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Carbonate minerals are largely associated with many geological and biological environments as well as several industrial and technological processes. The crystalline characteristics of these mineral phases can be modified by background salts present in the solution due to the effect of different electrolytes on the dynamics of ion-water interactions and ionic strength during precipitation. In the current research, we studied the effect of the presence of several electrolytes (i.e., Cs, Li, and Sr), combined with chloride and carbonate as transporting anions, on the growth and mineral evolution processes of carbonate precipitation in solution. The electrolyte composition during the reaction (experimental times from 24 h up to 30 days) determined the formation of specific calcium carbonate polymorphs. The Li presence induced the formation of vaterite which was progressively transformed into calcite during the reaction time, while Cs stabilized the calcite formation. The Sr presence in the system caused the precipitation of strontianite with modifications in its cell parameters and the structural arrangement of the carbonate molecular group. During the mineral evolution considering chloride and carbonate experimental set-ups, several compositional and cell parameters/crystallinity variations of the carbonated phases were also observed. A better understanding of the relationship between the compositional properties of the aqueous solvent and the crystallization mechanisms can contribute to a deeper comprehension of the mineral precipitation and transformation in different multicomponent solutions that occur in natural environments and in controlled synthesis processes, Spanish Ministry of Economy and Competitiveness, grant number PCI2019-111931-2, European Regional Development Fund (ERDF)—Next Generation/EU program

Supported lipid bilayers (SLBs) are a useful tool for studying the interactions between lipids and other biomolecules that make up a cell membrane. SLBs are typically formed by the adsorption and rupture of vesicles from solution. Although it is known that many experimental factors can affect whether SLB formation is successful, there is no comprehensive understanding of the mechanism. In this work, we have used a quartz crystal microbalance (QCM) to investigate the role of the salt in the buffer on the formation of phosphatidylcholine SLBs on a silicon dioxide (SiO2) surface. We varied the concentration of sodium chloride in the buffer, from 5 to 150 mM, to find the minimum concentration of NaCl that was required for the successful formation of an SLB. We then repeated the experiments with other group I chloride salts (LiCl, KCl, and CsCl) and found that at higher salt concentrations (150 mM) SLB formation was successful for all of the salts used, and the degree of deformation of the adsorbed vesicles at the critical vesicle coverage was cation-dependent. The results showed that at an intermediate salt concentration (50 mM) the critical vesicle coverage was cation-dependent and at low salt concentrations (12.5 mM) the cation used determined whether SLB formation was successful. We found that the successful formation of SLBs could occur at lower electrolyte concentrations for KCl and CsCl than it did for NaCl. To understand these results, we calculated the magnitude of the vesicle-surface interaction energy using the Derjaguin-Landau-Verwey-Overbeek (DLVO) and extended-DLVO theory. We managed to explain the results obtained at higher salt concentrations by including cation-dependent surface potentials in the calculations and at lower salt concentrations by the addition of a cation-dependent hydration force. These results showed that the way that different cations in solution affect the 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC)-SiO2 surface interaction energy depends on the ionic strength of the solution.

The formation of various mixed-ligand complexes in the Ni(II)–L-histidine (His)–L-ornithine (Orn) system was studied by potentiometric titration, calorimetry, and spectrophotometry. The thermodynamic parameters (logK, ΔrG0, ΔrH, and ΔrS) of complex formation reactions at 298.15 K and ionic strength I = 0.5 (KNO3) were determined. A comparative analysis of the thermodynamic parameters served as the basis to suggest the most likely coordination mode of amino acid moieties in mixed-ligand complexes.

The evolution of xylan-rich hemicelluloses (XH) aggregation behaviors in the presence of alkaline lignins (AL) under a wide range of pH values and NaCl concentration were investigated via dynamic light scattering and turbidity measurements. XH isolated from wheat straw contain a xylose backbone with arabinose side chains and a small amount of phenol groups. XH tend to aggregate in solution due to their low ratio of arabinose to xylose and hydrophobic phenol groups. AL interact with XH through the phenol groups bonded to the hemicellulose main chain to form an AL-XH complex. As the pH value decreases, the particle size and turbidity of AL, XH and their bonded complex all increase. The size of the AL-XH complex agglomerate is greater than the size of a XH at the same pH value, which indicates that the self-assembly of lignin molecules initiate the aggregation of XH. The particle size and turbidity of XH and AL-XH complexes increase as the XH concentration increase. At low pH values, e.g., 6.0, the particle size of the AL-XH complex more obviously increases compared to the XH particles. The size and turbidity of the AL, XH, and AL-XH complex agglomerates increased as the NaCl concentration increased.

The impact of different parameters on the chemical degradation of the Nafion polymer electrolyte membrane was investigated in detail under different concentrations of Fenton solution. As a consequence of chemical degradation, the performance and durability of the perfluorosulfonic acid-based electrolyte membrane in fuel cells was studied. Quantitative estimation of fluoride emitted after chemical degradation of the electrolyte membrane is done by an ex-situ fluoride emission rate-test using a potentiometric with an ion-selective electrode. The concentration of fluoride ions is easily affected by several external factors, such as total ionic strength, pH, temperature, and stirring speed, which causes many errors while reporting the fluoride concentration. Furthermore, the micromorphology of recast Nafion membranes before and after FER rest was thoroughly examined by scanning electron microscope (SEM) and X-ray photoelectric spectroscopy. Here, we report the influence of several external parameters over total fluoride concentration during the estimation of fluoride concentration for the proper correlation of the rate of chemical degradation in polymer electrolytes. This systematic study is beneficial for removing errors while measuring fluoride concentration and removing the discrepancy present in FER results reported in the literature.

