Gradient heating activated ammonium persulfate oxidation for efficient preparation of high-quality chitin nanofibers

APS is a cheap and eco-friendly oxidant which enables one-step extraction of nanochitin (NCh) from fishery wastes. However, it is challenging to improve the preparation efficiency and NCh quality simultaneously, owing to the uneven or uncontrollable oxidation. Herein, we propose a simple and controllable way to isolate chitin nanofibers (ChNFs) from squid pen by gradient heating activated (GHA)- ammonium persulfate (APS) oxidation. Compared to the isothermal activated (ITA)-APS oxidation, our strategy reduced the mass ratio of squid pen to APS from 1:45 to 1:6 and reaction time from 15 h to 8 h. Meanwhile, the as-prepared ChNFs exhibited high yield (91.5 %), light transmittance (98 % at 500 nm), crystallinity index (96.9 %), and carboxyl content (1.53 mmol/g). GHA-APS oxidation involved multiple continuous heating and isothermal stages. The former stimulates a moderate activation of APS and enhances the oxidation rate, while the latter provides a duration for surface chemistry. This non-isothermal heating facilitates the continuous decomposition of APS at a relatively high and consistent rate, thereby enhances its oxidation efficiency. Furthermore, green assessments indicate this method is simple, time-saving, eco-friendly and cost-effective. Overall, this work introduces a novel perspective for the industrial extraction of high-efficiency and high-quality nanomaterials.

Nonclassical crystallization of goethite nanorods in limpet teeth by self-assembly of silica-rich nanoparticles reveals structure-mechanical property relations

The intricate organization of goethite nanorods within a silica-rich matrix makes limpet teeth the strongest known natural material. However, the mineralization pathway of goethite in organisms under ambient conditions remains elusive. Here, by investigating the multi-level structure of limpet teeth at different growth stages, it is revealed that the growth of goethite crystals proceeds by the attachment of amorphous nanoparticles, a nonclassical crystallization pathway widely observed during the formation of calcium-based biominerals. Importantly, these nanoparticles contain a high amount of silica, which is gradually expelled during the growth of goethite. Moreover, in mature teeth of limpet, the content of silica correlates with the size of goethite crystals, where smaller goethite crystals are densely packed in the leading part with higher content of silica. Correspondingly, the leading part exhibits higher hardness and elastic modulus. Thus, this study not only reveals the nonclassical crystallization pathway of goethite nanorods in limpet teeth, but also highlights the critical roles of silica in controlling the hierarchical structure and the mechanical properties of limpet teeth, thus providing inspirations for fabricating biomimetic materials with excellent properties.

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

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

Bioinspired High-Magnesium Calcite for Efficiently Reducing Chemical Oxygen Demand in Lake Water

Organic matter accumulation in water can cause serious problems such as oxygen depletion and quality deterioration of waters. While calcium carbonate has been used as green and low-cost adsorbent for water treatment, its efficiency in reducing the chemical oxygen demand (COD) of water, which is a measure of organic pollution, is restrained by the limited specific surface area and chemical activity. Herein, inspired by the high-magnesium calcite (HMC) found in biological materials, a feasible method to synthesize fluffy dumbbell-like HMC with large specific surface area is reported. The magnesium inserting increases the chemical activity of the HMC moderately but without lowering its stability too much. Therefore, the crystalline HMC can retain its phase and morphology in aqueous environment for hours, which allows the establishment of adsorption equilibrium between the solution and the adsorbent that retains its initial large specific surface area and improved chemical activity. Consequently, the HMC exhibits notably enhanced capability in reducing the COD of lake water polluted by organics. This work provides a synergistic strategy to rationally design high-performance adsorbents by simultaneously optimizing the surface area and steering the chemical activity.

From salt water to bioceramics: Mimic nature through pressure-controlled hydration and crystallization

Modern synthetic technology generally invokes high temperatures to control the hydration level of ceramics, but even the state-of-the-art technology can still only control the overall hydration content. Magically, natural organisms can produce bioceramics with tailorable hydration profiles and crystallization traits solely from amorphous precursors under physiological conditions. To mimic the biomineralization tactic, here, we report pressure-controlled hydration and crystallization in fabricated ceramics, solely from the amorphous precursors of purely inorganic gels (PIGs) synthesized from biocompatible aqueous solutions with most common ions in organisms (Ca2+, Mg2+, CO32-, and PO43-). Transparent ceramic tablets are directly produced by compressing the PIGs under mild pressure, while the pressure regulates the hydration characteristics and the subsequent crystallization behaviors of the synthesized ceramics. Among the various hydration species, the moderately bound and ordered water appears to be a key in regulating the crystallization rate. This nature-inspired study offers deeper insights into the magic behind biomineralization.

Myriad Mapping of nanoscale minerals reveals calcium carbonate hemihydrate in forming nacre and coral biominerals

Calcium carbonate (CaCO3) is abundant on Earth, is a major component of marine biominerals and thus of sedimentary and metamorphic rocks and it plays a major role in the global carbon cycle by storing atmospheric CO2 into solid biominerals. Six crystalline polymorphs of CaCO3 are known-3 anhydrous: calcite, aragonite, vaterite, and 3 hydrated: ikaite (CaCO3·6H2O), monohydrocalcite (CaCO3·1H2O, MHC), and calcium carbonate hemihydrate (CaCO3·½H2O, CCHH). CCHH was recently discovered and characterized, but exclusively as a synthetic material, not as a naturally occurring mineral. Here, analyzing 200 million spectra with Myriad Mapping (MM) of nanoscale mineral phases, we find CCHH and MHC, along with amorphous precursors, on freshly deposited coral skeleton and nacre surfaces, but not on sea urchin spines. Thus, biomineralization pathways are more complex and diverse than previously understood, opening new questions on isotopes and climate. Crystalline precursors are more accessible than amorphous ones to other spectroscopies and diffraction, in natural and bio-inspired materials.

