Extraction of Cu(II) with Acorga M5640 using hollow fibre liquid membrane

The extraction of copper from sulphuric/sulphate solutions using a hollow fibre module as contactor was studied. The aldoxime Acorga M5640 was used as an extractant. The effects on the extraction rate of the flow-rates, the concentrations of copper and extractant, pH, and the presence of Na₂SO₄ in the feed phase were investigated. The overall mass transfer coefficient for copper extraction was calculated from the experimental data and was compared with the value evaluated by the resistance in the series model. The extraction process was found to be governed by the diffusion in the boundary aqueous layer and also by the chemical reaction. The kinetic data obtained were used to simulate the extraction of copper with the pseudo-emulsion-based hollow fibre with strip dispersion technique. The accordance between the results thus calculated and the experimental data was found to be satisfactory, particularly for dilute feed solutions.     

247. Intracatenar cross-linking in gelatin with carbodiimide

Under suitable conditions it is possible to introduce into dissolved denatured gelatin molecules intracatenar cross-links. Working with 2% solutions of commercial gelatin (M_n approximately 40000) at 40° and pH 5,75 and with water-soluble carbodiimid as a condensing agent we succeeded in inserting 7–8 intracatenar amide bonds per molecule. The number of cross-links introduced was determined by the decrease of free ? NH₂ and ? COOH groups. Using 4% solutions a gel melting point of the cross-linked preparations below 0° was obtained as compared with the gel melting point of untreated gelatin at 28°. The low viscosity and the behaviour in gel chromatography on Sepharose 6B show that the cross-linked peptide chains are fixed as rather dense coils. A small amount of the cross-linking reagent remains covalently bound to the protein, as was shown with tritium labeled carbodiimid. The side reactions possibly responsible for this occurrence are discussed. The bonds between reagent and gelatin are fairly stable at acidic pH, but labile at alkaline pH. The results of optical measurements (UV. and CD.) on cross-linked gelatin will be reported in another paper.     

Preparation of Silica-Gel Film with pH Indicators by the Sol–Gel Method

Gel films with various pH indicators were prepared by the sol–gel method without catalysts. The obtained gel films showed good response for various pH solutions as optical pH sensors and no leaching of the indicators was observed. The feature of absorption spectra of the indicators in the gel films was almost the same as that in the aqueous solutions. pKa of the indicators in the gel films was shifted with the increase of the TMOS content in the starting solutions. These results suggest that the pH indicators in the gel films were trapped in similar environment as in the solutions.     

Permeability control of metal ions using temperature- and pH-sensitive gel membranes

Temperature- and pH-sensitive copolymer gels were synthesized by the simultaneously occurring radiation-induced polymerization and self-bridging of acryloyl- -proline methyl ester (A-ProOMe) with acrylic acid (AAc) in aqueous solutions. The gel swelling behavior and the metal permeation characteristic of its gel membrane were investigated with regard to very slight changes of temperature and pH. The pH threshold of the swelling of a copoly(A-ProOMe/AAc, 70/30 mol%) gel in the range of 5–30°C lay in the region between pH 4.0 and 5.0. The permeability results of metal ions showed that at 40°C the gel membrane blocks the permeation of lithium (Li) and cesium (Cs) ions at pH values lower than 4.75 and 4.60, respectively. The permselectivity (P_Li/Cs value) of the two metal ions at 30°C was also studied and, as a result, its value was obtained to be 1.33 at pH 4.65 and 30°C. This permeation study indicates that the selective metal separation of copoly(A-ProOMe/AAc) gel membranes can be controlled by changing temperature and pH values.     

