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Crystals 2017, 7(12), 355; doi:10.3390/cryst7120355

Crystallization of Calcium Carbonate in Alginate and Xanthan Hydrogels

1
Meteorological and Hydrological Service, Air Quality Division, Grič 3, HR-10000 Zagreb, Croatia
2
Dipartimento di Chimica “Giacomo Ciamician”, Alma Mater Studiorum—Università di Bologna, via Selmi 2, 40126 Bologna, Italy
3
Ruđer Bošković Institute, P.O. Box 180, HR-10002 Zagreb, Croatia
*
Authors to whom correspondence should be addressed.
Academic Editor: Linda Pastero
Received: 20 September 2017 / Revised: 21 November 2017 / Accepted: 27 November 2017 / Published: 30 November 2017
(This article belongs to the Special Issue Carbonates)
View Full-Text   |   Download PDF [18918 KB, uploaded 30 November 2017]   |  

Abstract

Calcium carbonate polymorphs were crystallized in alginate and xanthan hydrogels in which a degree of entanglement was altered by the polysaccharide concentration. Both hydrogels contain functional groups (COOH and OH) attached at diverse proportions on saccharide units. In all systems, the precipitation process was initiated simultaneously with gelation, by the fast mixing of the calcium and carbonate solutions, which contain the polysaccharide molecules at respective concentrations. The initial supersaturation was adjusted to be relatively high in order to ensure the conditions suitable for nucleation of all CaCO3 polymorphs and amorphous phase(s). In the model systems (no polysaccharide), a mixture of calcite, vaterite and amorphous calcium carbonate initially precipitated, but after short time only calcite remained. In the presence of xanthan hydrogels, precipitation of either, calcite single crystals, porous polyhedral aggregates, or calcite/vaterite mixtures were observed after five days of ageing, because of different degrees of gel entanglement. At the highest xanthan concentrations applied, the vaterite content was significantly higher. In the alginate hydrogels, calcite microcrystalline aggregates, rosette-like and/or stuck-like monocrystals and vaterite/calcite mixtures precipitated as well. Time resolved crystallization experiments performed in alginate hydrogels indicated the initial formation of a mixture of calcite, vaterite and amorphous calcium carbonate, which transformed to calcite after 24 h of ageing. View Full-Text
Keywords: calcium carbonate; crystallization; hydrogels; alginate; xanthan calcium carbonate; crystallization; hydrogels; alginate; xanthan
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Kosanović, C.; Fermani, S.; Falini, G.; Kralj, D. Crystallization of Calcium Carbonate in Alginate and Xanthan Hydrogels. Crystals 2017, 7, 355.

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