In this work, a novel blue-green fluorescence phosphorous oxide quantum dots (PO QDs) was synthesized by solvothermal method in N-methyl-2-pyrrolidone (NMP) solution without any protection treatment during synthesis. Upon excitation at 400 nm, PO QDs emitted blue-green fluorescence with quantum yield of 0.28. PO QDs exhibited the high inertness to air or moisture, the excellent water solubility, and stable emission intensity in a wide pH range and in high ionic strength solution. Interestingly, PO QDs could give the positive optical response to iron ions (Fe3+) and iodine ion (I−). The photoluminescence (PL) of PO QDs could be directly quenched by Fe3+. While I− quenched the PO QDs PL by means of Ag+-mediated PO QDs system via the internal filtration effects (IFE) induced by the formation of AgI. Moreover, the biocompatibility and low toxicity of PO QDs verified in bean sprout and Hela cells indicated the promising application of PO QDs in medicine related fields. Furthermore, PO QDs could also be utilized in luminescent composite film for various application scenarios

In article, we have been reported the study of a concentration effect of sodium chloride (NaCl) salt on benzoic acid solubility and its dissociation in water at 298 K temperature. At this temperature the benzoic acid solubility into water and their dissociation value for six samples in range of 0.00, 0.05, 0.10, 0.30, 0.40 and 0.50 M. Each of these different ionic strength or concentration of sodium chloride is analyzed by titrimetrically against of 0.05 M sodium hydroxide (NaOH) basic solution. The pH of each solution is measured well by using of calibrated pH-meter. Observation reveals that the value of pH of benzoic acid into water at applying temperature is may inversely related with concentration of NaCl. Graphically, the value of ionic strength (I) of that benzoic acid is plotted versus with dissociation constant (Kc) of acid into water at specific 298 K temperature. The value of benzoic acid dissociation constant for given each six concentration of NaCl is found to be -4.169, -4.045, -3.993, -3.885, -3.848 and -3.788, respectively.

The acid-base interaction in the aminoethanesulfonic acid (taurine, Tau) – potassium aminoethanesulfonate – water system was studied by pH-, redox- and conductometric methods in the temperature range 293–313 K. The ion-molecular composition of NH2CH2CH2SO3H –NH2CH2CH2SO3K – H2O system was calculated. It is shown aminoethanesulfonic acid in aqueous solutions to exist at the ratio CKOH/QTau < 0.5 mainly in the zwitterion form similar to systems with glycine, aminomethanesulfonic acid and its N‑alkylated derivatives. The content of the aminoethanesulfonate anion is directly proportional to the CKOH/QGly ratio. The studied system ionic strength and acid-base dissociation constant for the second stage of the aminoethanesulfonic acid concentration and temperature dependences were determined. The ionic strength values at the isoelectric point (mi.p.)are directly proportional to С0Tau and practically do not depend on the temperature within the error for the same series С0Tau and С0KOH .The pH limits of the buffer action are determined and the buffer capacity of these systems is estimated. It has been established that effective buffer zones of Tau aqueous solutions can to maintain acidity in the higher then physiological pH range at temperature range 293–313 K. The buffer capacity of NH2CH2CH2SO3H – NH2CH2CH2SO3K – H2O system exceeds the analogous values of YNHCH2SO3H – YNHCH2SO3K – H2O (Y = H, CH3, CH2CH2OH, C(CH3)3 and C2H5C6H5) systems. The obtained data on the buffer capacity of the aminoethanesulfonic acid – potassium aminoethanesulfonate – water system can be used in chemical analysis, microbiological and biochemical studies, and the acidity data of the solutions studied can simulate the chemisorption of acid gases (carbon and sulfur dioxides).

The oxidation of S(IV) is a critical step in the fate of sulfur dioxide emissions that determines the amount of sulfate aerosol in the atmosphere. Herein, we measured accelerated S(IV) oxidation rates in micron-sized aqueous aerosols compared to bulk solutions. We have investigated both buffered and unbuffered systems across a range of pH values in the presence of atmospherically relevant transition-metal ions and salts and consistently found the oxidation rate to be accelerated by ca. 1-2 orders of magnitude in the aerosol. This enhancement is greater than can be explained by the enrichment of species in the aerosol compared to the bulk and indicates that surface effects and potentially aerosol pH gradients play important roles in the S(IV) oxidation process in the aqueous aerosol. In addition, our experiments were performed with dissolved S(IV) ions (SO32-/HSO3-), allowing us to demonstrate that acceleration occurs in the condensed phase showing that enhanced sulfate formation is not exclusively due to gas-aerosol partitioning or interfacial SO2 oxidation. Our findings are an important step forward in understanding larger than expected sulfate concentrations observed in the atmosphere and show that inorganic oxidation processes can be accelerated in micron-sized aqueous droplets compared to the bulk solution.

The uptake of iodide and chloride during the synthesis of green rust (GR), the Fe endmember of the layered double hydroxide (LDH) group, was investigated. GR compounds were prepared by aerial oxidation of Fe(OH)2 in suspension, considering various I/Cl ratios at constant ionic strength. Only GR compounds formed in all experiments, and the associated I/Cl ratio increased with that of the starting suspension. No preferential uptake of any halide could be detected, and all compounds had comparable morphology. Furthermore, the height of the interlayer gallery increased with the I/Cl ratio from ∼7.7 A for the chloride endmember to ∼8.3 A for the iodide endmember, and the observed linear increase was attributed to increasing interlayer iodide content. In all compounds, Fe K-edge X-ray absorption spectroscopy evidenced the presence of sixfold coordinated iron with a Fe2+/Fe3+ ratio of 3, homogeneously distributed within flattened octahedral sites, with six Fe as next-nearest neighbors. The Fe short-range environment was not affected by the interlayer composition, and no halide from the interlayer could be detected. Furthermore, iodide and chloride anions are located in a water-like environment, being loosely bound by weak electrostatic interactions to the octahedral sheet likely above ferric iron. Results consistently hint at the formation of a solid solution between chloride and iodide GR endmembers, certainly facilitated by the crystallization of both compounds in the same space group. This study provides further insights into the ability of LDH to simultaneously accommodate several anionic species of various sizes. The formation of such LDH compounds in a deep geological repository for nuclear waste thus represents a possible retention barrier to the migration to the far field of anionic species like 36Cl- and 129I- mobilized from the waste matrix. The extent of retention in disposal sites will depend, among others, on the availability of GR and on the concentration of competing anions.

