Morphology Of CaCO3 Research Articles

Role of bacteria on bio-induced calcium carbonate formation: insights from droplet microfluidic experiments

Microbially induced calcium carbonate precipitation (MICP) has emerged as a promising solution for geotechnical issues. However, the role of bacteria in the formation of calcium carbonate (CaCO3) remains incompletely understood. In this study, a droplet microfluidic chip was developed to observe the growth process of calcium carbonate and bacterial behaviour during the MICP process under various bacterial density conditions. Scanning electron microscope was then utilised to analyse the calcium carbonate morphology, and Raman spectroscopy was employed to identify calcium carbonate polymorphs. Nucleation within microspaces showed a stochastic nature. Within the droplets where crystals formed, all crystals manifested as cubic calcite. Higher bacterial density led to the formation of larger and more irregularly shaped crystals, with crystal size showing a significant correlation with urease activity. In droplets where no crystals formed, higher bacterial density and urease activity resulted in the precipitation of amorphous calcium carbonate on the bacterial surface. However, this precipitation pattern differed from the formation of monocrystalline calcium carbonate. The results demonstrate that bacteria act primarily as urease secretors to regulate crystal growth during the MICP process, while their role as nucleation sites for crystals remains debatable. This study provides new insights into the bio-induced calcium carbonate formation mechanism.

Elevating carbonation efficiency and CO2 capture capacity of steel slag by sodium tripolyphosphate (STP): The role of CaCO3 morphology modification

Carbonation degree significantly impacts the volume stability of steel slag powder. To elevate the carbonation efficiency of steel slag and thereby alleviate the volume unsoundness of steel slag powder, sodium tripolyphosphate (STP) was used to enhance the micro morphology of CaCO3 and accelerate Ca leaching and CO2 diffusion. Three methods for assessing CO2 uptake were employed to reliably determine the degree of carbonation. Results indicate that steel slag added with 0.05 wt% STP obtained a promotion exceeded 80 % in CO2 uptake. Additionally, STP increased the CO2 capture capacity of steel slag by 24.84 %. Under the influence of STP, the expansion of steel slag paste was reduced by up to 31.45 % following an autoclaving test. The formed micro CaCO3 particles in carbonated steel slag without STP were polyhedral grains and a dense carbonation layer was formed around calcium silicate. Contrastively, CaCO3 formed in the carbonated STP incorporated steel slag were conical or acicular particles and consequently generated a porous layer. The porous microstructure provided “tunnels” for the continuous CO2 diffusion and Ca2+ leaching and hence maintained relatively higher reaction speed throughout the carbonation process. Furthermore, STP also played the role as a chelator which accelerated the leaching of Ca2+.

Development of CaCO3 novel morphology through crystal lattice modification assisted by sulfate incorporation and vibration

CaCO3 has long been used as a filler to increase many properties of the material. The filler commonly consists of inexpensive materials that replace some volume of the more expensive materials, which can reduce the cost of the final product. CaCO3 morphology that can be used as filler depends on the filler's function, such as filler for paper, paint, rubber, or composite. A filler for composite materials is needed to increase interfacing interactions between the particulate fillers and the matrix. So, the particulate in a broader shape will be the best choice to function for such filler. In this research, in an attempt to increase the interfacing interaction, CaCO3 morphology was modified in such a way through crystal lattice modification assisted by sulfate incorporation and vibration. SEM analysis was implemented, and showed that the research successfully produced novel morphology in branchy-like polymorphs. FTIR analysis also proved that the crystal lattice has been modified. The morphology in branchy-like polymorph is supposed to increase interfacing interaction between CaCO3 as the filler and the matrix. The methods are also supposed to be implemented as the research is scaled up to commercial scale.

Influence of Different Ions on Pulse Electrodeposition of CaCO3 Scales in the Simulated Seawater.

