University thesis:
Dissertation, Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2020
Footnote:
Description:
This work is dedicated to the highly discussed formation mechanism of amorphous calcium carbonate (ACC), its role in nonclassical crystallization, and amorphous carbonates as a precursor for functional metal oxides. Decrypting the formation mechanism of ACC provides a new environmentally benign synthesis pathway for complex hierarchically structured nanomaterials. Therefore, different ACC synthesis pathways and the corresponding ACC is studied: ACC synthesis via carbonate released by hydrolysis, manual rapid mixing of calcium chloride and sodium carbonate, and controlled turbulent mixing in a stopped-flow device. Particularly three-dimensional nanonetworks of ACC are received, applying the stopped-flow synthesis approach, which indicates a formation mechanism via liquid-liquid phase separation and spinodal decomposition. Moreover, the existence of a liquid-condensed phase in the formation mechanism is emphasized by the break-down of the nanonetwork to energetically favored droplets over time and a pH-dependent hydration rate of ACC. The extraordinary synthesis pathway via liquid-liquid phase separation is further transferred to other alkaline earth and transition metal carbonates. Thereby, three-dimensional highly hydrated amorphous carbonates or hydroxycarbonates, depending on the relevant solubility products, are accessible, demonstrating the potential and applicability of the mechanism studied herein. The cation hydration enthalpy and radius are suggested to limit the ability of liquid phase formation. Amorphous zinc carbonate hydroxide reveals a peculiar pH dependency, regarding its morphology, composition, and hydration. Moreover, it serves as a tuneable precursor for zinc oxide formation. Besides nanostructured zinc oxide offering a high surface area, copper oxide is synthesized via a stable amorphous copper carbonate hydroxide precursor, georgeite. In contrast to the highly structured porous nanonetworks, smooth georgeite thin films are formed by assembly of the liquid-condensed phase at the air-water ...