Exploiting stored TiO2 electrons for multi-electron reduction of an azo dye methyl orange in aqueous suspension

The mechanism of multi-electron reduction of methyl orange (MO) azo dye on TiO₂ nanoparticles has been studied performing stopped flow technique. A multi-electron reduction of azo dye has been investigated. It was found that a multistep reduction of the dye takes place: the stored electrons reduce the conjugative system of the azo group resulting in the decolorization of the dye and leading to the formation of hydrazine derivative followed by further 2 electron transfer step leading to the cleavage of the N–N bond and the formation of aromatic amines. The FTIR analysis of the products confirms the proposed mechanism of the dye reduction. The kinetic parameters and of the multi-electrons reduction of the MO have been determined. The rate of MO reduction was found to be dependent on both the TiO₂ electrons and the dye concentrations.     

Removal and enrichment of copper ions from aqueous solution by 1,8-diaminonapthalene polymer

Microparticles of poly(1,8-diaminonapthalene) (PDAN) were prepared by chemically oxidative polymerization by (NH₄)₂S₂O₈. The effect of pH on the sorption of Cd(II), Cu(II), Ni(II), Mn(II), Zn(II) and Pb(II) on PDAN was examined by the batch procedure. PDAN showed good sorption capacity and high selectivity towards Cu(II) in comparison with the very popular chelating sorbent Chelex 100 containing iminodiacetic functional groups. The on-line preconcentration system containing the knotted reactor with the obtained polymer was examined for the sorption and desorption processes of copper ions. The applicability of this system was checked by analysis of Cu(II) content in standard reference material (NIST 1643e) and some natural water samples.     

Hydrophobic effect for anionic dye - cationic surfactant interaction in aqueous and mixed solvent

Abstract

The interaction between anionic dyes [Reactive Orange 122 (R.O 122), Reactive Blue 19 (R.B 19), Reactive Violet 5 (R.V 5) and Acid Green 20 (A.G 20)] with cationic surfactant cetyltrimethylammoniun bromide (CTAB) has been investigated by spectrophotometry and conductance technique. The used dyes are characterized by tautomeric behavior which affects the mechanism of the interaction. Various parameters such as dye structure, surfactant composition, solvent composition, temperature and pH of the medium were studied. The spectral data were applied for calculating the binding constant between dye and surfactant (K_b), fraction of micellization (?_mic), and standard free energy change of binding (ΔG°_b) in 0,10,20 and 30 v/v % acetonitile (AN). Conductance technique was constructed to estimate the ion pairing constant (K_a) at different temperatures and v/v % AN. Thermodynamic parameters (ΔG°, ΔH° and ΔS°) for ion pair formation were evaluated. The role of hydrophobic and electrostatic effect on dye-surfactant interaction was discussed.     

Regularities of homo- and heteroassociation of the pinacyanol cation in aqueous solution

The ability of the cation of the cyanine dye (pinacyanol) to association in an aqueous solution was studied. The most probable structures of the pinacyanol cation, its dimer, and heteroassociates with anionic forms of several dyes were proposed on the basis of an analysis of the spectral and calculated data. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1379–1389, July, 2008.     

Hydration and contact ion pairing of Ca2+ with Cl- in supercritical aqueous solution

X-ray absorption fine structure (XAFS) spectroscopy was used to measure the first-shell structure about Ca2+ in high-temperature aqueous solution. XAFS spectra were acquired at the Ca K edge at temperatures up to 400 degrees C and pressures up to 350 bars. For the system at 400 degrees C, both Ca (4038.5 eV) and Cl (2822.4 eV) K-edge data were acquired and a global model was used to fit the two independent sets of XAFS data. Measurements were made at the bending magnet beamline (sector 20) at the Advanced Photon Source, Argonne. Above 250 degrees C, a significant number of Ca2+-Cl- direct contact ion pairs form in agreement with existing thermodynamic data for this system. For a 1 m CaCl2 solution at 400 degrees C, the mean coordination structure about Ca2+ contains 3.2+/-0.6 water molecules at an average Ca-O distance of 2.356+/-0.026 A and 1.8+/-0.7 Cl- at a Ca-Cl distance of 2.677+/-0.007 A. An evaluation of the Ca and Cl preedge and near-edge (x-ray absorption structure) spectra provided further confirmation of the change in the Ca2+ first-shell structure and symmetry. Overall these measurements provide a structural basis for understanding solvation of Ca2+ in hydrothermal systems. These results also provide important new insights into the structural aspects of Ca2+ ion pairing that are the basis of many biological processes under ambient conditions.     

