Polymorph Switching of Calcium Carbonate Crystals by Polymer‐Controlled Crystallization

Polymer‐controlled crystallization of calcium carbonate crystals in solution by a gas diffusion method has been carried out in the presence of poly(sodium 4‐styrene sulfonate‐co‐N‐isopropylacrylamide) (PSS‐co‐PNIPAAM), and for the first time all three anhydrous polymorphs, calcite, vaterite, and aragonite could be selectively produced with a single additive. The selective polymorph synthesis can be nicely adjusted simply by concentration variations of polymer and calcium ions in the present reaction system. The simplicity of the system reveals the influence of Ca²⁺ and polymer concentration on the nucleation and crystal growth of CaCO₃ via the balance between thermodynamic and kinetic reaction control. A single mechanistic framework employing particle mediated as well as ion mediated crystallization for polymorph control is proposed.     

Synthesis and Patterning of Luminescent CaCO3–Poly(p‐phenylene) Hybrid Materials and Thin Films

Nature employs specialized macromolecules to produce highly complex structures and understanding the role of these macromolecules allows us to develop novel materials with interesting properties. Herein, we report the role of modified conjugated polymers in the nucleation, growth, and morphology of calcium carbonate (CaCO₃) crystals. In situ incorporation of sulfonated poly(p‐phenylene) (s(PPP)) into a highly oriented calcium carbonate matrix is investigated along with the synthesis and patterning of luminescent CaCO₃–PPP hybrid materials. Functionalized PPP with polar and nonpolar groups are used as additives in the mineralization medium. The polymer (P1) with polar groups give iso‐oriented calcite crystals, whereas PPP with an additional alkyl chain (P2) results in vaterite crystals. The crystallization mechanism can be explained based on self‐assembly and aggregation of polymers in an aqueous environment. Such light‐emitting hybrid composites with tunable optical properties are excellent candidates for optoelectronics and biological applications.     

Think Positive: Phase Separation Enables a Positively Charged Additive to Induce Dramatic Changes in Calcium Carbonate Morphology

Soluble macromolecules are essential to Nature's control over biomineral formation. Following early studies where macromolecules rich in aspartic and glutamic acid were extracted from nacre, research has focused on the use of negatively charged additives to control calcium carbonate precipitation. It is demonstrated that the positively charged additive poly(allylamine hydrochloride) (PAH) can also cause dramatic changes in calcite morphologies, yielding thin films and fibers of CaCO₃ analogous to those produced with poly(aspartic acid) via a so‐called PILP (polymer‐induced liquid precursor) phase. The mechanism by which PAH induces these effects is investigated using a range of techniques including cryo transmission electron microscopy (TEM), Raman microscopy, and thermogravimetric analysis, and the data show that hydrated Ca²⁺/PAH/CO₃^2? droplets initially form in solution, before coalescing and ultimately crystallizing to give calcite, together with small quantities of vaterite. It is suggested that it is the initial formation of hydrated Ca²⁺/PAH/CO₃^2? droplets that is key to this process, rather than a specific polymer/mineral interaction. These results are discussed in terms of their relevance to biomineralization processes and highlight the opportunity for using counter‐ion‐induced phase separation of polyelectrolytes as a method for generating minerals with non‐crystallographic morphologies.     

Site‐Selective In Situ Grown Calcium Carbonate Micromodels with Tunable Geometry,Porosity, and Wettability

Micromodels with simplified porous microfluidic systems are widely used to mimic the underground oil‐reservoir environment for multiphase flow studies, enhanced oil recovery, and reservoir network mapping. However, previous micromodels cannot replicate the length scales and geochemistry of carbonate because of their material limitations. Here a simple method is introduced to create calcium carbonate (CaCO₃) micromodels composed of in situ grown CaCO₃. CaCO₃ nanoparticles/polymer composite microstructures are built in microfluidic channels by photopatterning, and CaCO₃ nanoparticles are selectively grown in situ from these microstructures by supplying Ca²⁺, CO₃^2? ions rich, supersaturated solutions. This approach enables us to fabricate synthetic CaCO₃ reservoir micromodels having dynamically tunable geometries with submicrometer pore‐length scales and controlled wettability. Using this new method, acid fracturing and an immiscible fluid displacement process are demonstrated used in real oil field applications to visualize pore‐scale fluid–carbonate interactions in real time.     