In the circulating water system of coastal power plants, various kinds of ions have a great influence on the formation and growth of CaCO3 scales. This paper focuses on investigating the influence of existing ions on the pulse electrodeposition behaviors of CaCO3 scales. Different concentrations of ions, such as Fe3+, Mg2+, PO43- and SiO32-, are introduced to simulate the actual seawater environment, and their influence on the CaCO3 scale deposition behaviors is assessed by linear sweep voltammetry, chronoamperometry, and electrochemical impedance spectroscopy tests. The surface coverage of the CaCO3 scale layer is evaluated through the residual current density and polarization resistance values, while the crystal structure and surface compactness of the layer are confirmed by the scanning electron microscope and X-ray diffractometer tests. Results indicate that high concentrations of Mg2+, Fe3+, and PO43- ions have the most significant inhibitory effect on the pulse electrodeposition of CaCO3 scales, among which the inhibition effect of Mg2+ ions is mainly reflected in the change of crystal morphology of CaCO3, that is, the crystallization growth process is inhibited. The inhibition effect of PO43- ions is mainly reflected in the gradually reduced coverage and density of CaCO3 crystals on the electrode surface, suggesting that the crystallization nucleation process is inhibited, while Fe3+ ions have a certain inhibition effect on both the crystallization nucleation and growth processes. Furthermore, lower concentrations of SiO32- ions also display a significant inhibition effect on the crystallization nucleation and growth process, and the inhibition effect weakens with increased concentration. This study provides a theoretical basis for exploring the removal of ions in the industrial water softening field.

In-situ investigation on the carbonation behaviors of various mineral phases in steel slag: The role of RO phase

Exploring the mineral compositions of steel slag and the microstructure evolutions of its carbonation products is very important for deeply understanding the carbonation mechanism of steel slag, which can promote the application of steel slag in carbon capture and storage. In this paper, the carbonation behaviors of various mineral phases in steel slag were investigated by using an ingenious in-situ observation method through combing laser scanning confocal microscopy (LSCM), backscattered scanning electron microscopy (BSEM) and focused ion beam-transmission electron microscope (FIB-TEM). It is shown that dicalcium silicate (C2S) and free lime (f-CaO) had high carbonation reactivity, while the calcium aluminoferrite with different Al/Fe ratios and mayenite (C12A7) exhibited extremely poor carbonation reactivity. The carbonation reactivity of RO phase was positively correlated with its Mg/(Fe + Mn) ratio. RO phase with a Mg/(Fe + Mn) ratio below 0.5 owned almost no carbonation reactivity, while the Mg2+ would leach from RO phase with a Mg/(Fe + Mn) ratio higher than 2.0 during the carbonation process, inhibiting the precipitation of CaCO3, changing the micro morphology of CaCO3, and generating spheroidal aragonite. The ingenious in-situ observation method developed in this study provides a very visual information, which can be further extended to more fundamental research.

Facial preparation and in vitro bioactivity of rice-like Mg doped CaCO3 particles for bone tissue regeneration

Calcium carbonate (CaCO3) particles with controlled polymorphs, morphologies and specific sizes presented great application potential in biomedical field. In this work, CaCO3 particles with controlled morphologies and surface micro-structure were successfully synthesized by facile and eco-friendly processes. Results revealed that the morphology of CaCO3 could be controlled from spherical to rice-like and dumbbell shaped particles with different surface micro-structure by introducing Mg2+ and adjusting the molar ratio of Mg2+/Ca2+. Herein, the in vitro bio-activity of prepared rice-like CaCO3 particles was investigated by immersion in SBF solution for 1, 3 and 5 days. Moreover, in vitro cyto-compatibility of prepared rice-like CaCO3 particles has also been evaluated by CCK-8 and live/dead staining assay. Results demonstrated that the rice-like CaCO3 particles possess excellent bio-activity and in vitro cyto-compatibility, which suggest the great promise of prepared rice-like CaCO3 particles in bone tissue engineering.