The dynamic nature of natural and fatty acid modified calcite surfaces

Calcium carbonate, particularly in the form of calcite, is an abundant mineral widely used in both human-made products and biological systems. The calcite surface possesses a high surface energy, making it susceptible to the adsorption of organic contaminants. Moreover, the surface is also reactive towards a range of chemicals, including water. Consequently, studying and maintaining a clean and stable calcite surface is only possible under ultrahigh vacuum conditions and for limited amounts of time. When exposed to air or solution, the calcite surface undergoes rapid transformations, demanding a comprehensive understanding of the properties of calcite surfaces in different environments. Similarly, attention must also be directed towards the kinetics of changes, whether induced by fluctuating environments or at constant condition. All these aspects are encompassed in the expression "dynamic nature", and are of crucial importance in the context of the diverse applications of calcite. In many instances, the calcite surface is modified by adsorption of fatty acids to impart a desired nonpolar character. Although the binding between carboxylic acid groups and calcite surfaces is strong, the fatty acid layer used for surface modification undergoes significant alterations when exposed to water vapour and liquid water droplets. Therefore, it is also crucial to understand the dynamic nature of the adsorbed layer. This review article provides a comprehensive overview of the current understanding of both the dynamics of the calcite surface as well as when modified by fatty acid surface treatments.

Uncovering the Dynamics of Urease and Carbonic Anhydrase Genes in Ureolysis, Carbon Dioxide Hydration, and Calcium Carbonate Precipitation

The hydration of CO2 suffers from kinetic inefficiencies that make its natural trapping impractically sluggish. However, CO2-fixing carbonic anhydrases (CAs) remarkably accelerate its equilibration by 6 orders of magnitude and are, therefore, "ideal" catalysts. Notably, CA has been detected in ureolytic bacteria, suggesting its potential involvement in microbially induced carbonate precipitation (MICP), yet the dynamics of the urease (Ur) and CA genes remain poorly understood. Here, through the use of the ureolytic bacteriumSporosarcina pasteurii, we investigate the differing role of Ur and CA in ureolysis, CO2 hydration, and CaCO3 precipitation with increasing CO2(g) concentrations. We show that Ur gene up-regulation coincides with an increase in [HCO3-] following the hydration of CO2 to HCO3- by CA. Hence, CA physiologically promotes buffering, which enhances solubility trapping and affects the phase of the CaCO3 mineral formed. Understanding the role of CO2 hydration on the performance of ureolysis and CaCO3 precipitation provides essential new insights, required for the development of next-generation biocatalyzed CO2 trapping technologies.

High Mechanical Strength Alloy-like Minerals Prepared by Inorganic Ionic Co-cross-linking

Alloys often combine different metals to generate superior mechanical properties. However, it is challenging to prepare high mechanical strength minerals with similar strategies. Using calcium carbonate (CaC) and calcium phosphate (CaP) as examples, this work synthesizes a group of compounds with the chemical formulas Ca(CO3 )x (PO4 )2(1- x )/3 (0 < x < 1, CaCPs) by cross-linking ionic oligomers. Unlike mixtures, these CaCPs exhibit a single temperature for the phase transition from amorphous to crystallized CaC (calcite) and CaP (hydroxyapatite). By heat-induced synchronous crystallization, dual-phase CaC/CaP with continuous crystallized boundaries are resembled to alloy-like minerals (ALMs). The mechanical properties of the ALMs are adjusted by tailoring their chemical compositions to reach a hardness of 5.6 GPa, which exceed those of control calcite and hydroxyapatite samples by 430% and 260%, respectively. This strategy expands the chemical scope of inorganic materials and holds promise for preparing high-performance minerals.

Synthesis of porous calcium-guar gum benzoate nano-biohybrids for sorptive removal of congo red and phosphates from water

This work aims to develop an eco-sound nano-bio-hybrid sorbent using sustainable materials for sorptive elimination of congo red and phosphates from aquatic environment. An amphipathic biopolymer derivative, high DS guar gum benzoate (GGBN) was used for entrapment of as synthesized calcium carbonate nanoparticles using solvent diffusion nano-precipitation technique. Designer nano-biohybrids were developed upon experimenting with various materials stoichiometry. SEM, XRD and EDX studies confirmed near-uniform impregnation of rhombohedral calcium carbonate crystals throughout the biopolymer matrix. Average pore size distribution and surface area of final product Ca-GGBNC, were estimated from NDLFT and BET methods respectively. Analysis of adsorption findings acquired at study temperature 27 ± 2 °C showed that the maximum adsorption capacity of Ca-GGBNC recorded qmax, 333.33 mg/g for congo red azo dye and that for phosphate was at 500 mg/g. Adsorptive removal was noted and both components followed pseudo second order kinetics. Intra-particle diffusion kinetics investigation disclosed that the boundary layer effect was prominent and the adsorption rates were not solely directed by the diffusion stage. Activation energy, Ea was to be estimated using Arrhenius equation at 56.136 and 47.015 KJ/mol for congo red and phosphates respectively. The calculated thermodynamic parameters(ΔG°, ΔH°, and ΔS°) revealed the spontaneous, feasible and endothermic sorption process. Owing to active surface area, spherical size, functional moiety and porous network, antibacterial properties of nanobiohybrid were persistent and MIC against E. coli and S. aureus were recorded at 200 μg/mL and 350 μg/mL respectively.

Rationally designed calcium carbonate multifunctional trap for contaminants adsorption

Adsorption technology has been widely developed to control environmental pollution, which plays an important role in the sustainable development of modern society. Calcium carbonate (CaCO3) is characterized by its flexible pore design and functional group modification, which meet the high capacity and targeting requirements of adsorption. Therefore, its charm of "small materials for great use" makes it a suitable candidate for adsorption. Firstly, we comprehensively review the research progress of controlled synthesis and surface modification of CaCO3, and its application for adsorbing contaminants from water and air. Then, we systematically examine the structure-effect relationship between CaCO3 adsorbents and contaminants, while also intrinsic mechanism of remarkable capacity and targeted adsorption. Finally, from the perspective of material design and engineering application, we offer insightful discussion on the prospects and challenges of calcium carbonate adsorbents, providing a valuable reference for the further research in this field.

