Calcium Counterions Research Articles

One-pot synthesis of regenerative calcium counterions from waste chicken eggshells for SO2-to-sulfur reduction

Abating sulfur dioxide (SO2) emissions is increasingly critical for addressing environmental concerns and safeguarding human health. In this study, we propose a novel, sustainable approach utilizing in situ eggshell waste-derived calcium-based materials for the catalytic thermal reduction of SO2 to elemental sulfur. Our research focuses on the facile synthesis of calcium-based compounds, proceeding from chicken eggshells to CaO, CaSO4, and finally CaS, for treating hazardous SO2 gas in a one-pot reactor. The effects of gas hourly space velocity (GHSV), temperature, and catalyst stability were studied. Optimal conditions for sulfur yield (71.32%) and SO2 conversion (43.38%) were achieved at 800 °C with a GHSV of 117 L h/g. Our findings demonstrate that the calcium-based materials exhibit exceptional stability, maintaining activity for 6.5 h. Mechanistically, the synergistic pathways of Mars-Van Krevelen and Eley-Rideal mechanisms underlying the SO2 reduction process were elucidated. This research presents a sustainable solution for converting SO2 into a valuable sulfur commodity, and contributes to achieving Sustainable Development Goal No. 12 on Sustainable Consumption and Production. By harnessing CaS derived from eggshell waste, our work underscores the potential for environmentally friendly practices in addressing industrial emissions and advancing sustainable resource utilization.

Divalent ion partitioning through dense ion exchange membranes

Understanding the mechanism behind the permeation of multivalent ions through ion exchange membranes remains an ongoing challenge. Here we address this knowledge gap by presenting a molecular theory to elucidate the influence of counterion condensation and electrosteric effects on the (multivalent) divalent counterion permeation through such membranes. Building upon published experimental data (Galizia et al., 2017), we analyze the energetic tendencies of divalent counterions to associate with the fixed charge groups and their entropic preferences to disassociate to gain translational freedom, allowing us to quantitatively assess the partitioning of divalent ions at two distinct levels. (i) The global partitioning between the external 2:1 salt solution and the membrane, and (ii) the local partitioning within the interstitial solution and the crosslinked polymeric chains within the membrane. Notably, our observations reveal that the global partitioning of divalent counterions does not differ when the membranes operate separately in magnesium chloride (MgCl2) and calcium chloride (CaCl2) solutions. However, at the local partitioning level, we identify a higher preference for calcium counterions to associate with the fixed charge groups than magnesium ions. This preference arises from calcium ions’ more favorable charge density (physical size), facilitating their association/pairing with the fixed charge groups. The key takeaway message from this work is that when dealing with multivalent ions, we must downlevel our investigation, looking at how the counterions relax between the interstitial solution and the crosslinked polymeric chains and, in return, comprehending how it ultimately controls the global transport property of these membranes (such as their Donnan potential and water uptake).

A Further Study on Calcium Phosphate Gardens Grown from the Interface of κ-Carrageenan-based Hydrogels and Counterion Solutions.

Originating from the concept of classical chemical gardens, a new field coined 'chemobrionics' has recently emerged. In the present work, two chemobrionic systems grown from a hydrogel/liquid interface at different time scales (for 1, 7, 14 or 28 days) were investigated, i. e., a calcium-based hydrogel with a phosphate counterion solution (Ca-gel) and a phosphate-based hydrogel with a calcium counterion solution (P-gel). The initial pH changes of the systems were investigated, and the obtained tubular structures were studied using optical microscopy, SEM, AFM, PXRD and TGA. One of the important findings is that the tubes obtained in the Ca-gel system were straight and long, which could be explained by the larger pH difference observed between the hydrogel and the counterion solution in this system (ΔpH∼2.1) compared to the P-gel system (ΔpH∼0). The Ca-gel structures remained overall more amorphous even though increased crystallinity was observed in both systems with increased time spent in counterion solution. Both systems contained hydroxyapatite phases, with additional calcite phases observed for the P-gel structures and traces of κ-carrageenan for the Ca-gel structures. Our study provides a promising method for controlling tubular macrostructures through adjusting the reaction conditions such as maturation time and pH.

