Hydrophilic nanofiltration membranes with self-polymerized and strongly-adhered polydopamine as separating layer

Inspired by the self-polymerization and strong adhesion characteristics of dopamine in aqueous conditions,a novel hydrophilic nanofiltration（NF） membrane was fabricated by simply dipping polysulfone（PSf） ultrafiltration（UF） substrate in dopamine solution.The changes in surface chemical composition and morphology of membranes were determined by Fourier transform infrared spectroscopy（FTIR-ATR）,X-ray photoelectron spectroscopy（XPS）,scanning electron microscopy（SEM） and atomic force microscopy（AFM）.The experimental results indicated that the self-polymerized dopamine formed an ultrathin and defect-free barrier layer on the PSf UF membrane.The surface hydrophilicity of membranes was evaluated through water contact angle measurements.It was found that membrane hydrophilicity was significantly improved after coating a polydopamine（pDA） layer,especially after double coating.The dyes filtration experiments showed that the double-coated membranes were able to reject completely the dyes of brilliant blue,congo red and methyl orange with a pure water flux of 83.7 L/（m²·h） under 0.6 MPa.The zeta potential determination revealed the positively-charged characteristics of PSf/pDA composite membrane in NF process.The salt rejection of the membranes was characterized by 0.01 mmol/L of salts filtration experiment.It was demonstrated that the salts rejections followed the sequence:NaCl2SO₄422,and the rejection to CaCl₂ reached 68.7%.Moreover,the composite NF membranes showed a good stability in water-phase filtration process.     

Studies with inorganic precipitate membranes. III. Consideration of energetics of electrolyte permeation through membranes

The permeability of various electrolytes through parchment-supported ferrocyanide membranes of manganese, cobalt, silver, and cadmium has been measured at 10, 15, 20, 25, and 30°C. The order of permeability at a given temperature was Cl^- > NO₃^- > CNS^- > CH₃COO^- > SO₄^2- for both monovalent and divalent cations. For any given anion, the cations followed the sequence NH₄⁺ > Li⁺ > Ba²⁺ > Ca²⁺ > Mg²⁺ > Al³⁺. This sequence has been correlated with the size of the hydrated ion. Further, the data have been considered from the standpoint of the theory of rate processes and the values for the entropy of activation (ΔS′) have been derived assuming an equilibrium distance of 3 Å in the membrane. The values of ΔS′ were all negative and decreased with increasing valence of the ions. This was interpreted to mean electrolyte permeation with partial immobilization in the membrane.     

Cation exchange, interlayer spacing, and thermal analysis of Na/Ca-montmorillonite modified with alkaline and alkaline earth metal ions

Na-montmorillonites were exchanged with Li⁺, K⁺, Rb⁺, Cs⁺, Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺, while Ca-montmorillonites were treated with alkaline and alkaline earth ions except for Ra²⁺ and Ca²⁺. Montmorillonites with interlayer cations Li⁺ or Na⁺ have remarkable swelling capacity and keep excellent stability. It is shown that metal ions represent different exchange ability as follows: Cs⁺?>?Rb⁺?>?K⁺?>?Na⁺?>?Li⁺ and Ba²⁺?>?Sr²⁺?>?Ca²⁺?>?Mg²⁺. The cation exchange capacity with single ion exchange capacity illustrates that Mg²⁺ and Ca²⁺ do not only take part in cation exchange but also produce physical adsorption on the montmorillonite. Although interlayer spacing d ₀₀₁ depends on both radius and hydration radius of interlayer cations, the latter one plays a decisive role in changing d ₀₀₁ value. Three stages of temperature intervals of dehydration are observed from the TG/DSC curves: the release of surface water adsorbed (36?C84?°C), the dehydration of interlayer water and the chemical-adsorption water (47?C189?°C) and dehydration of bound water of interlayer metal cation (108?C268?°C). Data show that the quantity and hydration energy of ions adsorbed on montmorillonite influence the water content in montmorillonite. Mg²⁺-modified Na-montmorillonite which absorbs the most quantity of ions with the highest hydration energy has the maximum water content up to 8.84%.     

