Range Of Electrolyte Concentrations Research Articles

Modeling and experimental assessment of Nafion membrane properties used in SO2 depolarized water electrolysis for hydrogen production

A critical analysis of transport properties (diffusion, osmotic flux, conductivity, permeability) of Nafion membrane was carried out. Several correlations were elaborated to provide a consistent description of these properties in a wide range of electrolyte concentrations and membrane hydration states. A model for a sulfur dioxide depolarized electrolyzer (SDE) based on these new equations has been validated by experiments carried out with different electrode materials and electrolytes.

An analysis of the substantivity of hydrolysed reactive dyes and its implication for rinsing processes

Substantivity plays a key role in dyeing processes, for dye exhaustion and fixation as well as for dye removal during rinsing. The latter is especially relevant for reactive dyes when the hydrolysed dye has to be removed from the fibre. The substantivity of the hydrolysed form of 46 commercially important reactive dyes was analysed at two temperatures for a wide range of dye amounts, pH values and electrolyte concentrations. The results showed that substantivity was highly dye‐specific and varied, for each variable analysed, almost within the entire theoretically possible range of values. Substantivity values correlated best with the number of sulphatoethylsulphone groups in the dye molecule and dye solubility in the presence of sodium chloride. Sensitivity to electrolyte, pH, dye amount and temperature broadly correlated with each other, implying that a reduction in electrolyte concentration and an increase in pH and temperature are more beneficial in the removal of highly substantive reactive dyes. Some dyes remained highly substantive even at 90 °C, indicating that dye removal in industrial processes, too, would be difficult. For dyes with little substantivity, however, wash baths at the boil do not appear to be necessary, neither is the significant removal of electrolyte before rinsing at elevated temperature.

On the contact values of the density profiles in an electric double layer using density functional theory

A recently proposed local second contact value theorem [Henderson D., Boda D., J. Electroanal. Chem., 2005, 582, 16] for the charge profile of an electric double layer is used in conjunction with the existing Monte Carlo data from the literature to assess the contact behavior of the electrode-ion distributions predicted by the density functional theory. The results for the contact values of the co- and counterion distributions and their product are obtained for the symmetric valency, restricted primitive model planar double layer for a range of electrolyte concentrations and temperatures. Overall, the theoretical results satisfy the second contact value theorem reasonably well, the agreement with the simulations being semi-quantitative or better. The product of the co- and counterion contact values as a function of the electrode surface charge density is qualitative with the simulations with increasing deviations at higher concentrations.

Helium diffusion in aqueous sodium chloride solution at high pressures

A molecular dynamic investigation of self-diffusion coefficients of helium and water in aqueous NaCl solution is performed. To understand the nonlinear behavior of the self-diffusion coefficients, a number of structural characteristics (radial distribution functions, hydrogen bond network topology) are calculated. The electrolyte concentration range is discussed in which a local increase in helium self-diffusion coefficient is observed. It is shown that this behavior is caused by a breakdown of the network of hydrogen bonds due to competition between ion positions in the states of solvent-separated and contact pairs.

ION ASSOCIATION OF THE POLYVALENT ELECTROLYTES IN NON-AQUEOUS SYSTEMS

Abstract. The work deals with polyvalent electrolytes conductometric investigation of CuCl2,[Cu(en)2]Cl2, FeCl3 solutions in binary mixed solvent DMSO−CB in a wide range of electrolyteconcentrations (10-6–10-2 mol/dm3). Investigations were carried out at the temperature interval 298,15–323,15 K. Ion association constants (Kai) for given non-symmetrical electrolytes were calculated for twostages of association. Integral thermodynamic characteristics (Gai, Hai, Sai) of stage ion associationprocess were calculated. The comparison of thermodynamic characteristics of equilibrium processes allowsto make a conclusion about relative influence of polar and donor properties of medium on the processes ofstage ion association in polyvalent electrolyte solutions.Keywords: conductometric investigation, ion association constants, polyvalent electrolytes, solutionequilibrium processes, thermodynamic characteristics.