Rheological Behavior of Pectin Gels Obtained from Araçá (Psidium cattleianum Sabine) Fruits: Influence of DM, Pectin and Calcium Concentrations.

In this work, purified pectins from Araçá fruits (Psidium cattleianum Sabine) were obtained and characterized after partial demethylation. On each prepared sample, the carboxylic yield was obtained by titration, the degree of methylation (DM) by 1H-NMR, and the molecular weight distribution by steric exclusion chromatography (SEC). Then, the gelation ability in the presence of calcium counterions was investigated and related to DM (59–0%); the pectin concentration (2–10 g L−1); and the CaCl2 concentration (0.1–1 mol L−1) used for dialysis. The critical pectin concentration for homogeneous gelation was above 2 g L−1 when formed against 1 mol L−1 CaCl2. The elastic modulus (G′) increased with pectin concentration following the relationship G′~C2.8 in agreement with rigid physical gel network predictions. The purified samples APP and APP-A with DM ≥ 40% in the same conditions released heterogeneous systems formed of large aggregates. Gels formed against lower concentrations of CaCl2 down to 0.1 mol L−1 had a higher degree of swelling, indicating electrostatic repulsions between charged chains, thus, counterbalancing the Ca2+ cross-linkage. Compression/traction experiments demonstrated that an irreversible change in the gel structure occurred during small compression with an enhancement of the G′ modulus.

Channel Function of Polycystin-2 in the Endoplasmic Reticulum Protects against Autosomal Dominant Polycystic Kidney Disease.

Mutations of PKD2, which encodes polycystin-2, cause autosomal dominant polycystic kidney disease (ADPKD). The prevailing view is that defects in polycystin-2-mediated calcium ion influx in the primary cilia play a central role in the pathogenesis of cyst growth. However, polycystin-2 is predominantly expressed in the endoplasmic reticulum (ER) and more permeable to potassium ions than to calcium ions. The trimeric intracellular cation (TRIC) channel TRIC-B is an ER-resident potassium channel that mediates potassium-calcium counterion exchange for inositol trisphosphate-mediated calcium ion release. Using TRIC-B as a tool, we examined the function of ER-localized polycystin-2 and its role in ADPKD pathogenesis in cultured cells, zebrafish, and mouse models. Agonist-induced ER calcium ion release was defective in cells lacking polycystin-2 and reversed by exogenous expression of TRIC-B. Vice versa, exogenous polycystin-2 reversed an ER calcium-release defect in cells lacking TRIC-B. In a zebrafish model, expression of wild-type but not nonfunctional TRIC-B suppressed polycystin-2-deficient phenotypes. Similarly, these phenotypes were suppressed by targeting the ROMK potassium channel (normally expressed on the cell surface) to the ER. In cultured cells and polycystin-2-deficient zebrafish phenotypes, polycystin-2 remained capable of reversing the ER calcium release defect even when it was not present in the cilia. Transgenic expression of Tric-b ameliorated cystogenesis in the kidneys of conditional Pkd2-inactivated mice, whereas Tric-b deletion enhanced cystogenesis in Pkd2-heterozygous kidneys. Polycystin-2 in the ER appears to be critical for anticystogenesis and likely functions as a potassium ion channel to facilitate potassium-calcium counterion exchange for inositol trisphosphate-mediated calcium release. The results advance the understanding of ADPKD pathogenesis and provides proof of principle for pharmacotherapy by TRIC-B activators.

Ion Specificity of Confined Ion-Water Structuring and Nanoscale Surface Forces in Clays.