Morphological control of CaCO3 superstructures in seawater: Insights into Ca-source anion influence and formation mechanism

This work provides crucial insights into the crystallization and morphogenesis of CaCO3 polymorphs in seawater at elevated temperatures. Using Ca source anions as a controlling factor, we modify the crystallization of CaCO3 and demonstrate that stable and intricate particle morphologies of CaCO3, such as hexagonal bipyramidal, disks, and twin structures, can be generated in seawater without surfactants. The synthesis of CaCO3 was accomplished through a direct hydrothermal method utilizing water-soluble Ca salts (calcium chloride, calcium nitrate, and calcium acetate) as Ca source and urea as a carbonate source. Depending on the specific source anions used, various morphological changes were observed. The CaCO3 prepared with the nitrate source yields vaterite as the major polymorph with hexagonal bipyramidal morphology. Pseudohexagonal prisms of aragonite were the primary product obtained with calcium acetate as the source. In contrast, chloride ions yielded vaterite and aragonite depending on the reaction temperature and time. The purity of CaCO3 prepared with seawater was > 94 % regardless of the Ca source. We observe that the phase formation follows the order of gypsum-vaterite-aragonite with an increase in hydrothermal reaction time. Further, we propose the formation mechanism of vaterite hexagonal bipyramidal and aragonite pseudohexagonal prism superstructures where directional aggregation of particles occurs in the presence of ammonium ions and seawater solvent. These findings, obtained through the exploration of seawater and different Ca sources, offer a comprehensive understanding of how source anions influence the selective formation of CaCO3 polymorph and its morphological tuning. This information can be applied to tailor the synthesis of CaCO3 for specific applications.

Nonclassical and Classical Crystallization: The Formation of Spindle-Shaped CaCO3 Covered with Abundant Nanoscale Rhombic Calcite Subunits

As an essential inorganic material, calcium carbonate (CaCO3) is one of the most abundant minerals in nature, whose preparation by the carbonation of calcium hydroxide [Ca(OH)2] suspension involves complex physical and chemical processes due to the presence of gas–solid–liquid phases. It is challenging to accurately predict the final morphology of CaCO3. In this paper, a novel spindle-shaped CaCO3 covered with a mass of nanoscale rhombic calcite subunits was prepared via the carbonation method. This structure was mainly formed by the aggregation of nanoparticles in the pre-reaction stage and turned into a classical ion–ion growth process at the stage of the late reaction. During the pre-reaction period, solid Ca(OH)2 kept the solution supersaturated and made the aggregation of nanoparticles dominate and assemble to form the nanochains of CaCO3. Subsequently, the aggregation of nanochains formed a dumbbell shape, which was accompanied by the recrystallization of nanoparticles inside aggregates to create an ordered single-crystal spindle structure. Finally, the concentration of Ca(OH)2 decreased, and a layer of nanoscale rhombic calcite subunits grew on the surface of spindle CaCO3. This work will provide new insights into the industrial preparation of CaCO3 with controlled morphology and contribute to understanding the biomineralization of aggregation-based growth in aqueous solutions.

Corrosion Behavior of P110 Steel in Simulated CO<sub>2</sub> and Formation Water Environment

The corrosion behavior and mechanism of P110 steel tubing in in low CO2 particle pressure and high salinity formation water environment was investigated through high temperature and high pressure dynamic immersion tests, macro-morphology analysis, scanning electron microscopy(SEM) inspection, energy disperse spectroscopy(EDS) analysis and X-ray diffraction(XRD) analysis. The Results showed that the increasing of CO2 partial pressure accelerated the corrosion process of P110 tubing steel, and the corrosion rates of P110 tubing decreased with the increasing of temperature. Furthermore, the high content of Ca2+ in the formation water also had a big influence on the corrosion behavior of P110 tubing steel, for it could affect the precipitation quantity and morphology of CaCO3 at different temperature and CO2 particle pressure.

Influence of humic acid on microbial induced carbonate precipitation for organic soil improvement.