Atomic and molecular photostimulated desorption from complex ionic crystals

Calcium carbonate and sodium nitrate are isostructural crystals in which the covalently bonded polyatomic anions are also isoelectronic, however, the chemical properties of these crystals are distinctly different. In this study, we report results involving the photostimulated desorption (PSD) of neutral CO and O(³P) products from geologic calcite (CaCO₃) using low laser fluence at 193 nm. Product states are probed using (2+1) resonance enhanced multiphoton ionization for both neutrals. The CO products display a narrow angular distribution normal to the surface and a translational energy characterized, by a temperature (T=110K) significantly lower than that of the substrate (T=295K).¹ Atomic oxygen products display both broader angular and kinetic energy distributions than that of the CO fragments. Emission of O(³P) is seen at angles greater than 30° with respect to the surface normal. In contrast, recent PSD studies of product NO from single crystal sodium nitrate (NaNO₃) show product distributions with both thermal and hyper-thermal components.² Projected density of state plots computed using periodic Hartree-Fock theory indicate a strong overlap in the metal and carbonate bands of the low lying excited states in CaCO₃, while NaNO₃ was found to have a well-separated nitrate band in the excited state below the mixed metal/nitrate bands. The differences in the electronic structure of these materials may account for differences in the observed product distributions in the PSD of calcite and sodium nitrate.     

Insights into the In Vitro Formation of Apatite from Mg-Stabilized Amorphous Calcium Carbonate

A protein-free formation of bone-like apatite from amorphous precursors through ball-milling is reported. Mg²⁺ ions are crucial to achieve full amorphization of CaCO₃. Mg²⁺ incorporation generates defects which strongly retard a recrystallization of ball-milled Mg-doped amorphous calcium carbonate (BM-aMCC), which promotes the growth of osteoblastic and endothelial cells in simulated body fluid and has no effect on endothelial cell gene expression. Ex situ snapshots of the processes revealed the reaction mechanisms. For low Mg contents (<30%) a two phase system consisting of Mg-doped amorphous calcium carbonate (ACC) and calcite “impurities” was formed. For high (>40%) Mg²⁺ contents, BM-aMCC follows a different crystallization path via magnesian calcite and monohydrocalcite to aragonite. While pure ACC crystallizes rapidly to calcite in aqueous media, Mg-doped ACC forms in the presence of phosphate ions bone-like hydroxycarbonate apatite (dahllite), a carbonate apatite with carbonate substitution in both type A (OH⁻) and type B (PO₄³⁻) sites, which grows on calcite “impurities” via heterogeneous nucleation. This process produces an endotoxin-free material and makes BM-aMCC an excellent “ion storage buffer” that promotes cell growth by stimulating cell viability and metabolism with promising applications in the treatment of bone defects and bone degenerative diseases.     

The Intrinsic Ability of Silk Fibroin to Direct the Formation of Diverse Aragonite Aggregates

As an analogue of the main protein contained in naturally formed nacre, reconstituted silk fibroin (SF) from the Bombyx mori silkworm silk shows a strong preference for the formation of the aragonite form of CaCO₃ crystals and allows fine control over their size and morphology. The aragonite phase could be generated via two different routes: direct growth or dissolution and recrystallization, depending on the concentration of Ca²⁺ and SF. Generally, lower concentrations of Ca²⁺ and SF favor the formation of aragonite needles and their aggregates, of which the lattice structure of the precursor is similar to that of the organic matrix in natural shell. Higher concentrations lead to the formation of aragonite aggregates via a dissolution and recrystallization process through intermediates of lens‐like vaterite. Molecular modeling shows that the β‐strand conformers of silk fibroin molecules has an excellent match with the ionic spacing in the aragonite (010) plane, which can promote growth along the (001) long axis of aragonite crystals. This synergy between silk fibroin and the aragonite phase may help our understanding of the function of organic matrices involved in the biomineralization process, and facilitate the fabrication of synthetic materials with the potential for high performance mechanical properties.     

