Formation of calcium carbonate films on chitosan substrates in the presence of polyacrylic acid

In this investigation, chitosan membranes with different surface average degrees of deacetylation (DA) are prepared and then are employed as the support matrix to culture calcium carbonate (CaCO₃). In the presence of high concentration of polyacrylic acid (PAA), the CaCO₃ films obtained on the surface of all chitosan films mainly consisted of vaterite, which suggests the presence of bulk PAA plays an overwhelming part in stabilizing the vaterite. As a comparison, the influences of active groups indicate that only in case of low concentration PAA the thin CaCO₃ films grown on chitosan with 8% DA mainly consisted of vaterite owing to the strong nucleation ability of -NH₂ group, whereas, for those grown on chitosan with 80% DA the CaCO₃ films mainly consisted of aragonite. A more complex scenario revealed that in the case of intermediate concentration of PAA the formed polymorphs behave as mixtures of vaterite and aragonite.     

Green Synthesis of Calcium Carbonate Uniform Microspheres Using Vegetables

We report a novel strategy for the green synthesis of calcium carbonate (CaCO₃) microspheres by using four vegetables: potato, cucumber, aubergine, and carrot. The products were characterized by scanning electron microscopy, X‐ray powder diffractometry and/or Fourier transform infrared spectroscopy. The results show that the spherical calcite crystals are obtained in the presence of potato, cucumber and aubergine extracts, while uniform vaterite and calcite mixed microspheres are produced with the extracts of carrot. The possible formation mechanism of the CaCO₃ microspheres by using vegetables is also discussed, suggesting that the biomolecules especially proteins may induce and control the nucleation and growth of CaCO₃ crystals. CaCO₃ is an important biomineral and inorganic material. Uniform particles have numerous important applications in many areas. Therefore, this study is very significant not only for expanding the scope of crystal engineering, but also for biomineralization research and green synthesis of functional inorganic materials.     

珍珠质基底上CaCO3晶体的仿生生长研究

珍珠质是一种典型的有机，无机层状复合材料．其中95％以上是文石（CaCO3的一种晶型1小板片，填充在板片之间的薄层有机基质仅占1％-5％。这种精细的组织结构不仅使珍珠质具有绚丽的光泽。还赋予珍珠质超乎寻常的强度和韧性（为合成CaCO3晶体的3000多倍）。虽然在珍珠质中有机质的含量不足5％．然而正是这些有机质对珍珠质的结构、性能、晶体取向等起着至关重要的调控作用。     

Biomimetic synthesis of aragonite superstructures using hexamethylenetetramine

In this paper, biomimetic synthesis of aragonite superstructures using a low molecular weight organic-hexamethylenetetramine (HMT) as an additive in the presence of CO₂ supplied by an ammonium carbonate ((NH₄)₂CO₃) diffusion method at room temperature was studied. The products were characterized by scanning or transmission electron microscopy, Fourier transform infrared (FT-IR) spectroscopy, X-ray powder diffractometry, and selected area electron diffraction. The results showed the aragonite superstructures especially dumbbell-flower-like ones were obtained. The formation process of calcium carbonate (CaCO₃) in HMT aqueous solution was investigated, suggesting that the products transformed from calcite to vaterite primarily, and then changed into a mixture of aragonite and calcite with an increase of reaction time. The formation mechanism of CaCO₃ in HMT solution was also discussed, revealing that aragonite might be controlled by HMT molecules and NH₄⁺ ions together.     

Crystallization of calcium carbonate controlled by Pluronic P123 in room-temperature ionic liquid

The crystallization of calcium carbonate (CaCO₃) controlled by Pluronic P123 in a room-temperature ionic liquid, ethylamine nitrate (EAN), was investigated. The CaCO₃ aggregates were obtained by rapid mixing of ammonium carbonate ((NH₄)₂CO₃) and calcium chloride (CaCl₂). Cubic calcite, spherical vaterite, and bagel-like vaterite were obtained easily by changing P123 concentration and reaction temperature. The morphologies of the as-prepared CaCO₃ aggregates were investigated by transmission electron microscopy and scanning electronic microscopy. The phase change of the obtained crystals was confirmed by X-ray diffraction and Fourier transform infrared spectroscopy. It was shown that higher P123 concentration and higher reaction temperature favor the formation of vaterite in EAN. Unusual bagel-like vaterite was first obtained at 60 °C in the presence of 5 g/L P123 in EAN. Mineralization of CaCO₃ regulated by P123 in EAN is a simple, novel, and environment-friendly strategy for vaterite synthesis.     