Complexes of the divalent metal ions, Ca2+ and Zn2+ with the bio-relevant α-amino acids, l-cysteine and glycine were investigated by means of the potentiometric technique. The dissociation constants of the bio-ligands were determined and used for determining the stability constants of their binary and ternary complexes formed in aqueous solutions at 25 ± 0.1 °C and constant ionic strength of 0.20 mol·dm−3 NaNO3. The acid–base properties of glycine were investigated at different ionic strengths, ranging from 0.01 to 0.30 mol·dm−3 NaNO3 at 25.0 ± 0.1 °C. The concentration distribution of the different glycine species formed in solution due to variation of pH was evaluated and discussed. The formation of the different 1:1 and 1:2 binary complexes and 1:1:1 ternary complexes were inferred from the potentiometric pH-metric titration curves. The ternary complex formation occurred in a stepwise manner with l-cysteine acting as the primary ligand. The stability constants of these binary and ternary complex systems were evaluated. The ∆log10 K values, percentage of relative stabilization (%R.S.) and log10 X for the ternary complexes were evaluated and are discussed.

The use of copper complexes to alleviate inflammation associated with rheumatoid arthritis (RA) is well known. This study focuses on designing a new drug that could be used to increase the bioavailability of copper and hence be more effective. The ligand chosen was sarcosyl-l-lysyl-l-lysine (Sar-Lys-Lys). The thermodynamic stability of H+, CuII, NiII, and ZnII complexes of Sar-Lys-Lys was measured in an aqueous solution at 298 ± 0.01°C and an ionic strength of 0.15 M (NaCl) using glass electrode potentiometry. UV-Vis, ESR, and 1H NMR spectroscopy was used to investigate the solution structures of the different species. At physiological pH, the ligand was found to coordinate via two amide nitrogens, the terminal amine, and the terminal carboxy group. The ε-amino group of lysine did not coordinate with the metal ion. Dermal absorption is the preferred method of administration and so this study used partition coefficients and tissue permeability studies to assess the bioavailability of the different complexes. Sar-Lys-Lys was found to increase the copper lipophilicity by a factor of 10 and increased tissue permeability by 30 %.

A multiphasic mass action equilibrium model is used to show that the critical pH in the acid-base disproportionation of a solid salt into its corresponding solid free-base form in aqueous suspensions, widely known as "pHmax", is incompletely interpreted. It is shown that the traditional thermodynamic model does not predict the invariance of pH and solubility during the salt-to-free-base conversion process in an alkalimetric titration. Rather, the conversion entails a range of pH and solubility values, depending on the amount of added excess salt above that needed to form a saturated solution. A more precise definition is proposed for pHmax (pH at the max imum solubility of a eutectic mixture), and three new terms are introduced: pHmin (pH at the min imum solubility of the eutectic mixture), pHδ ( d isproportionation invariant pH within the eutectic, i.e., the equilibrium pH of a spontaneously disproportionating salt slurry), and pHγ ( G ibbs pH at which disproportionation yields equimolar amounts of excess salt and excess free-base solids within the eutectic). Two test compounds with reported multiple salts and the free-base solubility values were selected to illustrate the expanded concepts, the bases WR-122455 and RPR-127963. Also, dibasic calcium phosphate was selected as an ionizable test excipient. The salts are designated in the study as μ-type, when they are thermodynamically stable with respect to spontaneous disproportionation in pure water (e.g., WR-122455 salts), and δ-type, when they are predicted to spontaneously disproportionate in pure water (e.g., RPR-127963 salts). In an alkalimetric titration, when an acidified suspension of a salt of a basic molecule is titrated with a strong base (e.g., NaOH), the passage across the eutectic domain (bounded by pHmax and pHmin) is often characterized by (a) minimum in ionic strength either at pHmax (μ-type salt) or pHδ (δ-type salt) and (b) maximum buffer capacity at pHγ. When the alkalimetric titration is performed with a large excess of added salt, a wide eutectic domain forms: pHmax and pHδ remain invariant, but pHmin and pHγ shift substantially in pH. The acid-base mass action model described here can be useful in predicting the stability of salt formulations in mixtures with excipients that can act as pH modifiers.

The complex formation of H[AuCl4] with 2-methylimidazole was studied by the potentiometric method at 288–318 K. It was found that even with excess 2-methylimidazole in the solution, three chloride ions of H[AuCl4] are replaced. The general stability constants of the resulting complexes were calculated over a broad temperature range (at 298 K: log β1 = 8.04 ± 0.04; log β2 = 13.53 ± 0.03; log β3 = 19.23 ± 0.09). With increasing temperature and ionic strength of the solution, the general stability constants increase. The thermodynamic constants of formation of the complexes were calculated. The difference between the concentration and thermodynamic constants depends on the value Δνz2 (Δνz2 = $$\Delta \nu z_{{{\text{prod}}}}^{2}-\Delta \nu z_{{{\text{react}}}}^{2}$$ ). The formation of all complex species was accompanied by energy absorption. The ΔS value was positive for all complex formation steps. For the equilibrium [AuCl4]– + L ↔ [AuLCli]3 – i + (4 – i)Cl–, the numbers of moles of reactants and products remain invariable. The increase in entropy upon complexation is, most likely, due to appearance of water in the solution “unfrozen” from the hydration shells of ions as a result of the reactions. The ΔG value was negative for all complex formation steps. The spontaneous occurrence of the complex formation reaction is determined by the entropy component.

The mobility of heavy metal contaminants and radionuclides in the environment is directly controlled by their interactions with charged mineral surfaces, hence an assessment of their potential toxicity, e.g. in the context of nuclear waste disposal sites, requires understanding of sorption processes on the molecular level. Here, we investigate the sorption of a variety of rare earth elements (REE) and trivalent actinides (Am, Cm) on K-feldspar using batch sorption and column transport experiments, time-resolved laser-induced fluorescence spectroscopy (TRLFS), and a surface complexation model. Initially, a reliable pKa for K-feldspar’s surface deprotonation reaction was determined as 2.5 ± 0.02, in excellent agreement with a measured pHIEP of 2.8. Batch sorption experiments over a broad range of experimental conditions in terms of mineral grain size, pH, [M3+], ionic radius, solid/liquid ratio, ionic strength, and equilibration procedures were carried out to quantify macroscopic immobilization. Similar pH-dependent uptake behavior was found for all investigated trivalent REE and actinides. In parallel, spectroscopic investigations provided insight into surface speciation. Cm TRLFS spectra indicate the formation of three inner-sphere sorption complexes with increasing hydrolysis. Additionally, a ternary K-feldspar/Cm/silicate complex was found for pH > 10, and batch and spectroscopic data at low pH (< 4) point to small amounts of outer sphere sorption complexes. Based on TRLFS data, batch sorption, and titration data, a generic geochemical sorption model was developed, that describes sorption edges for all investigated M3+/K-feldspar systems satisfactorily. The derived stability constants for the binary sorption complexes (logK1-4 = −3.6, −7.7, −11.5, and −17.4, respectively) are in good agreement with previous studies on similar systems, and could successfully be used to reproduce literature data. The stability constants obtained for the surface complexes were included into the database for the Smart Kd-concept, which will further improve the safety assessment of potential repositories for radioactive waste.