Diffusion mobility of alkali metals in perfluorinated sulfocationic and carboxylic membranes as probed by <Superscript>1</Superscript>H, <Superscript>7</Superscript>Li, <Superscript>23</Superscript>Na,and <Superscript>133</Superscript>Cs NMR spectroscopy

Water self-diffusion and ion mobilities in various ionic forms (H⁺, Li⁺, Na⁺, Rb⁺, Cs⁺, and Ba²⁺) of perfluorinated sulfocationic membranes MF-4SK were studied by NMR and impedance spectroscopy. When degrees of hydration are low, the self-diffusion coefficients of water and ionic conductivities are considerably affected by the water content of the membrane. The self-diffusion coefficients decrease in the order H⁺ > Ba²⁺ > Cs⁺ > Rb⁺ > Na⁺ > Li⁺, whereas the ion mobility decreases in the order H⁺ > Li⁺ > Na⁺ > Cs⁺ > Ba²⁺.     

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.     

Selective ion exchange onto Slovakian natural zeolites in aqueous solutions

Ion exchange isotherms have been measured and plotted for the uptake of cesium, barium, cobalt, zinc, silver and amonium onto clinoptilolite- and mordenite-rich tuffs of Slovakian origin selectively for both the natural and near homoionic Na form as well, using the radioanalytical determination. The higher quality clinoptilolite-rich tuff has been proven to be effective for a potential radionucleides removal in native form according to the following selectivity sequence: Ag⁺,Ba²,Cs⁺>NH₄ ⁺>Co²⁺, while parent tuff in Na exchanged variety exhibited a little different sequence according to: Ag⁺?>?NH₄ ⁺?>?Ba²⁺?>?Cs⁺. The raw and Na exchanged mordenite-rich tuffs proved subsequently more or less similar selectivity : Ag⁺?>?Zn²⁺?>?Cs⁺, Ba²⁺?>?Co²⁺ and Ag⁺?>?Zn²⁺.     

Water self-diffusion and ionic conductivity in perfluorinated sulfocationic membranes MF-4SK

Water self-diffusion and ion mobilities in various ionic forms (H⁺, Li⁺, Na⁺, Rb⁺, Cs⁺, and Ba²⁺) of perfluorinated sulfocationic membranes MF-4SK were studied by NMR and impedance spectroscopy. When degrees of hydration are low, the self-diffusion coefficients of water and ionic conductivities are considerably affected by the water content of the membrane. The self-diffusion coefficients decrease in the order H⁺ > Ba²⁺ > Cs⁺ > Rb⁺ > Na⁺ > Li⁺, whereas the ion mobility decreases in the order H⁺ > Li⁺ > Na⁺ > Cs⁺ > Ba²⁺.     

New PCT probes featuring N-phenylmonoaza-18-crown-6 and aryl/pyridyl oxadiazoles: optical spectral studies of solvent effects and selected metal ions

Aryl/pyridyl oxadiazole chromophores 6, 8 and 10, carrying N-phenyl aza-18-crown-6 have been synthesized as new photo-induced charge transfer (PCT) probes. While, the absorption spectra of the hosts experienced a slight negative solvatochromism, however the emission bands were dramatically red shifted (Stokes shifts up to 178 nm) in solvents of increasing polarity. Among the metal ions tested, Li⁺, Na⁺, K⁺ and Mg²⁺ did not appreciably perturbed the optical properties of the hosts. On the other hand, Ba²⁺ and to a lesser extent Ca²⁺ induced marked blue shifts in both the absorption and emission spectra of the hosts. The magnitude of cation induced spectral blue shifts corresponded with the increasing acceptor strength of the attached aryl/pyridyl groups in the host molecules. The blue shifts and the stability constants were found to follow the order Ba²⁺ > Ca²⁺ ? Mg²⁺ > Na⁺ > Li⁺ > K⁺. Competitive experiments performed with a matrix of ions also revealed superior binding affinity of Ba²⁺ with all the hosts examined. Noteworthily, the deep yellow solution (λ_max, 386 nm) of the host 10 was completely bleached (λ_max, 320 nm), in the company of Ba²⁺ thereby allowing the naked eye detection of this ion.     

Evaluation of behaviour of linear monoamines CH3-(CH2)n−1-NH2 (n=1-6) in ion chromatography

This paper reports the results on a study of ion chromatography (IC) behaviour on strong cationic exchange column of CH₃-(CH₂)_n−1-NH₂ (n=1-6) type linear monoamines. The eluents were mixtures of HCl-NaCl, HNO₃-NaNO₃, HClO₄-NaClO₄, H₂SO₄-Na₂SO₄, HClO₄-NaClO₄-CH₃CN. Amines were revealed with an amperometric detector. The influence of different counter-ions on retention factors, k′, is discussed. Relationships between k′ and pE (E=sum of Na⁺ and H⁺ concentrations), and length of alkylic chain, and sensitivity coefficient S, are reported and discussed. The addition of acetonitrile (ACN) in the eluent was also taken into account. Suitable considerations are derived from these data. An example of monoamines separation is given.     