Ionic liquid as hollow fibre membrane carrier for extraction of fluoroquinolone antibiotics in milk coupled with high-performance liquid chromatography quantification

A new hollow fibre liquid phase microextraction technology with an ionic liquid as the carrier was developed to determine the fluoroquinolone antibiotics in milk. In this technology, a porous polypropylene hollow fibre was filled with aqueous ionic liquid and the extraction efficiency of different factors, such as the type of hollow fibre membrane carrier, the pH and ionic strength of the donor solution, the pH of the acceptor solution, the stirring rate and the extraction time, were investigated. The optimised extraction condition was: [OMim][BF₄] impregnated in the pores of the hollow fibre; 0.1?mol?L^?1 of Na₂HPO₄ (pH 11.0) as the acceptor solution was injected into the lumen of the hollow fibre; 0.1?mol?L^?1 H₃PO₄ (pH 5.0) was used as the donor solution; 600?rpm was selected as the stirring rate; 120?min was the optimum extraction time. The proposed method provided very high factors with 130-fold, 156-fold and 116-fold enrichment of ofloxacin, ciprofloxacin and enrofloxacin, respectively.     

Interpretation of relaxation and swelling phenomena in lyocell regenerated cellulosic fibres and textiles associated with the uptake of solutions of sodium hydroxide

The uptake of solutions of sodium hydroxide by lyocell fibre results in a phenomenon in textiles described as swelling–shrinkage. The response of woven fabrics in a tensile stress–relaxation experiment shows two time-dependent processes, corresponding to different mechanisms of pressure development. Rapid diffusion has been assigned to osmotic swelling through the interconnected pore structure of the fibre (D = 6–15 × 10⁻¹² m²/s), which is influenced by the extent of ionization of hydroxyl groups at the pore surfaces. A ratio for the cellulose and water dissociation constants (K_cell/K_w) of 70 provides best agreement with experimental data. A second slower diffusion process (D = 2–10 × 10⁻¹⁴ m²/s) is assigned to transport through the cellulose polymer structure, associated with the Na-cellulose transition. This can be modeled assuming an ion-exchange equilibrium, where the cellulose gel converts reversibly between compact hydrogen and expanded sodium forms, with K = 1.04 × 10¹⁴, in favour of the hydrogen form. The model successfully predicts the concentration dependence of the transition and the movement to higher concentration with external constraint. The slow diffusion process only becomes apparent at high alkali concentrations, as the pores in the fibre collapse due to the expansion of the gel. Continued gel-diffusion is only possible through the polymer phase, which then dominates over fast pore-diffusion.     

Preparation of Forsterite by the Geopolymer Technique—Gel Compositions as a Function of pH and Crystalline Phases

Mg-bearing silicate precursor gels have been prepared by mixing 0.74 mol/L sodium metasilicate and 1.48 mol/L magnesium nitrate solutions. Caustic soda solution of 1.0 mol/L concentration was introduced to regulate pH. The magnesium nitrate solution was added dropwise to the sodium silicate solution in equi-volume at various pH values. Raw and heat-treated gels were characterized by XRF, TG-DTA, XRD and FE-SEM. As a result, gel compositions were dependent on pH values of mixing solutions. The pH value yielding stoichiometric forsterite composition, MgO/SiO₂ = 2 was reached at pH 9.3. In addition, this value was pH 8.4 for stoichiometric enstatite composition, MgO/SiO₂ = 1. With decreasing pH from 9.3, the ratio became less than 2 and forsterite and enstatite precipitated by heating the gels. With increasing pH from 9.3, the ratio became more than 2 and forsterite and periclase precipitated by heating the gels. DTA curves showed a characteristic exothermic peak centered at 700–900^∘C, indicating relatively low temperature formation of crystalline phases due to the presence of polycondensed frame works of silicates in the precursor gels.     

Adsorption of Apollo reactive dyes on poly(N,N dimethylamino ethylmethacrylate) hydrogels

Poly(N,N-dimethylamino ethylmethacrylate) [P(DMAEMA)] hydrogels were prepared by irradiating the ternary mixtures of dimethylamino ethylmethacrylate (DMAEMA)/ethyleneglycol dimethacrylate (EGDMA)/water (H₂O) by γ-rays at ambient temperature. The swelling of four types of DMAEMA hydrogels in distilled water is higher than the swelling of these hydrogels in dye solutions. The value of equilibrium swelling of P(DMAEMA)1 hydrogel was 338% at pH 7.0 in distilled water, while it was 325% and 326% at pH 7.0 in Apollofix Red (AR) and Apollofix Yellow (AY) solutions, respectively. The adsorption capacity of P(DMAEMA)1 hydrogel was found to increase from 85 to 131 mg for AR g⁻¹ dry gel and from 58 to 111 mg for AY g⁻¹ dry gel with decreasing pH of the dye solutions.     