Unlocking the mysterious polytypic features within vaterite CaCO3

Calcium carbonate (CaCO3), the most abundant biogenic mineral on earth, plays a crucial role in various fields such as hydrosphere, biosphere, and climate regulation. Of the four polymorphs, calcite, aragonite, vaterite, and amorphous CaCO3, vaterite is the most enigmatic one due to an ongoing debate regarding its structure that has persisted for nearly a century. In this work, based on systematic transmission electron microscopy characterizations, crystallographic analysis and machine learning aided molecular dynamics simulations with ab initio accuracy, we reveal that vaterite can be regarded as a polytypic structure. The basic phase has a monoclinic lattice possessing pseudohexagonal symmetry. Direct imaging and atomic-scale simulations provide evidence that a single grain of vaterite can contain three orientation variants. Additionally, we find that vaterite undergoes a second-order phase transition with a critical point of ~190 K. These atomic scale insights provide a comprehensive understanding of the structure of vaterite and offer advanced perspectives on the biomineralization process of calcium carbonate.

Localized Phase Transformation Triggering Lattice Matching of Metal Oxide and Carbonate Hydroxide for Efficient CO2 Photoreduction

Orderly heterostructured catalysts, which integrate nanomaterials of complementary structures and dimensions into single-entity structures, have hold great promise for sustainability applications. In this work, it is showcased that air as green reagent can trigger in situ localized phase transformation and transform the metal carbonate hydroxide nanowires into ordered heterostructured catalyst. In single-crystal nanowire heterostructure, the in situ generated and nanosized Co3 O4 will be anchored in single-crystal Co6 (CO3 )2 (OH)8 nanowires spontaneously, triggered by the lattice matching between the (220) plane of Co3 O4 and the (001) plane of Co6 (CO3 )2 (OH)8 . The lattice matching allows intimate contact at heterointerface with well-defined orientation and strong interfacial coupling, and thus significantly expedites the transfer of photogenerated electrons from tiny Co3 O4 to catalytically active Co6 (CO3 )2 (OH)8 in single-crystal nanowire, which elevates the catalytic efficiency of metal carbonate catalyst in the CO2 reduction reaction (VCO = 19.46 mmol g-1 h-1 and VH2 = 11.53 mmol g-1 h-1 ). The present findings add to the growing body of knowledge on exploiting Earth-abundant metal-carbonate catalysts, and demonstrate the utility of localized phase transformation in constructing advanced catalysts for energy and environmental sustainability applications.

Room temperature bio-engineered multifunctional carbonates for CO2 sequestration and valorization

This contribution reports, for the first time, on an entirely green bio-engineering approach for the biosynthesis of single phase crystalline 1-D nano-scaled calcite CaCO3. This was validated using H2O as the universal solvent and natural extract of Hyphaene thebaica fruit as an effective chelating agent. In this room temperature green process, CaCl2 and CO2 are used as the unique source of Ca and CO3 respectively in view of forming nano-scaled CaCO3 with a significant shape anisotropy and an elevated surface to volume ratio. In terms of novelty, and relatively to the reported scientific and patented literature in relation to the fabrication of CaCO3 by green nano-chemistry, the current cost effective room temperature green process can be singled out as per the following specificities: only water as universal solvent is used, No additional base or acid chemicals for pH control, No additional catalyst, No critical or supercritical CO2 usage conditions, Only natural extract of thebaica as a green effective chelating agent through its phytochemicals and proper enzematic compounds, room Temperature processing, atmospheric pressure processing, Nanoscaled size particles, and Nanoparticles with a significant shape anisotropy (1-D like nanoparticles). Beyond and in addition to the validation of the 1-D synthesis aspect, the bio-engineered CaCO3 exhibited a wide-ranging functionalities in terms of highly reflecting pigment, an effective nanofertilizer as well as a potential binder in cement industry.

Fabrication of Ag-CaCO3 Nanocomposites for SERS Detection of Forchlorfenuron

In this study, Ag-CaCO3 nanocomposites were synthesized using silver nitrate as the precursor solution based on calcium carbonate nanoparticles (CaCO3 NPs). The synthesis involved the reaction of calcium lignosulphonate and sodium bicarbonate. The properties of Ag-CaCO3 nanocomposites were studied by various technologies, including an ultraviolet-visible spectrophotometer, a transmission electron microscope, and a Raman spectrometer. The results showed that Ag-CaCO3 nanocomposites exhibited a maximum UV absorption peak at 430 nm, the surface-enhanced Raman spectroscopy (SERS) activity of Ag-CaCO3 nanocomposites was evaluated using mercaptobenzoic acid (MBA) as the marker molecule, resulting in an enhancement factor of 6.5 × 104. Additionally, Ag-CaCO3 nanocomposites were utilized for the detection of forchlorfenuron. The results demonstrated a linear relationship in the concentration range of 0.01 mg/mL to 2 mg/mL, described by the equation y = 290.02x + 1598.8. The correlation coefficient was calculated to be 0.9772, and the limit of detection (LOD) was determined to be 0.001 mg/mL. These findings highlight the relatively high SERS activity of Ag-CaCO3 nanocomposites, making them suitable for analyzing pesticide residues and detecting toxic and harmful molecules, thereby contributing to environmental protection.

Insights into the precipitation kinetics of CaCO3 particles in the presence of polystyrene sulfonate using in situ small-angle X-ray scattering

The formation of calcium carbonate (CaCO3) nanoparticles (NPs) in the presence of polystyrene sulfonate (PSS) as an additive was examined by time-resolved small-angle X-ray scattering (SAXS) in a flow system that mimics experimental conditions used at home facilities where the precipitation can be achieved in a beaker. The experiments were carried out at low concentrations to remain in the dilute regime. A model-independent analysis was performed using the Porod invariant which defines the scale factor, leaving only the distribution of radii as the adjustable parameter. The presence of the PSS additive strongly retards the precipitation of CaCO3 NPs. The formation of NPs reaches a state of equilibrium after a few minutes. Here, it is shown that the concentration of precursors at a fixed PSS concentration plays a key role in determining the size of the NPs obtained. A full analysis of the SAXS patterns was carried out using the Hurd-Flower model to account for the weaker intensity decay than the classical Porod behaviour. The temporal evolution of the particle radii was determined. Wide-angle X-ray scattering experiments carried out simultaneously show that the particles formed have the structure of vaterite with growth consistent with the evolution of the Porod invariant.