A Mesocrystal‐Like Morphology Formed by Classical Polymer‐Mediated Crystal Growth

Growth by oriented assembly of nanoparticles is a widely reported phenomenon for many crystal systems. While often deduced through morphological analyses, direct evidence for this assembly behavior is limited and, in the calcium carbonate (CaCO₃) system, has recently been disputed. However, in the absence of a particle‐based pathway, the mechanism responsible for the creation of the striking morphologies that appear to consist of subparticles is unclear. Therefore, in situ atomic force microscopy is used to investigate the growth of calcite crystals in solutions containing a polymer additive known for its ability to generate crystal morphologies associated with mesocrystal formation. It is shown that classical growth processes that begin with impurity pinning of atomic steps, leading to stabilization of new step directions, creation of pseudo‐facets, and extreme surface roughening, can produce a microscale morphology previously attributed to nonclassical processes of crystal growth by particle assembly.     

The Coral Protein CARP3 Acts from a Disordered Mineral Surface Film to Divert Aragonite Crystallization in Favor of Mg‐Calcite

Stony corals construct their aragonite skeleton by calcium carbonate precipitation, in a process recently suggested to be biologically controlled. Amorphous calcium carbonate and small amounts of calcite are also reported recently, however, their functional role is unknown. Coral acid‐rich proteins (CARPs) are extracted from the coral skeleton and are shown to be active in calcium carbonate precipitation in vitro. However, individual function of these proteins in coral mineralization is not known. Here, the regulatory activity of the aspartate‐rich CARP3 protein is examined. The whole protein and two peptides representing its acidic domain and its variable domain are used in CaCO₃ precipitation reactions from Mg‐rich solutions. The biomolecules alter crystallization pathways, promoting Mg‐calcite in place of aragonite, with the acidic peptide capable of eradicating aragonite formation. The activity of CARP3 and its representative peptides is exerted from disordered CaCO₃ mineral phases, coating the crystals formed, as shown by 2D ¹H–¹³C heteronuclear correlation nuclear magnetic resonance (NMR) measurements, localizing organic protons in atomic proximity to disordered carbonate carbons. The structures of the protein and individual domains as derived from NMR measurements and folding calculations and their amino acid compositions are discussed in the context of their observed activity and its implication to mineralization in hard corals.     

Structure and Properties of Nanocomposites Formed by the Occlusion of Block Copolymer Worms and Vesicles Within Calcite Crystals

This article describes an experimentally versatile strategy for producing inorganic/organic nanocomposites, with control over the microstructure at the nano‐ and mesoscales. Taking inspiration from biominerals, CaCO₃ is coprecipitated with anionic diblock copolymer worms or vesicles to produce single crystals of calcite occluding a high density of the organic component. This approach can also be extended to generate complex structures in which the crystals are internally patterned with nano‐objects of differing morphologies. Extensive characterization of the nanocomposite crystals using high resolution synchrotron powder X‐ray diffraction and vibrational spectroscopy demonstrates how the occlusions affect the short and long‐range order of the crystal lattice. By comparison with nanocomposite crystals containing latex particles and copolymer micelles, it is shown that the effect of these occlusions on the crystal lattice is dominated by the interface between the inorganic crystal and the organic nano‐objects, rather than the occlusion size. This is supported by in situ atomic force microscopy studies of worm occlusion in calcite, which reveal flattening of the copolymer worms on the crystal surface, followed by burial and void formation. Finally, the mechanical properties of the nanocomposite crystals are determined using nanoindentation techniques, which reveal that they have hardnesses approaching those of biogenic calcites.     

