Synthesis and photophysical behavior of a water-soluble fluorescein-bearing polymer for Fe<Superscript>3+</Superscript> ion sensing

An acrylic monomer bearing xanthene group, acryloylfluorescein (Ac-Flu) was synthesized from fluorescein and acryloyl chloride in the presence of triethylamine in dry dichloromethane (CH₂Cl₂) at room temperature. The synthesized Ac-Flu was identified by IR, MS and ¹HNMR spectra. Copolymer of Ac-Flu and acrylamide (AM) was synthesized with thermal initiator and it was characterized by the method of IR, UV–Vis and DSC. The photophysical behaviors of Ac-Flu and its copolymer were explored by recording the fluorescence spectra in solution, solid state and film in detail. In addition, the ability of the copolymer to detect different metal cations (Mn²⁺, Fe³⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺) in aqueous solution was investigated. The results showed that poly(Ac-Flu-co-AM) had a good linear response between the logarithm of concentration of Fe³⁺ (lg[Fe³⁺]) against the relative fluorescence intensity for Fe³⁺ concentration. The results suggest that this copolymer may offer potential as a reusable polymer sensor for Fe³⁺ ion in aqueous solution.     

Co-precipitation of radionuclides by water-soluble melanin from the chitin—melanin glucan complex “Mikoton” in solutions

Co-precipitation of ²³³UO₂ ²⁺, ¹⁵²Eu³⁺, and ⁹⁰Sr²⁺ on melanin isolated from the preparation Mikoton, a chitin—melanin glucan complex, was studied in solutions. It was shown that the degree of coprecipitation (α) of the radionuclides depended on the solution content of polymer. The maximum value of α was at least 80% for metal-ion concentration 250 mg/L and 0.8% melanin. It was hypothesized that UO₂ ²⁺, Eu³⁺, and Sr²⁺ were bound mainly by carboxylic and phenolic groups of melanin. The developed co-precipitation process could be recommended for isolation and concentration of radionuclides from low-salt process solutions and natural media.     

Autothermal reforming of methane to syngas with palladium catalysts and an electric metal monolith heater

The autothermal reforming of methane to syngas for use in the Fischer-Tropsch synthesis was studied in this work over PdO containing various combinations of CeO₂, BaO or SrO in a washcoated form on a metallic monolith at atmospheric pressure. This study focused on the autothermal operation of the system, in which an electric heater inside the reactor was used only to reach the ignition temperature, and thereafter the autothermal reaction successfully sustained itself without any external heat source. It was concluded from the experiments that the PdO/Al₂O₃ catalyst was better than the others, except for PdO-CeO₂-BaO-SrO/Al₂O₃, which showed similar performance in terms of the CH₄ conversion and H₂+CO selectivity, while affording a higher H₂/CO ratio (close to ca. 3) than the PdO/Al₂O₃ catalyst did (close to ca. 2). The gas hourly space velocity and O₂/CH₄ ratio governed the methane conversion, while the H₂O/CH₄ ratio controlled the H₂/CO ratio. A methane conversion of ∼87%, H₂+CO selectivity of ∼94%, H₂/CO ratio of ∼2.9, and M factor ∼2.15 were obtained under the conditions of a gas hourly space velocity (GHSV) of 120,000 h⁻¹, O₂/CH₄=0.6 and H₂O/CH₄=0.5.     

Direct incorporation of vanadium into three-dimensional KIT-6: 2. Reactivity test for styrene oxidation

The direct incorporation of vanadium into the three-dimensional (3-D) cubic Ia3d mesostructure designated as V-KIT-6 was prepared, and the material obtained therein showed a very high specific surface area of ∼1,000 m²/g with tunable pore diameters in a narrow distribution of sizes, ∼5.7 to 6.0 nm. The coordination and nature of the V sites in V-KIT-6 were characterized by ⁵¹V-spin-echo NMR analysis. It shows that after calcination, the V⁴⁺ species are totally oxidized to the V⁵⁺ state with 4- and 6-coordinated V-O environments in a highly dispersed state with much less crystalline V₂O₅ formation. The calcined V-KIT-6 materials showed excellent catalytic activity in the direct oxidation of styrene using tert-butyl hydroperoxide (TBHP) as an oxidant.     