An Engineering Method for Resonant Microcantilever Using Double-Channel Excitation and Signal Acquisition Based on LabVIEW

Resonant microcantilevers have the advantages of ultra-high heating rates, analysis speed, ultra-low power consumption, temperature programming, and trace sample analysis when applied in TGA. However, the current single-channel testing system for resonant microcantilevers can only detect one sample at a time, and need two program heating tests to obtain the thermogravimetric curve of a sample. In many cases, it is desirable to obtain the thermogravimetric curve of a sample with a single-program heating test and to simultaneously detect multiple microcantilevers for testing multiple samples. To address this issue, this paper proposes a dual-channel testing method, where a microcantilever is used as a control group and another microcantilever is used as an experimental group, to obtain the thermal weight curve of the sample in a single program temperature ramp test. With the help of the LabVIEW's convenient parallel running method, the functionality of simultaneously detecting two microcantilevers is achieved. Experimental validation showed that this dual-channel testing system can obtain the thermogravimetric curve of a sample with a single program heating test and detect two types of samples simultaneously.

Bioprocess inspired formation of calcite mesocrystals by cation-mediated particle attachment mechanism

Calcite mesocrystals were proposed, and have been widely reported, to form in the presence of polymer additives via oriented assembly of nanoparticles. However, the formation mechanism and the role of polymer additives remain elusive. Here, inspired by the biomineralization process of sea urchin spine comprising magnesium calcite mesocrystals, we show that calcite mesocrystals could also be obtained via attachment of amorphous calcium carbonate (ACC) nanoparticles in the presence of inorganic zinc ions. Moreover, we demonstrate that zinc ions can induce the formation of temporarily stabilized amorphous nanoparticles of less than 20 nm at a significantly lower calcium carbonate concentration as compared to pure solution, which is energetically beneficial for the attachment and occlusion during calcite growth. The cation-mediated particle attachment crystallization significantly improves our understanding of mesocrystal formation mechanisms in biomineralization and offers new opportunities to bioprocess inspired inorganic ions regulated materials fabrication.

Earthworm granules: A model of non-classical biogenic calcium carbonate phase transformations

Different non-classical crystallization mechanisms have been invoked to explain structural and compositional properties of biocrystals. The identification of precursor amorphous nanoparticle aggregation as an onset process in the formation of numerous biominerals (crystallization via particle attachment) constituted a most important breakthrough for understanding biologically mediated mineralization. A comprehensive understanding about how the attached amorphous particles transform into more stable, crystalline grains has yet to be elucidated. Here, we document structural, biogeochemical, and crystallographic aspects of the formation as well as the further phase transformations of the amorphous calcium carbonate particles formed by cultured specimens of earthworm Lumbricus terrestris. In-situ observations evidence the formation of proto-vaterite after dehydration of earthworm-produced ACC, which is subsequently followed by proto-vaterite transformation into calcite through nanoparticle attachment within the organic framework. In culture medium spiked with trace amounts of Mn²⁺, the cauliflower-like proto-vaterite structures become longer-lived than in the absence of Mn²⁺. We propose that the formation of calcite crystals takes place through a non-classical recrystallization path that involves migration of proto-vaterite nanoparticles to the crystallization site, and then, their transformation into calcite via a dissolution-recrystallization reaction. The latter is complemented by ion-by-ion crystal growth and associated with impurity release. These observations are integrated into a new model of the biocrystallization of earthworm-produced carbonate granules which highlights the sensibility of this process to environmental chemical changes, its potential impact on the bioavailability of contaminants as well as the threat that chemical pollution poses to the normal development of its early stages. STATEMENT OF SIGNIFICANCE: Understanding the mechanisms of nucleation, stabilization and aggregation of amorphous calcium carbonate (ACC) and factors controlling its further transformation into crystalline phases is fundamental for elucidation of biogenic mineralization. Some species of earthworms are natural workbench to understand the biogenic ACC, stabilization and the transformation mechanisms, because they create millimeter-sized calcareous granules from amorphous calcium carbonate, which crystallize to a more stable mineral phase (mostly calcite). This study undergoes into the mechanisms of ACC stabilization by the incorporation of trace elements, as manganese, and the ulterior precipitation of calcareous granules by a coupled process of amorphous particle attachment and ion-by-ion growth. The study points to sensibility of this process to environmental chemical changes.

17O solid state NMR as a valuable tool for deciphering reaction mechanisms in mechanochemistry: the case study on the 17O-enrichment of hydrated Ca-pyrophosphate biominerals

The possibility of enriching in ¹⁷O the water molecules within hydrated biominerals belonging to the Ca-pyrophosphate family was investigated, using liquid assisted grinding (LAG) in the presence of ¹⁷O-labelled water. Two phases with different hydration levels, namely triclinic calcium pyrophosphate dihydrate (Ca₂P₂O₇·2H₂O, denoted t-CPPD) and monoclinic calcium pyrophosphate tetrahydrate (Ca₂P₂O₇·4H₂O, denoted m-CPPT β) were enriched in ¹⁷O using a "post-enrichment" strategy, in which the non-labelled precursors were ground under gentle milling conditions in the presence of stoichiometric quantities of ¹⁷O-enriched water (introduced here in very small volumes ∼10 μL). Using high-resolution ¹⁷O solid-state NMR (ssNMR) analyses at multiple magnetic fields, and dynamic nuclear polarisation (DNP)-enhanced ¹⁷O NMR, it was possible to show that the labelled water molecules are mainly located at the core of the crystal structures, but that they can enter the lattice in different ways, namely by dissolution/recrystallisation or by diffusion. Overall, this work sheds light on the importance of high-resolution ¹⁷O NMR to help decipher the different roles that water can play as a liquid-assisted grinding agent and as a reagent for ¹⁷O-isotopic enrichment.

