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Anhydrous Amorphous Calcium Oxalate Nanoparticles from Ionic Liquids: Stable Crystallization Intermediates in the Formation of Whewellite
Author(s) -
Gehl Aaron,
Dietzsch Michael,
Mondeshki Mihail,
Bach Sven,
Häger Tobias,
Panthöfer Martin,
Barton Bastian,
Kolb Ute,
Tremel Wolfgang
Publication year - 2015
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201502229
Subject(s) - crystallization , anhydrous , amorphous solid , chemical engineering , dissolution , oxalate , materials science , calcium oxalate , nanoparticle , aqueous solution , biomineralization , chemistry , inorganic chemistry , crystallography , organic chemistry , nanotechnology , engineering
The mechanisms by which amorphous intermediates transform into crystalline materials are not well understood. To test the viability and the limits of the classical crystallization, new model systems for crystallization are needed. With a view to elucidating the formation of an amorphous precursor and its subsequent crystallization, the crystallization of calcium oxalate, a biomineral widely occurring in plants, is investigated. Amorphous calcium oxalate (ACO) precipitated from an aqueous solution is described as a hydrated metastable phase, as often observed during low‐temperature inorganic synthesis and biomineralization. In the presence of water, ACO rapidly transforms into hydrated whewellite (monohydrate, CaC 2 O 4 ⋅ H 2 O, COM). The problem of fast crystallization kinetics is circumvented by synthesizing anhydrous ACO from a pure ionic liquid (IL‐ACO) for the first time. IL‐ACO is stable in the absence of water at ambient temperature. It is obtained as well‐defined, non‐agglomerated particles with diameters of 15–20 nm. When exposed to water, it crystallizes to give (hydrated) COM through a dissolution/recrystallization mechanism.