The inducing effect of lecithin liposome organic template on the nucleation and crystal growth of calcium carbonate

Lecithin liposome was employed as an organic template to control the nucleation and growth of calcium carbonate. The specific interaction of lecithin liposome and calcium ions was investigated by measuring the Zeta potential of the lecithin liposome compound with Ca²⁺. The morphology and polymorphs of the CaCO₃ synthesized in lecithin liposome suspensions of different concentrations were studied. SEM and TEM images showed that spherical particles of CaCO₃, which were synthesized under the effect of lecithin liposome, composed of nano-particles in a hierarchical structure. The polymorph of the calcium carbonate was also modified by lecithin liposome. XRD results indicated lecithin liposome can induce the polymorph of vaterite of calcium carbonate as well.     

Preparation of calcium carbonate microparticles containing organic fluorescent molecules from vaterite

The encapsulation of fluorescent organic molecules into crystalline calcium carbonate was examined using calcium carbonate microcapsule, whose crystalline phase is vaterite as a metastable phase of calcium carbonate. A calcium carbonate microcapsule with impregnated pyrene that is a water insoluble fluorescent molecule was soaked into suitable aqueous solutions to promote the phase transition of vaterite toward calcite as the stable phase of calcium carbonate. When 0.2 M calcium chloride solution was used, the largest amount of pyrene (approximately 0.06 wt%) was encapsulated into the calcite particle. Pyrene thus included was not eliminated even after thorough washing with THF. The calcite particle thus prepared produced the excimer emission of pyrene by UV irradiation. Rhodamine B was also introduced into calcium carbonate by the immersion of the microcapsule into the aqueous solutions of Rhodamine B. The fluorescence of rhodamine B was observed from the calcium carbonate particles by visible light irradiation. Acetaminophen, a common drug poorly soluble in water, was also included in the calcium carbonate particle by the same procedures as the pyrene encapsulation. As acetaminophen thus encapsulated was released by the dissolution of the calcium carbonate particle in acidic solution, the particle is expected to be applied for a dissolution-triggered drug delivery.     

Synthesizing a composite material of amorphous calcium carbonate and aspartic acid

A composite material of amorphous calcium carbonate and aspartic acid (Asp) was synthesized using a highly concentrated solution of calcium aspartate: a new approach. A transparent and amorphous solid with approximately 1 mm thickness was obtained. UV-vis transmittance spectrum of the composite shows no characteristic absorption in visible region. A Raman spectrum of the composite revealed a peak assigned to the symmetric stretching of carbonate ion. This study demonstrated that amorphous calcium carbonate could be stabilized using not only organic artificial macromolecules but also using Asp, a small biomolecule. This result is expected to engender development of new biomimetic materials.     

Mimicking the biomineralization of aragonite (calcium carbonate) using reverse-micelles under ambient conditions

Reverse micelles have been used, for the first time, to mimic the conditions suitable for the low-temperature (40 degrees C) synthesis of the high temperature and high pressure orthorhombic phase of calcium carbonate (aragonite) normally crystallizing in the sea as abalone shells and as natural pearls. The aragonite phase undergoes morphological changes under higher temperatures with long Y-junctions (at 40 degrees C) to shorter rod-like structures (at 85 degrees C). Pure calcite is obtained at higher reaction temperature. At a lower temperature (5 degrees C) homogeneous and monodisperse spheres of vaterite is obtained. The spherical particles after longer aging (168 h) aggregate to form nanorods and the self assembly is clearly seen at various stages by electron microscopic images.     