Morphology and Kinetics of Growth of CaCO<Subscript>3</Subscript> Precipitates Formed in Saline Water at 30°C

The crystallization kinetics and morphology of CaCO₃ crystals precipitated from the high salinity oilfield water were studied. The crystallization kinetics measurements show that nucleation and nuclei growth obey the first order reaction kinetics. The induction period of precipitation is extended in the high salinity solutions. Morphological studies show that impurity ions remain mostly in the solution phase instead of filling the CaCO₃ crystal lattice. The morphology of CaCO₃ precipitates can be changed from a smooth surface (calcite) to rough spheres (vaterite), and spindle rod bundles, or spherical, ellipsoid, flowers, plates and other shapes (aragonite).     

Assembled structures of nanocrystals in polymer/calcium carbonate thin-film composites formed by the cooperation of chitosan and poly(aspartate)

Assembled structures of calcium carbonate (CaCO₃) nanocrystals have been examined for polymer/CaCO₃ thin-film composites synthesized through a self-organization process inspired by biomineralization. For the crystallization of CaCO₃, a thin-film matrix of chitosan has been used as a polymeric substrate. When the matrix is immersed into a supersaturated aqueous solution of CaCO₃ containing 1.4 × 10⁻³ wt % poly(aspartate) (PAsp), thin-film crystals of CaCO₃ are formed spontaneously. Three kinds of disklike films have been observed under a polarizing optical microscope. Electron diffraction analyses of each film have revealed that one is aragonite, displaying radial orientation of the c axes, and the others are vaterite, exhibiting different orientations. Detailed observation by scanning electron microscopy has clarified that these films are assemblies of crystalline particles 10–20 nm in size. The thin-film composites have been obtained over a PAsp concentration range of 4.4 × 10⁻⁴ to 1.0 × 10⁻² wt %. Vaterite formation becomes dominant when the concentration of PAsp is increased. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5153–5160, 2006     

Characterization of a Novel CaCO3-Forming Alkali-Tolerant Rhodococcus erythreus S26 as a Filling Agent for Repairing Concrete Cracks

Biomineralization, a well-known natural phenomenon associated with various microbial species, is being studied to protect and strengthen building materials such as concrete. We characterized Rhodococcus erythreus S26, a novel urease-producing bacterium exhibiting CaCO₃-forming activity, and investigated its ability in repairing concrete cracks for the development of environment-friendly sealants. Strain S26 grown in solid medium formed spherical and polygonal CaCO₃ crystals. The S26 cells grown in a urea-containing liquid medium caused culture fluid alkalinization and increased CaCO₃ levels, indicating that ureolysis was responsible for CaCO₃ formation. Urease activity and CaCO₃ formation increased with incubation time, reaching a maximum of 2054 U/min/mL and 3.83 g/L, respectively, at day four. The maximum CaCO₃ formation was achieved when calcium lactate was used as the calcium source, followed by calcium gluconate. Although cell growth was observed after the induction period at pH 10.5, strain S26 could grow at a wide range of pH 4–10.5, showing its high alkali tolerance. FESEM showed rhombohedral crystals of 20–60 µm in size. EDX analysis indicated the presence of calcium, carbon, and oxygen in the crystals. XRD confirmed these crystals as CaCO₃ containing calcite and vaterite. Furthermore, R. erythreus S26 successfully repaired the artificially induced large cracks of 0.4–0.6 mm width.     

PREPARATION OF CaCO3 PARTICLES IN WATER POOL IN NONAQUEOUS NONIONIC SURFACTANT SOLUTIONS

ABSTRACT

CaCO₃ particles were prepared by bubbling of CO₂ into the systems consisting of polyoxyethylene(6) nonylphenyl ether/aqueous Ca(OH) ₂/cyclohexane. Spherical particles were formed in any systems, but those size distribution depended on the solubility behavior of aqueous Ca(OH) ₂ in surfactant solutions, i.e., monodisperse particles were formed in colorless solution, whereas in blue translucent solution they became bimodal. Such change was also observed for the size of reversed micelles. This suggested that the formation of CaCO₃ particles were related with that of micelles. On the other hand, the particles obtained were consisted of calcite, vaterite and aragonite. Those fraction differed also from the solubility behavior of aqueous Ca(OH) ₂. Both the vaterite and aragonite were transformed into calcite and those rate constants were order of 10^?6 sec^?1.     

