Reactive CaCO3 Formation from CO2 and Methanolic Ca(OH)2 Dispersions: Transient Methoxide Salts, Carbonate Esters and Sol-Gels

A combination of ex situ and in situ characterization techniques was used to determine the mechanism of calcium carbonate (CaCO3) formation from calcium hydroxide (Ca(OH)2) dispersions in methanol/water (CH3OH/H2O) systems. Mid-infrared (mid-IR) analysis shows that in the absence of carbon dioxide (CO2) Ca(OH)2 establishes a reaction equilibrium with CH3OH, forming calcium hydroxide methoxide (Ca(OH)(OCH3)) and calcium methoxide (Ca(OCH3)2). Combined ex situ mid-IR, thermogravimetric analysis (TGA), X-ray diffraction (XRD), X-ray absorption spectroscopy and scanning electron microscopy examination of the reaction product formed in the presence of CO2 reveals the formation of calcium dimethylcarbonate (Ca(OCOOCH3)2). This strongly suggests that carbonation takes place by reaction with the Ca(OCH3)2 formed from a Ca(OH)2 and CH3OH reaction. Time-resolved XRD indicates that in the presence of H2O the Ca(OCOOCH3)2 ester releases CH3OH and CO2, forming ACC, which subsequently transforms into vaterite and then calcite. TGA reveals that thermal decomposition of Ca(OCOOCH3)2 in the absence of H2O mainly leads to the reformation of Ca(OCH3)2, but this is accompanied by a significant parallel reaction that releases dimethylether (CH3OCH3) and CO2. CaCO3 is the final product in both decomposition pathways. For CH3OH/H2O mixtures containing more than 50 mol % H2O, direct formation of calcite from Ca(OH)2 becomes the dominant pathway, although the formation of some Ca(OCOOCH3)2 was still evident in the in situ mid-IR spectra of 20 and 40 mol % CH3OH systems. In the presence of ≤20 mol % H2O, hydrolysis of the ester led to the formation of an ACC sol-gel. In both the 90 and 100 mol % CH3OH systems, diffusion-limited ACC → vaterite → calcite transformations were observed. Traces of aragonite were also detected. We believe that this is the first time that these reaction pathways during the carbonation of Ca(OH)2 in a methanolic phase have been systematically and experimentally characterized.

Evaluation of precipitated CaCO3 produced from locally available limestone as a reinforcement filler for PVC pipe

The current experimental work aimed at developing PCC through two major process steps: dissolution and precipitation, using raw materials domestically available as SL, which are intensively used in construction inputs. The pH level was the decisive parameter used to determine the time required to complete the dissolution and carbonation processes during precipitation. The optimal pH levels were found to be 13 for dissolution and 7.1 for precipitation, respectively. The produced PCC was characterized based on chemical analysis, crystallinity, and morphology, showing an increment of CaCO3 content exceeding 99%, sharper crystal peaks, and predominantly calcite PCC. The compatibility of the PCC was assessed by incorporating 25%, 50%, 75%, and 100% of PCC with commercial filler, followed by selected mechanical tests, such as stress at yield, density, and elongation at break. The results indicated that mixing ratios of 25%, 50%, and 75% of PCC with the commercial filler met the standards, with stress at a yield above 45 MPa and density within the range of 1.35 to 1.46 g/cm3. However, complete substitution slightly lowered these properties. Nevertheless, the elongation at break was acceptable at all treatment levels.

The biocide triclosan as a potential developmental disruptor in Mytilus early larvae

The broadly utilized biocide triclosan (TCS) is continuously discharged in water compartments worldwide, where it is detected at concentrations of ng-µg/L. Given its lipophilicity and bioaccumulation, TCS is considered potentially harmful to human and environmental health and also as a potential endocrine disruptor (ED) in different species. In aquatic organisms, TCS can induce a variety of effects: however, little information is available on its possible impact on invertebrate development. Early larval stages of the marine bivalve Mytilus galloprovincialis have been shown to be sensitive to environmental concentrations of a number of emerging contaminants, including EDs. In this work, the effects of TCS were first evaluated in the 48 h larval assay in a wide concentration range (0.001-1,000 μg/L). TCS significantly affected normal development of D-veligers (LOEC = 0.1 μg/L; EC50 = 236.1 μg/L). At selected concentrations, the mechanism of action of TCS was investigated. TCS modulated transcription of different genes involved in shell mineralization, endocrine signaling, ceramide metabolism, and biotransformation, depending on larval stage (24 and 48 h post-fertilization-hpf) and concentration (1 and 10 μg/L). At 48 hpf and 10 μg/L TCS, calcein staining revealed alterations in CaCO3 deposition, and polarized light microscopy showed the absence of shell birefringence due to the mineralized phase. Observations by scanning electron microscopy highlighted a variety of defects in shell formation from concentrations as low as 0.1 μg/L. The results indicate that TCS, at environmental exposure levels, can act as a developmental disruptor in early mussel larvae mainly by interfering with the processes of biomineralization.