Uptake and oxidation of malonaldehyde by cultured mammalian cells

Primary cultures of rat skin fibroblasts were used as a model system to investigate the cellular uptake and oxidation of malonaldehyde (MA). The cells were grown in a medium containing 10⁻⁵ M, 10⁻⁴ M or 10⁻³ M concentrations of [1,3-¹⁴C]MA. There was a limited, concentration-dependent uptake of MA by 24 hr (∼4% at all concentrations). The uptake of [1,2-¹⁴C]acetate by 24 hr was ∼24%; 83–89% of the¹⁴C in the MA taken up was oxidized to¹⁴CO₂ by 24 hr and ∼5% was recovered in the major lipids. Despite its low uptake and rapid oxidation to CO₂, pretreatment of the cells with 10⁻³ M MA for 24 hr produced a latent inhibition of [¹⁴C]glucose oxidation. Limited cellular uptake of MA may explain the tolerance of cells grown in culture to relatively high MA concentrations.     

A study on the photo-reductive precipitation rate of europium sulfate from rare earth mixture by addition of hydrogen peroxide

The influence of H₂O₂ on the photo-reductive precipitation of Eu³⁺ from a solution containing Sm³⁺, Eu³⁺ and Gd³⁺ was investigated. The solution contains isopropanol as a reduction agent, ammonium sulfate as a precipitation agent, and hydrogen peroxide as an acceleration agent of precipitation rate. A mercury lamp emitting a wavelength of 254 nm was used as a light source. Adding a small amount of H₂O₂ considerably increased the photo-reductive precipitation rate of Eu³⁺. OH radicals obtained from the photodecomposition of H₂O₂ oxidized isopropanol into the radical (CH₃)₂C’OH and the resulting radicals reduced Eu³⁺ rapidly. It was found that the organic radical has the ability to reduce only Eu³⁺ in the solution containing Sm³⁺, Eu³⁺ and Gd³⁺. The precipitation yields of Eu, Sm and Gd were about 99%, 10% and 4%, respectively. It was also found that the Sm and Gd were not photo-reduced and co-precipitated with Eu.     

Some environmentally friendly formulations as inhibitors for mild steel corrosion in sulfuric acid solution

The corrosion resistance of mild steel in 1 M H₂SO₄ solution was evaluated after addition of Sn²⁺ and Zn²⁺, N-acetylcystein (ACC) and S-benzylcystein (BzC) as a function of concentration (5–1000 μM) and solution temperature (35–50°C). Eight blends were also investigated. Both polarization resistance (R _p) and electrochemical impedance spectroscopy (EIS) were employed. For single additives, Zn²⁺ ions acted as accelerator for mild steel corrosion while the other additives showed good performance. The most effective additive was Sn²⁺. Adsorption of Sn²⁺, ACC and BzC obeyed the Temkin adsorption isotherm and had a very high negative value of free energy of adsorption (−ΔG°_ads). All blends provided good inhibition which increased with rise in temperature. Corrosion kinetic parameters such as activation energy (E _a) and the pre-exponential factor (λ) were calculated and discussed. EIS revealed that the interface of the uninhibited and inhibited systems can be represented by the simple equivalent circuit R _e(R _ct Q _dl).     

Nonoxidative dehydrogenation and aromatization of methane over W/HZSM‐5‐based catalysts

Highly active and heat‐resisting W/HZSM‐5‐based catalysts for nonoxidative dehydro‐aromatization of methane (DHAM) have been developed and studied. It was found from the experiments that the W−H₂SO₄/HZSM−5 catalyst prepared from a H₂SO₄‐acidified solution of ammonium tungstate (with a pH value at 2–3) displayed rather high DHAM activity at 973–1023 K, whereas the W/HZSM‐5 catalyst prepared from an alkaline or neutral solution of (NH₄)₂WO₄ showed very little DHAM activity at the same temperatures. Laser Raman spectra provided evidence for existence of (WO₆)^n- groups constructing polytungstate ions in the acidified solution of ammonium tungstate. The H₂‐TPR results showed that the reduction of precursor of the 3% W–H₂SO₄/HZSM‐5 catalyst may occur at temperatures below 900 K, producing W species with mixed valence states, W⁵⁺ and W⁴⁺, whereas the reduction of the 3% W/HZSM‐5 occurred mainly at temperatures above 1023 K, producing only one type of dominant W species, W⁵⁺. The results seem to imply that the observed high DHAM activity on the W–H₂SO₄/HZSM‐5 catalyst was closely correlated with (WO₆)^n- groups with octahedral coordination as the precursor of catalytically active species. Incorporation of Zn (or La) into the W–H₂SO₄/HZSM‐5 catalyst has been found to pronouncedly improve the activity and stability of the catalyst for DHAM reaction. Over a 2.5% W–1.5% Zn–H₂SO₄/HZSM‐5 catalyst and under reaction conditions of 1123 K, 0.1 MPa, and GHSV=1500 ml/(h g−cat.), methane conversion (XCH₄) reached 23% with the selectivity to benzene at ∼96% and an amount of coke for 3 h of operation at 0.02% of the catalyst weight used. This revised version was published online in July 2006 with corrections to the Cover Date.     

