How the Influence of Different Salts on Interfacial Properties of Surfactant–Oil–Water Systems at Optimum Formulation Matches the Hofmeister Series Ranking

In this work, we present the effects of salts on sodium dodecyl benzene sulfonate micellization and on the interfacial performance of a sodium dodecyl benzene sulfonate–heptane–brine system at optimum formulation, i.e., hydrophilic–lipophilic deviation (HLD) = 0. In order to do that, interfacial tension and dilational interfacial rheology properties of surfactant–heptane–water systems at optimum formulation are measured using an interfacial spinning drop tensiometer with an oscillating velocity, which can accurately measure interfacial rheology properties at both low and ultralow interfacial tensions. The brines used contain one of the following salts: MgCl₂, CaCl₂, NaCl, NH₄Cl, NaNO₃, CH₃COONa, or Na₂SO₄. We performed a one-dimensional salinity scan with each of these salts to achieve an optimum formulation. In relation to the Hofmeister series, we found that, at optimum formulation, systems with chaotropic ions (NH₄⁺, NO₃⁻) present interfaces with ultralow interfacial tensions, very low dilational modulus, and a low phase angle, whereas kosmotropic ions (Mg²⁺, Ca²⁺, SO₄⁻²) generate high interfacial tension and high rigidity monolayers. Intermediate ions in the Hofmeister series (Na⁺, CH₃COO⁻, Cl⁻) present interfaces with intermediate properties. Furthermore, according to the Hofmeister series, interfaces can be respectively ordered from higher to lower rigidity for surfactant counterions Mg²⁺ > Ca²⁺ > Na⁺ > NH₄⁺ and coions SO₄²⁻ > CH₃COO^– > Cl⁻ > NO₃⁻, which correspond to a salting-out (highest rigidity) and salting-in (lowest rigidity) effect. We observed that counterions have a more significant effect on surfactant–oil–water system properties than those that act as coions.     

A multifunctional strontium/silver-co-substituted hydroxyapatite derived from biogenic source as antibacterial biomaterial

The bioactive properties of hydroxyapatite (HAp) facilitate bone regeneration, however, its physico-chemical and bioactive properties can be further enhanced by ionic substitutions within the crystalline lattice. In this work, substitution with Sr²⁺ and Ag⁺ ions was investigated for the improvement of osseointegration and antibacterial activity in potential treatment of traumatic bone injuries. A series of single substituted HAp with Sr²⁺ or Ag⁺ ions and Ag/Sr-co-substituted HAp with different degrees of substitution (0, 1, 2.5, and 5 mol%) were obtained by wet precipitation from cuttlefish bone. Rietveld refinement indicated successful Ca²⁺ substitution by increasing cell parameters due to the larger ionic radii of Sr²⁺ and Ag⁺ compared to Ca²⁺, which was confirmed by elemental mapping showing uniform distribution of substituent cations. Characterization of the zeta-potential of Ag/Sr-co-substituted HAp showed negatively charged populations, at potentials not lower than ?15 mV. Increasing the degree of substitution resulted in decreasing zeta-potential. The higher absorption capacity of bovine serum albumin was determined on Ag/Sr-co-substituted HAp powders as compared to non-substituted HAp. All Ag-substituted HAps have shown an antibacterial activity towards Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli, as determined by inhibition zone, viability analysis and scanning electron microscopy. In addition, non-cytotoxicity towards human cells was confirmed by in vitro tests with embryonic kidney 293 and mesenchymal stem cells.     

Effect of step-by-step depolarization on electret performance of OH defect-controlled ceramic hydroxyapatite

Ceramics electrets of hydroxyapatite (HAp) have been developed for both power generators and artificial bones. However, the formation mechanisms of the HAp electrets have not yet been completely understood. In particular, it is unclear how the OH⁻ ion-dipoles in HAp lattices contribute to electret performance. Herein, we show that HAp with controlled OH⁻ ion content exhibits excellent performance as an electret. We prepare OH⁻-defect-controlled HAp samples either by restricted dehydration during thermal process or by valence control through the substitution of Ca²⁺ with Nd³⁺. The experimental results prove that the electrets prepared by partially dehydrated HAp and Nd-substituted HAp with a small number of OH⁻ ions showed better performance. Our results suggest that the OH⁻ ion-dipole polarization contributes negatively to the electret performance.     