Kinetic studies of the novel oxidation of acetaminophen by sodium periodate are discussed with an emphasis on structure and reactivity by using kinetic approach. The reactions were catalyzed by Os(VIII). The kinetics of the reaction was studied as a function of temperature, ionic strength, dielectric constant of the medium, concentrations of the salt and the added reaction product to learn the mechanism of the reaction. The active species of catalyst and oxidant have been identified. Activation parameters have also been evaluated using the Arrhenius and Eyring plots. A suitable mechanism consistent with the observed kinetic results has been suggested and the related rate law deduced.

Graphitic carbon nitride (CN) has been widely used in environmental pollution remediation. However, the adsorption of organic compounds on CNs, which has practical significance for the environmental application of CNs, is poorly understood. For the first time, this study systematically investigated the adsorption behaviors and mechanisms of humic substances (HSs), i.e., humic acid (HA) and fulvic acid (FA), on CNs derived from four typical precursors. Intriguingly, CN derived from urea (CN-U) showed a great capacity for HS adsorption due to its porous structure and large surface area, with maximum adsorption amounts of 73.24 and 51.62 mgC/g for HA and FA, respectively. The formation, influencing factors, and relative contributions of multiple interactions to HS adsorption on CNs were thoroughly elucidated. HS adsorption on CNs was mainly mediated by electrostatic interactions, π-π interactions, and H-bonding. The dominance of electrostatic interactions resulted in HS adsorption being highly dependent on pH and ionic strength. HS components with high aromaticity and high molecular weight were preferentially adsorbed due to π-π interactions. These multiple interactions were largely affected by amino groups and tri-s-triazine units of CNs, as well as the moieties of aromatic rings and oxygen-containing groups of HSs.

Mixing of oppositely charged macromolecules can, under certain conditions, lead to the formation of electrostatically cross-linked coacervate gels. In this simulation study, we determine the condit...

Acidic biotrickling filters (BTF) can be used for simultaneous removal of hydrogen sulfide (H2S) and siloxane from biogas. In this study, the performance of a BTF under different acidic pH conditions was investigated. The removal profile of H2S showed that 90% of H2S removal was achieved during the first 0.4 m of BTF height with down-flow biogas. Decamethylcyclopentasiloxane (D5) removal decreased from 34.5% to 15.6% when the pH increased from 0.88 to 3.98. Furthermore, the high partition coefficient of D5 obtained in under higher pH condition was attributed to the higher total ionic strength resulting from the addition of sodium hydroxide solution and mineral medium. The linear increase in D5 removal with the mass transfer coefficient (kL) indicated that the acidic recycling liquid accelerated the mass transfer of D5 in the BTF. Therefore, the lower partition coefficient and higher kL under acidic pH conditions lead to the efficient removal of D5. However, the highly acidic pH 0.9 blocked mass transfer of H2S and O2 gases to the recycling liquid. Low sulfur oxidation activity and low Acidithiobacillus sp. content also deteriorated the biodegradation of H2S. Operating the BTF at pH 1.2 was optimal for simultaneously removing H2S and siloxane. HIGHLIGHTS Effect of pH on the performance of acidic BTF for simultaneous removal of H2S and siloxane was investigated.; A linear positive correlation was observed between the mass transfer coefficient and the removal efficiency of D5.; Evolution in microbial community under various acidic pH conditions was investigated.; Operating the BTF at pH 1.2 was optimal for simultaneous efficient removal of H2S and siloxane from biogas.

Kinetics of phosphate adsorption by Ca/Cr layered double hydroxide (LDH) in a batch reactor was investigated in this study. The kinetic experiments indicated that the sorption of phosphate from the synthetic feed solution by the synthesised LDH was very fast, with over 98% removal being achieved within 5 min of contact. Kinetic modeling of the sorption process to different kinetic models (pseudo first order, pseudo second order, Elovich and intraparticle diffusion) showed that the pseudo-second order model best described the process. Studies of effect of hydrochemistry on the sorption process such as initial solution pH, ionic strength and organic load contamination interference, indicated nominal effect on the amount of phosphate removed by the LDH. Overall, the study indicated that chemisorption and precipitation are active contributory mechanisms to the sorption of phosphate by Ca/Cr LDH from solution. Key words: Adsorption kinetics, chemisorption, layered double hydroxide, phosphate removal, precipitation.

Removal of hexavalent chromium [Cr(VI)] from water was evaluated using a low-cost coated sand adsorbent for potential application in a flow-through filter system using permeable adsorption media. Manganese-aluminum coated sand (MACS) was investigated as a hybrid metal oxide based adsorbent due to the potential efficacy of manganese oxide and aluminum oxide for adsorption of Cr(VI) from water. Adsorbent characterization was performed using XRD, SEM/EDX, XPS and BET. Adsorption experiments were performed to determine adsorption capacity and kinetics. The effect of pH, common co-existing ions found in natural water, and the recyclability of adsorbent were investigated. Adsorbent characterization showed that the MACS sorbent contained aluminum oxide, manganese (III) oxide and manganese (IV) oxide. Adsorption followed the Langmuir and Freundlich adsorption equations, indicating favorable adsorption of Cr(VI) onto the MACS sorbent, while results from the Dubinin-Radushkevich equation were suggestive of physical adsorption of Cr(VI). Cr(VI) adsorption onto the MACS sorbent followed pseudo-second order kinetics. The adsorbent was effective in removing Cr(VI) over a broad pH range from 3 to 9.5, while surface charge analysis confirmed the adsorption of Cr(VI) onto the acidic surface of the MACS sorbent with a pH

A metal–organic framework, UiO-66-NH2, was designed, synthesized and characterized in this study. By conducting solvothermal method, Salicylaldehyde (Sal) and 2,4-dihydroxybenzaldehyde (MHBA) were grafted onto UiO-66-NH2 via post-treatment to obtain the functionalized material UiO-66-Sal and UiO-66-MHBA. The three materials above were characterized, and the effects of solid–liquid ratio, pH, ionic strength, and oscillation time on U(VI) adsorption were studied. The relevant experimental results fitted well with pseudo-second-order kinetic equation and thermodynamic adsorption model.

