Ab Initio Molecular Dynamics Reveal Spectroscopic Siblings and Ion Pairing as New Challenges for Elucidating Prenucleation Aluminum Speciation
- Washington State Univ., Pullman, WA (United States)
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Washington State Univ., Pullman, WA (United States); Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Washington River Protection Solutions, LLC, Richland, WA (United States)
We report the characterization of prenucleation species is essential to understand crystallization mechanisms across many chemical systems and often involves the use of vibrational spectroscopy. Nowhere is this more evident than in the development of “green” aluminum processing technologies, where detailed understanding of the speciation of aluminum and its polynuclear analogues in highly alkaline, low water solutions is elusive. The aluminate anion Al(OH)4– predominates in alkaline conditions, yet equilibrium with dimeric species, either μ-oxo Al2O(OH)62– or di-μ-hydroxo Al2(OH)82–, can be assumed. Using ab initio molecular dynamics with full solvation and the presence of counterions, this work reconciles previous contradictory studies that had concluded only a single species under relevant solution conditions. We reveal that the two dimers are energetically separated by 2 kcal/mol in pure water but that the stability of each can be reversed by ion pairing expected in saturated salt solutions. Simulated Raman and IR spectra for each species (accounting for anharmonicity and the fluctuating solvating environment) provide the first proof that the considered species are “spectroscopic siblings”, whose multiple overlapping bands prevent definitive assertions in terms of speciation when compared to the experimental spectra. Lastly, these observations are likely to hold in higher order aluminate oligomers and as such present a massive challenge toward understanding the crystallization mechanisms relevant to aluminum processing.
- Research Organization:
- Pacific Northwest National Laboratory (PNNL), Richland, WA (United States); Energy Frontier Research Centers (EFRC) (United States). Interfacial Dynamics in Radioactive Environments and Materials (IDREAM); Univ. of California, Berkeley, CA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES); USDOE Office of Science (SC), Biological and Environmental Research (BER)
- Contributing Organization:
- IDREAM (Interfacial Dynamics in Radioactive Environments and Materials); Environmental Molecular Sciences Laboratory (EMSL)
- Grant/Contract Number:
- AC05-76RL01830; AC02-05CH11231
- OSTI ID:
- 1504422
- Alternate ID(s):
- OSTI ID: 1596344
- Report Number(s):
- PNNL-SA-132755
- Journal Information:
- Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical Chemistry, Vol. 122, Issue 29; ISSN 1520-6106
- Publisher:
- American Chemical SocietyCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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