Electro-Assisted Photocatalytic Degradation of Methyl Orange on TiO<sub>2</sub> Film Using CaСl<sub>2</sub> as Electrolyte

Porous and smooth TiO2 film electrodes prepared by sol-gel method were used on methyl orange degradation by an electro-assisted photocatalytic degradation process. Methyl orange cannot be degraded under applied potential solely below 2.0 V. When the applied potential was below 1.3 V, methyl orange degradation rates on porous TiO2 film increased from 5% at 0 V to 65.3% at 1.3 V, and degradation rates on smooth TiO2 film changed from 2.2% at 0 V to 61.1% at 1.3 V. Electro-assisted photocatalytic degradation rate on porous film was better than that on smooth film in the whole electrolyte concentration range. Electro-assisted degradation exhibited the same rising trend along with reaction time on the porous and smooth films.

Photocatalytic Activities of HZSM-5 Supported TiO<sub>2</sub> in Different Electrolyte Solutions

Zeolite HZSM-5 was pre-treated by oxalic acid and used as support for TiO2prepared by sol-gel method. Photocatalytic activities of the supported TiO2on HZSM-5 were investigated with existence of three kinds of electrolytes, ie. NaCl, NaHCO3and NH4C. The use of these electrolytes encountered very similar influences on adsorption and photocatalytic degradation on HZSM-5 supported TiO2. Methyl orange total decoloration and photocatalytic degradation rates increased with electrolyte concentration when the concentration was lower than 0.1 mol/l. Adsorption of methyl orange of the photocatalyst went up constantly as electrolyte concentration rising from 0 to 1.0 mol/l. Photocatalytic degradation efficiencies undertook a slowly decrease at a long range of electrolyte concentration.

Electrohydrodynamics of Soft Polyelectrolyte Multilayers: Point of Zero-Streaming Current

We report a comprehensive formalism for the electrokinetics (streaming current, I(str)) at soft multilayered polyelectrolyte films. These assemblies generally consist of a succession of permeable diffuse layers that differ in charge density, thickness, and hydrodynamic softness. The model, which extends one that we recently reported for the electrokinetics of monolayered soft thin films (Langmuir 2010, 26, 18169-18181), is valid without any restriction in the number and thickness of layers, or in the degree of dissociation and density of ionizable groups they carry. It further covers the limiting cases of hard and free draining films and correctly compares to semianalytical expressions derived for I(str) under conditions where the Debye-Hückel approximation applies. The flexibility of the theory is illustrated by simulations of I(str) for a two-layer assembly of cationic and anionic polymers over a large range of pH values and electrolyte concentrations. On this basis, it is shown that the point of zero streaming current (PZSC) of soft multilayered interphases, defined by the pH value where I(str) = 0, generally depends on the concentration of the (indifferent) electrolyte. The magnitude and direction of the shift in PZSC with varying salinity are intrinsically governed by the dissymmetry in protolytic characteristics and density of dissociable groups within each layer constituting the film, together with the respective film thickness and hydrodynamic softness. The fundamental effects covered by the theory are illustrated by streaming current measurements performed on two practically relevant systems, a polyelectrolyte bilayer prepared from poly(ethylene imine) (PEI) and poly(acrylic acid) (PAA) and a polymer-cushioned (PEI) bilayer lipid membrane.

Divalent Metal Cation Speciation and Binding to Surface-Bound Oligonucleotide Single Strands Studied by Second Harmonic Generation

The binding of Sr(II), Ca(II), Mg(II), Ba(II), Mn(II), Zn(II), and Cd(II) to silica/water interfaces functionalized with A(15)T(6) oligonucleotides was quantified at pH 7 and 10 mM NaCl using the Eisenthal χ((3)) technique. The binding free energies range from -31.1(6) kJ/mol for Ba(II) to -33.8(4) kJ/mol for Ca(II). The ion densities were found to range from 2(1) ions/strand for Zn(II) to 11(1) ions/strand for Cd(II). Additionally, we quantified Mg(II) binding in the presence of varying background electrolyte concentrations which showed that the binding free energies changed in a linear fashion from -39.3(8) to -27(1) kJ/mol over the electrolyte concentration range of 1-80 mM, respectively. An adsorption free energy versus interfacial potential analysis allowed us to elucidate the speciation of the bound Mg(II) ions and to identify three possible binding pathways. Our findings suggest that Mg(II) binds as a fully hydrated divalent cation, most likely displacing DNA-bound Na ions. These measurements will serve as a benchmark for computer simulations of divalent metal cation/DNA interactions for geochemical and biosensing applications.