Highly hydrated paramagnetic amorphous calcium carbonate nanoclusters as an MRI contrast agent

Amorphous calcium carbonate plays a key role as transient precursor in the early stages of biogenic calcium carbonate formation in nature. However, due to its instability in aqueous solution, there is still rare success to utilize amorphous calcium carbonate in biomedicine. Here, we report the mutual effect between paramagnetic gadolinium ions and amorphous calcium carbonate, resulting in ultrafine paramagnetic amorphous carbonate nanoclusters in the presence of both gadolinium occluded highly hydrated carbonate-like environment and poly(acrylic acid). Gadolinium is confirmed to enhance the water content in amorphous calcium carbonate, and the high water content of amorphous carbonate nanoclusters contributes to the much enhanced magnetic resonance imaging contrast efficiency compared with commercially available gadolinium-based contrast agents. Furthermore, the enhanced T₁ weighted magnetic resonance imaging performance and biocompatibility of amorphous carbonate nanoclusters are further evaluated in various animals including rat, rabbit and beagle dog, in combination with promising safety in vivo. Overall, exceptionally facile mass-productive amorphous carbonate nanoclusters exhibit superb imaging performance and impressive stability, which provides a promising strategy to design magnetic resonance contrast agent.

Sensitive, biocompatible and stable contrast agents for MRI are in demand. Here, the authors combine gadolinium ions with amorphous calcium carbonate to make stable paramagnetic amorphous carbonate nanoclusters with high MRI contrast and significantly improved biocompatibility over commercial gadolinium-based agents.

Calcium carbonate: controlled synthesis, surface functionalization, and nanostructured materials

Calcium carbonate (CaCO₃) is an important inorganic mineral in biological and geological systems. Traditionally, it is widely used in plastics, papermaking, ink, building materials, textiles, cosmetics, and food. Over the last decade, there has been rapid development in the controlled synthesis and surface modification of CaCO₃, the stabilization of amorphous CaCO₃ (ACC), and CaCO₃-based nanostructured materials. In this review, the controlled synthesis of CaCO₃ is first examined, including Ca²⁺-CO₃^2- systems, solid-liquid-gas carbonation, water-in-oil reverse emulsions, and biomineralization. Advancing insights into the nucleation and crystallization of CaCO₃ have led to the development of efficient routes towards the controlled synthesis of CaCO₃ with specific sizes, morphologies, and polymorphs. Recently-developed surface modification methods of CaCO₃ include organic and inorganic modifications, as well as intensified surface reactions. The resultant CaCO₃ can then be further engineered via template-induced biomineralization and layer-by-layer assembly into porous, hollow, or core-shell organic-inorganic nanocomposites. The introduction of CaCO₃ into nanostructured materials has led to a significant improvement in the mechanical, optical, magnetic, and catalytic properties of such materials, with the resultant CaCO₃-based nanostructured materials showing great potential for use in biomaterials and biomedicine, environmental remediation, and energy production and storage. The influences that the preparation conditions and additives have on ACC preparation and stabilization are also discussed. Studies indicate that ACC can be used to construct environmentally-friendly hybrid films, supramolecular hydrogels, and drug vehicles. Finally, the existing challenges and future directions of the controlled synthesis and functionalization of CaCO₃ and its expanding applications are highlighted.

Stabilization of Waste-to-Energy (WTE) fly ash for disposal in landfills or use as cement substitute

This study investigated two approaches for managing Waste-to-Energy (WTE) fly ash (FA): (i) phosphoric acid stabilization of FA and disposal in non-hazardous landfills, so that it can pass the U.S. TCLP procedure and meet the U.S. Resource Conservation and Recovery Act (RCRA) standards; (ii) use of FA or phosphoric acid stabilized fly ash (PFA) as cement substitute in construction for avoiding disposal in landfills and reducing the consumption of Portland cement. The effect of stabilization was identified by TCLP tests and XRD quantification (QXRD), which showed that the economically optimal concentration for PFA to pass the RCRA was 1 mol/L H₃PO₄ (equivalent to 0.4 mol of H₃PO₄/kg of FA). Zn/Pb-phosphates were formed in treated ash by using high concentration H₃PO₄ (e.g., 3 mol/L). Thus, the hazardous FA was chemically stabilized to PFA, that were both discussed as cement substitute. QXRD and SEM results showed that both FA and PFA (1 mol/L H₃PO₄) chemically reacted with cement and water. Up to 25 vol% of the cement can be replaced by FA or PFA, with similar mechanical performance of cement mortars than that of reference. Testing by LEAF Method 1313-pH dependence showed that the FA and PFA cement mortars exhibited the same leachability of heavy metals; therefore, this study demonstrated the technical feasibility of utilizing either raw FA or stabilized PFA as supplementary cementitious material. The leachability of heavy metals in optimal FA or PFA 25 vol% cement mortar was under the U.K. WAC non-hazardous limits.

Crystal Nucleation and Growth of Inorganic Ionic Materials from Aqueous Solution: Selected Recent Developments, and Implications

In this review article, selected, latest theoretical, and experimental developments in the field of nucleation and crystal growth of inorganic materials from aqueous solution are highlighted, with a focus on literature after 2015 and on non-classical pathways. A key point is to emphasize the so far underappreciated role of water and solvent entropy in crystallization at all stages from solution speciation through to the final crystal. While drawing on examples from current inorganic materials where non-classical behavior has been proposed, the potential of these approaches to be adapted to a wide-range of systems is also discussed, while considering the broader implications of the current re-assessment of pathways for crystallization. Various techniques that are suitable for the exploration of crystallization pathways in aqueous solution, from nucleation to crystal growth are summarized, and a flow chart for the assignment of specific theories based on experimental observations is proposed.