Microbial induced carbonate precipitation (MICP) is one of the most commonly researched topics on biocementation, which achieves cementation of soil particles by carbonate from urea hydrolysis catalyzed by microbial urease. Although most MICP studies are limited to stabilizing sandy soils, more researchers are now turning their interest to other weak soils, particularly organic soils. To stabilize organic soils, the influence of humic substances should be investigated since it has been reported to inhibit urease activity and disrupt the formation of calcium carbonate. This study investigates the effect of humic acid (HA), one fraction of humic substances, on MICP. For this purpose, the effects of HA content on CaCO3 precipitation using three strains and on CaCO3 morphology were examined. The results showed that native species in organic soils were less adversely affected by HA addition than the exogenous one. Another interesting finding is that bacteria seem to have strategies to cope with harsh conditions with HA. Observation of CaCO3 morphology revealed that the crystallization process was hindered by HA to some extent, producing lots of fine amorphous precipitates and large aggregated CaCO3. Overall, this study could provide an insightful understanding of possible obstacles when using MICP to stabilize organic soils.

Facile encapsulation of nano zero-valent iron with calcium carbonate: synthesis, characterization and application for iron remediation.

In this study, CaCO3 was used as a modifier for nano zero-valent iron (nZVI) surface to prevent rapid aggregation and effectively utilized for iron remediation from aqueous solution. Surface chemistry and morphology of CaCO3 encapsulated nZVI (CaCO3-nZVI) before and after treatment of contaminant iron solution were characterized by scanning electron microscopy-energy dispersive X-ray (SEM-EDX), X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The mechanisms of surface modification as well as iron remediation were well depicted with the help of these characterisation tools. Iron removal efficacy of 96.4% was achieved with 0.25g/L adsorbent dose for an influent iron of 0.5mg/L at pH 10 after a 3h treatment process. When the influent concentration was increased to 10mg/L, the removal capacity decreased to 92.1%. The study demonstrates that CaCO3 and nZVI in the encapsulated nanoparticle have a significant synergistic effect. The pseudo-second- order reaction kinetics and Freundlich isotherm model correctly portrayed the experimental data for iron removal by CaCO3-nZVI. The CaCO3-nZVI is a viable option for iron removal from various aqueous media due to its facile preparation, high iron removal capability, and reusability.

A promising strategy for the large-scale preparation of spherical calcium carbonate by efficiently using carbon dioxide

Spherical calcium carbonate (CaCO3) is widely used in industries. However, its large-scale synthesis still remains a challenging issue. Herein, we report the preparation of spherical CaCO3 at a high calcium hydroxide (Ca(OH)2) concentration (1.08 M) using CO2 highly efficiently in methanol (CH3OH)-water mixed solvent with polyethyleneimine (PEI) as a crystal modifier by carbonation method. Experimental results revealed that the introduction of CH3OH in the reaction systems decreased the saturation Ca2+ concentration in the solvent, and then formed spherical CaCO3 under the controlled action of PEI. Besides, spherical CaCO3 with a particle size of about 1 µm can be obtained at concentration of Ca(OH)2 of 1.08 M, PEI of 5 g/L, and CH3OH volume content of 30%, stirring rate of 450 rpm, and CO2 flow rate of 1.4 m3/h. The formation mechanism of spherical CaCO3 indicated that the particles converted from an initial amorphous precursor, to needle-like, bundle-like, block-like and hemispherical shaped aggregates, and finally to a complete spherical CaCO3 morphology. This research provides an effective method for the preparation of high yield spherical CaCO3 by industrial carbonation method.