Ion specificity and related Hofmeister effects, which are ubiquitous in aqueous systems, can have spectacular consequences in hydrated clays, where ion-specific nanoscale surface forces can determine large-scale cohesive swelling and shrinkage behaviors of soil and sediments. We have used a semiatomistic computational approach and examined sodium, calcium, and aluminum counterions confined with water between charged surfaces representative of clay materials to show that ion-water structuring in nanoscale confinement is at the origin of surface forces between clay particles which are intrinsically ion-specific. When charged surfaces strongly confine ions and water, the amplitude and oscillations of the net pressure naturally emerge from the interplay of electrostatics and steric effects, which cannot be captured by existing theories. Increasing confinement and surface charge densities promote ion-water structures that increasingly deviate from the ions' bulk hydration shells, being strongly anisotropic, persistent, and self-organizing into optimized, nearly solid-like assemblies where hardly any free water is left. Under these conditions, strongly attractive interactions can prevail between charged surfaces because of the dramatically reduced dielectric screening of water and the highly organized water-ion structures. By unravelling the ion-specific nature of these nanoscale interactions, we provide evidence that ion-specific solvation structures determined by confinement are at the origin of ion specificity in clays and potentially a broader range of confined aqueous systems.

Dynamic and molecular association in premicellar aqueous solutions of dicarboxylate amino acid‐based surfactant as studied by 1H NMR

We examined a series of amino acid-based surfactants with two carboxylic groups separated by a spacer of one, two, or three carbon atoms with sodium and calcium counterions in the premicellar concentration region near the CMC. 1 H nuclear magnetic resonance (NMR) spectroscopy and NMR diffusometry techniques were used to study the local environment, association, and translational dynamics of the surfactant's molecules. We measured the self-diffusion coefficients of the micelles, calculated the effective hydrodynamic radii, and determined the temperature region in which the premicelles exist. With an increase in temperature from 295 to 335 K, the premicellar state of the surfactant is replaced by the monomeric state.

Using fillers to tune material properties of an ion-containing semi-crystalline poly(ethylene glycol) for fused filament fabrication additive manufacturing

Abstract The materials library for Fused Filament Fabrication (FFF) additive manufacturing processes has been primarily dominated by amorphous thermoplastic materials. Semi-crystalline polymers form tough plastics due to their strong intermolecular forces, which makes them well suited for applications requiring wear and chemical resistance, thermal stability, and structural loading. However, they are infrequently used in FFF because of large shrinkage that occurs due to recrystallization during cooling, which causes printed layers to warp. The authors have previously evaluated a semi-crystalline polymer series (sulfonated poly(ethylene glycol) (SPEG)) for FFF printability. The influence of divalent counter-ions in the SPEG series altered the material properties and crystallization to enable processing via FFF. The SPEG containing a calcium counterion resulted in the print quality due to the higher viscosity (105 Pa∙s) allowing the material to hold shape in the melt and high-nucleation and small spherulite size mitigating the layer warping. However, the dialysis used for the ion exchange in the polymer synthesis procedure proved challenging for mass manufacturing scale-up. To circumvent this limitation, the authors explore the incorporation of ionically charged filler materials in the SPEG with a sodium counter-ion, poly(PEG8k-co-NaSIP), to achieve the desired properties for FFF processing. Both ionic (calcium chloride and calcium carbonate) and non-ionic (silica and starch) filler particles were added to poly(PEG8k-co-NaSIP) and the resulting material properties and effect on FFF printability were measured. The calcium chloride filler changed the viscosity, crystallinity, spherulite growth, and spherulite size which improved the processing via FFF without requiring an ion exchange. This technique may be applicable to other ionic polymers in order to alter their material properties to enable FFF printing.

Counterion exchanged hydrophobic polyelectrolyte multilayer membrane for organic solvent nanofiltration

Organic solvent nanofiltration is a promising separation technology for removing solute from an organic medium. However, the fabrication of organic solvent nanofiltration membranes with stable separation performance is still a challenge. Herein, a hydrophobic polyelectrolyte multilayer membrane was prepared through a layer-by-layer self-assembly and counterion exchange method. Poly(diallyl dimethyl ammonium chloride) (PDDA)/polyacrylic acid (PAA) multilayer was self-assembled on the surface of the hydrolyzed polyacrylonitrile substrate through electrostatic interaction. Simultaneously, calcium silicate hydrate (CSH) nanoparticles were in situ grown during the multilayer formation process due to the incorporation of precursor in polyelectrolyte solutions. Therefore, the surface roughness of the membrane was enhanced and the anti-swelling property of the polyelectrolyte multilayer was also improved. The hydrophilic [(PDDA/PAA-CSH)2.5]+Cl− membrane was then converted to the hydrophobic membrane through the counterion exchange between Cl− and perfluorooctanate (PFO−) ions. The obtained [(PDDA/PAA-CSH)2.5]+PFO− membrane has a water contact angle of 118°, which can be used to separate dyes from ethanol. Both the separation performance and stability of the polyelectrolyte multilayer membrane were improved through the in situ growth of calcium silicate hydrate nanoparticles and counterion exchange by perfluorooctanate ions. Therefore, this strategy may open a new avenue to prepare organic solvent nanofiltration membranes.