In this article, the extraction behavior of halogen-free ionic liquid, 1-butyl-3-methylimidazolium octyl sulfate, was investigated in the separation of lead from the aqueous solution. Experimental parameters include time, impact of pH, feed concentration, amount of ionic liquid, ionic strength, and temperature were optimized for the evaluation of the lead extraction. From the optimum conditions, it was emanated that the maximum extraction efficiency of lead was 97% with the feed concentration of 10 ppm in an equilibrium time of 60 min at the pH of 5 and 2 g of the ionic liquid, respectively. Furthermore, the extraction results revealed that the higher efficiency was achieved without the addition of salt and that the extraction process was spontaneous and endothermic in nature. The metal complexation was formed by the exchange of ionic liquid anion to the aqueous phase, and thereby, the extraction mechanism was proposed. The ionic liquid in the organic phase was stripped using sodium sulfate as a stripping agent. FTIR analysis confirmed the recoverable ionic liquid and effectively reused it five times in the course of extraction. From the analysis, it was authenticated that the ionic liquid, 1-butyl-3-methylimidazolium octyl sulfate, was an effective extractant for the elimination of lead (II) and could be employed for the tertiary treatment of industrial wastes.

A three-dimensional (3D) activated framework carbon (3D AFC) was prepared in our research group and applied to adsorb U(VI) from radioactive waste water. Meanwhile, The effects of solid–liquid ratio, contact time, pH value, ionic strength and ionic concentration of adsorbate on the adsorption of U(VI) by the 3D AFC were studied. The calculated maximum adsorption capacity of 3D AFC was 127.5 mg/g under the condition that pH was 5.8. Combined with the properties of excellent three-dimensional network structure, simple synthesis methodology, and the adsorption capacity for U(VI), 3D AFC is considered to be feasible for recycling U(VI) from waste water solutions.

Uranyl ion, UO2 2+, and its aqueous complexes with organic and inorganic ligands can be the dominant species for uranium transport on the Earth surface or in a nuclear waste disposal system if an oxidizing condition is present. As an important biodegradation product, oxalate, C2O4 2−, is ubiquitous in natural environments and is known for its ability to complex with the uranyl ion. Oxalate can also form solid phases with uranyl ion in certain environments thus limiting uranium migration. Therefore, the determination of stability constants for aqueous and solid uranyl oxalate complexes is important not only to the understanding of uranium mobility in natural environments, but also to the performance assessment of nuclear waste disposal. Here we developed a thermodynamic model for the UO2 2+–Na+–H+–Cl––ClO4 ––C2O4 2––NO3 ––H2O system to ionic strength up to ∼11 mol•kg−1. We constrained the stability constants for UO2C2O4(aq) and UO2(C2O4)2 2− at infinite dilution based on our evaluation of the literature data over a wide range of ionic strengths up to ∼11 mol•kg−1. We also obtained the solubility constants at infinite dilution for solid uranyl oxalates, UO2C2O4•3H2O, based on the solubility data over a wide range of ionic strengths. The developed model will enable for the accurate stability assessment of oxalate complexes affecting uranium mobility under a wide range of conditions including those in deep geological repositories.

A TiO2 aerogel with a high removal percentage and adsorption capacity was manufactured via template synthesis. Subsequently, the as-prepared TiO2 aerogel was characterized by various techniques and applied as an adsorbent for the removal of U(vi). The results revealed that the U(vi) adsorption was very rapid and reached apparent equilibrium within 100 min. The maximum removal percentage was 97.1%, which was calculated using the pseudo-second-order kinetic model (T = 298 K, t = 180 min, pH = 5, m/V = 0.1 g L-1 and C0 = 10 mg g-1). The Langmuir isotherm model was used to determine the maximum adsorption capacity and it achieved 638.0 mg g-1 (T = 298 K, pH = 5 and m/V = 0.1 g L-1). In addition, the removal of U(vi) on the TiO2 aerogel was relatively good in acidic solution and the removal behavior was independent of the influence of ionic strength. The removal percentage of the as-prepared TiO2 aerogel was higher than 90% after five cycles. Due to these excellent properties such as easy recovery, fast adsorption kinetics, high adsorption capacity and high removal percentage, the TiO2 aerogel might become an extremely employable adsorbent for the extraction of U(vi) in seawater.

The Villermaux–Dushman test reaction for micromixing characterization has been used by many researchers to investigate homogeneous mixing systems. Due to the complexity of the iodine-forming reaction, the strong effect of ionic strength of reaction medium on its reaction rate constant, as well as the dependence of the sulfuric acid dissociation on its concentration, the kinetic model of the iodide/iodate test reaction with sulfuric acid is complicated. Therefore, a quantitative evaluation of such a test reaction is challenging and remains an open problem. In this paper, the pH of the sulfuric acid solutions with different values of ionic strength is investigated using the model of Pitzer. The numerical results of the simulation are compared with the experimental data and good agreement is obtained. It is also shown that simple equilibrium calculations for sulfuric acid do not give correct pH results when the ionic strength of its solution is increased by the addition of sulfate salts. However, such an assumption yields satisfactory results for the cases without additional salt and with an acid concentration lower than 0.2 M. Finally, the engulfment model of micromixing using activities to calculate proton concentrations is applied to analyze the experimental results from previous papers employing the iodide/iodate method.