Synthesis of calcium hydroxyapatite from calcium carbonate and different orthophosphate sources: A comparative study

The synthesis of calcium hydroxyapatite (Ca-HA) starting from calcium carbonate and different orthophosphate sources, including orthophosphoric acid, potassium, sodium and ammonium dihydrogen orthophosphates, was investigated under ambient conditions. The reaction started with calcium carbonate dissolution in an acid medium, followed by rapid precipitation of calcium cations with orthophosphate species to form calcium phosphate based particles which were in the size range of 0.4–1 μm. These particles then agglomerated into much larger ones, up to 350 μm in diameter (aggregates). These aggregates possessed an unstable porous structure which was responsible for the porosity of the final products. The highest specific surface area and pore volume were obtained with potassium dihydrogen orthophosphate. On the other hand, orthophosphoric acid led to the highest dissolution of calcium carbonate and the complete precipitation of orthophosphate species. Under ambient conditions, calcium phosphate based solid products of low crystallinity were formed. Different intermediates were identified and a reaction pathway proposed.     

Morphology of calcium carbonate coating on amorphous silicate powder

The amorphous silicate powders containing sodium, calcium,barium and magnesium were prepared by sol-gel and ion-exchangemethod, and calcium carbonate was coated on the powders for thepurpose of industrial re-circulation of calcium carbonate. Thecalcium carbonate powder with micro pores was obtained bycoating on amorphous CaO-SiO₂ powder, and the pore sizedistribution would be influenced by calcium on the surface ofthe powder. The coating on amorphous MgO-SiO₂ powderresulted in a hedgehog-like powder, which allowed needle-likecrystal extended radially, and the coated powder was the mixedphase of aragonite and calcite. The use of amorphousBaO-SiO₂ and Na₂O-SiO₂ powders also led to the coatingpowder with the single phase of calcite. The morphology ofcalcium carbonate coating would be ascribed to cations on thesurface of the amorphous silicate powders, because the amount ofcations that would be dissolved in soaking solution was smalland insufficient to affect the morphology.     

Control the polymorphism and morphology of calcium carbonate precipitation from a calcium acetate and urea solution

Two metastable calcium carbonate polymorphs, rod-like aragonite and spherical vaterite are selectively formed in this study. Aragonite rods were synthesized from a calcium acetate (Ca(AC)₂) and urea (CO(NH₂)₂) solution under a given condition. In contrast, the addition of polyacrylamide (PAM) and oleic acid results in the formation of spherical vaterite. The morphology, size and crystal structure were characterized by means of Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), and X-ray diffraction (XRD). The results show that PAM and oleic acid can be used as additives to select the polymorph from aragonite and vaterite. The contact angle of the modified products reached 112.49°. We have succeeded in surface modification of particles in situ at the same time.     

Assemblage of nano-calcium carbonate particles on palmitic acid template

As research continues, the control on the polymorph and morphology of calcium carbonate (CaCO₃) becomes a hot topic because its application is limited by these parameters. The assemblage of nano-CaCO₃ particles on palmitic acid template was successfully realized in the carbonation of calcium hydroxide (Ca(OH)₂) slurry. The polymorph and morphology of CaCO₃ particles were investigated by XRD and TEM, respectively, and the interaction between palmitic acid and CaCO₃ particles was studied by FTIR. It reveals that the amount of palmitic acid does not change the crystalline phase of CaCO₃ particles. However, the morphology of CaCO₃, from nano-cubic single particle to micro rod-like aggregation, can be controlled by varying the amount of palmitic acid. The assemblage of CaCO₃ particles is discussed from the view of the deformation of the micelle when it is absorbed on the Ca(OH)₂ particles and of the aggregation of extremely small CaCO₃ particles under the driving force of high surface energy.     

Thermal decomposition of calcium carbonate polymorphs precipitated in the presence of ammonia and alkylamines

Precipitated calcium carbonate was obtained by CO₂ bubbling in CaCl₂ solution. Ammonia and alkylamines were used to enhance CO₂ absorption and control the polymorphic phases. Vaterite and calcite mixtures were obtained, mainly vaterite in ammonia and mono-methylamine and mostly calcite in tri-methylamine environment. The thermal decomposition of precipitated calcium carbonate leads to high purity CaO. During the thermal decomposition the vaterite to calcite transformation was noticed but the final spherical shape of vaterite was maintained. As the use of CaO as catalyst in biodiesel synthesis may recommend a spherical shape and high contact surface, a precipitated calcium carbonate, rich in vaterite phase, may be a good precursor for CaO catalyst preparation.     