Aggregation Kinetics of Citrate and Polyvinylpyrrolidone Coated Silver Nanoparticles in Monovalent and Divalent Electrolyte Solutions

The aggregation kinetics of silver nanoparticles (AgNPs) that were coated with two commonly used capping agents-citrate and polyvinylpyrrolidone (PVP)--were investigated. Time-resolved dynamic light scattering (DLS) was employed to measure the aggregation kinetics of the AgNPs over a range of monovalent and divalent electrolyte concentrations. The aggregation behavior of citrate-coated AgNPs in NaCl was in excellent agreement with the predictions based on Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, and the Hamaker constant of citrate-coated AgNPs in aqueous solutions was derived to be 3.7 × 10(-20) J. Divalent electrolytes were more efficient in destabilizing the citrate-coated AgNPs, as indicated by the considerably lower critical coagulation concentrations (2.1 mM CaCl(2) and 2.7 mM MgCl(2) vs 47.6 mM NaCl). The PVP-coated AgNPs were significantly more stable than citrate-coated AgNPs in both NaCl and CaCl(2), which is likely due to steric repulsion imparted by the large, noncharged polymers. The addition of humic acid resulted in the adsorption of the macromolecules on both citrate- and PVP-coated AgNPs. The adsorption of humic acid induced additional electrosteric repulsion that elevated the stability of both nanoparticles in suspensions containing NaCl or low concentrations of CaCl(2). Conversely, enhanced aggregation occurred for both nanoparticles at high CaCl(2) concentrations due to interparticle bridging by humic acid aggregates.

The weighted correlation approach for density functional theory: a study on the structureof the electric double layer

Within the framework of density functional theory, a weighted correlation approach isdeveloped in order to obtain the density distributions of an inhomogeneous fluid. It resultsin a formally exact expression, by means of the concept of a weighted pair correlationfunction, used to evaluate the change of the single-particle direct correlation function of thesystem relative to that of a reference state. When applying the approach for practical use,however, an approximation of the pair correlation function has to be made, along with anappropriate definition of a weight function. Noticeably, combining this approach withfundamental measure theory gives rise to a new method, which we call the FMT/WCA-k2 approach, for studying the structural and thermodynamic properties of a charged hard-spherefluid subjected to a spatially varying external potential. Application of the FMT/WCA-k2 approach in a range of electrolyte concentrations and surface charge densities, against theMonte Carlo simulations, shows that it is superior to the typical approaches of densityfunctional theory in predicting the ionic density profiles of both counter-ions and co-ionsnear a highly charged surface. It is capable of capturing the fine features of thestructural properties of the electric double layers, to well reproduce the layeringeffect and the charge inversion phenomenon, also in strongly coupled cases wheredivalent counter-ions are involved. In addition, it is found that the FMT/WCA-k2 approach even has an advantage over the anisotropic, hyper-netted chain approaches ingiving better agreement with the Monte Carlo results.

Process intensification: water electrolysis in a centrifugal acceleration field

Intensification of hydrogen production by carrying out water electrolysis in a centrifugal acceleration field has been demonstrated. A prototype single cell rotary water electrolyser was constructed, and a number of design challenges with regard to the practical application were addressed. The rotary electrolyser was tested over a range of current density, centrifugal acceleration, electrolyte concentration, temperature, and electrode geometry. The test results showed that at normal cell operating conditions (7.7 M KOH solution, 348 K) much of the cell voltage benefits were achieved at an acceleration of about 16 g (g = 9.81 m s−2), equivalent to a rotational speed of 500 rpm (revolution per minute) for the rotary cell. The rotary electrolyser cell voltage was about 0.25–0.5 V, less than the equivalent static cell under similar operating conditions, depending on the current density. The cell voltages achieved, without an effective electrode catalytic coating, were comparable with typical industrial values of fully developed pressurised cells. At a higher acceleration of 41 g, the rotary cell’s current density can be up to 13.5 KA m−2 without causing gas bubble blinding of the membranes and electrodes. When comparing with typical current densities (about 5 kA m−2) found in commercial systems, this study demonstrated the potential of intensification.