Tunable Morphosynthesis of Calcium Carbonate in Aqueous Solution Enabled by Janus Membrane

Targeted and high throughput manufacture of crystalline biominerals with diverse morphologies is of importance, due to the significant impact of shape and texture on the material properties, while tunable morphosynthesis of crystalline is restrained by the proper ion transfer process during the reactive crystallization, and is commonly regulated using organic soluble additives. Herein, Janus membranes (JMs) are facilely produced for the continuous confined reactive crystallization of calcium carbonate. Fabricated JM simultaneously achieves rapid and uniform directional CO₃²⁻ ions transfer in the aqueous solution through the straight, uniform nanoscale hydrophilic channels, and the interfacial reactive crystallization is generated with confined ion adsorption and gating effect at the hydrophobic side. Hollow CaCO₃ microcomposites via JM system are continuously and directly synthesized in the aqueous system without any assisted organic solvent or polymer additive, which is green and highly efficient. In addition, the reversed ion transfer direction in JM can be ideally managed resulting in highly selective manufacturing of cube or sphere-type microcomposites. This study provides a feasible route for the rapid production of advanced particle materials with tunable morphology, displaying great potential applications of JM in material engineering.     

Structure of Na Species in Promoted CaO-Based Sorbents and Their Effect on the Rate and Extent of the CO2 Uptake

To advance CaO-based CO₂ sorbents it is crucial to understand how their structural parameters control the cyclic CO₂ uptake. Here, CaO-based sorbents with varying ratios of Na₂CO₃:CaCO₃ are synthesized via mechanochemical activation of a mixture of Na₂CO₃ and CaCO₃ to investigate the effect of sodium species on the structure, morphology, carbonation rate and cyclic CO₂ uptake of the CO₂ sorbents. The addition of Na₂CO₃ in the range of 0.1–0.2 mol% improves the CO₂ uptake by up to 80% after 10 cycles when compared to ball-milled bare CaCO₃, while for Na₂CO₃ loadings >0.3 mol% the cyclic CO₂ uptake decreases by more than 40%. Energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy, X-ray absorption spectroscopy (XAS), and ²³Na MAS NMR, reveal that in sorbents with Na₂CO₃ contents <0.3 mol% Na exists in highly distributed, noncrystalline [Na₂Ca(CO₃)₂] units. These species stabilize the surface area of the sorbent in pores of diameters >100 nm, and enhance the diffusion of CO₂ through CaCO₃. For Na₂CO₃ contents >0.3 mol%, the accelerated deactivation of the sorbents via sintering is related to the formation of crystalline Na₂Ca(CO₃)₂ and the high mobility of Na.     

Structural and Spectroscopic Characterization of Nominal Yb3+:Ca8La2(PO4)6O2 Oxyapatite Single Crystal Fibers Grown by the Micro‐Pulling‐Down Method

Yb‐doped Ca₈La₂(PO₄)₆O₂ (CLPA) single crystals with the apatite‐type structure and having <0001> orientation were grown by the micro‐pulling‐down (μ‐PD) method. The apatite structure is represented by the monophased field of Ca₈(La_2–xYb_x)‐(PO₄)₆O₂ (CLYPA) where it is assumed that 2 Ca²⁺ sites are substituted by La³⁺ and Yb³⁺ cations. Its monophased range was found to be from x = 0.0 to 0.2. The segregation of Yb³⁺ in CLPA single crystals and the maximum Yb³⁺ concentration are discussed. The crystallinity was studied using X‐ray rocking curve analysis. Absorption, emission and fluorescence decay studies of Yb³⁺ ions in CLPA were also carried out both at low temperature and room temperature. Spectroscopic data reveal Yb³⁺ ion occupation within different crystallographic sites of the apatite‐type structure. The potential for a diode‐pumped Yb³⁺ laser is evaluated.     