Surfactant assisted synthesis of precipitated calcium carbonate nanoparticles using dolomite: Effect of pH on morphology and particle size

Synthesis of nanomaterials from readily available minerals for industrial applications is a growing research area. Understanding the causes of their properties becomes handy in utilization. In this study, an effective sucrose solution based method was employed for the extraction of calcium from dolomite to synthesize precipitated calcium carbonate nanostructures with different morphologies and sizes. It was found that 30% (w/v) sucrose solution extracted approximately 91% of calcium from dolomite forming a calcium-sucrate complex. Carbonation was achieved by CO₂ bubbling and aqueous sodium carbonate addition. Precipitation was performed under different pH values of 7.5, 10.5 and 12.5 in the absence of an anionic surfactant and in the template of sodium dodecyl sulfate (SDS)/calcium-sucrate at pH 12.5. It was found that CO₂ bubbling slightly promotes smaller particles. The anionic surfactant enables particle size and agglomeration reduction while introducing some hydrophobicity. The smallest particles were achieved at a range of 40–55 nm in the presence of SDS/sucrose template and were of spherical morphology. By changing the pH, a tendency to form different polymorphs and shapes of calcium carbonate was observed.     

Effect of a new functional double-hydrophilic block copolymer PAAL on the morphology of calcium carbonate particles

Calcium carbonate (CaCO₃) particles with various shapes were prepared by the reaction of sodium carbonate with calcium chloride in the presence of a new functional double-hydrophilic block copolymer poly (acrylic acid)-block-(acrylic hydroxy lactide) (PAAL) at room temperature. The as-prepared products were characterized with scanning electron microscopy and X-ray diffraction. The effects of pH, concentration of PAAL and CaCO₃ on the crystal form and morphologies of the as-prepared CaCO₃ were investigated. The results show that pH, concentration of PAAL and CaCO₃ are important parameters for the control of morphologies of CaCO₃. Depending on the experimental conditions, various morphologies of CaCO₃, such as plate-like aggregates, poly-nucleated spheres, ellipsoids, monodispersed spheres, rhombohedras, etc., can be obtained. Especially, the optimal experimental conditions for the production of monodispersed spherical CaCO₃ particles were determined.     

Synthesis of ultra-small hollow silica nanoparticles using the prepared amorphous calcium carbonate in one-pot process

The ultra-small hollow silica nanoparticles were synthesized using the prepared amorphous calcium carbonate (ACC) particles as a template. The ACC particles were firstly prepared by carbonation method, which procedure was conducted in the methanol solvent to form the Ca(OCH₃)₂ layers on the ACC particles. An effect of methanol concentration on the morphology of ACC particles was also investigated. The prepared ACC particles were directly coated by silica through adding tetraethoxysilane (TEOS) into the methanol solvent. Hence, the ACC-silica core-shell particles were obtained since the ACC particles have a positive charge and interact with hydrolyzed TEOS. The ACC particles could be stabilized through the reaction between methanol and calcium ions when the methanol concentration was increased over than 40?vol%.     

Carbonate-containing apatite (CAP) synthesis under moderate conditions starting from calcium carbonate and orthophosphoric acid