Polymerization of pyrrole on cellulose fibres using a FeCl3 impregnation- pyrrole polymerization sequence

Polypyrrole was polymerized on the surface of cellulose fibres using a sequence of fibre impregnation in FeCl₃ solutions, thickening and re-dispersion in a pyrrole solution. ζ-Potential and adsorption isotherms of the FeCl₃-cellulose systems showed that the adsorption of iron III was associated with the formation of free Fe³⁺ cations in the impregnation liquor. Moreover, under the test conditions applied, the amount of adsorbed iron III was not sufficient to promote the polymerization of a adequate amount of pyrrole on the fibre surface. Optimization of the polymerization reaction required that the FeCl₃ concentration in the impregnation liquor be increased to approximately 1 mol/l with a subsequent decrease of pH to approximately1.8. Based on scanning electron (SEM) micrographs and the low cellulose polymerization degree measured after pyrrole polymerization, we concluded that the decrease in the electric resistance of bulky polypyrrole/cellulose compounds was associated with a not negligible degradation of the cellulose fibres due to acid hydrolysis and the subsequent impossibility to prepare hand sheets with modified fibres due to the insufficient strength of the wet fibre network. The results of this investigation bring into question the use of FeCl₃-pyrrole-cellulose systems for the elaboration of conducting paper sheets with good and stable mechanical properties.     

Entrap-immobilization of enzyme on composite gel fibre using a gel formation of cellulose acetate and metal (Ti,Zr) alkoxide

An enzyme is entrap-immobilized in the gel fibre of a cellulose acetate-metal oxide composite using a gel formed from cellulose acetate and metal (Ti, Zr) alkoxide. It seems that the gel formation is due to coordination bondings between OH and carbonyl groups on the pyranose ring and the metal. The gel fibre is stable in common solvents, phosphate solution and electrolyte solution over a wide range of pH from 4 to 10. The immobilized enzyme is stable for a long period and can be used in a packed column. The pH maximum of activity shifts to a more alkaline side compared to the native enzyme, reflecting the amphoteric property of the metal oxide. This immobilization can be easily and quickly accomplished. However, the process is not applicable to an enzyme which is deactivated by exposure to an organic solvent.     

Sorption of a complex of europium (III) with acetylacetone on hydrophobized hexadecyl silica gel and hyper crosslinked polysterene

The sorption of a complex of europium (III) with acetylacetone on silica gel chemically modified with hexadecyl groups (SiO₂-C₁₆) and hyper crosslinked polystyrene (HLPS) was studied. Maximum extraction was observed at pH 5–7 when SiO₂-C₁₆ was used as the sorbent and at pH 4–7 in the case of crosslinked polystyrene. The partition coefficients for HLPS and silica gel were calculated as 7 × 10³ and 1 × 10² cm³/g, respectively. Quantitative extraction of the europium (III) complex was possible in dynamic conditions using a microcolumn (length, 10 mm; internal diameter, 3mm) packed with HLPS at pH 5 (10–50 mL sample volume). Desorption of europium using solutions of nitric acid at different concentrations was investigated. Quantitative desorption was achieved using 5 mL of 1 M HNO₃. A linear range of detection was observed at an amount of europium from 5 to 25 μg in a 10-mL sample (650 nm).     

Microscopic Imaging of Chiral Amino Acids in Agar Gel through Circularly Polarized Luminescence of EuIII Complex

We recently found that [Eu(pda)₂]^? (pda: 1,10‐phenanthroline‐2,9‐dicarboxylic acid), which has an achiral structure in crystals, exhibits circularly polarized luminescence (CPL) in aqueous solutions containing chiral amino acids such as arginine and histidine. CPL measurements were performed for agar gel, which includes an aqueous solution of [Eu(pda)₂]^? and chiral arginine or histidine. The spectral shape, concentration, and pH dependences on CPL intensity in the agar gels were very close to those in aqueous solutions, indicating that the CPL of the Eu^III complex in the agar gels was induced by mechanism similar to that in aqueous solutions. We performed spatially resolved CPL measurements using a laboratory‐built microscopic CPL spectroscopic system for agar‐gel samples, where d ‐ and l ‐ amino acids were separately dispersed. We successfully recorded CPL imaging maps showing spatial dispersions of d ‐ and l ‐amino acid in the agar gels.     