Superionic conductivity in TlGaTe<Subscript>2</Subscript> crystals

Temperature dependences of electrical conductivity σ(T) and permittivity ɛ(T) of one-dimensional (1D) TlGaTe₂ single crystals are investigated. At temperatures higher than 305 K, superionic conductivity of the TlGaTe₂ is observed and is related to diffusion of Tl⁺ ions via vacancies in the thallium sublattice between (Ga³⁺Te₂^{2− −} nanochains. A relaxation character of dielectric anomalies is established, which suggests the existence of electric charges weakly bound to the crystal lattice. Upon the transition to the superionic state, relaxors in the TlGaTe₂ crystals are Tl⁺ dipoles ((Ga³⁺Te₂²⁻)⁻ chains) that arise due to melting of the thallium sublattice and hops of Tl⁺ ions from one localized state to another. The effect of a field-induced transition of the TlGaTe₂ crystal to the superionic state is detected.     

Recent Advances in Calcium-Based Anticancer Nanomaterials Exploiting Calcium Overload to Trigger Cell Apoptosis

Calcium ion is vital for the regulation of many cellular functions and serves as a second messenger in the signal transduction pathways. Once the intracellular Ca²⁺ level exceeds the tolerance of cells (called Ca²⁺ overload), oxidative stress, mitochondrial damage, and cell/mitochondria apoptosis happen. Therefore, Ca²⁺ overload has started to be deeply exploited as a new strategy for cancer therapy due to its high efficiency and satisfactory safety. This review aims to highlight the recent development of Ca²⁺-based nanomaterials (such as Ca₃(PO₄)₂, CaCO₃, CaO₂, CaH₂, CaS, and others) able to trigger intracellular Ca²⁺ overload and apoptosis in cancer therapy. The intracellular mechanisms of varied Ca²⁺-based nanomaterials and the different types of strategies to enhance Ca²⁺ overload are discussed in detail. Moreover, the design of more efficient Ca²⁺ overload-mediated cancer therapies is prospected mainly based on 1) the enhanced cellular uptake by surface modification and morphology optimization of nanomaterials, 2) the accelerated Ca²⁺ release from nanomaterials by increasing the intracellular H⁺ level and by photothermal effect, and 3) the overload maintenance by Ca²⁺ efflux inhibition, Ca²⁺ influx promotion, or promoting Ca²⁺ release from the endoplasmic reticulum.     

A Novel Mesoporous CaO‐Loaded In2O3 Material for CO2 Sensing

A mesoporous CaO‐loaded In₂O₃ material (with Ca/In₂O₃ ratios ranging from 2.5 to 8.5 at %) has been synthesized and used as resistive gas sensor for the detection of CO₂. A nanostructured In₂O₃ matrix has been obtained by hard template route from the SBA‐15 silica template. Additive presence does not distort the lattice of In₂O₃, which crystallizes in the Ia3 cubic space group. It has been proved by XRD, HRTEM, Raman and XPS measurements that samples contain not only CaO but also CaCO₃ in calcite phase as a consequence of CaO carbonation. Pure In₂O₃ based sensors are low sensitive to CO₂, whereas those containing the additive show an important response in the 300–5000 ppm range of gas concentrations. As seen by DRIFTS, the electrical response arises from the interaction between CO₃^2– and CO₂, yielding bicarbonates products. The reaction is water‐assisted, so that hydration of the sensing material ensures sensor reliability whilst its dehydration would inhibit sensor response. The use of CaCO₃ instead of CaO does not cause significant differences in electrical and DRIFTS data, which corroborates the important role played by carbonate species in the sensing mechanism.     