The europium sorption on Tamusu clay was investigated by batch sorption experiments and spectroscopic study under the condition of strong ionic strength. The results demonstrated that europium sorption on Tamusu clay increased rapidly with pH value, but decreased with the ionic strength of solution increased. The europium sorption also increased in the presence of humic acid, especially at low pH value. The sorption could be fitted by Freundlich isotherm model and the europium sorption on clay was spontaneous and endothermic reaction. Besides, the result indicates that ion exchange was the main process at low pH value, while inner-sphere surface complexation dominated the sorption process at high pH value. The Backscatter electron scanning/Energy Dispersive Spectrometer(BSE/EDS) and the effect of Na for europium sorption results further suggested that europium sorption on Tamusu clay mainly competed with Na at low pH value. Overall, the results in this research were of significance to understand the sorption behavior of europium on the geological media under high ionic strength.

An adsorption method for immobilizing the components of various natures on the surface of ultrafiltration membranes based on aromatic copolyamide containing 5 and 10 mol % units with sulfonate groups [PA-5(–) and PA-10(–)] was invetigated. The components of immobilization were copper(II) ions, histidine, lysine, and 3,6-diamino-10-methylacridine chloride. It was shown that immobilization mainly occurs due to the electrostatic interaction of the corresponding functional groups of the component and copolyamide. The maximum experimental adsorption capacity of the PA-5(–) and PA-10(–) samples for copper(II) cations, histidine, lysine, and 3,6-diamino-10-methylacridine chloride was 0.42 and 0.87, 1.12 and 1.79, 0.74 and 1.30, 0.63 and 1.07 μmol cm–2, respectively. The stability of the immobilization of the components was studied in static and dynamic regimes. It was found that the stability of the fixation of the active component on the surface of the support is largely determined by the nature of the ligand. It was shown that for the systems under consideration and the selected type of immobilization of components, its stability also depends on pH, ionic strength, and polarity of the medium. In a neutral medium with a salt concentration not exceeding 10–3 mol dm–3, all the immobilized component/membrane systems studied demonstrate good stability. Under the most unfavorable conditions (in the studied ranges of change in the parameters of the filtration medium), the residual adsorption capacity of the PA-10(–) membrane for copper(II) ions, histidine, lysine, and 3,6-diamino-10-methylacridine chloride is 0.86, 1.25, 0.70, and 1.04 μmol cm–2, respectively.

Herein, the interaction of a protein, bovine serum albumin (BSA), with tetradecyltrimethylammonium bromide (TTAB, a cationic surfactant), has been investigated using the conductivity measurement technique in pure water and some sodium salts (NaCl, Na2SO4, Na2CO3, and Na3PO4) solutions at temperature range of 295.15–320.15 K. Results reveal that, in the plot of specific conductivity versus the concentration of TTAB, only a single critical micelle concentration (cmc) was found for the TTAB + BSA mixed system in all solvents media studied. The addition of BSA in aqueous TTAB solution, the value of cmc undergoes a change from its pure form, which indicates the presence of strong interaction operating between the BSA and TTAB molecules. In aqueous system, the cmc values of the TTAB + BSA mixtures are obtained higher compared to the values found for single TTAB surfactant. However, the addition of salt decreases the cmc value of mixed TTAB + BSA system. The values of cmc of the BSA + TTAB mixed system at 310.15 K and 1.00 mmol·kg−1 ionic strength of salt followed the order: cmcNa2CO3 > cmcNa3PO4 > cmcNaCl > cmcNa2SO4. The cmc values of TTAB + BSA mixture were found to be lowered in urea solution within the concentrations studied. The values of degree of dissociation (α) and fraction of counter ion binding (β) were found to be dependent on additives and temperature. The free energy of micellization (∆ Gmo) is negative for all the systems, which manifests that the micellization phenomenon is energetically spontaneous. The enhancement of the negative value of ∆ Gmo in aqueous salt solutions reveals an increase of spontaneity of the TTAB + BSA micellization process. The values of ∆ Gmo also reveal that the spontaneity of micelle formation is enhanced at higher temperatures in all media studied. The values of free energy of transfer (∆ Gm, to) were also determined for numerous solvent media used in the present study and described with appropriate reasoning.

A novel magnetic activated carbon composite (AC/NiF) was synthesized by a precipitation method and applied in retention of Cu(II), and Zn(II) ions from aqueous solutions. The impact of different sorption parameters such as: equilibration time, solution pH value, competing cations and ionic strength on the amount sorbed of Cu(II), and Zn(II) was clarified. Results illustrated that the magnetic composite had retention ability towards both metal ions significantly higher than that of activated carbon (AC). The magnetic composite exhibited an affinity to adsorb Cu(II) higher than Zn(II) ions. The maximum sorption capacities (Qmax) of the applied magnetic composite (AC/NiF) towards Cu(II) and Zn(II) were 105.8 and 75.1 mg·g−1, respectively. Retention of Cu(II) and Zn(II) was proposed to be achieved though an ion exchange and surface adsorption in neutral conditions, while precipitation was believed to be the relevant mechanism in their removal from basic solutions. The kinetic studies showed that sorption process followed the kinetics of pseudo-second-order reactions with rate constant of 3 × 10−3 and 2 × 10−3 min−1 for sorption of Cu(II) and Zn(II) onto AC/NiF composite. Removal of Cu(II) slightly decreased with increasing the ionic strength of aqueous solution, using NaCl as a background electrolyte. In contrast, presence of Mn(II), Mg(II) and Co(II) in reaction solutions highly depressed the sorption of Cu(II) and Zn(II) with a competing efficiency followed the order: Mg(II) > Mn(II) > Co(II).The magnetic composite was rapidly recovered from aqueous solution by an external magnetic field, and effectively regenerated using 0.1 mol·L−1 HCl and 0.1 mol·L−1 FeCl3as eluents. Sorption of Cu(II) and Zn(II) onto the surface of AC/NiF composite occurred via a spontaneous reaction. And thermodynamically favorable process had ΔHo values of 30.9 kJ·mol−1 and 19.7 kJ·mol−1, respectively. The results confirm that the magnetic composite can be viewed as a promising novel composite opens new opportunities for the attainment of required adsorption and operative magnetic separation.