Surface Modification of TiO2 Nanoparticles with Vitamin B12: Relationships between Vitamin B12 Content and Its Optical Properties

Anatase TiO₂ nanoparticles (NPs) with particle size of 10–20 nm were prepared via sol gel technique. The as‐synthesized NPs were immerged in vitamin B₁₂ (VB₁₂) solutions with different concentrations. The in‐ fluences of the solution concentration on photoluminescence and photocatalytic activity of the modified NPs were studied. Fourier transform infrared spectroscopy (FTIR) results demonstrated that TiO₂ NPs adsorb VB₁₂ molecules and that a new band is formed at ～2300 cm^?1. The VB₁₂ loading process led to dimin‐ ishing of the aggregation of NPs and formation of a fibre shape structure. The best photoactivity and PL effect among the modified samples was related to sample ‘d’. The optimum processing conditions to achieve this sample was found to be VB₁₂ concentration of 5 g/L.     

Stabilization of glucose oxidase fromPenicillium vitale entrapped in high-concentration gels

Glucose ixidase fromPenicillium vitale was immobilized in a 2-hydroxyethyl methacrylate (HEMA) gel containing 0.3 to 2% of methacrylic acid (MAA) or MAA neutralized by allylamine (AA). Depending on the MAA quantity of MAA in the gel, the thermal irreversible inactivation(k _in) constants of the immobilized enzymes sharply decrease at gel concentrations higher than 29 to 50% at pH 5.8. A 220- to 250-fold decrease ofk _in was observed in 60 to 80% gel. The inactivation rate of enzyme in HEMA gel also decreases considerably under the action of urea. Over the range of pH 5.0 to 9.0 thek _in of the native enzyme depends on pH by a degree of 2.1, and of the immobilized enzyme, 0.3 to 0.55. Over the pH range of 5.2 to 5.7,k _in of the native and immobilized enzymes are approximate, whereas at pH 8 and over the difference betweenk _in values exceeds four orders of magnitude. The activity dependence of the immobilized enzyme on pH is shifted two units to the alkaline region. This shift depends on the ionic strength of the solution. This dependence is best reflected in the high gel concentrations. A mechanism of enzymes stabilization in the concentrated HEMA gel is discussed.     

Features of the Interaction of Alcian Blue with Gels Based on Copolymer of <Emphasis Type="Italic">N</Emphasis>-Vinylcaprolactam and Methacrylic Acid

The interaction of N-vinylcaprolactam–methacrylic acid copolymer hydrogel and N-vinylcaprolactam homopolymer hydrogel with alcian blue in aqueous solutions is studied. It is shown that copolymer gel are thermo- and pH-sensitive. Dye sorption by the copolymer gel and gel swelling degree depends on the pH of the solution. The features of the system behavior resulting from the pH sensitivity of both the gel and the dye are shown. The thermocollapse of gels incubated in aqueous solutions of alcian blue is studied. It is shown that the transition temperature of N-vinylcaprolactam–sodium methacrylate copolymer gel to the collapsed state decreases with the dye absorption. The temperature-induced collapse of homopolymer gels in dye solutions is reversible, while the copolymer gel mass restores incompletely during the return temperature decrease. The dye absorption by the copolymer gel leads to decreased hysteresis.     

Effects of amine-pretreatment of silica gel on the TLC behaviour of rare earths

The TLC behaviour of all the rare earths except Pm has been examined on silica gel pretreated with aqueous solutions of four different amines [iminodi-2-ethanol, tris(hydroxymethyl)aminomethane, nitrilotri-2-ethanol, and 1,3-diazole] in a 1 mol/l NH₄Cl solution. The Rf value of each metal decreased with increasing pKa value of the amines and also with increasing concentration and pH of the amine solution used for the pretreatment. The technique is simple and reproducible, and makes it possible to arbitrarily regulate the adsorbability of silica gel. Thus, the use of the amine-treated silica gels serves to develop many solvent systems for the separation of the rare earths.     