Porphyran capped gold nanoparticles as a novel carrier for delivery of anticancer drug: In vitro cytotoxicity study

In the present study, we have explored porphyran as a reducing agent for one pot size controlled green synthesis of gold nanoparticles (AuNps) and further investigated its application as a carrier for the delivery of an anticancer drug. The prepared AuNps showed surface plasmon resonance centered at 520 nm with average particle size of 13 ± 5 nm. FTIR spectra suggested that the sulfate moiety is mainly responsible for reduction of chloroauric acid. The capping of the AuNps with porphyran was evident from the negative zeta potential value responsible for the electrostatic stability. Thus, porphyran acts as reducing as well as capping agent. These AuNps are highly stable in a wide range of pH and electrolyte concentration. Porphyran capped AuNps exhibited enhanced cytotoxicity on human glioma cell line (LN-229) as compared to native porphyran. Consequently, these AuNps have been utilized as a carrier for delivery of the anticancer drug doxorubicin hydrochloride (DOX). Spectroscopic examination revealed that DOX conjugated onto AuNps via hydrogen bonding. The release of DOX from DOX loaded AuNps was found to be sixfold higher in acetate buffer (pH 4.5) as compared to physiological buffer (pH 7.4). Further, the DOX loaded AuNps demonstrated higher cytotoxicity on LN-229 cell line as compared with an equal dose of native DOX solution. This established the potential of these AuNps as a carrier for anticancer drug delivery.

Green synthesis of silver nanoparticles using marine polysaccharide: Study of in-vitro antibacterial activity

The present contribution deals with one pot method for synthesis of silver nanoparticles through green route using sulfated polysaccharide isolated from marine red algae ( Porphyra vietnamensis). The obtained silver nanoparticles showed surface plasmon resonance centered at 404 nm with average particle size measured to be 13 ± 3 nm. FTIR spectra revealed the involvement of sulfate moiety of polysaccharide for reduction of silver nitrate. The capping of anionic polysaccharide on the surface of nanoparticles was confirmed by zeta potential measurement (−35.05 mV) and is responsible for the electrostatic stability. The silver nanoparticles were highly stable at wide range of pH (2–10) and electrolyte concentration (up to 10 −2 M of NaCl). The dose dependent effect of synthesized silver nanoparticles revealed strong antibacterial activity against gram negative bacteria as compared to gram positive bacteria.

Study of ultrafiltration recovery of sulfate lignin from its dilute aqueous solutions in the presence of Al2(SO4)3

Filtration on track membranes was used to study the coagulation recovery of sulfate lignin in the presence of aluminum sulfate in a wide range of pH values (9.5–2.0) and electrolyte concentrations.

A new approach to calculating activity coefficients in a wide range of electrolyte concentration

A new approach to calculating activity coefficients in a wide range of electrolyte concentration

Impact of the virulence-associated MAb3/1 epitope on the physicochemical surface properties of Legionella pneumophila sg1: An issue to explain infection potential?

The relationship between the presence/absence of the virulence-associated MAb3/1 epitope of sixteen Legionella pneumophila serogroup 1 strains and their respective surface physicochemical properties is evidenced from electrokinetic measurements (microelectrophoresis) performed as a function of KNO 3 electrolyte concentration (range 1–100 mM, pH ∼ 6.5). Among the bacteria selected, nine original strains constitute the Dresden reference panel and differ according to the presence/absence of the virulence-associated monoclonal antibody MAb3/1 of the O-specific chain of the lipopolysaccharides (LPS). Five isogenic Lens strains, also investigated in the current study, present the epitope MAb3/1 of their LPS and were involved to some extent in the outbreak that stroke the Nord Pas-de-Calais region (France) in 2004. All bacteria exhibit the typical electrokinetic features of soft (permeable) particles. On the basis of Ohshima's model, analysis of the electrophoretic mobility data allows evaluating the intraparticular flow penetration length 1/ λ 0 and the (negative) volume charge density ρ 0 that both reflect the structure and chemical composition of the soft bacterial component. Our results show that the virulent MAb3/1 positive strains are characterized on average by 1/ λ 0 and ǀ ρ 0ǀ values that are about 1.5 times larger and 5 times lower, respectively, than those derived for lesser virulent (MAb3/1 negative) strains. In other words, on average the soft surface layer of MAb3/1 positive strains is significantly less charged and more permeable than those of MAb3/1 negative strains. The intimate correlation between virulence-associated MAb3/1 epitope and charge density carried by the bacterial envelop was further confirmed by lower 1/ λ 0 and greater ǀ ρ 0ǀ values for lag-1 mutant CS332 strain, lacking the MAb3/1 epitope, compared to the parental strain AM511. A closer inspection of the dispersion in 1/ λ 0 and ǀ ρ 0ǀ data over the ensemble of analysed bacteria together with the reported number of Legionnaires’ disease cases they are responsible for, points out the charge density ǀ ρ 0ǀ as the parameter that is most suitable for discriminating highly virulent (MAb3/1 positive) from less virulent (MAb3/1 negative) strains. Although short-range interaction determines infection process, our results suggest that the infection potential of Legionella pneumophila serogroup 1 may be also controlled significantly by non-specific long-range electrostatic repulsion the bacteria undergo when approaching negatively charged host cells to be infected.