Phase and morphology of calcium carbonate precipitated by rapid mixing in the absence of additives

Calcium carbonate is one of the most common minerals, and its polymorphic formation and transformation pathways from the amorphous to crystalline phases are well documented. However, the effects of locally created pH changes on the preferential formation of amorphous calcium carbonate (ACC) or its crystalline phase remain poorly understood. In this study, the influence of the initial solution pH on the precipitated polymorphs of calcium carbonate was investigated by the rapid mixing of each solution containing calcium or carbonate ions in the absence of additives. The results showed that the amount of recovered ACC particles was associated with the availability of fully deprotonated carbonate ions. A secondary crystalline phase was identified as the vaterite phase, but no polymorphic change to produce the more stable calcite was detected during 5 h of stirring. Interestingly, during the early stage of pouring, the vaterite morphology was dependent on the generated pH range, over which ACC particles were stabilized (pH > 10.3), followed by the hydration–condensation processes. When the pH was sufficiently low (pH < 10.3) for bicarbonate ions to participate in the carbonation reaction, croissant- or cauliflower-like aggregates with layered structures were obtained. In contrast, typical spherical vaterite particles were obtained at a high initial pH when the carbonate ions were dominant. Meanwhile, vaterite particles that were formed in the presence of an excess of carbonate ions were irregular and separate agglomerates. These results elucidate the formation of ACC and the morphologies of the vaterite products.

Vaterite with various polymorphs was prepared using different solution pH values. The effects of local solution differences in pH were systematically investigated.

Thermogravimetric Analysis on a Resonant Microcantilever

Thermogravimetric analysis (TGA) is a widely applied classic method for material characterization. However, the existing TGA method has reached its technical ceiling in regard to its sensitivity, efficiency, application scope, and extensibility. With temperature-programming and a picogram (10^-12 g) mass resoluble measurement function, an integrated resonant microcantilever is proposed and developed into micro-electromechanical system-based TGA (MEMS TGA) technology to satisfy the significantly higher TGA requirements. With only a nanogram (10^-9 g) level of a loaded sample, the microcantilever can conduct ultrasensitive mass-loss analysis along with ultrafast and controllable heating up to 1200 °C. Experiments have verified that MEMS TGA can improve heating efficiency by at least one order of magnitude compared to conventional TGA while maintaining measurement accuracy. The trace sample requirement also enables MEMS TGA to directly test explosive substances in an air atmosphere, while conventional TGA with a larger amount of sample has difficulty in avoiding explosion-induced equipment damage during heating. The silicon MEMS TGA microchip also exhibits functional combination (even integration) with other analytical techniques such as Raman spectroscopy to realize operando characterization.

Microreactor-Based TG-TEM Synchronous Analysis

It is challenging to measure the heating-induced mass change of the material during its morphological/structural evolution process. Herein, a silicon microreactor is developed for thermogravimetric-transmission electron microscopy synchronous analysis (TG-TEM synchronous analysis). A self-heating resonant microcantilever for mass-change detection and a dummy microcantilever with electron-beam transparent SiN_x windows for in situ TEM imaging are integrated back-to-back inside the microreactor. The TEM resolution of the microreactor reaches the Ångström level in an air atmosphere of 100 mbar, and the TGA function is realized by the heatable resonant microcantilever. The TG-TEM synchronous analysis has been successfully used to characterize two Ni(OH)₂ samples. During the in situ TEM observing process, the desorption of the intercalated H₂O molecules and dehydration of the lattice OH groups in the amorphous Ni(OH)₂·xH₂O nanosheets can be clearly distinguished from the microcantilever-based TGA. For single-crystal Ni(OH)₂ nanosheets, the TG-TEM synchronous analysis can distinguish the desorption of physiosorbed water, the condensation of surface OH groups, and the dehydration of lattice OH groups. The amorphous Ni(OH)₂ nanosheets transformed to polycrystalline NiO completed at 290 °C, and the decomposition from the single-crystalline Ni(OH)₂ nanoplates to NiO at 315 °C is also clearly recognized. The proposed microreactor-based TG-TEM synchronous analysis provides an interrelated characterization platform to obtain more comprehensive information on materials.

Transcriptome analysis of the bivalve Placuna placenta mantle reveals potential biomineralization-related genes

The shells of window pane oyster Placuna placenta are very thin and exhibit excellent optical transparency and mechanical robustness. However, little is known about the biomineralization-related proteins of the shells of P. placenta. In this work, we report the comprehensive transcriptome of the mantle tissue of P. placenta for the first time. The unigenes of the mantle tissue of P. placenta were annotated by using the public databases such as nr, GO, KOG, KEGG, and Pfam. 24,343 unigenes were annotated according to Pfam database, accounting for 21.48% of the total unigenes. We find that half of the annotated unigenes of the mantle tissue of P. placenta are consistent to the annotated unigenes from pacific oyster Crassostrea gigas according to nr database. The unigene sequence analysis from the mantle tissue of P. placenta indicates that 465,392 potential single nucleotide polymorphisms (SNPs) and 62,103 potential indel markers were identified from 60,371 unigenes. 178 unigenes of the mantle tissue of P. placenta are found to be homologous to those reported proteins related to the biomineralization process of molluscan shells, while 18 of them are highly expressed unigenes in the mantle tissue. It is proposed that four unigenes with the highest expression levels in the mantle tissue are very often related to the biomineralization process, while another three unigenes are potentially related to the biomineralization process according to the Quantitative Real-Time Polymerase Chain Reaction (qRT-PCR) analysis. In summary, the transcriptome analysis of the mantle tissue of P. Placenta shows the potential biomineralization-related proteins and this work may shed light for the shell formation mechanism of bivalves.

N-(2-hydroxyl)-propyl-3-trimethylammonium chitosan chloride/carboxymethyl cellulose films filled with in-situ crystallized calcium carbonate

The research and development of substitutes for petroleum-based plastics has become a hot topic. The N-(2-hydroxyl)-propyl-3-trimethylammonium chitosan chloride (HTCC, 10 wt%)/sodium carboxymethyl cellulose (CMC) films have showed enhanced mechanical properties, which also provide a potential substitute to petroleum-based plastics. In this paper, calcium carbonate was crystallized (cry-CaCO3) in HTCC/CMC film-forming solutions, and the effects of the cry-CaCO3 particles on HTCC/CMC film properties including microstructures, mechanical properties, thermal stability, whiteness, and wettability were characterized. An HTCC/CMC film with commercially available CaCO3 (com-CaCO3) was used as a control. The results showed that the cry-CaCO3 promoted the homogeneous distribution of the HTCC/CMC matrix and significantly improved mechanical properties, but showed little effect on the thermal stability, whiteness and wettability of the films. To reveal the affecting mechanism of cry-CaCO3 on HTCC/CMC film properties, the cry-CaCO3 particles were isolated from film-forming solutions and characterized by scanning electron microscope (SEM), powder X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), thermogravimetric analysis (TGA) methods. The results showed that the HTCC/CMC matrix modulated spherical CaCO3 particles, and the macromolecules were encapsulated in cry-CaCO3 particles, decreasing their adhesion to the HTCC/CMC matrix while increasing their distribution in the HTCC/CMC matrix. The strong electrostatic, hydrogen bonding and flexible interaction between CMC and cry-CaCO3 particles played a key role in improving the mechanical properties of HTCC/CMC films.

