determining the onset of phase separation still remain an open question, and the nucleation mechanism itself largely unclear. While it is well known that the presence of spectator anions or organic molecules influences the hydrolysis-(polymerization)-nucleation cascade by (de-/)stabilizing specific Al(III) species and affecting the pH development during AlOx precipitation, data on the relevance of spectator cations is rather scarce. There appears to be no intuitive chemical rationalization for their influence on Al(III) hydrolysis/condensation. Here, based on the state-of-the-art presented in the literature, and preliminary work on the nucleation mechanism in the aqueous Al(III) system, and on corresponding effects of calcium ions, we propose a project aiming at a fundamental improvement of the understanding of the means towards controlling these processes. One emphasis lies on calcium ions —which are key players in biological signaling pathways and neural function, and may lie at the heart of some detrimental health effects of aluminium. Also, we will explore the effects of organic molecules that are important in the above-mentioned areas; fumaric acid, polyacrylic acid, poly-L-aspartic acid, poly-L-glutamic acid, and polyphenolic ellagic acid. The research plan is designed based upon using complimentary methods, i.e., advanced potentiometric titration assays, isothermal titration calorimetry, analytical ultracentrifugation, NMR, electron microscopies, and more. We define five milestones, the first two of which are achieved upon finalizing the detailed speciation of the early stages of AlOx formation with and without additives, requiring roughly half of the project time. We demonstrate that this achievement is viable, which will facilitate the finalization of the following three milestones that will provide detailed insights into the early- and later-stage interactions of AlOx precursors, intermediates and solids with the additives. Our vision is finding correlations between additive structures and effects on AlOx formation, as a first step towards the establishment of an additive library, and target-oriented materials synthesis. In any case, the project will generate a fundamentally improved understanding of the aqueous Al(III) chemistry, which is required for the advancement of applications of aluminium in various topical fields, especially, its impacts on human health.

• DFG Programme: Research Grants
• Major Instrumentation: Isothermes Titrationskalorimeter (ITC)
• Instrumentation Group: 8660 Thermoanalysegeräte (DTA, DTG), Dilatometer