Asymmetric properties of ion current 1/f noise in conically shaped nanopores

We study ion currents in single rectifying conically shaped nanopores of various opening diameters and analyze the 1/f spectral behavior of the current fluctuations. The 1/f noise characteristics show an asymmetry with respect to the externally applied voltage. When in the high conductance state, the normalized 1/f noise associated with ion current signals increases with applied voltage, while in the low conductance state the 1/f noise shows equilibrium, voltage-independent fluctuations. The pore diameter and salt concentration play a direct role in defining these noise properties and influence the frequency range of the 1/f noise occurrence. We describe this behavior for a range of nanopore diameters and electrolyte concentrations.

Effect of added monovalent electrolytes on the myelin formation from charged lipids

The effect of added monovalent electrolytes on the myelin formation of cardiolipin is investigated by optical microscopy observations. The results show that the myelin formation strongly depends on the concentration rather than the type of electrolytes. Myelin figures are observed only in a certain concentration range of electrolytes, and the diameter of the myelin figures decreases with increasing of the electrolyte concentration. Furthermore, the theoretical model of myelin formation for the neutral lipids developed by Huang–Zou–Witten [J.R. Huang, L.N. Zou, T.A. Witten, Eur. Phys. J. E. 18 (2005) 279–285] is extended to the charged membrane system by taking into account the electrostatic interaction to understand the mechanism of myelin formation. The theoretical results well produce our experimental results.

Zeta Potential of Mica Covered by Colloid Particles: A Streaming Potential Study

The streaming potential of mica covered by monodisperse latex particles was measured using the parallel-plate channel, four-electrode cell. The zeta potential of latex bearing amidine charged groups was regulated by the addition of NaCl (10(-4)-10(-2) M) and MgCl(2) (10(-4)-10(-2) M) at a constant pH 5.5 and by the change in pH (4-12) at 10(-2) M NaCl. The size of the latex particles, determined by dynamic light scattering, varied between 502 and 540 nm for the above electrolyte concentration range. Mica sheets have been covered with latex particles under diffusion transport conditions. The latex coverage was regulated by the bulk suspension concentration in the channel and the deposition time. The coverage was determined, with a relative precision of 2%, by the direct enumeration of particles by optical microscopy and AFM. The streaming potential of mica was then determined for a broad range of particle coverage 0 < theta < 0.5, the particle-to-substrate zeta potential ratio zeta(p)/zeta(i), and 8.8 < kappa a < 143 (thin double-layer limit). These experimental data confirmed that the streaming potential of covered surfaces is well reflected by the theoretical approach formulated in ref 32. It was also shown experimentally that variations in the substrate streaming potential with particle coverage for theta < 0.3 and zeta(p)/zeta(i) < 0 are characterized by a large slope, which enables the precise detection of particles attached to interfaces. However, measurements at high coverage and various pH values revealed that the apparent zeta potential of covered surfaces is 1/2(1/2) smaller than the bulk zeta potential of particles (in absolute terms). This is valid for arbitrary zeta potentials of substrates and particles, including the case of negative particles on negatively charged substrates that mimics rough surfaces. Therefore, it was concluded that the streaming potential method can serve as an efficient tool for determining bulk zeta potentials of colloids and bioparticles.