Mechanism of Calcium Incorporation Inside Sol–Gel Silicate Bioactive Glass and the Advantage of Using Ca(OH)2 over Other Calcium Sources

Calcium is an essential component of osteogenesis and is often required for imparting significant bioactivity to synthetic bone substitutes and, in particular, silicate-based materials. However, the mechanism of calcium incorporation inside sol-gel silicates is poorly understood. In this work, we shed light on the determinant parameters for incorporation of calcium into acid-base-catalyzed sol-gel silicates at ambient temperature: increasing the pH above the isoelectric point of silicic acid and the nature of the calcium counterion in the calcium precursor are found to be the key. Based on our proposed reaction sequence, we were able to compare calcium precursors and select an ideal candidate compound for the synthesis of bioactive glasses (BG) and organic-inorganic hybrids at ambient temperature. Reproducible syntheses and gel times of SiO2-CaO BG were obtained using calcium hydroxide (CH), and we demonstrate its usability in the synthesis of promising BG-polycaprolactone hybrid scaffolds. BG and hybrids prepared with CH were able to form nanocrystalline nonstoichiometric apatite in simulated body fluid. The increased reliability of low-temperature syntheses associated with the use of a stable and inexpensive alkaline-earth precursor are major steps toward the translation of calcium silicate hybrids or other alkaline-earth silicates from bench to clinic.

Modeling counterion partition in composite gels of BSA with gelatin following high pressure treatment

We examine the morphology of hydrogels made of bovine serum albumin and gelatin following high pressure processing at 300 MPa for 15 min at 10 and 80 °C. Emphasis is on the distribution of added calcium counterions between the polymeric phases seen in changes in the structural properties of the composite gel. Protocol includes thermal and HPP treatments, dynamic oscillation rheology, ESEM, and modeling from the “synthetic polymer approach” to rationalize results. Pressurization at 10 °C produced continuous gelatin networks with dispersed BSA inclusions whereas pressurization at 80 °C yielded an inverse dispersion of BSA as the continuous phase supporting liquid gelatin inclusions. Lewis and Nielsen equations were adapted to predict the counterion distribution between the polymeric phases that profoundly affected the structural properties of the pressurized gels. The concept of counterion partition (pc) is introduced to the literature to follow the phase behavior of the composites in the presence of added calcium counterions.

Interfacial Connection Mechanisms in Calcium-Silicate-Hydrates/Polymer Nanocomposites: A Molecular Dynamics Study.

Properties of organic/inorganic composites can be highly dependent on the interfacial connections. In this work, molecular dynamics, using pair-potential-based force fields, was employed to investigate the structure, dynamics, and stability of interfacial connections between calcium-silicate-hydrates (C-S-H) and organic functional groups of three different polymer species. The calculation results suggest that the affinity between C-S-H and polymers is influenced by the polarity of the functional groups and the diffusivity and aggregation tendency of the polymers. In the interfaces, the calcium counterions from C-S-H act as the coordination atoms in bridging the double-bonded oxygen atoms in the carboxyl groups (-COOH), and the Ca-O connection plays a dominant role in binding poly(acrylic acid) (PAA) due to the high bond strength defined by time-correlated function. The defective calcium-silicate chains provide significant numbers of nonbridging oxygen sites to accept H-bonds from -COOH groups. As compared with PAA, the interfacial interactions are much weaker between C-S-H and poly(vinyl alcohol) (PVA) or poly(ethylene glycol) (PEG). Predominate percentage of the -OH groups in the PVA form H-bonds with inter- and intramolecule, which results in the polymer intertwining and reduces the probability of H-bond connections between PVA and C-S-H. On the other hand, the inert functional groups (C-O-C) in poly(ethylene glycol) (PEG) make this polymer exhibit unfolded configurations and move freely with little restrictions. The interaction mechanisms interpreted in this organic-inorganic interface can give fundamental insights into the polymer modification of C-S-H and further implications to improving cement-based materials from the genetic level.