The synthesis of carbonate-containing apatite (CAP) from calcium carbonate and orthophosphoric acid under moderate conditions was investigated. In all cases, complete precipitation of orthophosphate species was observed. The reaction temperature influenced strongly the decomposition of calcium carbonate and therefore the composition of formed products. The reaction temperature of 80 °C was found to be effective for the complete decomposition of calcium carbonate particles after 48 h of reaction. Infra-red spectroscopy (IR), nuclear magnetic resonance (NMR), thermogravimetry/mass spectroscopy (TG–MS) coupling, and X-ray diffraction (XRD) characterizations allowed the identification of the composition of formed products. By increasing the reaction temperature from 20 °C to 80 °C, the content of A-type CAP increased and that of B-type CAP decreased, according to the favorable effect of temperature on the formation of A-type CAP. The total amount of carbonate content incorporated in CAP's structure, which was determined by TG–MS analysis, increased with the reaction temperature and reached up to 4.1% at 80 °C. At this temperature, the solid product was mainly composed of apatitic components and showed the typical flat-needle-like structure of CAP particles obtained in hydrothermal conditions. These results show an interesting one-step synthesis of CAP from calcium carbonate and orthophosphoric acid as low cost but high purity starting materials.     

Effect of particle morphology on mechanical properties of liquid marbles

In order to better understand the influence of the shape of solid particles on the stability of liquid marbles, we investigated liquid marbles stabilized by hydrophobized calcium carbonate particles with spherical and rod-shaped morphologies. Static properties, such as the effective surface tension, and the dynamic behavior i.e. the compression-decompression features for several cycles of the liquid marbles were investigated. Liquid marbles stabilized with spherical CaCO₃ particles show an elastic response to mechanical deformation almost up to collapse. In contrast, liquid marbles prepared with rod-like particles exhibit a more plastic response to compression. It is concluded that the main differences in behavior of the prepared liquid marbles arise from how the solid particles can arrange/orient at the air/water interface.     

Growth of calcium carbonate on non-covalently modified carbon nanotubes

The crystallization of calcium carbonate was investigated on pristine and non-covalently modified carbon nanotubes (CNTs) using the vapor diffusion technique in a calcium chloride solution. Non-covalent modification was accomplished by treating the carbon nanostructures with the amphiphilic copolymer poly(isoprene-b-acrylic acid). Calcium carbonate crystals grown on the surface and in the interstitial channels of CNT buckypapers were observed in both cases. Scanning electron microscopy analysis of the untreated CNTs showed the characteristic rhombohedral morphology of calcite crystals, while in the case of modified material spherical and ellipsoidal crystals, consisted of nanocrystallites, were observed. X-ray diffraction analysis showed the presence of calcite crystals in both cases.     

Calcium carbonate microspheres as carriers for the anticancer drug camptothecin

Biogenic calcium carbonate has come to the attention of many researchers as a promising drug delivery system due to its safety, pH sensitivity and the large volume of information already in existence on its medical use. In this study, we employed bovine serum albumin (BSA) as an additive to synthesize a series of porous calcium carbonate microspheres (CCMS). These spheres, identified as vaterite, are stable both in aqueous solutions and organic solvents. Camptothecin, an effective anticancer agent, was loaded into the CCMS by simple diffusion and adsorption. The camptothecin loaded CCMS showed sustained cell growth inhibitory activity and a pH dependent release of camptothecin. With a few hours, the release is negligible under physiological conditions (pH = 7.4) but almost complete at pH 4 to 6 (i.e. pHs found in lysosomes and solid tumor tissue respectively). These findings suggest that porous, biogenic calcium carbonate microspheres could be promising carriers for the safe and efficient delivery of anticancer drugs of low aqueous solubility.     

不同形貌碳酸钙颜料粒子的制备及在喷墨印刷中的应用

目的研究碳酸钙颜料粒子的形貌对喷墨打印涂层性能的影响。方法通过改变分散剂的种类制备不同的碳酸钙颜料粒子,并通过扫描电子显微镜(SEM)、傅里叶变换红外光谱仪(FT-IR)、粒径分析仪对制备的颜料粒子进行表征,研究分散剂种类对颜料形貌和粒径的影响。将4种不同形貌的碳酸钙分别作为颜料,将其应用于喷墨打印纸的表面涂层,并测试涂布纸张的动态渗透性、物理性能、喷墨打印性能。结果 CMC作为分散剂有助于形成粒径分布均匀的球形碳酸钙颜料粒子;纺锤形碳酸钙颜料粒子有助于提高涂布纸的平滑度和光泽度;球状体碳酸钙颜料粒子有助于改善涂布纸的喷墨印刷性能和渗透性;颜料粒子的粒径分布均匀性对涂布纸的动态渗透性影响较大,其影响超过颜料粒子形貌对涂布纸渗透性的影响。结论粒径分布均匀的球状体碳酸钙颜料粒子最适合用于喷墨印刷涂层,可以提高纸张的物理性能、印刷性能和动态渗透性能。     