Simultaneous co-substitution of Sr2+/Fe3+ in hydroxyapatite nanoparticles for potential biomedical applications

In human, strontium (Sr) follows the same physiological pathway as calcium and thus could be used for improving the bioactivity and osteoconductivity of hydroxyapatite (HAp) in bone tissues. Similarly, iron (Fe) can potentially play an important role in bone remodeling due to its magnetic properties. Therefore, the current study was aimed to simultaneously co-substitute Sr²⁺/Fe³⁺ in HAp nanoparticles for various potential biomedical applications. The Sr²⁺/Fe³⁺ co-substituted HAp nanoparticles were systematically synthesized through sonication-assisted aqueous precipitation method. The as-synthesized nanoparticles were evaluated for different physicochemical and biological properties. X-ray diffraction (XRD) patterns of Sr²⁺/Fe³⁺ co-substituted HAp nanoparticles confirmed their phase purity and showed hexagonal-like structure. Scanning electron microscope (SEM) micrographs showed an agglomerated rod-like morphology of HAp nanoparticles which contained pores consisted of small spheroids. The nanoparticles displayed magnetization (Ms) reliance on the loading level of mole % (X?=?Fe³⁺) and exhibited tunable porosity and microhardness (Hv) upon heat treatment. The nanoparticles showed less than 5% hemolysis demonstrating high blood compatibility with high in vitro bioactivity performance. The multifunctional properties of synthesized nanoparticles make them a potential candidate for various biomedical applications; including bone grafting and guided bone regeneration, targeted drug delivery, magnetic resonance imaging, and hyperthermia based cancer treatment.     

Mixed Cationic Surfactant Vesicles in (Dioctadecyldimethylammonium Bromide)/NaCl and (Dioctadecyldimethylammonium Chloride)/NaBr Aqueous Dispersions

One of the most challenging characteristics not fully understood yet of the cationic surfactant salt dioctadecyldimethylammonium (DODA⁺) halide is concerned with the effects of the counterion (usually Br⁻ and Cl⁻) on the surfactant assembly into vesicle structures in aqueous solution. These counterions play a key role in the self-organization of DODA⁺ into bilayer structures. Differential scanning calorimetry (DSC) and dynamic light scattering (DLS) techniques were used here to investigate systematically the effects of the single salts NaCl and NaBr, respectively, on the thermal behavior and structural organization of the cationic dioctadecyldimethylammonium bromide and chloride (DODAB and DODAC) in water. The results undoubtedly indicate that the added Br⁻ or Cl⁻, respectively, into DODAC and DODAB aqueous dispersions, replaces partially the bound counterions (Cl⁻ and Br⁻) from the vesicles, yielding formation of DODAB/DODAC mixed vesicles. As a conclusion, single salts may be used to tune the thermal and structural characteristics of cationic vesicles.     

Isotopic ion-exchange studies in heteroionic systems

Isotopic ion-exchange studies were carried out for Mn²⁺ ions in the presence of Ba²⁺, Sr²⁺ Cs⁺ and Na⁺ ions, and for Na⁺ ions in the presence Ba²⁺ and Mn²⁺ ions, from 0.1 N chloride solutions. Single Particle Radioactive Tracer technique was employed, and the exchanger Dowex 5OW-X8 was used. The Nernst-Planck model, taking into account the diffusion processes both in the film and in the resin bead, was employed to analyse the data Resin-phase self-diffusion coefficients obtained from the isotopic exchanges in the homo-ionic systems, and liquid-phase diffusion coefficients calculated from limiting ionic conductance data, were used. The computer results agreed well with the experimental data for the following cases: (i), Na⁺ exchange in the presence of Ba²⁺ and Mn²⁺ ions; (ii), Mn²⁺ ion in the presence of Na+ ions; and (iii), Mn²⁺ exchange in the presence of Ba²⁺, Sr²⁺ and Cs⁺ ions at higher fractions of Mn²⁺ ions. However, lower values of diffusion coefficient of Mn²⁺ ions could correlate the data with smaller fractions of Mn²⁺ ions. It has been shown ibat resinphase diffusion mechanism of homovalent ions under similar environments is similar.     