A simple sum rule in raman theory

It is shown that in the limit of large detuning energy and in the absence of coordinate dependence of the transition moment, the resonance Raman amplitude for a 0 → n transition on a harmonic potential surface is proportional to (δ²_? + δ²₊)^?1 × ?^∞_?∞ exp (?q²) · [?ⁿΔV(q)/?q¹¹] dq< where ΔV(q) is the difference between the arbitrary excited-state surface and the initial harmonic potential. The resonant and non-resonant detuning energies are given by δ_? = E ? hv and δ₊ = E + hv, where v is the incident laser frequency and E is the minimum separation between the potential surfaces.     

Successful location of tin dopant cations on surface sites of anatase-type TiO2 crystallites evidenced by 119Sn Mössbauer spectroscopic probe and XPS techniques

The present study provides the first experimental evidence for the stabilization of tin dopant cations immediately on the surface of an oxide having a tetragonal structure. ¹¹⁹Sn Mössbauer spectra of the dopant, introduced by air annealing into the bulk of anatase microcrystals, showed that it was located, in the tetravalent state, in somewhat distorted octahedral sites of a unique type. On the contrary, the reduced tin species, formed upon subsequent hydrogen annealing the Sn⁴⁺-doped samples, are found to occupy different sites being characterized by two sets of the isomer shift δ and quadrupole splitting ΔE_Q values (δ_I = 3.25 mm s⁻¹, ΔE_QI = 1.75 mm s⁻¹; and δ_II = 2.85 mm s⁻¹, ΔE_QII = 1.71 mm s⁻¹). Either of them implies both the divalent state of tin atoms and their presence at low-coordination sites that can be assigned to the surface of crystallites. Mössbauer spectra of Sn^4+←2+ daughter ions, formed upon contact with air of Sn²⁺, consist of a symmetrically broadened peak characterized by only slightly different average values of both the isomer shift (<δ> = 0.07 mm s⁻¹) and quadrupole splitting (<ΔE_Q> = 0.50 mm s⁻¹), as compared to the δ and ΔE_Q values for the bulk-located Sn⁴⁺. However, considerable broadening of Sn^4+←2+ doublet components (Γ = 0.97 mm s⁻¹) allows one to suggest that these secondary formed ions remain distributed over the non equivalent sites inherited from their Sn²⁺ precursors. The occurrence of Sn^4+←2+ at surface sites is independently proven by XPS measurements that revealed a greater than 10-fold enrichment with tin of 3–5 nm thick surface layers.     

Enhanced photoluminescence of Ba2GdNbO6: Eu/Dy phosphors by Li doping

The Ba₂GdNbO₆: Eu³⁺/Dy³⁺ and Li⁺-doped Ba₂GdNbO₆: Eu³⁺/Dy³⁺ phosphors were prepared by solid-state reaction process. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and photoluminescence (PL) as well as lifetimes, was utilized to characterize the resulting phosphors. Under the excitation of ultraviolet light, the Ba₂GdNbO₆: Eu³⁺/Dy³⁺ and Li⁺-doped Ba₂GdNbO₆: Eu³⁺/Dy³⁺ show the characteristic emissions of Eu³⁺ (⁵D₀-⁷F_1,2,3 transitions dominated by ⁵D₀-⁷F₁ at 593 nm) and Dy³⁺ (⁴F_9/2-⁶H_15/2,_13/2 transitions dominated by ⁴F_9/2-⁶H_15/2 at 494 nm), respectively. The incorporation of Li⁺ ions into the Ba₂GdNbO₆: Eu³⁺/Dy³⁺ phosphors has enhanced the PL intensities depending on the doping concentration of Li⁺, and the highest emission was obtained in Ba₂Gd_0.9NbO₆: 0.10Eu³⁺, 0.01Li⁺ and Ba₂Gd_0.95NbO₆: 0.05Dy³⁺, 0.07Li⁺, respectively. An energy level diagram was proposed to explain the luminescence process in the phosphors.     

Thermodynamics of Sr(NO3)2 and Cd(NO3)2 in aquo-organic solvents from conductance data

The ion-solvent interaction of Sr(NO₃)₂ and Cd(NO₃)₂ in 10, 20 and 30 wt.% organic solvent (dioxane, glycol, methyl alcohol)-water mixtures at different temperatures has been studied using electrolytic conductivity data. The dissociation constant of the ion-pair Sr(NO₃)⁺ and Cd(NO₃)⁺ has been calculated along with ΔG⁰_t, ΔG⁰_t(cl) and ΔG⁰_t(ch). The ion pairs interact with the solvents and the interaction is of the order dioxane+water>methyl alcohol+water>glycol+water.     