The fundamental understanding about dielectric properties is not completely understood even though it is crucial in microwave-assisted heating. The present work was aimed at evaluating the dielectric properties of reagent mixtures and solids of potassium hydroxide-treated castor residue carbons at varying frequencies and temperatures. Chemical treatment at solid mass ratios (KOH pellet:castor residue) of 0.0 to 2.0 in 50 mL water was carried out using a microwave oven at 70% intensity. The dielectric properties were determined using an open-ended co-axial probe. Results show that the dielectric properties of materials changed with frequency, temperature, water content and ionic strength. Also, the presence of potassium hydroxide solution aids in improving the propensity of castor residue to be heated via microwave. The potassium hydroxide-treated carbons exhibit a 90% removal efficiency of methylene blue at Co = 189 mg/L.

A new method is proposed for the quantitative determination of critical pH values during the formation of complexes between nonionic polymers and polyacids in aqueous solutions. As an indicator reflecting the pH value, where there is a transition from a solution containing noninteracting macromolecules to a solution in which the formation of an interpolymer complex occurs, the pH value should be taken with a yield of the complex formation reaction 1/2 of the maximum. The expediency of using just such an indicator is due to the fact that there is a fairly extended pH boundary region with the coexistence of noninteracting macromolecules and the reaction product between them. It is shown that the indicator determined in this way can be conveniently to calculated using the phase portrait method. This technique was tested by analyzing families of experimentally obtained curves describing the effect of potassium chloride additives on the complexation process between a copolymer of 2-hydroxyethyl acrylate and butyl acrylate and poly(acrylic acid) in an aqueous solution. It was found that for this system, the nature of the dependence of the effect of ionic strength on the formation of the polycomplex significantly depends on the composition of the copolymer, while the increase of only 4.9 mol % in the content of hydrophobic butyl acrylate units in the copolymer is accompanied by the transition of this system from a weak complex to strong complex.

By taking advantage of the powerful oxidation property of hypochlorite (OCl−), we developed a solid-phase colorimetric sensor for the detection of OCl− based on 13 nm AuNPs immobilized on a 3-aminopropyltriethoxysilane APTES-coated substrate. This colorimetric sensor utilizes the aggregation and anti-aggregation properties of AuNPs arising from the interaction between dithiothreitol (DTT) and OCl−. When the amount of OCl− increases, the color of the substrate changes from blue to red, allowing for naked-eye detection at concentrations as low as 2.48 μM within the reaction time of 5 minutes. Unlike conventional solution-based colorimetric sensors that can be easily affected by ionic strength, pH values, and temperature, this solid-phase sensor shows a more stable detection performance. Additionally, this solid-phase sensor can be further miniaturized, providing high availability and durability for use in daily life.

The adsorption of aspartic and glutamic acids from aqueous solutions on a nanocrystalline titania surface is described as the formation of complexes of two types: outer-sphere electrostatic and inner-sphere covalent complexes. The constants of the stability of adsorption by the two types of complexes are calculated using experimental dependences of adsorption on the pH and ionic strength of solutions, in terms of basic Stern model of surface complexation.

The formation constants and specific ion interaction coefficients of MgUO2(CO3)32− complex were determined in 0.1 to 1.0 mol kgw−1 NaCl and 0.10 to 2.21 mol kgw−1 NaClO4 media in the framework of the specific ion interaction theory (SIT), by time-resolved laser-induced luminescence spectroscopy. The upper limits of ionic strength were chosen in order to limit luminescence quenching effects generated by high concentrations of Cl− and ClO4− already observed during our earlier studies on CanUO2(CO3)3(4−2n)− complexes (Shang & Reiller, Dalton Trans., 49, 466; Shang et al., Dalton Trans., 49, 15443). The cumulative formation constant determined is , and the specific ion interaction coefficients are e(MgUO2(CO3)32−, Na+) = 0.19 ± 0.11 kgw mol−1 in NaClO4 and e(MgUO2(CO3)32−, Na+) = 0.09 ± 0.16 kgw mol−1 in NaCl. Two gratings of 300 and 1800 lines per mm were used to acquire MgUO2(CO3)32− luminescence spectra, where the high-resolution 1800 lines per mm grating detected slight spectral shifts for the principal luminescent bands relative to CanUO2(CO3)3(4−2n)−. The applications of the consistent set of thermodynamic constants and e values for MnUO2(CO3)3(4−2n)− (M = Mg and Ca) were examined in different geochemical contexts, where Mg over Ca concentration ratio varies to help defining the relative importance of these species.

The mechanism of adsorption of anionic dyes on montmorillonite modified with sodium metasilicate is investigated. The kinetics of dye adsorption is approximated by a pseudo–second order model, and the adsorption isotherm is analyzed on the basis of the Langmuir and Dubinin–Radushkevich models. The value of average free energy of adsorption E > 8 kJ/mol for all studied dyes, testifying to a surface chemical reaction between dye molecules and protonated silanol and aluminol groups on the surface of the edges of the aluminosilicate layers of the mineral. The adsorption of dyes is directly proportional to the increase in the temperature, mass, and charge of the organic anion and is inversely proportional to the increase in the ionic strength of the solution.

The solubility of solid calcium oxalate monohydrate (CaC2O4·H2O, COM) has been measured in aqueous solutions of four 1:1 electrolytes (NaCl, KCl, CsCl, and Me4NCl) at temperatures T = 298.15, 323.15, and 343.15 K. Solubilities at industrially relevant electrolyte concentrations of up to 5.0 mol·kg–1 were determined by atomic absorption spectrophotometry of the dissolved calcium ions. The solubility of COM in 1.0 mol·kg–1 electrolyte solutions was 2–4 times higher than in pure water but varied little at higher ionic strengths for all of the systems studied. Most of the observed solubilities were well correlated at all temperatures and electrolyte concentrations using a simple Specific Ion-interaction Theory (SIT) model with only one adjustable, temperature-independent, interaction parameter. For Me4NCl solutions, an additional empirical ionic strength dependence of the SIT parameter significantly improved the fit.