Keggin polyoxoanions in aqueous solution: ion pairing and its effect on dynamic properties by molecular dynamics simulations

The dynamics of Keggin polyoxoanions in aqueous solution in the presence of monovalent cations is analyzed through molecular dynamics simulations. Together with structural information yielding the radial distribution functions of Li(+), Na(+), and K(+) with three polyoxometalates (POMs) bearing 3-, 4-, and 5- charges, the diffusion coefficient of these POMs is calculated. We found that the effect of the microscopic molecular details of the solvent is a key aspect to interpreting the structural and dynamic data because a competition between electrostatic interactions between the ions and the stability of the solvation shell is established. Furthermore, we show that solvent-shared structures weakly bound to the POM anion play a crucial role in the determination of the dynamic properties of the anion. The nature of these ion pairs, structurally characterized for the first time, is consistent with experimental data available.     

The effect of the finite size of ions and Debye layer overspill on the screened Coulomb interactions between charged flat plates

Screened repulsion between uniformly charged plates with an intervening electrolyte is analyzed for strongly overlapped electrical double layers (EDL), accounting for the steric effect of ions and their expulsion from EDL edges into the surrounding solution. As a generalization of a study by Philipse et al. which does not account for these effects, an analytical expression is derived for the repulsion pressure in the limit of infinitely long plates with a zero-field assumption, which agrees closely with the corresponding numerical solution at low inter-plate separations. Our results show an augmented repulsive pressure for finite-sized ions at strong EDL overlaps. For plates with a finite lateral size, we demonstrate a further extended domain of low inter-plate gaps where the repulsion pressure increases with ion size due to a strong interplay between the steric interaction of ions and the EDL overspill phenomenon, considered earlier in a study by Ghosal & Sherwood limited to the linear Debye-Hückel regime (which cannot account for the steric effect of ions). This investigation on a simple model should enhance our understanding of the interaction between charged particles in electrophoresis, nanoscale self-assembly, active particles, and various other electrokinetic systems.     

The effect of ferric ions on the conductivity of various types of polymer cation exchange membranes

Recently, rejuvenated interest to fuel cells has posed a number of problems regarding the polymer electrolyte membrane properties and their behaviour in different electrolyte solutions. This work was dedicated to study the conductivity of H⁺-, Fe³⁺- and mixed H⁺/Fe³⁺-forms of cation exchange membranes Neosepta CMS, Nafion 112, 115 and 117 and Selemion HSF under conditions similar to these in the Fe³⁺/Fe²⁺–H₂/H⁺ fuel cell in the range of current densities 0–90 mA/cm². It was found that the conductivities of these membranes in 1.09 M H₂SO₄ solution decrease in the following order: Selemion HSF › Nafion 117 ≈ Nafion 115 ≈ Neosepta CMS › Nafion 112. Conductivities of perfluorinated membranes were discussed in terms of Hsu and Gierke percolation theory [20]. The Fe³⁺-forms of Nafion membranes studied displayed a monotonous decline in the resistance when current increased, which is a manifestation of gradual conversion of the Fe³⁺-form into H⁺-form of these membranes. Unlike the Nafion membranes, the Fe³⁺-forms of Neosepta CMS and Selemion HSF membranes exhibited a sharp jump of resistance at relatively high current densities (more than 70 mA/cm²) that is most probably a result of concentration polarization.     

Evaluation of Gibbs free energy for the transfer of a highly hydrophilic ion from an acidic aqueous solution to an organic solution based on ion pair extraction

A method to determine the standard Gibbs free energy for the transfer, ΔG°_tr, of a highly hydrophilic metal ion from an aqueous solution, W, in the presence of high concentration of H⁺ to an organic solution, O, was proposed based on the theoretical consideration of the distribution process of ions between W and O. The usefulness of the proposed method was verified experimentally by comparing ΔG°_tr of Mg²⁺ determined by the method with that obtained by voltammetry for the ion transfer at the W|O interface. The O examined were nitrobenzene (NB) and 1,2-dichloroethane (DCE). By applying the proposed method, ΔG°_tr of NpO₂⁺, UO₂²⁺, NpO₂²⁺ and PuO₂²⁺ from an acidic W to NB were determined.     

Study the effect of metal ion on wool fabric dyeing with tea as natural dye

Aqueous extract of natural dye, tea was dyed on the wool fabric with dark brown for 2% and 5% shade. The tea containing tannins as the main colorant species to produce different shade with different mordant salts. The mordant salts Alum, CuSO₄, FeSO₄, ZnSO₄, Na₂SO₄, and MgSO₄ were used to dye fabric using three different dyeing methods: pre-mordanting, meta-mordanting and post-mordanting. The color of the fabric was investigated on Data Color matching system in terms of K/S and CIE Lab-color difference values. The post-mordanting method gave the great depth of shade of natural dye tea with 2% and 5% shade, it also give good light fastness and wash fastness properties. Copper was found as a good mordant to achieve the best results with transition metal ions effect. Deep shades (K/S = 17.50) were obtained for original sample of 5% with color difference ΔE value is 0.17, as compare to 2% original sample of tea of light brown shades (K/S = 10.50) with color difference ΔE value is 0.50 under maintained temperature at 85 °C for 35 min of dyeing.     