New ICT probes: synthesis and photophysical studies of N-phenylaza-15-crown-5 aryl/heteroaryl oxadiazoles under acidic condition and in the presence of selected metal ions

Molecular probes 6 and 7, incorporating N-phenylaza-15-crown-5 and aryl/heteroaryl oxadiazole have been designed to function as the new intramolecular charge transfer (ICT) probes. Photophysical properties have been studied under acidic condition as well as in the presence of selected metal ions, Ca²⁺, Ba²⁺, Mg²⁺, Na⁺, K⁺, and Li⁺. The changes in the ICT character of the probes, following the addition of trifluoroacetic acid, were interpreted in terms of site and degree of protonations. Based on the cation affinity, the ICT bands in both UV-vis and emission spectra experienced varying degrees of blue shifts due to removal of the aza-crown ether nitrogen from conjugation. The cation-induced spectral shifts and the stability constants revealed binding strength in the order Ca²⁺>Ba²⁺?Li⁺>Na⁺>K⁺>Mg²⁺. Competitive experiments performed in a matrix of ions also indicated superior interaction of 6 and 7 with Ca²⁺. The excited state decay profiles remained largely unperturbed in the presence of metal ions. The studied probes displayed positive solvatochromism and the Stokes shifts and excited state lifetimes increased with increasing solvent polarity. These findings can be rationalized by invoking highly polar nature of the emittive states. The chemoionophores 6 and 7 constitute potentially interesting Ca²⁺ sensitive probes due to their relatively high binding interaction for Ca²⁺ (log K_s=3.55-3.10) vis-a-vis that of biologically interfering Mg²⁺ (log K_s=1.67-1.30).     

Collinear quantum mechanical calculations for the reaction: He + H2+ → HeH+ + H

An integral equation reaction path technique has been used to calculate, within the collinear approximation, reaction probabilities for the reaction He + H₂⁺ → HeH⁺ + H over the energy range 0.95 <- E <- 1.19 eV. This reaction differs from those that have been studied previously within the collinear approximation in that a severe oscillatory behavior is exhibited in the energy dependence of the reaction probabilities.     

Biosorption of strontium from aqueous solutions onto spent coffee grounds

A set of experiments was carried out to evaluate the strontium uptake potential of spent coffee grounds (SCG) by batch tests in aqueous medium. Adsorption of Sr²⁺ as a function of contact time and adsorbent dose, pH, particles size, agitation speed, temperature and co-ions presence was investigated. Obtained results revealed that the maximum adsorption took place at pH range of 5–8 and temperature values between 283 and 333 K. Particles size effect was not very significant and agitation speed influenced on the equilibrium time. Competitive adsorption experiments allowed us to classify the negative effect on the Sr²⁺ uptake according to this order Al³⁺ ? Co²⁺ > Mg²⁺ > Ca²⁺ ? Na⁺ > K⁺ > Cs⁺. Kinetic study indicated that the Sr²⁺ uptake was fast and it was well fitted by the pseudo second order reaction model. Adsorption isotherm was well interpreted by Langmuir model. The maximum adsorption capacity was found to be 69.01 mg g^?1 at pH 7, 293 K, particles sizes = 200–400 μm and agitation speed 250 rpm. The thermodynamic study revealed that the process was spontaneous (ΔG ⁰ < 0), exothermic (ΔH ⁰ < 0) with a raised affinity for Sr²⁺ (ΔG ⁰ < 0, ΔS ⁰ > 0) and occurred by physical adsorption (E _a = 8.37 kJ mol^?1). FTIR analysis showed carboxylic acid and amino group presence on SCG surface playing a vital role in Sr²⁺ biosorption.     

