2019-08-15, Neira-Carrillo, Andrónico, Vásquez-Quitral, Patricio, Sánchez, Marianela, Farhadi-Khouzani, Masoud, Aguilar-Bolados, Héctor, Yazdani-Pedram, Mehrdad, Cölfen, Helmut

Multiwalled carbon nanotubes (MWCNTs) are interesting high-tech nanomaterials. MWCNTs oxidized and functionalized with itaconic acid and monomethylitaconate were demonstrated to be efficient additives for controlling nucleation of calcium carbonate (CaCO₃) via gas diffusion (GD) in classical as well as nonclassical crystallization, yielding aragonite and truncated calcite. For the first time, all amorphous calcium carbonate (ACC) proto-structures, such as proto calcite-ACC, proto vaterite-ACC and proto aragonite-ACC, were synthesized via prenucleation cluster (PNC) intermediates and stabilized at room temperature. The MWCNTs also showed concentration-dependent nucleation promotion and inhibition similar to biomolecules in nature. Incorporation of fluorescein-5-thiosemicarbazide (5-FTSC) dye-labeled MWCNTs into the CaCO₃ lattice resulted in fluorescent hybrid nanosized CaCO₃. We demonstrate that functionalized MWCNTs offer a good alternative for controlled selective crystallization and for understanding an inorganic mineralization process.

2016, Farhadi-Khouzani, Masoud, Chevrier, Daniel M., Zhang, Peng, Hedin, Niklas, Gebauer, Denis

Temperatur und pH-Wert können die Nahordnung in proto-strukturiertem, amorphem Calciumcarbonat (ACC) in Abwesenheit von Additiven beeinflussen. Während im Proto-Vaterit(pv)-ACC bei pH 9.80 bei >45 °C eine ausgeprägte Veränderung stattfindet, ist dies beim Proto-Calcit(pc)-ACC innerhalb des untersuchten Temperaturbereichs von 7 bis 65 °C nicht der Fall. Mit IR- und NMR-Spektroskopie sowie EXAFS konnte gezeigt werden, dass die temperaturbedingten Veränderungen auf die Bildung von Proto-Aragonit(pa)-ACC zurückzuführen sind. Die experimentellen Befunde sprechen zudem dafür, dass bei pa-ACC durch die Bindung von Wassermolekülen ein Dipolmoment innerhalb der Carbonationen induziert wird, vergleichbar mit dem Effekt der Kristallsymmetrie auf die Carbonationen in der Aragonitstruktur. So kann in Abhängigkeit von Zustandsgrößen wie der Temperatur und Lösungsparametern wie dem pH-Wert die Polyamorphie von CaCO3 anhand eines (Pseudo-)Phasendiagramms, in dem Wasser eine Schlüsselrolle spielt, dargestellt werden.

2017, Farhadi-Khouzani, Masoud

Amorphous mineral phases, e.g. amorphous calcium carbonate (ACC) that occurs ubiquitously in nature, play a pivotal role in biomineralization processes and as such, are a focal point of vast interdisciplinary research. Studies into biogenic ACCs indicate the existence of different short-range orders, which can be understood within the notion of amorphous polymorphism (polyamorphism). It is speculated that distinct short-range orders in biogenic ACCs are triggered by various ions and biomolecules. However, it was shown that additive-free ACCs obtained from metastable solutions with equilibrated pre-nucleation clusters (PNCs) can also exhibit different proto-crystalline structures. The first part of this thesis concern with the importance of the existence of equilibrated PNCs for the development of proto-structures in ACCs. This was accomplished by directprecipitation of ACC in alcoholic media. Second, the role of pH and temperature in the development of short-range orders of ACCs is further explored. The aim is to complete and thereby corroborate the notion of ACC polyamorphism with the proto-aragonite (pa)-ACC form, which has not been reported for ambient pressures until now. Last, polymer-stabilized liquid precursors of CaCO3 were employed to selectively mineralize nanocellulose films via controlling the mineralization sites on nanocellulose fibres. The controlled mineralization enabled formation of mineralized and unmineralized layers of nanocellulose. This, in turn, yielded a bio-inspired, layered, nacre-like material outperforming the biological example in terms of plasticity.

2016, Farhadi-Khouzani, Masoud, Chevrier, Daniel M., Zhang, Peng, Hedin, Niklas, Gebauer, Denis

Temperature and pH value can affect the short-range order of proto-structured and additive-free amorphous calcium carbonates (ACCs). Whereas a distinct change occurs in proto-vaterite (pv) ACC above 45 °C at pH 9.80, proto-calcite (pc) ACC (pH 8.75) is unaffected within the investigated range of temperatures (7-65 °C). IR and NMR spectroscopic studies together with EXAFS analysis showed that the temperature-induced change is related to the formation of proto-aragonite (pa) ACC. The data strongly suggest that the binding of water molecules induces dipole moments across the carbonate ions in pa-ACC as in aragonite, where the dipole moments are due to the symmetry of the crystal structure. Altogether, a (pseudo-)phase diagram of the CaCO3 polyamorphism in which water plays a key role can be formulated based on variables of state, such as the temperature, and solution parameters, such as the pH value.

2017, Farhadi-Khouzani, Masoud, Schütz, Christina, Durak, Grazyna Malgorzata, Fornell, Jordina, Sort, Jordi, Salazar-Alvarez, Germán, Bergström, Lennart, Gebauer, Denis

Nacre continues to be an inspiration for the fabrication of strong and tough materials from renewable and earth-abundant raw materials. Herein, we showed how a nacre-like hybrid material based on nanocellulose (NC) and CaCO₃ can be prepared via the sequential infiltration of polymer-stabilised CaCO₃ liquid precursors into layers of pre-deposited NC films. Layer-by-layer assembly of the NC films followed by controlled spreading and infiltration with liquid CaCO₃ precursors generated a lamellar material with an architecture and iridescent appearance similar to those of nacre. The wettability of the NC films towards the liquid CaCO₃ precursors was controlled by hydroxyl and carboxyl functionalization of the NC fibrils and the addition of magnesium ions. The combination of a high stiffness and plasticity of the nacre-like NC/CaCO₃ hybrid materials show that excellent mechanical properties can be obtained employing a fibrillar organic constituent that is relatively hard. The fabrication of a nacre-like hybrid material via an aqueous route of assembly and infiltration processing demonstrates how a sustainable composite material with outstanding properties can be produced using the most abundant biopolymer and biomineral on earth.

2015, Farhadi-Khouzani, Masoud, Chevrier, Daniel M., Güttlein, Patricia, Hauser, Karin, Zhang, Peng, Hedin, Niklas, Gebauer, Denis

Amorphous calcium carbonate (ACC) is known to play a prominent role in biomineralization. Different studies on the structure of biogenic ACCs have illustrated that they can have distinct short-range orders. However, the origin of so-called proto-structures in synthetic and additive-free ACCs is not well understood. In the current work, ACC has been synthesised in iso-propanolic media by direct precipitation from ionic precursors, and analysed utilising a range of different techniques. The data suggest that this additive-free type of ACC does not resemble clear proto-structural motifs relating to any crystalline polymorph. This can be explained by the undefined pH value in iso-propanolic media, and the virtually instantaneous precipitation. Altogether, this work suggests that aqueous systems and pathways involving pre-nucleation clusters are required for the generation of clear proto-structural features in ACC. Experiments on the ACC-to-crystalline transformation in solution with and without ethanol highlight that polymorph selection is under kinetic control, while the presence of ethanol can control dissolution re-crystallisation pathways.