Nested Formation of Calcium Carbonate Polymorphs in a Bacterial Surface Membrane with a Graded Nanoconfinement: An Evolutionary Strategy to Ensure Bacterial Survival

It is the intention of this study to elucidate the nested formation of calcium carbonate polymorphs or polyamorphs in the different nanosized compartments. With these observations, it can be concluded how the bacteria can survive in a harsh environment with high calcium carbonate supersaturation. The mechanisms of calcium carbonate precipitation at the surface membrane and at the underlying cell wall membrane of the thermophilic soil bacterium Geobacillus stearothermophilus DSM 13240 have been revealed by high-resolution transmission electron microscopy and atomic force microscopy. In this Gram-positive bacterium, nanopores in the surface layer (S-layer) and in the supporting cell wall polymers are nucleation sites for metastable calcium carbonate polymorphs and polyamorphs. In order to observe the different metastable forms, various reaction times and a low reaction temperature (4 °C) have been chosen. Calcium carbonate polymorphs nucleate in the confinement of nanosized pores (⌀ 3–5 nm) of the S-layer. The hydrous crystalline calcium carbonate (ikaite) is formed initially with [110] as the favored growth direction. It transforms into the anhydrous metastable vaterite by a solid-state transition. In a following reaction step, calcite is precipitated, caused by dissolution of vaterite in the aqueous solution. In the larger pores of the cell wall (⌀ 20–50 nm), hydrated amorphous calcium carbonate is grown, which transforms into metastable monohydrocalcite, aragonite, or calcite. Due to the sequence of reaction steps via various metastable phases, the bacteria gain time for chipping the partially mineralized S-layer, and forming a fresh S-layer (characteristic growth time about 20 min). Thus, the bacteria can survive in solutions with high calcium carbonate supersaturation under the conditions of forced biomineralization.

Classical and Nonclassical Nucleation and Growth Mechanisms for Nanoparticle Formation

All solid materials are created via nucleation. In this evolutionary process, nuclei form in solution or at interfaces and expand by monomeric growth, oriented attachment, and phase transformation. Nucleation determines the location and size of nuclei, whereas growth controls the size, shape, and aggregation of newly formed nanoparticles. These physical properties of nanoparticles can determine their functionalities, reactivities, and porosities, as well as their fate and transport. Recent advances in nanoscale analytical technologies allow in situ real-time observations, enabling us to uncover the molecular nature of nuclei and the critical controlling factors for nucleation and growth. Although a single theory cannot yet fully explain such evolving processes, we have started to better understand how both classical and nonclassical theories can work together, and we have begun to recognize the importance of connecting these theories. This review discusses the recent convergence of knowledge about the nucleation and the growth of nanoparticles. Expected final online publication date for the Annual Review of Physical Chemistry, Volume 73 is April 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Pyrophosphate-stabilised amorphous calcium carbonate for bone substitution: toward a doping-dependent cluster-based model

Multiscale and multitool advanced characterisation of pyrophosphate-stabilised amorphous calcium carbonates allowed building a cluster-based model paving the way for tunable biomaterials.

Multiple Crystallization Pathways of Amorphous Calcium Carbonate in the Presence of Poly(Aspartic acid) with a Chain Length of 30

The crystallization pathways of amorphous calcium carbonate (ACC) have attracted tremendous interests because of the importance of ACC in biomineralization. Here, by using poly(Aspartic acid) with a chain length of...

Amorphous calcium carbonate monohydrate containing a defect hydrate network by mechanochemical processing of mono-hydrocalcite using ethanol as auxiliary solvent

Calcium carbonate monohydrate-like ACC was made by ball-milling with ethanol as auxiliary solvent. IR and solid-state NMR, diffraction and total scattering show that defects of the hydrate network due to partial displacement of water by ethanol are crucial for amorphization.

Influence of foreign salts on the CaCO3 pre-nucleation stage: application of the conductometric method

Calcium carbonate crystallization process has been studied for more than a century. Nevertheless, little is known about the early stages of nucleation since the in situ observations are difficult at...

In vitro crystallization of calcium carbonate mediated by proteins extracted from P. placenta shells

The ASM extracted from the shells of P. placenta can stabilize ACC and inhibit secondary nucleation for 10 hours, and an explosive secondary nucleation and quick crystal growth from 50 nm to 10 μm can be finished on the shell surface in one hour.

Advances in biomineralization-inspired materials for hard tissue repair

Biomineralization is the process by which organisms form mineralized tissues with hierarchical structures and excellent properties, including the bones and teeth in vertebrates. The underlying mechanisms and pathways of biomineralization provide inspiration for designing and constructing materials to repair hard tissues. In particular, the formation processes of minerals can be partly replicated by utilizing bioinspired artificial materials to mimic the functions of biomolecules or stabilize intermediate mineral phases involved in biomineralization. Here, we review recent advances in biomineralization-inspired materials developed for hard tissue repair. Biomineralization-inspired materials are categorized into different types based on their specific applications, which include bone repair, dentin remineralization, and enamel remineralization. Finally, the advantages and limitations of these materials are summarized, and several perspectives on future directions are discussed.