Effect of singly,doubly and triply ionized ions on downconversion photoluminescence in Eu3+ doped Na2Sr2Al2PO4Cl9 phosphor: A comparative study

We report a change in the red photoluminescence of the Eu³⁺ doped Na₂Sr₂Al₂PO₄Cl₉ phosphor via doping of singly, doubly and triply ionized ions. The synthesized phosphors show good crystalline nature. The EDS analysis confirms the presence of desired elements in the phosphor samples. The vibrational feature of the phosphor was confirmed by FTIR analysis. The photoluminescence excitation spectra of the phosphor show three peaks at 317, 395 and 467 nm. The Eu³⁺ doped Na₂Sr₂Al₂PO₄Cl₉ phosphor emits intense red color on excitations with 395 and 467 nm wavelengths. However, the photoluminescence intensity of the phosphor is larger for 395 nm excitation. When the singly, doubly and triply ionized ions are co-doped in the Eu³⁺ doped Na₂Sr₂Al₂PO₄Cl₉ phosphor (i.e. F⁻, WO₄²⁻, MoO₄²⁻, VO₄³⁻, La³⁺, and Y³⁺) the photoluminescence intensity of the phosphor is decreased significantly. The decrease in photoluminescence intensity is due to change in local crystal structure created by these ions. Interestingly, the photoluminescence intensity of phosphor increases many times when the (Y³⁺) ion incorporated phosphor is excited with 317 nm wavelength. The CIE diagram shows color emitted in the red region of visible spectrum and the color purity is larger for triply ionized (Y³⁺) ion. Thus, the singly, doubly and triply ionized ions activated Na₂Sr₂Al₂PO₄Cl₉: Eu³⁺ phosphor may be used in displays devices, photonic devices, solid state lighting and white LEDs.     

Phase separation induced by hydration of the mixed Ca/Sr aluminates Ca3−xSrxAl2O6: A crystallographic study

The compounds formed by the hydration of single-phase samples of the mixed, solid solution, Ca/Sr aluminates, Ca_3−xSr_xAl₂O₆, 3≤x≤0 have been studied using high-resolution synchrotron powder diffraction. Hydration of these mixed metal aluminates generally resulted in the formation of at least two hydrogarnet phases, one Ca-rich and the other Sr-rich. The structures of these hydrogarnets have been refined from neutron or synchrotron powder X-ray diffraction (XRD) data. A simple solubility model to explain the phase separation is presented.     

Ion exchange in concentrated media. Correlations for variation of selectivity coefficients with medium

An attempt to relate the different values of the ion-exchange selectivity coefficient in different media is made by considering the two phases as ionic solutions where the activity coefficients of species can be evaluated by means of Mikulin's equation.The selectivity coefficients of the NH₄⁺/H⁺, Na⁺/H⁺, and Li⁺/H⁺ exchanges in a sulfonated cation exchanger and of the NO₃⁻/Cl⁻ exchange in a quaternary ammonium anion exchanger have been measured under different conditions characterized by the degree of crosslinking of the ion exchanger, the water activity of the solution, the concentration ratio of two counterions, and the concentration ratio of a third possible counterion.The water activity of the solution is an essential parameter to be controlled, particularly in dilute or moderately concentrated solutions. A representation of the experimental results on the ion-exchange selectivity coefficient is given in terms of two parameters allowing the selectivity coefficient to be predicted even in very concentrated ionic media.     

Rapid Separation of Tl+ and Pb2+ from Various Binary Cation Mixtures Using Dicyclohexano-18-crown-6 Incorporated into Emulsion Membranes

Abstract

Relative transport rates of metal cation nitrates (Na⁺, K⁺, Rb⁺, Cs⁺, Ag⁺, Tl⁺, Ca²⁺, Sr²⁺, Ba²⁺, and Pb²⁺) in a water-toluene-water emulsion membrane system were measured. The toluene component contained the surfactant Span 80 and the crown ether dicyclohexano-18-crown-6. The aqueous receiving phase contained Li₄P2O₇. When each metal cation was individually present in the aqueous source phase, metal extraction was complete within 10 min with the order of extraction being Tl⁺ > Cs⁺ > Ag⁺ > Rb⁺ > K⁺ ≥m Na⁺ and Pb⁺ > Ca²⁺ > Sr²⁺ > Ba²⁺ for uni-and bivalent cations, respectively. Significant extraction was found for all cations except Na⁺, K⁺, and Ba²⁺. Some metal ions were concentrated nearly 10-fold in a 10-min period. Relative transport rates were determined when binary cation mixtures of either Tl⁺ or Pb²⁺ were present at equal concentrations with each of the remaining metal ions in the source phase. Tl⁺, when present with either Na⁺, Cs⁺, or Rb⁺, was selectively extracted from the source phase. Complete and nearly exclusive extraction of Pb²⁺ was observed in the presence of all cations including Tl⁺. The enrichment ratios of Pb²⁺ in the binary mixtures were approximately 10 while those of the second cation were less than 0.5 except for Sr²⁺ which was 0.86. Corresponding separation factors for Pb²⁺ ranged from 1000 to > 6000.     