Functional polymers for modeling the formation of biogenic calcium carbonate and the design of new materials

AbstractSkeletal elements of living organisms (bones, teeth, horns, frustules of diatomic algae, mollusk shells, sea urchin needles, and sponge spicules) are biogenic composite materials consisting of an inorganic part (calcium phosphate and carbonate, silica) and various organic compounds. The first step in the synthesis of these materials is the condensation of an inorganic precursor under the control of biopolymers capable of interacting with the growing inorganic particle. We studied formation of calcium carbonate in the presence of copolymers of acrylic acid, 1‐vinylimidazole and vinylamine. Some of the copolymers were new, so their acid–base properties were characterized. The polymers have an influence on the precipitation of CaCO3 in aqueous medium, and depending on the polymer structure and the polymer‐calcium ratio, composite precipitates or stable dispersions were obtained. Composite nanoparticles have a negative charge, and they can interact with polymer bases to form calcium‐organic composite materials. Calcium carbonate formation under the control of organic polymers is a chemical model of calcium skeletal growth in living nature. The resulting composites containing micrometer‐range CaCO3 particles are promising materials for the design of microstructured coatings with a high surface density of functional groups. Some of the polymers studied are not involved in the resulting material, but affect the morphology of CaCO3, forming particles in the micrometer range, which are promising as fillers for plastics.

Impact of metal ions (Cr+6/Mn+7) loaded CaCO3 extracted from tap water for adsorption/ degradation of toxic pollutants under sunlight

The present work involves the extraction and characterization of highly efficient CaCO3 from tap water. The resulting white powder was sintered at 900 °C and study for the adsorption/degradation of Rhodamine-B (RB) dye. After sintering at a higher temperature, it was found that CaCO3 was decomposed into CaO and Ca(OH)2 which results in the superior adsorption of RB dye relative to CaCO3 dried at room temperature. The degradation efficiency of CaCO3 was further enhanced by loading two metal ions (Cr+6, Mn+7) having different oxidation states. The as-prepared composites were characterized by different techniques i.e., dynamic light scattering, X-ray diffraction, diffuse reflectance spectroscopy, scanning electron microscopy (SEM) and UV-Visible spectrophotometer and examined for photocatalytic degradation of Rhodamine-B (RB) dye under sunlight. The average hydrodynamic size of bare CaCO3 (900 °C) found to be 0.63 µm which was increased to 1.34 µm and 1.48 µm after loading of Cr+6 and Mn+7 ions respectively. SEM images suggested the hierarchical morphology of CaCO3 and energy dispersive X-ray spectroscopy (EDS)-mapping also confirms the presence of Cr+6 and Mn+7 ions on the surface CaCO3. It was observed that Mn+7-CaCO3 (900 °C) shows higher degradation efficiency of RB dye under solar radiation relative to bare and Cr+6 loaded CaCO3 and exhibited a higher rate constant of 4.6 × 10-2 min-1.

The effect of Bacillus cereus LV-1 on the crystallization and polymorphs of calcium carbonate.

The study of CaCO3 polymorphism is of great significance for understanding the mechanism of carbonate mineralization induced by bacteria and the genesis of carbonate rock throughout geological history. To investigate the effect of bacteria and shear force on CaCO3 precipitation and polymorphs, biomineralization experiments with Bacillus cereus strain LV-1 were conducted under the standing and shaking conditions. The results show that LV-1 induced the formation of calcite and vaterite under the standing and shaking conditions, respectively. However, the results of mineralization in the media and the CaCl2 solution under both kinetic conditions suggest the shear force does not affect the polymorphs of calcium carbonate in abiotic systems. Further, mineralization experiments with bacterial cells and extracellular polymeric substances (EPS) were performed under the standing conditions. The results reveal that bacterial cells, bound EPS (BEPS), and soluble EPS (SEPS) are favorable to the formation of spherical, imperfect rhombohedral, and perfect rhombohedral minerals, respectively. The increase in the pH value and saturation index (SI) caused by LV-1 metabolism under the shear force played key roles in controlling vaterite precipitation, whereas bacterial cells and EPS do not play roles in promoting vaterite formation. Furthermore, we suggest that vaterite formed if pH > 8.5 and SIACC > 0.8, while calcite formed if pH was between 8.0-9.0 and SIACC < 0.8. Bacterial cells and BEPS are the main factors affecting CaCO3 morphologies in the mineralization process of LV-1. This may provide a deeper insight into the regulation mechanism of the polymorphs and morphologies during bacterially induced carbonate mineralization.