Oxygen permeation and phase structure properties of partially A-site substituted BaCo0.7Fe0.225Ta0.075O3-δ perovskites

Ba_0.9R_0.1Co_0.7Fe_0.225Ta_0.075O_3-δ (BRCFT, R = Ca, La or Sr) membranes were synthesized by a solid-state reaction. Metal cation Ca²⁺, La³⁺ or Sr²⁺ doping on A-site partially substituted Ba²⁺ in BaCo_0.7Fe_0.225Ta_0.075O_3-δ oxides, and its subsequent effects on phase structure stability, oxygen permeability and oxygen desorption were systematically investigated by XRD, TG-DSC, H₂-TPR, O₂-TPD techniques and oxygen permeation experiments. The partial substitution with Ca²⁺, La³⁺ or Sr²⁺, whose ionic radii are smaller than that of Ba²⁺, succeeded in stabilizing the cubic perovskite structure without formation of impurity phases, as revealed by XRD analysis. Oxygen-involving experiments showed that BRCFT with A-site fully occupied by Ba²⁺ exhibited good oxygen permeation flux under He flow, reaching about 2.3 mL·min⁻¹ ·cm⁻² at 900 °C with 1 mm thickness. Of all the membranes, BLCFT membrane showed better chemical stability in CO₂, owing to the reduction in alkalinity of the mixed conductor oxide by La doping. In addition, we also found the stability of the perovskite structure under reducing atmospheres was strengthened by increasing the size of A-site cation (Ba²⁺>La³⁺>Sr²⁺>Ca²⁺).     

Crystal growth, structures, and optical properties of the cubic double perovskites Ba2MgWO6 and Ba2ZnWO6

Single crystals of the tungstates Ba₂MgWO₆ and Ba₂ZnWO₆ have been grown for the first time. The crystals were prepared with molten potassium carbonate acting as a flux. According to the single-crystal X-ray diffraction structure determination, the compounds crystallize in space group Fm3¯m of the cubic system with a double perovskite structure, A₂BB′O₆. These structural findings were confirmed with neutron diffraction on polycrystalline samples synthesized by a high-temperature solid-state route. Both sets of diffraction data reveal that the M²⁺ and W⁶⁺ cations are fully ordered on the B and B′ sites. Ba₂MgWO₆ and Ba₂ZnWO₆ exhibit room-temperature luminescence with green and yellow emissions, respectively.     

Kinetics and mechanism of some fast anation reactions of a series of substituted dien complexes of palladium(II). Temperature and pressure dependencies in weakly acidic aqueous solution1

Anation reactions of the type [Pd(L)(H₂O)]²⁺ + X^? »[Pd(L)X]⁺ + H₂O with L = 1, 4, 7-Et₃dien, 1, 1, 7, 7-Me₄dien and 1, 1, 4, 7, 7-Me₅dien and X^? = Cl^?, Br^?, I^? and N₃? have been studied kinetically as a function of [X?], temperature and pressure (up to 1 kbar). Second-order anation rate constants decrease with an increase in the size of L, and are accompanied by an increase in ΔH≠. For a given L the sequence Cl^? < Br^? < I^? < N₃^? holds, and the values of ΔS≠ and ΔV≠ are consistent with an associative mechanism. The results are discussed with reference to similar anation reactions previously investigated.     

Beam-gas chemiluminescent reactions of Eu and Sm with O3, N2O,NO2 and F2

Studies are made of the visible chemiluminescence resulting from the reaction of an atomic beam of samarium or europium with O₃, N₂O, NO₂ and F₂ under single-collision conditions (～10^?4 torr). The spectra obtained for SmO, EuO, SmF, and EuF are considerably more extensive than previously observed. The variation of the chemiluminescent intensity with metal flux and with oxidant flux is investigated, and it's concluded that the reactions are bimolecular. From the short wavelength curoff of the chemiluminescent spectra, the following lower bounds to the ground state dissociation energies are obtained: D⁰₀(SmO) > 135.5 +- 0.7 kcal/mole, D⁰₀(EuO) > 131.4 ± 0.7 kcal/mole, D⁰₀(SmF) > 123.6 ± 2.1 kcal/mole, and D⁰₀(EuF) > 129.6 ± 2.1 kcal/mole. Using the Clausius-Clapeyron equation, the latent heats of sublimation are found to be ΔH₁₀₅₂ (Eu) = 42.3 ± 0.7 kcal/mole for europium and ΔH₁₀₈₄(Sm) = 47.9 ± 0.7 kcal/mole for samarium. Total phenomena- logical cross sections are determined for metal atom removal. Relative photon yields per product molecule are calculated from the integrated chemiluminescent spectra and it is found that Sm + F₂ → SmF^* + F is the brightest reaction. The comparison of the photon yields under single-collision conditions with those at several torr shows that energy transfer collisons play an important role in the mechanism for chemiluminescence at the higher pressures. A simple model is presented which explains the larger photon yields of the Sm reactions compared to the Eu reactions in terms of the greater number of electronic states correlating with the reactants in the case of samarium.