Effect of pH on the formation and combustion process of sol-gel auto-combustion derived NiZn ferrite/SiO2 composites

A nitrate-citrate-silica gel was prepared from metallic nitrates, citric acid, and silica powder by sol-gel process, and it was further used to synthesize Ni_0.5Zn_0.5Fe₂O₄/5wt% SiO₂ nanocomposites by auto-combustion. The effect of pH on the formation of NiZn ferrite/SiO₂ and thermal properties of gel precursors was studied by XRD, IR, EPR, TGA and DTA techniques. The results revealed that the ratio of the citrate ion to the nitrate ion is directly related to the pH of the solution. The pH in the starting solution affects the combustion process, and then determines the particle size of the as-synthesized powder. The EPR parameters (peak-to-peak linewidth, g factor, and spin number) increased with increasing pH, whereas the spin-spin relaxation time (T₂) decreased. The thermal stability and enthalpy of the decomposition process in air decreased with increasing pH, whereas the enthalpy in nitrogen increased. Moreover, the activation energy (E_a) of thermo-oxidative degradation of the gel precursor at pH 3 was much lower than the gel precursor at pH 5 and 7, and that increased with increasing pH.     

Ion-sieve properties of an inorganic gel loaded with some complex cations of cobalt(III) a radiochemical study

Distribution coefficients of a number of uni-, di-, tri- and quadrivalent metal ions have been determined on chromium ferrocyanide gel loaded with [Co(NH₃)₆]³⁺ and [Co(en)₃]³⁺ ions at 25 °C, and the observed K_d values are compared with those obtained on the unloaded exchanger in H-form. The gel is found to develop ion-sieve properties after being loaded with the complex cations. The variation in K_d values with the pH of Rb⁺, Cs⁺, Ti⁺ and Ag⁺ solutions has also been studied to understand the mechanism of their uptake.     

Crystal growth in syndiotactic poly(vinyl alcohol) hydrogels

Aqueous solutions of syndiotacticity-rich poly(vinyl alcohol) (s-PVA) form gels easily. The optimum condition of growth of the calcium tartrate crystal formed by diffusing calcium chloride into hydrogels containing tartaric acid was studied with use ofs- PVA of a syndiotacticity of 56 % and a degree of polymerization of 1460. The crystal grew in the gel of the concentrations of 2 % s-PVA and of 0.5 N tartaric acid at pH=4. The relation between the formation of Liesegang rings and shear modulus of a gel was studied by diffusing silver nitrate into gels containing potassium chromate. The distance between rings decreased with increasing shear modulus of a gel in the range from 670 to 7500 dyne/cm². The Liesegang rings were not formed for the shear modulus gel for 280 and 16200 dyne/cm₂.     

Physical-chemistry of sodium silicate gelation in an alkaline medium

The behavior of sodium silicate solutions in an alkaline medium has been studied in the 11.56–9 pH range by adding different amount of hydrochloric acid into a concentrated commercial solution ([Si] = 7 mol/L, Si/Na = 1.71, pH = 11.56). The formed products and their evolution during long ripening (up to 150 days) have been characterized by cryo-SEM, elementary analysis (ICP-AES), X-ray diffraction and surface area and relative density measurements. In the studied narrow ranges of pH (11.56–9) and silicon concentration (7–0.2 mol/L) four different situations have been observed: (i) a stable and clear solution, (ii) a reversible and transparent physical gel; (iii) a soluble white gel characterized by a significant contraction during ripening and (iv) an irreversible gel which presents a slow syneresis leading to a consolidate solid. The characterizations of the different solids, liquids and gels have shown that the observed behaviors were the results of the formation of nanometric soluble NaSi_1.87O_4.24 particles and/or insoluble silica-like (NaSi_12.66O_25.82) grains and of the contribution of a dissolution/precipitation mechanism.