Contamination of water and soil with toxic metals is a serious environmental issue. To study the Pb, Cu, Cd, and Zn sorption behavior by diatomite, batch experiments were carried out with increasing levels of initial concentration (0-200 mg/L) under different contact times (0-360 min) and temperatures (283, 293, 303, and 313 K). The effects of concentration (0-200 mg/L), pH (3-6), and ionic strength (0.01-0.06 mol/L) on the sorption were modeled using response surface methodology (RSM). Results showed that adsorption data were well-fitted by the Langmuir equation. The sorption of metals intensified by increasing initial concentration and pH but ionic strength had inverse effect. High value for R2 (0.99) and adjusted R2 (0.99) showed that the removal of ions can be described by response surface method. One-way ANOVA showed (p-value

The structure-activity relationship (SAR) for toluene absorption and desorption in ionic liquids (ILs) has been investigated for seven commercial ILs in bulk and thin liquid layer. ILs with imidazolium cations of different alkyl chain lengths and a Hofmeister series of anions including [CH3COO], [I], [BF4], [HSO4], and [PF6] were included. Absorption capacity for toluene increases with increasing kosmotropicity of the cation and anion, while the absorption rate in bulk ILs is governed by viscosity and that in thin ILs layer by the oil-water partition coefficient (Kow). A regenerability coefficient (Rp) measures toluene desorption and IL regeneration. The release rate as measured by dRp/dt correlates well with the Kow and viscosity of the ILs and tx, the time required to completely desorb toluene is related to its ionic strength as measured from v(C2H) of the imidazolium cation. These properties are in turn governed by the kosmotropicity of the cation and anion pair forming the IL.

This research describes the formation of samarium complexation with organic ligands (Schiff bases of anti-mycobacterial agent isonicotinic acid hydrazide) through pH-metric technique at 25, 35, and 45°C in 70% (v/v) ethanol/water medium at 1M (NaClO4) ionic strength. Organic ligands have been synthesized and their structures have been confirmed by various characterization techniques such as TLC, MP, IR, 1H NMR, 13C NMR, UV-Vis spectroscopies and elemental analysis. They have been evaluated for biological activity against gram positive, gram negative bacteria, and fungi showing moderate to significant results. Complexation study of these binary complexes has been evaluated and calculated using Calvin–Bjerrum technique. The order of stability constant has been found to be as follows N-[(E)-(4-hydroxy-3-methoxyphenyl)methylene]isonicotinohydrazide (L2) < N-[(E)-(4-chlorophenyl)methylene]isonicotinohydrazide (L1) < N-[(E)-(4-hydroxyphenyl)methylen]isonicotinohydrazid (L4) < N-[(E)-(2-hydroxyphenyl)methylen]isonicotinohydrazid (L5) < N-[(E)-(2-nitrophenyl)methylen]isonicotinohydrazide (L3). Thermodynamic parameters associated with the samarium complexation have been observed to be negative in ΔH and ΔG. This indicates the exothermic reaction in complexation.

A potentiometric titration technique has been used to determine protonation constants of neocuproine {(neo): 2,9-dimethyl-1,10-phenanthroline} and bioactive ligands {(N,O-donor chelator, N,O): glycine (gly), leucine (leu), methionine (met), phenylalanine (phe), tyrosine (tyr), tryptophan (trp), asparagines (asn), glutamine (gln), aspartic acid (asp), glutamic acid (glu)} and their binary and ternary stability constants with copper(II) ion were determined at the constant ionic strength 0.1 M KCl and at 298.15 K. The protonation constants of neo and bioactive ligands and their stability constants of the binary and ternary copper(II) complexes were computed from the potentiometric titration data using BEST program. Furthermore, SPE program was used to determine the distribution of the species formed in solution medium. The stability of the ternary copper(II) complexes are compared with those of the corresponding the stability of the binary copper(II) complexes with regard to ΔlogK values.

Gels are attractive for applications in drug delivery, tissue engineering, and 3D printing. Here, physical colloidal gels were prepared by freeze–thaw (FT) cycling of cellulose nanocrystal (CNC) suspensions. The aggregation of CNCs was driven by the physical confinement of CNCs between growing ice crystal domains. FT cycling was employed to form larger aggregates of CNCs without changing the surface chemistry or ionic strength of the suspensions. Gelation of CNC suspensions by FT cycling was demonstrated in water and other polar solvents. The mechanical and structural properties of the gels were investigated using rheometry, electron microscopy, X-ray diffraction, and dynamic light scattering. We found that the rheology could be tuned by varying the freezing time, the number of FT cycles, and concentration of CNCs in suspension.

Affinity partitioning refers to the preferential dissolution of solute molecules in a particular liquid phase of an immiscible liquid-liquid mixture, such as an aqueous two-phase system (ATPS). Affinity partitioning in ATPS is widely used to achieve extraction and purification of biomolecules. However, the potential of applying it to direct the self-assembly of solutes into controlled structures has been largely overlooked. Here we introduce the affinity partitioning of polyelectrolytes in ATPS to induce their self-assembly into polyelectrolyte microcapsules. The approach is purely based on the preferential solubility of different polyelectrolytes in different aqueous phases; therefore it has wide applicability and exhibits excellent compatibility with bioactives. The release of encapsulated components can be triggered by changing the pH value or ionic strength of the surrounding environment. The proposed method represents an important advance in fabricating multifunctional materials and inspires new ways to engineer sophisticated structures with hydrophilic macromolecules.

In this study, we provide the first demonstration that aqueous complex coacervates can be electrospun into chemically robust polyelectrolyte complex (PEC) fiber mats. PECs form due to electrostatic complexation between oppositely charged polymers. Here, we exploit the ability of salt to plasticize PECs, thus enabling the electrospinning of solid fibers. Electrospinning solutions were composed of a pair of strong polyelectrolytes, poly(4-styrenesulfonic acid, sodium salt) and poly(diallyldimethylammonium chloride) using potassium bromide as the plasticizing salt. We systematically investigated the effect of salt concentration and electrospinning apparatus parameters on fiber formation. Electrospun PEC fiber mats were stable over a wide range of pH values, ionic strength conditions, and many organic solvents. This study demonstrates that the electrospinning of aqueous complex coacervates can generate chemically robust, free-standing PEC fiber mats while circumventing the reliance on organic solvents, the challenge of working with entangled polyelectrolytes in solution, and the need to chemically cross-link the as-spun fibers. These PEC fiber mats hold potential in applications where environmentally benign fiber mats are imperative, such as tissue engineering scaffolds and water purification technologies.