Organic Controls over Biomineral Ca-Mg Carbonate Compositions and Morphologies

Calcium carbonate minerals, such as aragonite and calcite, are widespread in biomineral skeletons, shells, exoskeletons, and more. With rapidly increasing pCO₂ levels linked to anthropogenic climate change, carbonate minerals face the threat of dissolution, especially in an acidifying ocean. Given the right conditions, Ca-Mg carbonates (especially disordered dolomite and dolomite) are alternative minerals for organisms to utilize, with the added benefit of being harder and more resistant to dissolution. Ca-Mg carbonate also holds greater potential for carbon sequestration due to both Ca and Mg cations being available to bond with the carbonate group (CO₃^2-). However, Mg-bearing carbonates are relatively rare biominerals because the high kinetic energy barrier for the dehydration of the Mg²⁺-water complex severely restricts Mg incorporation in carbonates at Earth surface conditions. This work presents the first overview of the effects of the physiochemical properties of amino acids and chitins on the mineralogy, composition, and morphology of Ca-Mg carbonates in solutions and on solid surfaces. We discovered that acidic, negatively charged, hydrophilic amino acids (aspartic and glutamic) and chitins could induce the precipitation of high-magnesium calcite (HMC) and disordered dolomite in solution and on solid surfaces with these adsorbed biosubstrates via in vitro experiments. Thus, we expect that acidic amino acids and chitins are among the controlling factors in biomineralization used in different combinations to control the mineral phases, compositions, and morphologies of Ca-Mg carbonate biomineral crystals.

An acidic protein, Hf15, from Haliotis fulgens involved in biomineralization

Biomineralization leads to the hardening of mineralized materials, such as the shell of Mollusk, to fulfill a wide range of functions, such as (but not limited to) skeletal support, protection of the soft tissues, navigation, etc. The study of the proteins responsible for this process, shell matrix proteins (SMPs), allows addressing questions related to structure-function relationship and to the mechanism of mineral formation, which is limited in gastropod species. In this study, a low molecular weight protein was isolated from the insoluble fraction after decalcification with acetic acid of the shell of Haliotis fulgens and, named Hf15. The unglycosylated protein has a theoretical molecular weight of 15 kDa, it possesses calcium and chiting binding properties. Hf15 can precipitate calcium carbonate in vitro in presence of different salts. Analysis by LC-MS of the five peptide sequences of Hf15 generated by trypsinization revealed that two peptides displayed homology to an uncharacterized protein 3-like from Haliotis rufescens, Haliotis asinia and H. sorenseni. The results obtained indicated that Hf15 is a novel SMP involved in shell mineralization in Haliotis fulgens.

Application of Different Fourier Transform Infrared (FT-IR) Methods in the Characterization of Lime-Based Mortars with Oxblood

Organic compounds have frequently been added into lime mortars for property modifications, in order to satisfy various functional needs in building techniques. This study applies Fourier transform infrared (FT-IR) spectroscopy in transmission, reflection, and attenuated total reflection (ATR) modes to characterize lime-based mortar specimens containing oxblood, which has been used as additive as a common practice of long history in many parts of the world. The specimens were prepared basing upon a 19th-century Italian historic recipe, with the intention to have a better understanding on the possible characteristics of such mortars. Thermal analysis, color measurement, and static contact angle test were also used. After curing, the specimens show a distinctive dark-red color on the top surface, which is different from the bulk. Color measurements on the surface suggest that this color was formed at an early stage and was able to maintain stable for a relatively long period of time. Both transmission and reflection FT-IR confirm the preferential accumulation of proteins on the top surface, which should have induced their water repellency according to the static contact angle test. In addition, specimens show weaker calcite bands in FT-IR transmission, reflection, as well as ATR spectra; the pattern of ATR spectra after the thermal analysis to 500 °C suggests the formation of amorphous calcium carbonate, which is related to the presence of oxblood.

A novel basic matrix protein of Pinctada fucata, PNU9, functions as inhibitor during crystallization of aragonite

The injection of dsRNA of PNU9 could lead to the overgrowth of nacreous lamellas and the matrix membrane.

Effect of low-temperature plasma treatment of electrospun polycaprolactone fibrous scaffolds on calcium carbonate mineralisation

This article reports on a study of the mineralisation behaviour of CaCO3 deposited on electrospun poly(ε-caprolactone) (PCL) scaffolds preliminarily treated with low-temperature plasma. This work was aimed at developing an approach that improves the wettability and permeability of PCL scaffolds in order to obtain a superior composite coated with highly porous CaCO3, which is a prerequisite for biomedical scaffolds used for drug delivery. Since PCL is a synthetic polymer that lacks functional groups, plasma processing of PCL scaffolds in O2, NH3, and Ar atmospheres enables introduction of highly reactive chemical groups, which influence the interaction between organic and inorganic phases and govern the nucleation, crystal growth, particle morphology, and phase composition of the CaCO3 coating. Our studies showed that the plasma treatment induced the formation of O- and N-containing polar functional groups on the scaffold surface, which caused an increase in the PCL surface hydrophilicity. Mineralisation of the PCL scaffolds was performed by inducing precipitation of CaCO3 particles on the surface of polymer fibres from a mixture of CaCl2- and Na2CO3-saturated solutions. The presence of highly porous vaterite and nonporous calcite crystal phases in the obtained coating was established. Our findings confirmed that preferential growth of the vaterite phase occurred in the O2-plasma-treated PCL scaffold and that the coating formed on this scaffold was smoother and more homogenous than those formed on the untreated PCL scaffold and the Ar- and NH3-plasma-treated PCL scaffolds. A more detailed three-dimensional assessment of the penetration depth of CaCO3 into the PCL scaffold was performed by high-resolution micro-computed tomography. The assessment revealed that O2-plasma treatment of the PCL scaffold caused CaCO3 to nucleate and precipitate much deeper inside the porous structure. From our findings, we conclude that O2-plasma treatment is preferable for PCL scaffold surface modification from the viewpoint of use of the PCL/CaCO3 composite as a drug delivery platform for tissue engineering.

Transformation of amorphous calcium carbonate nanoparticles into aragonite controlled by ACCBP

Polymorph switching of calcium carbonate controlled by amorphous calcium carbonate-binding protein, an extrapallial fluid (EPF) protein from the pearl oyster, is investigated. The polymorph selection in nacre or pearl growth may be controlled not only by the nucleating template on the matrix but also by the physicochemical effects of EPF proteins.