微纳分级结构碳酸钙中空微球的可控制备

以CaCl₂和Na₂CO₃为反应原料, 以聚乙烯吡咯烷酮(PVP)和十二烷基磺酸钠(SDSN)为模板剂, 在50℃采用化学沉淀反应, 干燥、煅烧后成功制备了具有微纳分级结构的CaCO₃中空微球。采用扫描电子显微镜、透射电子显微镜和X射线衍射等检测手段对所制备的样品形貌、结构进行了表征, 结果显示：所制备的微纳分级结构CaCO₃中空微球直径为4~6 μm, 壳壁由直径约60 nm的CaCO₃颗粒组成, 壳层厚度约为200 nm, CaCO₃中空微球晶相组成为方解石和球霰石的共混体。同时, 在反应温度为50℃、PVP添加量为0.4 g, SDSN浓度为0.1 mol/L的条件下, 所制备的微纳分级结构CaCO₃中空微球分散性好, 且形貌比较完整。     

In-vitro study on calcium carbonate crystal growth mediated by organic matrix extracted from fresh water pearls

For the purpose of studying the mediation of organic matrix on the crystallization of calcium carbonate, water soluble matrix (WSM), acid soluble matrix (ASM) and acid insoluble matrix (AIM) were extracted from aragonite pearls and vaterite pearls respectively. Then, in-vitro calcium carbonate crystallization experiments under the control of these six organic matrices were carried out in the present study. Scanning electron microscopy (SEM) was utilized to observe the morphology of CaCO₃ and Raman spectroscopy as a powerful technique was used to distinguish the crystal polymorph. Influences of the six kinds of organic matrices on the calcium carbonate crystal growth are proposed. ASM of vaterite pearls can induce vaterite to crystallize and WSM of aragonite pearls mediates to produce aragonite crystals. The single AIM membranes of the two pearls have no pronounced effect on the CaCO₃ crystallization. Additionally, the crystal size obtained with the additive of WSM of the two kinds of pearls is smaller than that with the additive of ASM. Moreover, self-assembly phenomenon in the biomineralization process and the distorted morphology calcite are observed. Current results demonstrate important aspects of matrix protein-controlled crystallization, which is beneficial to the understanding of nacre biomineralization mechanism. Further study of the precise control of these matrix proteins on CaCO₃ crystal growth is being processed.     

Effects of organic additives on the morphology of calcium carbonate particles in the presence of CTAB

In this paper, calcium carbonate particles with unusual morphologies could be easily obtained by a precipitation reaction of sodium carbonate with calcium chloride from mixed solution of organic solvents and water in the presence of cetyltrimethylammonium bromide (CTAB) at 80 °C. The as-prepared products were characterized with scanning electron microscopy and X-ray diffraction. The effects of different organic additives–glycol, glycerine, formaldehyde, acetaldehyde, glycol-methyl ether and glycol-ethylether, on the crystal form and morphology of the as-prepared CaCO₃–were investigated and discussed. The results show that organic additives can have great influence on the forms and morphologies of CaCO₃ at relative high temperature in the presence of CTAB. Various unusual crystal morphologies, such as dendrite-shaped, flower-like, wheatgrass-like, needle-like, whiskers, double-taper-like, etc., can be obtained depending on the experimental conditions. In particular, pure aragonite with unusual morphologies can be produced in the presence of glycol, glycerine, glycol-methyl ether at 80 °C, respectively.