Adsorption Kinetics and Equilibria of Strontium onto Kaolinite

Adsorption of Sr²⁺ onto kaolinite has been studied by means of a radiotracer technique using the ⁹⁰Sr isotope. Bangham’s and McKay models have been applied to kinetic results in Sr²⁺ concentrations between trace ?0.1 mol.L^?1. The magnitudes of film and intra-particle diffusion coefficients are 10?10 and 10?14 m²·s^?1, respectively. Concentration dependence of diffusion coefficients indicated that Sr²⁺ ions are adsorbed on two different adsorption sites by an exothermic and spontaneous process. The Freundlich isotherm parameters and exchange equilibrium constants derived from selectivity coefficients indicate that Sr adsorption are depressed by competing cations in the order of Na⁺< Mg²⁺< Al³⁺.     

Tuning the luminescence properties of Mn4+-activated CaYAlO4 phosphor by co-doping cations for indoor plant cultivation

To fulfil the demands of high-power plant growth lamps, cation co-doping is an effective way to tune the photoluminescence properties of manganese (Ⅳ)-activated aluminate phosphors. Therefore, we managed to synthesize a series of cations co-doped CaYAlO₄:xMn⁴⁺, mSr²⁺, M⁺ (M⁺ = Li⁺, Na⁺, and K⁺) (CYAO:Mn, Sr, M) far-red-emitting phosphors. The excitation spectrum of these phosphors contained two excitation bands, and the opposite effects of these two bands on the luminescence intensity have been observed with the increase of Mn⁴⁺ concentration. By adding 0.1 mol Sr²⁺ ions to replace Ca²⁺ site, the emission intensity and thermal stability of CYAO:Mn phosphors can be enhanced. Furthermore, the luminescence properties of CSYAO:Mn can be further improved by co-doping monovalent alkali metal ions to serve as charge compensators, the increased number of Mn⁴⁺ luminescence centers. Moreover, 0.6 mol% Na⁺ can increase the initial emission intensity of the phosphors by 117% as the best ratio. The characteristic emission spectrum of the phosphors CYAO:Mn,Sr,M correspond to the phytochrome P_FR of plants. These experiments and characterization results have certified that these phosphors have a potential application in indoor plants cultivation.     

Broadband emission phosphor Sr3Al2O5Cl2:Bi3+: Luminescence modulation and application for a white-light-emitting diode

Bi³⁺ ions can regulate and control the fluorescence of a phosphor by transferring energy to the activating agent or occupying different luminescent centers, which is important for modifying phosphors and revealing fluorescence mechanisms. As a base material, Sr₃Al₂O₅Cl₂ has three types of Sr sites (Sr 1, Sr 2, and Sr 3) that may be occupied by Bi³⁺ ions (Sr²⁺ has a similar radius to Bi³⁺). Herein, we successfully synthesized a series of Sr₃Al₂O₅Cl₂:x%Bi³⁺ phosphors using the high-temperature solid-state method and determined a two-site-occupying emission mechanism. X-ray diffraction patterns indicated that the samples were synthesized well, and Rietveld refinement results provided their structural information. Photoluminescence spectra showed 490 nm (λ_ex = 345 nm) and 556 nm (λ_ex = 376 nm) emission peaks, which might arise from different luminescent centers. The concentration quenching study, peak separation analysis, fluorescence lifetime spectra, and diffuse reflection spectra indicated that the Bi³⁺ ions occupied two of the three Sr sites. Calculations of relative system energies and distortion index proved that the occupation only occurred in the Sr 1 and Sr 3 sites, and crystal splitting analysis determined that Sr 1 site generated 490 nm emission light and Sr 3 site generated 556 nm emission light. The charge compensator and flux were added to enhance the fluorescence intensity of the phosphor, and 5% K⁺ along with 1% BaF₂ is the optimal dosage. Finally, the SrAlSiN₃:Eu²⁺, BaMgAl₁₀O₁₇:Eu²⁺, and optimized Sr₃Al₂O₅Cl₂:5%Bi³⁺ phosphors were combined as a luminous layer and a warm-white light-emitting diode was realized; the color rendering indices were 84.3, 85.8, 86.4, and 86.2 under working currents of 20, 30, 40, and 50 mA, respectively.     