Tuning the Stability of CaCO3 Crystals with Magnesium Ions for the Formation of Aragonite Thin Films on Organic Polymer Templates

Thin‐film growth of aragonite CaCO₃ on annealed poly(vinyl alcohol) (PVA) matrices is induced by adding Mg²⁺ into a supersaturated solution of CaCO₃. Both the growth rate and surface morphology of the aragonite thin films depend upon the concentration of Mg²⁺ in the mineralization solution. In the absence of PVA matrices, no thin films are formed, despite the presence of Mg²⁺. Molecular dynamics simulation of the CaCO₃ precursor suggests that the transition of amorphous calcium carbonate to crystals is suppressed in the presence of Mg²⁺. The role for ionic additives in the crystallization of CaCO₃ on organic templates obtained in this study may provide useful information for the development of functional hybrid materials.     

Role of Polyelectrolytes in Crystallogenesis of Calcium Carbonate

The effects anionic polyelectrolytes, having various molecular weights and repeating unit structures, on the crystallization of calcium carbonate in supersaturated solutions are studied. The induction times of the crystals grown in the presence of the polymers were optically evaluated; X-ray diffraction and Scanning Electronic Microscopy (SEM) analyses were performed to determine, respectively, their crystalline structures and morphologies. The polyelectrolyte is found to lengthen the induction time and to reduce the size of CaCO₃ nanocrystallites, to an extent depending on the interaction efficiency between the polymer anionic repeating units and the calcium ions. Further, depending on their sizes and their crystalline structures (calcite, vaterite) the nanocrystallites aggregate and yield final calcium carbonate particles having various sizes and morphologies. The data indicate that nanocrystals having vaterite structure, as determined by X-ray analysis, give spherical CaCO₃ final particles, while nanocrystals having calcite structure lead to either acicular or flower shapes of CaCO₃ final particles.     

Investigation of Calcium Carbonate Scaling Inhibition and Scale Morphology by AFM

The calcium carbonate scale inhibition by two inhibitors, polyacrylic acid (PAA) and 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA), has been studied in two heat transfer systems: recirculating cooling water and pool boiling systems. It is found that PBTCA has a better inhibition effect than PAA under identical conditions. The inhibition effect increases with increasing fluid velocity for the cooling water system, whereas in the presence of inhibitors, the fluid velocity has less effect on the scaling behavior. When the initial surface temperature increases, the inhibition efficiency decreases. In the presence of inhibitors, the scaling behavior is insensitive to the change of surface temperature. The relationship between the inhibition effect and the fractal dimension has also been investigated. The results show that the fractal dimension is higher in the presence of inhibitors. The better the inhibition effect, the higher the fractal dimension. XRD and FTIR analyses demonstrate that for the CaCO₃ formed in the pool boiling system, the content of vaterite increases with the increase of inhibition effects. The metastable crystal forms of vaterite and aragonite are stabilized kinetically in the presence of inhibitors. The step morphology has been observed by atomic force microscopy. It is shown that the step space on the CaCO₃ surface increases in the presence of inhibitors. Moreover, with the increase in inhibition effect, both the step space and the fractal dimension increase. Step bunching is also found and discussed in this paper.     

Effects of macromolecules on the crystallization of CaCO3 the Formation of Organic/Inorganic Composites

The effects of macromolecules as soluble additives and solid matrices have been examined for the crystallization of CaCO₃. A vaterite form grows on a glass substrate in the presence of poly(glutamic acid) (PGA) containing a carboxylic acid group as a soluble additive. In contrast, no crystal growth has been observed when poly(acrylic acid) (PAA) exists as an additive though it has the same functional group. The conformation or the backbone structure of the polymers may have an influence on the crystal polymorph of CaCO₃. Thin film states of CaCO₃ crystals have been obtained as organic/inorganic composites with chitosan that acts as a solid matrix in the presence of PAA or PGA as a soluble additive.     

