Calcium carbonate (CaCO3) is one of the most abundant minerals in nature and thus one of the most intensively examined systems. It is formed by the precipitation processes that encompass the processes of formation of a new solid phase from a homogeneous system. CaCO3 in marine calcifying organisms (molluscs, corals, algae, sponges, foraminifera…) is formed via biomineralization. Biomineralization is highly controlled process and precipitation processes are the physical-chemical basis of biomineralization. The main driving force controlling the precipitation of CaCO3 is supersaturation, but other parameters such as concentration of constituent ions and dissolved carbon dioxide (CO2), presence of additives, temperature, pH, ionic strength or hydrodynamics are also known to influence and control CaCO3 precipitation and consequently, together with the variety of biological constituents and processes, influence the biomineralization.

The marine calcifying organisms are adapted to a stable environment: narrow range of pH and temperature. However, the increase of CO2 concentration in the atmosphere over the last two centuries (and the increase still continues), as a direct consequence of human activity, consequentially promotes global warming (GW) and ocean pH reduction (ocean acidification, OA). As a result of OA and GW marine organisms are now forced to exist in increasingly acidic water and at higher temperatures and this raises concerns about potential extinction of species and thus massive marine biodiversity losses. In order to survive, organisms are now trying to adapt so marine algae and seagrasses produce secondary metabolites such as phenolic compounds to adapt and acclimate to environmental stressors. Although increased production of phenolic compounds might protect algae and seagrasses from adverse effects of GW and OA, the question arises what consequences will the increased concentration of these compounds have on other marine organisms such as mollusks or corals, also present in this environment. More precisely, will phenolic compounds perhaps react with CaCO3, which is primary building block of their hard tissues, and in that way change the structure of their hard tissues?

The main goal of this research is to determine how the addition of gallic acid into CaCO3 precipitation system influences kinetics, mineralogical composition and morphology of precipitated CaCO3. Gallic acid is going to be used as a model molecule for phenolic compounds. It can be assumed that due to the addition of the gallic acid into the CaCO3 precipitation system, preferential formation of one of the CaCO3 phases will occur as well as change in morphology of precipitated CaCO3. As was said earlier, an understanding of the mechanism(s) of biomineralization requires knowledge of the physical chemistry of CaCO3 precipitation and the results of this work will contribute to a deeper understanding of the fundamental mechanisms of CaCO3 precipitation in relation to changing environment, especially related to biomineralization, in the context of climate change.

In order to evaluate the hypothesis that gallic acid has an effect on CaCO3 formation, precipitation experiments in the presence of gallic acid will be performed. Isolated precipitates will be analysed by scanning electron microscopy (SEM), powder X-ray diffraction (XRD), infrared spectroscopy (IR), specific surface area analysis (BET) and nanoindentation.

By detailed structural and morphological characterization of the obtained precipitates and comparative analysis of the main kinetic parameters (e.g., growth rate as a function of supersaturation), it will be possible to specify the prevailing mechanism governing this particular process and thus the possible role of gallic acid (as model molecule for phenolic compounds) in CaCO3 biomineral formation.