Donor doping of K0.5Na0.5NbO3 ceramics with strontium and its implications to grain size,phase composition and crystal structure

In this study, the particular effects of A-site donor doping, such as crystal-structure change, the secondary-phase formation and the grain-size decrease, in a lead-free piezoceramic material K_0.5Na_0.5NbO₃ (KNN) doped with Sr²⁺, were investigated. Extended X-ray absorption fine structure (EXAFS) analyses proved that Sr occupies the perovskite A-sublattice, and locally modifies the KNN monoclinic structure to cubic. Introducing Sr into the A-sublattice, as well as accounting for the charge-compensating A-site vacancies in the starting composition, causes increasing lattice disorder and microstrain, as determined from a Rietveld refinement of the synchrotron X-ray diffraction data. Above 2% Sr the system segregates the A-site vacancies in a secondary phase in order to release the chemical pressure, as revealed by Raman spectroscopy. All these effects result in an increasing number of low-angle grain boundaries that limit the grain growth and finally lead to a significant grain-size decrease.     

A new composite of crystalline silicotitanate for sequestration of 137Cs and 90Sr from low-level aqueous waste solution

ABSTRACT

A new composite of crystalline silicotitanate (CST) has been synthesized for the sequestration of Cs and Sr from low-level liquid waste generated in the nuclear industry. The product characterization using X-RAY DEFRACTION (XRD) and Fourier-transform infrared spectroscopy (FTIR) confirmed the presence of CST crystals in the composite. Sorption studies carried out under various test conditions showed that the composite has high affinity for both Cs and Sr. Results of structural characterization of Cs and Sr-loaded CST indicated that the overall structural integrity remained intact after substitution of Na⁺ by Cs⁺ or Sr²⁺. The exceedingly good Cs and Sr sorption performance displayed by the CST composite will find applications in the treatment of nuclear waste.     

Effects of Additives on the Activity and Enantioselectivity of Candida rugosa Lipase in a Biphasic Medium

The effects of Li⁺, Na⁺, K⁺, Mg²⁺ and Zn²⁺ ions on the activity and enantioselectivity of Candida rugosa lipase (CRL) were investigated in a biphasic medium composed of phosphate buffer solution (containing a metal ion within a 50–500 mM concentration range) and isooctane. The hydrolytic activities of CRL towards p‐nitrophenyl acetate were measured after incubation of the enzyme in the presence of metal ions for 24 h, and they were compared to that obtained after incubation in the absence of any metal ion. The CRL activity was stimulated by the chloride salts of Li⁺, K⁺ and Mg²⁺ for all concentrations considered and the highest enhancement was achieved by Li⁺ with a 1.24–1.75 fold increase observed. The effects of metal ions on the enantioselectivity of CRL were investigated by performing the hydrolysis of racemic Naproxen methyl ester in the same biphasic medium containing Li⁺, Na⁺, K⁺, Mg²⁺ and Zn²⁺ ions. The addition of metal ions increased the hydrolysis rate by ca. 1.31–1.45 fold relative to the control, whereas the enantiomeric excess of product increased slightly in the presence of the metal ions. The effect of Triton X‐100 on the activity and enantioselectivity of the CRL was also investigated by employing 0.05, 0.1, 0.2, 0.3, 0.4, and 0.5 mM concentrations of it in phosphate buffer solution of the biphasic medium. High concentrations of Triton X‐100 stimulated the enzyme activity up to 1.66 fold after 24 h incubation. Triton X‐100 increased the hydrolysis rate almost independently of the concentration.     