Effects of Hydroxypropylmethylcellulose macromolecules used as organic template on the crystallization of CaCO<Subscript>3</Subscript>

Hydroxypropylmethylcellulose (HPMC) was used as an organic template to synthesize calcium carbonate. Crystals were synthesized in HPMC solution and HPMC hydrogel, respectively. For the mineralization system of HPMC solution, the effects of adding HPMC and rotating the reaction system on the crystal polymorph and morphology of CaCO₃ were investigated by X-ray diffractometer (XRD) and scanning electron microscope (SEM). The results showed that the presence of HPMC induced the formation of aragonite. And its content became higher when the concentration of solution increased or when rotating the system with the presence of HPMC. Moreover, it can be seen from SEM that bundle-like CaCO₃ appeared and became more with the increase of concentration. The structure and shape of the crystal had close relationship with the condition of mineralization. On the other hand, for the first time, CaCO₃ was synthesized in HPMC gel, SEM results indicated that a special structure, a long bar with some slight slots at intervals on the surface, of the crystals which may be caused by the network structure of the gel was found. Thermogravimetry (TG) results showed that CaCO₃ crystal products contained some HPMC. Further research on how the gel network modulates the growth of crystals is left to be done in the future.     

Localized quantification of anhydrous calcium carbonate polymorphs using micro-Raman spectroscopy

Micro-Raman spectroscopy is a powerful technique for qualitative and quantitative analysis of different mineral mixtures. In this paper, micro-Raman spectroscopy was used for quantification in local regions (180 × 180 μm area) of ternary mixtures of the synthetic calcium carbonate (CaCO₃) polymorphs (vaterite, aragonite, calcite) as well as CaCO₃ formed during the carbonation of nanolime suspension. The obtained results of localized quantification were in agreement with the detected concentrations obtained from bulk quantitative phase analysis of X-ray powder diffraction patterns. The detection limits were found to be below 0.5 wt.% for each CaCO₃ polymorphs. Through the use of 2D mapping, localized quantification of CaCO₃ polymorphs can be achieved. This information could be potentially useful for conservation of valuable Cultural Heritage objects, as it might influence the consolidation treatment chosen.     

Facile synthesis of calcium carbonate with an absolutely pure crystal form using 1-butyl-3-methylimidazolium dodecyl sulfate as the modifier

Calcium carbonate (CaCO₃) nanocrystals with controllable polymorph and morphology have been successfully synthesized with the aid of an effective control agent, a halogen-free, low-cost ionic liquid surfactant, 1-butyl-3-methylimidazolium dodecylsulfate ([C₄mim][C₁₂SO₄]) in a supersaturated aqueous solution. For the first time, facile preparation of pure lens-like vaterite, sheet-like calcite, and peanut-like aragonite was all achieved in the [C₄mim][C₁₂SO₄] aqueous solution through changing the concentration, temperature, and initial pH value and adding magnesium ions. Washed by water and ethanol, all the aggregates were free of [C₄mim][C₁₂SO₄] and can be stable at least 1 month in air. The crystal form of the aggregates changed from pure calcite to pure vaterite at room temperature only through increasing [C₄mim][C₁₂SO₄] concentration. Formation of the ordered CaCO₃ structures is mainly ascribed to the aggregation of the primary nanoparticles whose formation mechanism is related to the change of supersaturation. This study can provide a facile and environment-friendly method to fabricate CaCO₃ crystal aggregates with various morphologies and polymorphs and can be used for large-scale industrial production and biomimetic synthesis.     

Nucleation activity of nanosized CaCO3 on crystallization of isotactic polypropylene, in dependence on crystal modification, particle shape, and coating

A detailed analysis of the effect of calcium carbonate nanoparticles on crystallization of isotactic polypropylene (iPP) is reported in this contribution. CaCO₃ nanoparticles with different crystal modifications (calcite and aragonite) and particle shape were added in small percentages to iPP. The nanoparticles were coated with two types of compatibilizer (either polypropylene-g-maleic anhydride copolymer, or fatty acids) to improve dispersion and adhesion with the polymer matrix.It was found that the type of coating agent used largely affects the nucleating ability of calcium carbonate towards formation of polypropylene crystals. CaCO₃ nanoparticles coated with maleated polypropylene can successfully promote nucleation of iPP crystals, whereas the addition of nanosized calcium carbonate coated with fatty acids delays crystallization of iPP, the effect being mainly ascribed to the physical state of the coating in the investigated temperature range for crystallization of iPP, as well as to possible dissolution by fatty acids of heterogeneities originally present in the polypropylene matrix.     