Ultraviolet photo-oxidation of polyvinylpyrrolidone (PVP) coatings on gold nanoparticles.

Polymeric coatings are commonly applied to impart functionality and colloidal stability to engineered nanoparticles. In natural environments, transformations of the coating can modify the particle transport behavior, but the mechanisms and outcomes of these transformations have not yet been thoroughly evaluated. This study investigates the photo-transformations of polyvinylpyrrolidone (PVP) coatings on gold nanoparticles (AuNPs) under ultraviolet (UV) irradiation, representing light exposure in surface waters or other sunlit environments, and the impact on the AuNP colloidal stability. Multiple orthogonal characterization methods were applied to interrogate UV-induced transformations and their consequences. Rapid oxidation of the PVP coating occurred upon UV exposure. The transformed PVP largely persisted on the AuNP surface, albeit in a collapsed polymer layer around the AuNP surface. This transformation resulted in drastically diminished colloidal stability of the AuNPs, consistent with loss of steric stabilization. While the residual coating modified the interaction of the AuNPs with calcium counterions, it did not prevent subsequent stabilization by humic acid. This study demonstrates the importance of both chemical and physical coating transformations on nanoparticles, and hence the need for orthogonal and complementary characterization methods to fully characterize the coating transformations. Finally, the specific transformations of the PVP-coated AuNPs investigated here are discussed more broadly with respect to generalizability to other polymer-coated NPs and the implications for their fate in sunlit or other reactive environments.

Sequence-dependent association of alginate with sodium and calcium counterions

Molecular dynamics simulation is used to study in detail the binding of sodium and calcium ions to alginate chains, and its dependence on the content of guluronic (G) acid residues. Our previous studies showed that chains with different G content associate through different structural mechanisms due to differing degrees of rigidity of the ion-alginate chain complexes. Polymannuronate and polyguluronate chains form highly ordered structures due to their more rigid nature. Heteropolymer chains are more flexible and hence associate at higher ion and alginate concentrations, however, with association behavior that has a clear dependence on G content. The nature of interactions of sodium and calcium ions are shown to differ for poly-M, poly-G, and the heteropolymer compositions. Scattering curves of Ca2+-alginate solutions where found to have good agreement with the broken-rod SAXS model with nontrivial but clear dependence on G content, which is explained by chain flexibility and its relation to ion condensation.

Ionic complexation and adsorption of small organic molecules on calcium silicate hydrate: Relation with their retarding effect on the hydration of C3S

The ion complexing power and the adsorption of set-retarders such as sugar derivatives (d-glucitol, d-gluconate…), amino-carboxylates and phosphonates (EDTA, EDTMP, …) on C-S-H were identified and compared. The complexation equilibria of the predominant calcium and/or hydroxide complex and its relative constant were determined after measuring the solubilizing effect of the molecules in suspensions buffered by portlandite. The adsorption of the molecules on C-S-H as well as their possible complexation with silicate ions in solution were also investigated. All the molecules studied are shown to complex calcium and/or hydroxide ions but only amino-phosphonates, d-gluconate and d-glucitol complex silicate ions. They all adsorb on portlandite and C-S-H but to different extents. These organic compounds are also revealed to be sensitive to the presence of calcium counter-ions at the surface of C-S-H. Finally, the relation between their ionic complexing powers, adsorption properties and retarding effects on the hydration of C3S are discussed.

The structural influence of Ca(2+) counter-ions on uranyl(VI) tricarbonate in aqueous solution.