Amorphization Boost Multi-Ions Storage for High-Performance Aqueous Batteries

Regarding the complex properties of various cations, the design of aqueous batteries that can simultaneously store multi-ions with high capacity and satisfactory rate performance is a great challenge. Here an amorphization strategy to boost cation-ion storage capacities of anode materials is reported. In monovalent (H⁺, Li⁺, K⁺), divalent (Mg²⁺, Ca²⁺, Zn²⁺) and even trivalent (Al³⁺) aqueous electrolytes, the capacity of the resulting amorphous MoO_x is more than quadruple than that of crystalline MoO_x and exceeds those of other reported multiple-ion storage materials. Both experimental and theoretical calculations reveal the generation of ample active sites and isotropic ions in the amorphous phase, which accelerates cation migration within the electrode bulk. Amorphous MoO_x can be coupled with multi-ion storage cathodes to realize electrochemical energy storage devices with different carriers, promising high energy and power densities. The power density exceeded 15000 W kg⁻¹, demonstrating the great potential of amorphous MoO_x in advanced aqueous batteries.     

High-Power and Ultrastable Aqueous Calcium-Ion Batteries Enabled by Small Organic Molecular Crystal Anodes

Calcium ion batteries (CIBs) are pursued as potentially low-cost and safe alternatives to current Li-ion batteries due to the high abundance of calcium element. However, the large and divalent nature of Ca²⁺ leads to strong interaction with intercalation hosts, sluggish ion diffusion kinetics and low power output. Herein, a small molecular organic anode is reported, tetracarboxylic diimide (PTCDI), involving carbonyl enolization (CO↔C O⁻) in aqueous electrolytes, which bypasses the diffusion difficulties in intercalation-type electrodes and avoid capacity sacrifice for polymer organic electrodes, thus manifesting rapid and high Ca storage capacities. In an aqueous Ca-ion cell, the PTCDI presents a reversible capacity of 112 mAh g⁻¹, a high-capacity retention of 80% after 1000 cycles and a high-power capability at 5 A g⁻¹, which rival the state-of-the-art anode materials in CIBs. Experiments and simulations reveal that Ca ions are diffusing along the a axis tunnel to enolize carbonyl groups without being entrapped in the aromatic carbon layers. The feasibility of PTCDI anodes in practical CIBs is demonstrated by coupling with cost-effective Prussian blue analogous cathodes and CaCl₂ aqueous electrolyte. The appreciable Ca storage performance of small molecular crystals will spur the development of green organic CIBs.     

Silk Fibroin‐Regulated Crystallization of Calcium Carbonate

Mollusk shell is one of the best studied of all calcium carbonate biominerals. Its silk‐like binder‐matrix protein plays a pivotal role during the formation of aragonite crystals in the nacre sheets. Here, we provide novel experimental insights into the interaction of mineral and protein compounds using a model system of reconstituted Bombyx mori silk fibroin solutions serving as templates for the crystallization of calcium carbonate (CaCO₃). We observed that the inherent (self‐assembling) aggregation process of silk fibroin molecules affected both the morphology and crystallographic polymorph of CaCO₃ aggregates. This combination fostered the growth of a novel, rice‐grain‐shaped protein/mineral hybrid with a hollow structure with an aragonite polymorph formed after ripening. Our observations suggest new hypotheses about the role of silk‐like protein in the natural biomineralization process, but it may also serve to shed light on the formation process of those ‘ersatz’ hybrids regulated by artificially selected structural proteins.     

Biomimetic Crystallization of Calcium Carbonate Spherules with Controlled Surface Structures and Sizes by Double‐Hydrophilic Block Copolymers

Big CaCO₃ spherules with controlled surface structures and sizes ranging from several hundreds of nanometers and micrometers can be easily fabricated through a slow gas–liquid diffusion reaction at room temperature by using double‐hydrophilic block copolymers (DHBCs) as crystal modifiers. The influence of the DHBCs with different functionalities such as carboxyl, partially phosphated, and phosphorylated groups on the crystallization and structure of calcite formation was investigated. The morphology evolution process and the early stage of the big spherical superstructures were followed. Such big spherules with complex surface structure made of calcite rhombohedra are not easily produced by conventional solution growth methods, and furthermore show high potential for chromatographic purposes due to their exposition of multiple calcite faces and the huge particle sizes suitable for chromatographic column packings.