碳酸岩矿化菌诱导碳酸钙晶体形成机理研究

选用碳酸盐矿化菌(芽孢杆菌系), 分别研究了不同浓度细菌液、细菌体及其分泌物对碳酸钙晶体形成的影响. 研究表明, 细菌液浓度越高, 控制碳酸钙晶体形貌作用越显著; 细菌体为碳酸钙结晶提供异相成核点而对形貌并没有实质影响; 细菌分泌物可诱导出球形、纺锤形等多种形态亚稳态球霰石; 在微生物环境的长期作用下可形成有机-无机复合碳酸钙硬质膜. 通过对电导率测定结果和碳酸钙红外图谱分析得出, 生物有机质分子链的极性基团(COOH, C＝O等)与Ca^2＋产生静电、配位等一系列作用, 调控晶体的生长. 本研究对于微生物诱导碳酸钙的工程性应用, 如混凝土微裂缝修复、古建筑表面防护处理、微纳米碳酸钙颗粒制备等具有一定指导意义.     

Effect of the self-assembly of collagen on crystallisation of calcium carbonate in aqueous solution

In order to investigate how the self-assembly of organic matrix influences crystallisation and growth of inorganic minerals, we selected collagen as the matrix and conducted three experiments of crystallisation of CaCO₃ in different reaction systems: H₂O system, as-assembled collagen fibrils system and self-assembling of collagen system. It is found that (i) the self-assembly process of organic matrix had a remarkable effect on the morphology of inorganic minerals: CaCO₃ crystals formed in the as-assembled collagen fibrils system were global clusters and those formed in the self-assembling of collagen system appeared as interlaced networks and (ii) the organic matrix decided the polymorph of crystals: CaCO₃ crystals were calcite in the H₂O system and appeared vaterite in the collagen system. From this study, we can conclude that the self-assembly of collagen fibrils greatly affect the crystallisation and growth of CaCO₃. Such results are significant in understanding the mechanism of biomineralisation in calcified tissues in general, and useful in the synthesis of biominerals.

(a)?CaCO₃ formed in the as-assembled collagen fibrils system. (b)?CaCO₃ formed in the self-assembling of collagen monomer system.The TEM images of samples obtained in the as-assembled collagen fibrils and self-assembling of collagen monomer system, were observed, respectively. The result shows that crystals CaCO₃ formed in the as-assembled collagen fibrils system were global clusters; crystals CaCO₃ formed in the self-assembling of collagen monomer system appeared interlaced networks.     

Crystal growth of CaCO3 induced by monomethylitaconate grafted polymethylsiloxane

We report the preparation of a new monomethylitaconate grafted polymethylsiloxane (CO₂H-PMS) copolymer and its effect as template for crystal growth of CaCO₃. The in vitro crystallization of CaCO₃ was carried out using the gas diffusion method at different pH values at room temperature for 24 h. The CO₂H-PMS was prepared using polydimethylsiloxane-co-methylhydrogensiloxane (PDMS-co-PHMS), obtained through cationic ring opening polymerization, from cyclic monomers and monomethyltaconate (MMI) via hydrosilylation reactions with platinum complex as catalyst. FTIR results are in an agreement with the proposed template structure and confirmed that the hydrosilylation was complete. Experimental results from pH values and SEM analysis showed that the carboxylate groups of CO₂H-PMS alter the nucleation, growth and morphology of CaCO₃ crystals. SEM revealed single-truncated (ca. 5 μm) modified at pH 7-9, aggregated-modified (ca. 20 μm) at pH 10-11, and donut-shaped crystals at pH 12. These morphologies reflect the electrostatic interaction of carboxylic moieties with Ca²⁺ modulated by CO₂H-PMS adsorbed onto the CaCO₃ particles. EDS confirmed the presence of Si atoms on the crystals surface. XRD analysis showed the existence of only two polymorphs: calcite and vaterite revealing a selective control of CaCO₃ polymorphisms. In summary, the use of grafted polymethylsiloxane template offer a good alternative for polymer controlled crystallization and a convenient approach for understanding the biomineralization process useful for the design of novel materials.