The presented study elucidates the influence of calcium(II) counter-ions on the structure of the environmentally relevant uranyl tricarbonates using hybrid quantum mechanical/molecular mechanical (QM/MM) MD simulations. Since experimental investigations may be subject to limitations in detecting the presence of counter-ions in solution, the present study is of importance to obtain a profound understanding of the effects counter-ions may have on coordination complexes. It can be concluded from the obtained simulation data that two calcium(II) ions are essential for stabilizing the experimentally observed uranyl tricarbonate complex in aqueous solution. Including only one calcium(II) ion in the coordination sphere was found to be insufficient to form a six-fold equatorial coordination of carbonates, but a five-fold coordination is adopted similar to the counter-ion free case in aqueous solution reported in a previous study.

Stability of negatively charged platelets in calcium-rich anionic copolymer solutions.

Controlling the stability of anisotropic particles is key to the development of advanced materials. Here, we report an investigation, by means of mesoscale molecular dynamics simulations, of the stability and structural change of calcium-rich dispersions containing negatively charged nanoplatelets, neutralized by calcium counterions, in the presence of either comb copolymers composed of anionic backbones with attached neutral side chains or anionic-neutral linear block copolymers. In agreement with experimental observations, small stacks of platelets (tactoids) are formed, which are greatly stabilized in the presence of copolymers. In the absence of polymers, tactoids will grow and aggregate strongly due to large attractive Ca(2+)-Ca(2+) correlation forces. Unlike comb copolymers which only adsorb on the external surfaces, block copolymers are found to intercalate between the platelets. The present results show that the stabilization is the result of a free energy barrier induced by the excluded volume of hydrophilic chains, while the intercalation is due to bridging forces. More generally, the results shed new light on the recent finding of the first hybrid cementitious mesocrystal.

Biomaterials based on a natural polysaccharide: alginate

In this short review, our objective was to describe few new applications of a natural polysaccharide extracted from algae, the alginates. Firstly, the chemical composition is recalled and the main techniques used for characterization are cited. The role of guluronic acid blocks (GG blocks) is particularly important for gel mechanical properties in presence of calcium counterions. Then, the main applications in food and biomedicine are briefly mentioned followed by tentative applications in packaging, paper, textil and wound dressing which are described. Especially, fine fibers are produced now industrially under mixed sodium/calcium ionic form.

The Structures of Salicylate Surfactants with Long Alkyl Chains in Non-Aqueous Media

The self-assembled structures formed by alkyl salicylate surfactants, as a function of metal headgroup counterion, in dodecane and toluene have been investigated. Results from optical microscopy are combined with small angle neutron scattering to show that moisture in the organic phase can have a dramatic effect on the observed structures. A simple acidic cation produces a cluster of surfactant chains irrespective of the oil type or presence of water. However, systems with an alkali metal counterion (potassium or sodium) result in cylindrical micelles in dry dodecane changing to lamellar structures in the wet case and fuzzy spheres in dry toluene changing to bidisperse emulsions with the presence of water. However, if magnesium or calcium counterions are used, this leads to different structures, depending on the oil type and the presence of moisture.

Influence of processing history on water and salt transport properties of disulfonated polysulfone random copolymers

Disulfonated poly(arylene ether sulfone)s are high glass transition temperature polymers, and their water and salt transport properties depend sensitively on thermal processing history. In this study, films of a 32 mol% disulfonated poly(arylene ether sulfone) random copolymer (BPS-32), polymerized in the potassium counter-ion form, were acidified using solid state and solution routes. The resulting acid counter-ion form materials were then converted to sodium, potassium, and calcium counter-ion forms via ion exchange. Additionally, several films were subjected to various thermal treatments in the solid state. Water uptake as well as water and NaCl permeability of these BPS-32 films were measured. Acidification via immersion of BPS-32 films in boiling sulfuric acid solution increased water uptake, and water and salt permeability increased. Exposure of samples to elevated temperature also influenced transport properties. For example, immersing BPS-32 films in boiling water for 4 h increased water sorption by 50%, water permeability by 2.3 times, and NaCl permeability by 8 times. The counter-ion form of the sulfonated polymer influenced the polymer’s transport properties, but these effects were weaker than the effect of thermal treatment. Generally, the BPS-32 samples prepared with different processing histories followed a trade-off between water/salt permeability selectivity and water permeability. These results suggest that, like many other glassy polymers, thermal processing history influences small molecule transport in these materials.