Equilibrium Study on Ion-Pair Formation in Water and Distribution Between Water and m-Xylene of Tetraalkylammonium Picrates

The 1:1 ion-pair formation constants (K _IP) of tetraalkylammonium (Me₄N⁺, Et₄N⁺, Pr₄N⁺, Bu₄N⁺, and Bu₃MeN⁺) picrates in water were determined by capillary electrophoresis at 25°C. The ion-pair extraction constants (K _ex,ip) of the picrates from water to m-xylene were determined by a batch-extraction method at 25°C, and the distribution constants (K _D) of the neutral ion-pairs were calculated from the relationship K _D = K_ex,ip/K _IP. The tetraalkylammonium ion having more methylene groups generally forms a slightly more stable ion-pair with the picrate ion in water, which is attributed to the lower hydration of the cation. For Me₄N⁺, Et₄N⁺, Pr₄N⁺, and Bu₄N⁺, the distribution of the ion pair into m-xylene increases in that order, and a linear relationship was found between log K _D and the number of methylene groups in the cation. This is consistently explained by the regular solution theory. It was also revealed that the ion pairs have a strong specific interaction with water. The ion pair of Bu₃MeN⁺ has a higher distribution constant than that expected from the relationship between log K _D and the number of methylene groups for the symmetrical tetraalkylammonium ions. The cation dependence of the ion pair extractability is mostly governed by that of the distribution of the ion pair.     

Complex formation of alkali and alkaline earth metal ions with cryptands containing thiourea units as a part of macrocyclic framework in aqueous methanol

The stability constants (K_s) of the complexes of alkali and alkaline earth metal ions with new type of the cryptands containing one or two thiourea moieties in one of the bridges were determined by means of pH-metric measurements in 95% aqueous methanol at 25 °C. Cryptands studied do not show any regular alteration of complexes stability depending on the mutual relation of cryptand cavity and cation sizes. In all cases, they form the most stable complexes with K⁺ along the series of alkali metal ions and with cations of Ba²⁺ or Sr²⁺ in the series of alkaline earth ions independently of variations of their structure. The log K_s values for K⁺, Sr²⁺ and Ba²⁺ vary in limits 3.51-5.90, 2.29-7.05 and 2.35-7.51, respectively, depending on the cryptands structure. The complexes stability of the studied cryptands increases in the order Li⁺ < Na⁺ (Cs⁺) < Cs⁺ (Na⁺) < Rb⁺ < K⁺ and Mg²⁺ < Ca²⁺ < Sr²⁺ (Ba²⁺) < Ba²⁺ (Sr²⁺). However, cryptands containing at least one oxygen atom between the nitrogen bridgehead and group of thiourea form considerably more stable complexes with respect to cryptands in which thiourea group connected with nitrogen bridgeheads via ethylenic chain. The origins of the cryptands complexation behavior are discussed in terms of ligands and complexes structural features.     

Controlled crystal phase and particle size of loaded-TiO2 using clinoptilolite as support via hydrothermal method for degradation of crystal violet dye in aqueous solution

TiO₂-supported clinoptilolites (TiO₂/clinoptilolites) were successfully synthesized with controlled crystal phase and particle size via hydrothermal method to enhance photocatalytic performance of TiO₂. The effects of various parameters including temperature, acidity and concentration of Ti-containing solutions on the particle size, crystal phase and agglomeration of TiO₂ supported on clinoptilolite were investigated thoroughly by characterizations of X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscope (SEM), transmission electron microscope (TEM), BET isotherm, UV–visible (UV–vis) spectrophotometer and Malvern zetasizer. The results demonstrate that increasing temperature and strengthen acidity are beneficial to enhance the crystallinity and particle size of supported TiO₂. Increase in acidity also leads to more uniform distribution of TiO₂ on the surface of clinoptilolite. The TiO₂ nano-crystals deposited on the surface of clinoptilolite, exhibit rutile or anatase phase, strongly depending on the preparation procedure. The resultant TiO₂/clinoptilolites could be used as photo-catalysts for the degradation of crystal violet (CV) dye in aqueous solution, showing a higher photo-catalytic activity with 89% degradation within 100 min. The effect of operational parameters, such as pH values of reaction media, dose of used catalyst, and concentration of CV dye on the CV degradation performance were investigated, in which the kinetics of CV dye degradation was found to follow the pseudo-first order kinetic model.     