The Synthesis of Europium-Doped Calcium Carbonate by an Eco-Method as Free Radical Generator Under Low-Intensity Ultrasonic Irradiation for Body Sculpture.

Body sculpture is a common method to remove excessive fat. The diet and exercise are the first suggestion to keep body shape; however, those are difficult to keep adherence. Ultrasound has been developed for fat ablation; however, it could only serve as the side treatment along with liposuction. In the study, a sonosensitizer of europium-doped calcium carbonate (CaCO3: Eu) would be synthesized by an eco-method and combined with low-intensity ultrasound for lipolysis. The crystal structure of CaCO3: Eu was identified by x-ray diffractometer (XRD). The morphology of CaCO3: Eu was analyzed by scanning electron microscope (SEM). The chemical composition of CaCO3: Eu was evaluated by energy-dispersed spectrophotometer (EDS) and inductively coupled plasma mass spectrometer (ICP-MS). The electronic diffraction pattern was to further check crystal structure of the synthesized individual grain by transmission electron microscope (TEM). The particle size was determined by Zeta-sizer. Water-soluble tetrazolium salt (WST-1) were used to evaluate the cell viability. Chloromethyl-2′,7′-dichlorofluorescein diacetate (CM-H2DCFDA) and live/dead stain were used to evaluate feasibility in vitro. SD-rat was used to evaluate the safety and efficacy in vivo. The results showed that CaCO3: Eu had good biocompatibility and could produce reactive oxygen species (ROS) after treated with low-intensity ultrasound. After 4-weeks, the CaCO3: Eu exposed to ultrasound irradiation on SD rats could significantly decrease body weight, waistline, and subcutaneous adipose tissue. We believe that ROS from sonoluminescence, CO2-bomb and locally increasing Ca2+ level would be three major mechanisms to remove away adipo-tissue and inhibit adipogenesis. We could say that the combination of the CaCO3: Eu and low-intensity ultrasound would be a non-invasive treatment for the body sculpture.

Role of Na-Montmorillonite on Microbially Induced Calcium Carbonate Precipitation.

The use of additives has generated significant attention due to their extensive application in the microbially induced calcium carbonate precipitation (MICP) process. This study aims to discuss the effects of Na-montmorillonite (Na-MMT) on CaCO3 crystallization and sandy soil consolidation through the MICP process. Compared with the traditional MICP method, a larger amount of CaCO3 precipitate was obtained. Moreover, the reaction of Ca2+ ions was accelerated, and bacteria were absorbed by a small amount of Na-MMT. Meanwhile, an increase in the total cementing solution (TCS) was not conducive to the previous reaction. This problem was solved by conducting the reaction with Na-MMT. The polymorphs and morphologies of the CaCO3 precipitates were tested by using X-ray diffraction and scanning electron microscopy. Further, when Na-MMT was used, the morphology of CaCO3 changed from an individual precipitate to agglomerations of the precipitate. Compared to the experiments without Na-MMT in the MICP process, the addition of Na-MMT significantly reduced the hydraulic conductivity (HC) of sandy soil consolidated.

Valorization of Crocus Sativus L waste extracts as efficient, eco-friendly and economical inhibitors of scaling: Experimental and computational investigations