Chloride‐Ion‐Stabilized Strontium Mayenite: Expansion of Versatile Material Family

Sr‐mayenite (S₁₂A₇) incorporating Cl^? ions in its crystallographic cages up to the theoretical maximum occupancy, Sr₁₂Al₁₄O₃₂Cl₂, is reported in our study. The addition of a stoichiometric amount of SrCl₂ to the starting mixture is effective for the formation of Sr₁₂Al₁₄O₃₂Cl₂ with high phase purity. Almost 100% densification is achieved using spark plasma sintering (SPS). Evaporation of SrCl₂ from Sr₁₂Al₁₄O₃₂Cl₂, which becomes significant at sintering temperatures above ~1300°C, degrades the phase purity. However, SrCl₂ effusion is significantly suppressed in the samples fully densified by SPS, impeding the decomposition of Sr₁₂Al₁₄O₃₂Cl₂ up to temperature as high as ~1400°C. The crystal structure of Sr₁₂Al₁₄O₃₂Cl₂ was investigated by Rietveld analysis of the X‐ray diffraction pattern. It is found that the Cl^? ion is incorporated in the center of the inner cage with nearly theoretical maximum occupancy, which is responsible for the phase stability. Porous Sr₁₂Al₁₄O₃₂Cl₂ exhibits humidity‐sensitive surface protonic conductivity. Dense Sr₁₂Al₁₄O₃₂Cl₂ prepared under reducing conditions such as SPS exhibits electronic conductivity. Sr‐mayenite has various potential applications derived from its multifunctionalities.     

Zur Rolle von EDA-Komplexen bei kationischen Polymerisationen. VI[1]. Wechselwirkung von Halogenidionen mit organischen aπ-Elektronenacceptoren

The Role of Donor-Acceptor Complexes in Cationic Polymerisations. The Interaction of Halide Ions with Organic aπ-Acceptors The anions of salts of the type Kat⁺X⁻ (Kat⁺  Li⁺, Na⁺, Et₄N⁺; X⁻  Cl⁻, Br⁻, I⁻) form donor-acceptor complexes with organic a π-acceptors. The long-wave charge-transfer absorption show a bathochrome shift with higher periodic numbers of X⁻ and increasing electron affinity of the acceptors Acc. Strong acceptors form radical ions very rapidly with X  I and slowly with X  Br. Cl. The interactions in the system Kat⁺X⁻ → Acc are influenced by solvents in a very complex way. As acceptors they interact preferably with the halide ion X⁻ and, hence, reduce its donicity for the competing acceptor Acc. As donors they change the dissociation of the ion pair Kat⁺X⁻ by solvation of the cation Kat⁺ and influence in that indirect way also the donicity of X⁻ for the acceptor Acc.     

Uptake of cesium and strontium cations by potassium-depleted phlogopite

Phlogopite mica was equilibrated with 1.0 N sodium chloride (NaCl)–0.2 N sodium tetraphenylborate (NaTPB)–0.01 M disodium ethylenediaminetetraacetic acid (EDTA) solution at room temperature resulting in an almost complete removal (92%) of the mica's interlayer K. X-ray powder diffraction analysis provides additional evidence that hydrated Na⁺ ions had almost completely replaced the interlayer K⁺. Following equilibration, the c-axis spacing of the mica increased from 10.0 Å to approximately 12.2 Å. Cesium and Sr ion exchange isotherms indicate that K-depleted phlogopite is highly selective for both elements, the Cs⁺ exchange capacity is 1.26 meq/g or 65% of the theoretical cation exchange capacity and the Sr²⁺ exchange capacity is 1.94 meq/g or 100% of the theoretical exchange capacity of the mica. Kielland plots indicated that the mica was selective for Cs⁺ when the equivalent exchange capacity of Cs⁺ in the exchanger phase (X¯_Cs) was < 0.66 and selective for Sr²⁺ when X¯_Sr < 0.41. At equivalent fractions greater than these levels, layer collapse and/or steric effects limit the diffusion of these ions into the interlayers of the mica. Analysis of the Cs⁺ equilibrated mica utilizing XRD indicated that a collapse of the c-axis spacing had occurred. Based on the high selectivity of < 45-μm K-depleted phlogopite for Sr²⁺ and Cs⁺, this material may prove useful as an inorganic ion exchanger for these radioactive isotopes.