Spontaneous vesicle formation in aqueous solution of zwitterionic and anionic surfactant mixture

Vesicles form spontaneously in the aqueous mixtures of dodecyl sulfonate betaine (DSB) and sodium bis(2-ethylhexyl) sulfosuccinate (Aerosol OT (AOT)) at certain mixing ratios, which has been demonstrated by microcalorimeter, negative-staining transmission electronic microscopy (TEM) and quasi-elastic light scattering (QELS) methods. The addition of NaCl will expand the range of vesicle formation, and monodispersed vesicles are obtained in the solution from the salinity of 0.03 to 0.09 M at the mixing molar ratio of 7/3 (DSB/AOT, mol/mol), with the polydispersity of the system lower than 0.1. To learn more about the structural change in the mixture, ultrasonic was employed finally. Meanwhile analysis was made from the viewpoint of molecular geometry structure.     

Selective detection of Fe(III) ions in aqueous solution with a 1,8-diacridylnaphthalene-derived fluorosensor

The syn-isomer of 1,8-bis(4,4′-diisopropyl-9,9′-diacridyl)naphthalene, 1, has been prepared by two consecutive Pd(PPh₃)₄-catalyzed Stille cross-coupling steps. This highly congested sensor undergoes Fe(III)-selective fluorescence quenching in water/acetonitrile even in the presence of excess of other metal ions.     

Interaction of water with poly(vinyl methyl ether) in aqueous solution

Near-infrared, viscometric, and calorimetric measurements were made on aqueous poly(vinyl methyl ether) (PVME) solutions at temperatures between 15 and 43°C. We found a hydrogen-bonded structure of water around the polymer chain (a polymer-water complex), which is characterized by two distinct hydration numbers (i.e., 2.7 and 5.0 water molecules on each monomer unit of the chain) by analyzing the concentration dependence of endothermic enthalpies at a cloud point temperature, ca. 35°C. In particular, the 2.7 water-polymer complex has been suggested to be cooperatively formed by using data of the near-infrared (nir) absorption spectrum around 1930 nm. Furthermore, the peak-wavelength of the nir spectrum has been observed to change drastically at the cloud point when the temperature is raised. This can be interpreted as a cooperative collapse of the hydrogen-bonded water structure to free water, resulting in the aggregation of the polymer chains due to the exposure of their hydrophobic groups at the cloud point. © 1994 John Wiley & Sons, Inc.     

Retention behavior of ions in high performance ion chromatography: III effect of the nature of the cation on anion retention

The affects of alkali metal cations on the retention behavior of halide ions has been investigated. In general, the retention times of the anions were found to decrease as the size of the metal ion increased, although an inversion was observed for the rubidium and cesium ions. A similar inversion has been reported for calculated anion polarizabilities.     

Conductance study of complex formation of thallium and silver ions with several crown ethers in acetonitrile,acetone and dimethylformamide solutions

The complexation reactions between Tl⁺ and Ag⁺ ions and several crown ethers have been studied conductometrically in acetonitrile, acetone and dimethylformamide solutions at 25°C. The stability constants of the resulting 1:1 complexes were determined, and found to decrease in the order DA18C6>DC18C6>DB30C10>18C6>DB21C7>DB24C8>DB18C6>B15C5 >12C4, in the case of Tl⁺ complexes, and in the order DA18C6>DC18C6>18C6>DB18C6 >DB24C8>DB30C10B15C5>DB21C7 for Ag⁺ complexes. There is an inverse relationship between the stabilities of the complexes and the Gutamnn donicity of the solvents. The influence of a number of atoms in the macrocycle and of substituents in the polyether ring on the stability of the complexes is discussed.     

Extraction Equilibria between Benzene and Water of Uni- and Bivalent Metal Picrates with Lariat 16-Crown-5: Effect of the Side Arms on the Extraction Ability and Selectivity

The overall extraction constants (K_ex) of uni- andbivalent metal picrates with 15-(2,5-dioxahexyl)-15-methyl-16-crown-5(L16C5) were determined between benzene and water at 25°C. TheK_ex values were analyzed into the constituent equilibriumconstants, i.e., the extraction constant of picric acid, the distributionconstant of the crown ether, the stability constant of the metalion–crown ether complex in water, and the ion-pair extraction constantof the complex cation with the picrate anion. The K_ex valuedecreases in the orders Ag⁺ > Na⁺ >Tl⁺ > K⁺ > Li⁺ andPb²⁺ > Ba²⁺ > Sr²⁺ for theuni- and bivalent metals, respectively, which are the same as those observedfor 16C5. The extraction selectivity was found to be governed by theselectivity of the ion-pair extraction of the L16C5–metal picratecomplex rather than by that of the complex formation in water. Theextraction ability of L16C5 is smaller for all the metals than that of 16C5,which is mostly attributed to the higher lipophilicity of L16C5. Differencesin the extraction selectivity between L16C5 and 16C5 were observed for thebivalent metals but little for the univalent metals. The side-arm effect onthe extraction selectivity was interpreted on the basis of the negativecorrelation between the effect on the complex stability constant in waterand that on the ion-pair extraction constant.