Progress on Biomimetic Mineralization and Materials for Hard Tissue Regeneration

Biomineralization is a process in which natural organisms regulate the crystal growth of inorganic minerals, resulting in hierarchical structured biominerals with excellent properties. Typical biominerals in the human body are the bones and teeth, and damage to these hard tissues directly affect our daily lives. The repair of bones and teeth in a biomimetic way, either by using a biomimetic mineralization strategy or biomimetic materials, is the key for hard tissue regeneration. In this review, we briefly introduce the structure of bone and tooth, and highlight the fundamental role of collagen mineralization in tissue repair. The recent progress on intra-/extrafibrillar collagen mineralization by a biomimetic strategy or materials is presented, and their potential for tissue regeneration is discussed. Then, recent achievements on bone and tooth repair are summarized, and these works are discussed in the view of materials science and biological science, providing a broader vision for the future research of hard tissue repair techniques. Lastly, recent progress on hard tissue regeneration is concluded, and existing problems and future directions are prospected.

Controlling the calcium carbonate microstructure of engineered living building materials

The fabrication of responsive soft materials that enable the controlled release of microbial induced calcium carbonate (CaCO3) precipitation (MICP) would be highly desirable for the creation of living materials that can be used, for example, as self-healing construction materials. To obtain a tight control over the mechanical properties of these materials, needed for civil engineering applications, the amount, location, and structure of the forming minerals must be precisely tuned; this requires good control over the dynamic functionality of bacteria. Despite recent advances in the self-healing of concrete cracks and the understanding of the role of synthesis conditions on the CaCO3 polymorphic regulation, the degree of control over the CaCO3 remains insufficient to meet these requirements. We demonstrate that the amount and location of CaCO3 produced within a matrix, can be controlled through the concentration and location of bacteria; these parameters can be precisely tuned if bacteria are encapsulated, as we demonstrate with the soil-dwelling bacterium Sporosarcina pasteurii that is deposited within biocompatible alginate and carboxymethyl cellulose (CMC) hydrogels. Using a competitive ligand exchange mechanism that relies on the presence of yeast extract, we control the timing of the release of calcium ions that crosslink the alginate or CMC without compromising bacterial viability. With this novel use of hydrogel encapsulation of bacteria for on-demand release of MICP, we achieve control over the amount and structure of CaCO3-based composites and demonstrate that S. pasteurii can be stored for up to 3 months at an accessible storage temperature of 4 °C, which are two important factors that currently limit the applicability of MICP for the reinforcement of construction materials. These composites thus have the potential to sense, respond, and heal without the need for external intervention.

Calcium carbonate particles: synthesis, temperature and time influence on the size, shape, phase, and their impact on cell hydroxyapatite formation

To develop materials for drug delivery and tissue engineering and to study their efficiency with respect to ossification, it is necessary to apply physicochemical and biological analyses. The major challenge is labor-intensive data mining during synthesis and the reproducibility of the obtained data. In this work, we investigated the influence of time and temperature on the reaction yield, the reaction rate, and the size, shape, and phase of the obtained product in the completely controllable synthesis of calcium carbonate. We show that calcium carbonate particles can be synthesized in large quantities, i.e., in gram quantities, which is a substantial advantage over previously reported synthesis methods. We demonstrated that the presence of vaterite particles can dramatically stimulate hydroxyapatite (HA) production by providing the continued release of the main HA component - calcium ions - depending on the following particle parameters: size, shape, and phase. To understand the key parameters influencing the efficiency of HA production by cells, we created a predictive model by means of principal component analysis. We found that smaller particles in the vaterite state are best suited for HA growth (HA growth was 8 times greater than that in the control). We also found that the reported dependence of cell adhesion on colloidal particles can be extended to other types of particles that contain calcium ions.

Recent advances in dopamine-based materials constructed via one-pot co-assembly strategy

Dopamine-based materials have attracted widespread interest due to the outstanding physicochemical and biological properties. Since the first report on polydopamine (PDA) films, great efforts have been devoted to develop new fabrication strategies for obtaining novel nanostructures and desirable properties. Among them, one-pot co-assembly strategy offers a unique pathway for integrating multiple properties and functions into dopamine-based platform in a single simultaneous co-deposition step. This review focuses on the state of the art development of one-pot multicomponent self-assembly of dopamine-based materials and summarizes various single-step co-deposition approaches, including PDA-assisted adaptive encapsulation, co-assembly of dopamine with other molecules through non-covalent interactions or covalent interactions. Moreover, emerging applications of dopamine-based materials in the fields ranging from sensing, cancer therapy, catalysis, oil/water separation to antifouling are outlined. In addition, some critical remaining challenges and opportunities are discussed to pave the way towards the rational design and applications of dopamine-based materials.

Tuning Polymorphs and Morphology of Microbially Induced Calcium Carbonate: Controlling Factors and Underlying Mechanisms

Microbially precipitated calcium carbonate (CaCO₃) has drawn broad attention due to its potential applications in various areas, for example, biocementation, medicine, and soil reinforcement. Sporosarcina pasteurii (S. pasteurii), formerly known as Bacillus pasteurii, has been investigated for CaCO₃ biomineralization due to its high ureolytic activity. A high degree of supersaturation with respect to the presence of bacterial cell wall, extracellular polymeric substances, and organic byproducts of bacterial activity plays an important role in the formation and stabilization of CaCO₃ polymorphs. Although microbially induced CaCO₃ and its polymorphs have been investigated broadly, the mechanisms of polymorph selection and morphological evolution are not well understood. This study employs ex situ approaches to address the complication of biomineralization in the presence of living organisms and to elucidate how solution chemistry, bacterial activity, and precipitation kinetics alter the polymorphism and morphology of CaCO₃ induced by S. pasteurii. The results indicate that in the presence of enough calcium ions and urea (as a carbonate source), the bacterial activity favors the formation and stabilization of vaterite. The morphological observations also provide valuable information on the particles' microstructure. The morphology of calcite evolves from single crystal to polycrystalline structures, and the morphology of vaterite evolved from spherical to oval-shaped structures on increasing the organic material concentration. Specific functional groups also exert morphological control on CaCO₃ polymorphs. However, the sensitivity of the calcite polymorph to the composition and orientation of these functional groups is higher compared to that of the vaterite polymorph. These findings offer important insights that can be used to constrain a set of experimental conditions for synthesizing a certain polymorph ratio for vaterite/calcite or a particular morphology of each polymorph and shed light on the crystallization and phase transformation mechanisms in such complicated bioenvironments.