The valorization of biomass and the use of plant extracts as new green inhibitors of scaling are amongthe most innovative research topics. In this light, this study aims to evaluate the effectiveness of two extracts of Crocus Sativus L (CSL) wastes towards the formation of calcareous scale, namely the Aqueous Extract of Leaf (ALE) and the Aqueous Extract of Petal and Stamen (AEPS). Folin-Ciocalteau and colorimetric methods are used to determine thetotal polyphenols and flavonoids contents, respectively. Then, the anti-scaling property of the investigated extracts is determined using a conductivity test and the Laboratory of Chemistry and Genie of the Environment (LCGE) technique at a temperature of 25 °C. After that, scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) analysesare employed to examine the formed scale during the LCGE tests. To support the experimental findings, Molecular Dynamic (MD) simulations and Density Functional Theory (DFT) calculations are carried out. The data obtained revealed that AEPS has a higher concentration of total polyphenol and flavonoids than ALE. Total inhibition occurs after the addition of 60 mg‧L-1 of AEPS to the calco-carbonic solution with a hardness of 40°F. Whereas an amount of 82 mg‧L-1 of ALE was the optimal concentration to completely inhibit CaCO3 formation. This allows us to conclude that the anti-scaling effectiveness is correlated with polyphenols and flavonoids contents in CSL extracts. SEM and FTIR analyses reveal that the crystallization of CaCO3 without inhibitor was a stable variety of calcite with a rhombohedral form. However, the presence of a low concentration of AEPS (20 mg‧L-1) resulted in a significant modification on the morphology of CaCO3 and a mixture of vaterite with calcite phases. The theoretical outcomes agree with the anti-scaling efficiencies reported experimentally. Based on these results, the CSL biomass could be an interesting renewable source of eco-friendly and inexpensive inhibitors of scaling.

Amylopectin Regulated Mineralization of Calcium Carbonate and Its Application in Removing of Pb(II)

AbstractAs an ecological and environment‐friendly building material, sticky rice mortar has attracted the attention of many researchers. Amylopectin is the most important organic matter of it, which can improve the mechanical properties and durability of sticky rice mortar by inducing mineralization of calcium carbonate (CaCO3). However, amylopectin induced formation of CaCO3 has not been reported. In this paper, mineralization of CaCO3 induced by gelatinized amylopectin is investigated. For comparison, the different morphologies of CaCO3 are studied in the presence of Mg2+, Fe3+. Moreover, these CaCO3 products with different morphologies are used to clean the waste water. The results indicate that gelatinized amylopectin is conducive to formation of pumpkin‐like vaterite. It forms uniform rod and dumbbell‐shaped calcite in the presence of Mg2+, form calcite with stepped depressions in the presence of Fe3+. The adsorption of Pb(II) can reach extremely high level (1445.86 mg g−1) with the rod‐like calcite.

Morphology control and luminescent properties of Eu/Tb-doped calcium carbonate nanoparticles using natural limestone

The Eu/Tb-doped CaCO3 nanocrystals including nanoneedles, nanorods and nanospheres are respectively synthesized from natural limestone via carbonation technique. The doping of Eu/Tb ions can not change the polymorph, but the morphologies and sizes of synthesized CaCO3 differ significantly depending on the species and concentrations of Eu/Tb ions. The undoped CaCO3 nanoneedles exhibit a length of 280–920 nm and a diameter of 55–78 nm, while the 6% Eu doped CaCO3 nanorods exhibit a length of 1.68–2.56 μm and a diameter of 560–680 nm, respectively. The introduction of Tb ions changes the CaCO3 morphology from nanoneedle to irregular sphere and the diameter of CaCO3: 8% Tb primary particle is around 110–200 nm. Under the excitation of 318 nm or 384 nm ultraviolet light, CaCO3: x% Eu nanorods exhibit characteristic emission bands at 360 nm and 420 nm assigned to 4f6 5 d1(t2g) →8S7/2 transition of Eu2+ ions and sharp peaks at 596 nm from the 5D0 →7F1 transitions of Eu3+ ions. XPS data further confirm the coexistence of Eu2+ and Eu3+ ions. The CaCO3: y% Tb nanospheres present intense blue-green emission at 424 nm and 545 nm under excitation at 397 nm, which are originating from both 5D3→7FJ and 5D4→7FJ transitions of Tb3+ ions. However, under 343 nm excitation, in addition to the emission of Tb3+, Eu3+ ions also present intense emissions at 572 nm, 596 nm, 624 nm and 650 nm, which may be caused by the unknown Eu -containing impurities from natural limestone. Whiteemitting and color-tunable photoluminescence performance of CaCO3 nanostructures are realized by regulating the excitation wavelengths and doping ions.