In situ probing calcium carbonate formation by combining fast controlled precipitation method and small-angle X-ray scattering

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...

Variation in Properties of Pre-Nucleation Calcium Carbonate Clusters Induced by Aggregation: A Molecular Dynamics Study

Numerous studies have speculated calcium carbonate (CaCO3) nucleation induced by pre-nucleation clusters (PNCs) aggregation. However, it is challenging for experiments to directly obtain the relationship between PNCs aggregation and nucleation. Herein, we employ molecular dynamics simulations to explore the variation during PNCs aggregation, which can describe the beginning stage of CaCO3 nucleation induced by PNCs aggregation in supersaturated solutions. The results reveal that the formation of CaCO3 nucleus consists of PNCs spontaneous growth, PNCs solubility equilibrium, and aggregation of PNCs inducing nucleation. The PNCs aggregation, accompanied by the variation in the configuration and stability of CaCO3 aggregate, breaks the solubility equilibrium of PNCs and creates conditions for the formation of the more stable nucleus. Besides, the CaCO3 nucleus with the higher coordination number and the lower hydration number form when decreasing the CaCO3 concentration or increasing the temperature. This work not only sheds light on the formation of the CaCO3 nucleus but also contributes to the explanation for CaCO3 polymorphism.

Water: How Does It Influence the CaCO3 Formation?

Nature produces biomineral-based materials with a fascinating set of properties using only a limited number of elements. This set of properties is obtained by closely controlling the structure and local composition of the biominerals. We are far from achieving the same degree of control over the properties of synthetic biomineral-based composites. One reason for this inferior control is our incomplete understanding of the influence of the synthesis conditions and additives on the structure and composition of the forming biominerals. In this Review, we provide an overview of the current understanding of the influence of synthesis conditions and additives during different formation stages of CaCO₃ , one of the most abundant biominerals, on the structure, composition, and properties of the resulting CaCO₃ crystals. In addition, we summarize currently known means to tune these parameters. Throughout the Review, we put special emphasis on the role of water in mediating the formation of CaCO₃ and thereby influencing its structure and properties, an often overlooked aspect that is of high relevance.

In Situ Synchrotron X-ray Characterization Shining Light on the Nucleation and Growth Kinetics of Colloidal Nanoparticles

Rational synthesis of colloidal nanoparticles with desirable properties relies on precise control over the nucleation and growth kinetics, which is still not well understood. The recent development of in situ high energy synchrotron X-ray techniques offers an excellent opportunity to quantitatively monitor the growth trajectories of colloidal nanoparticles in real time under real reaction conditions. The time-resolved, quantitative data of the growing colloidal nanoparticles are unique to reveal the mechanism of nanoparticle formation and determine the corresponding intrinsic kinetic parameters. This review discusses the kinetics of major steps of forming colloidal nanoparticles and the capability of in situ synchrotron X-ray techniques in studying the corresponding kinetics.

A versatile liquid-jet/sessile droplet system for operando studies of reactions in liquid dispersions and solutions by X-ray absorption spectroscopy

X-ray absorption spectroscopy for operando studies of liquid dispersions and solutions.

Study of the influence of the supersaturation coefficient on scaling rate using the pre-calcified surface of a quartz crystal microbalance

Scale deposition is a common issue in industrial plants, which creates technical problems, i.e. reduction of heat transfer, decrease of flow rate due to an obstruction of pipes. Therefore, the development of some appropriate methods based on well suitable in situ sensors to evaluate and predict the scaling propensity of water is a major concern in current research. This would be a good strategy for the optimization of anti-scaling treatments. In this study, scaling tests were carried out using a sensitive sensor, which has been developed using a quartz crystal microbalance with a pre-calcified electrode surface (SQCM). This technique allowed studying the influence of the supersaturation on the scaling rate. The set-up was tested with different water samples which were brought to a given supersaturation coefficient by degassing the dissolved CO₂. The prediction of the scaling propensity of water was then possible through the relationship between the scaling rate on a pre-calcified surface and the supersaturation coefficient. In addition, the kinetics of CaCO₃ deposit on the pre-calcified SQCM surface was found to be slower for natural water than for synthetic water (same calcium concentration). Furthermore, the activation energy for scale deposit, in synthetic water, was found to be 22 kJ.mol^-1, which may be related to the diffusion of ions and/or CaCO₃ nuclei in solution.

Chemical Stabilization and Electrochemical Destabilization of the Iron Keggin Ion in Water

The iron Keggin ion is identified as a structural building block in both magnetite and ferrihydrite, two important iron oxide phases in nature and in technology. Discrete molecular forms of the iron Keggin ion that can be both manipulated in water and chemically converted to the related metal oxides are important for understanding growth mechanisms, in particular, nonclassical nucleation in which cluster building units are preserved in the aggregation and condensation processes. Here we describe two iron Keggin ion structures, formulated as [Bi₆FeO₄Fe₁₂O₁₂(OH)₁₂(CF₃COO)₁₀(H₂O)₂]³⁺ (Kegg-1) and [Bi₆FeO₄Fe₁₂O₁₂(OH)₁₂(CF₃COO)₁₂]¹⁺ (Kegg-2). Experimental and simulated X-ray scattering studies show indefinite stability of these clusters in water from pH 1-3. The tridecameric iron Keggin-ion core is protected from hydrolysis by a synergistic effect of the capping Bi³⁺ cations and the trifluoroacetate ligands that, respectively, bond to the iron and bridge to the bismuth. By introducing electrons to the aqueous solution of clusters, we achieve complete separation of bismuth from the cluster, and the iron Keggin ion rapidly converts to magnetite and/or ferrihydrite, depending on the mechanism of reduction. In this strategy, we take advantage of the easily accessible reduction potential and crystallization energy of bismuth. Reduction was executed in bulk by chemical means, by voltammetry, and by secondary effects of transmission electron microscopy imaging of solutions. Prior, we showed a less stable analogue of the iron Keggin cluster converted to ferrihydrite simply upon dissolution. The prior and currently studied clusters with a range of reactivity provide a chemical system to study molecular cluster to metal oxide conversion processes in detail.

Research on the synthesis and scale inhibition performance of a new terpolymer scale inhibitor

A new terpolymer named β-CD-MA-SSS was produced using free-radical polymerization of β-cyclodextrin (β-CD), maleic-anhydride (MA) and sodium-styrene-sulfonate (SSS) as monomers, with potassium persulfate (KPS) as initiator. Its performance as a scale inhibitor to prevent deposition of calcium carbonate (CaCO3) has been investigated. Experimental results demonstrated that β-CD-MA-SSS performed excellent scale inhibition and exhibited a high conversion rate under the following conditions: initiator consisting of 6%, molar ratio of reaction monomers SSS:MA = 0.8:1, MA:β-CD = 6:1, reaction temperature of 80 °C, reaction time of 6 h, and dropping time of 40 min when MA was dosed as a substrate, and SSS and KPS were dosed as dropping reactants simultaneously. Use of a Fourier transform infrared spectrometer for this inhibitor showed that the polymerization reaction had taken place with the reaction monomers under the above specified conditions. Scanning electron microscopy indicated that the β-CD-MA-SSS had a strong chelating ability for calcium (Ca(2+)) and a good dispersion ability for calcium carbonate (CaCO3).