Highly selective and sensitive Th<Superscript>4+</Superscript>-PVC-based membrane sensor based on 2-(diphenylphosphorothioyl)-<Emphasis Type="Italic">N</Emphasis>′,<Emphasis Type="Italic">N</Emphasis>′-diphenylacetamide

A Th⁴⁺ ion-selective membrane sensor was fabricated from poly (vinyl chloride) (PVC) matrix membrane containing 2-(diphenylphosphorothioyl)-N′,N′-diphenyl acetamide (DPTD) as a neutral carrier, potassium tetrakis (p-chlorophenyl) borate (KTpClPB) as anionic excluder and o-nitrophenyloctyl ether (NPOE) as a plasticizing solvent mediator. The effects of the membrane composition, pH and additive anionic influence on the response properties were investigated. The sensor, comprising 30% PVC, 63% solvent mediator, 4% ionophore and 3% anionic additive demonstrates the best potentiometric response characteristics. It displays Nernstian behavior (15.2 ± 0.5 mV per decade) over the concentration range 1.0 × 10⁻²–1.0 × 10⁻⁶ M. The detection limit of the electrode is 6.3 × 10⁻⁷ M (∼140 ng/ml). The response time of the electrode is 30 s .The sensor can be used in the pH range 3.0–9.0 for about 6 weeks. The membrane sensor was used as an indicator electrode in the potentiometric titration of Th⁴⁺ ions with EDTA. It was successfully applied to the determination of thorium ions in binary mixture.     

Physicochemical and corrosive properties of oxidation catalysts based on solutions of Mo-V-phosphoric heteropoly acids

Modified aqueous solutions of Mo-V-phosphoric heteropoly acids (HPAs) are used as high-performance catalysts for the oxidation of substrates from different classes with oxygen. The oxidation of n-butenes to methyl ethyl ketone (MEK) with oxygen in the presence of aqueous solution (6 × 10⁻³ M Pd + 0.25 M HPA-7′), where HPA-7′ is a modified HPA whose molecular formula is H₁₂P₃Mo₁₈V₇O₈₅, is an industrially important process. At the first Pd-catalyzed stage of the process, n-C₄H₈ is oxidized with HP acid. At the second stage, the catalyst is regenerated and the reduced form of HPA-7′ is oxidized with atmospheric oxygen, closing the catalytic cycle. In such two-stage redox processes, HPA solutions act as reversible oxidizers whose physicochemical properties are continuously changing. The modified solutions of HPAs are attractive because of their thermal stability and increased regeneration rates. However, no data have yet been reported in the literature about their physicochemical and corrosive properties. This undoubtedly hinders the practical application of processes involving these solutions. Using the 0.25 M HPA-7′ solution as an example, we show how the physicochemical properties of the catalyst change. During the first stage of the process, the pH, density (ρ), and viscosity (η) of the HPA solution increase to their maxima, but its redox potential (E) decreases to its minimum. At the second stage, E increases, while ρ, η, and pH decrease to their initial values. Thus, in the processes with the alternating reduction and oxidation of the HPA-based catalyst solution, the changes in the physicochemical properties of the catalyst are completely reversible. We first have obtained the data on the corrosive properties of the modified HPA-7′ solution with respect to metals and alloys widely used in industrial processes. The corrosion stability of various engineering materials against 0.25 M solution of HPA-7′ was found to decrease in the series Ti (∼0.009 mm year⁻¹) > 06KhN28MDT > 10Kh17N13M2T > 12Kh18N10T > KhN65MV (∼0.68 mm year⁻¹). The unique ability of the modified Mo-V-P HPA solutions to recover completely their properties after regeneration with oxygen permits one to use them successfully for long periods of time in the many-cycled processes. This opens up good prospects for the development of industrial homogeneous catalytic oxidative processes involving these HPAs.     

Synthesis and properties of a new green water‐soluble polymer for proton and metal‐cation sensing

A novel water‐soluble colored polymer, based on 1,8‐naphthalimide, was synthesized through a series of easy reactions with high yields. It emitted green fluorescence both in an aqueous solution and in a solid state. Fluorescence characteristics of the polymer as a function of pH were investigated in aqueous solutions. The polymer solution showed weaker fluorescence in a more acidic medium. When the pH of the solution was higher than 5, stronger fluorescence could be seen with a pK_a value of 3.5. The presence of metal cations (Mn²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺) could quench the fluorescence intensity of an aqueous solution of this polymer to different levels. It was highly sensitive to Cu²⁺ and Fe³⁺ present in the studied system. The results suggest that this newly synthesized compound could work as a polymeric sensor responding to water polluted by Cu²⁺, Fe³⁺, and protons. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

A Novel Dinucleating Ligand-Containing Hexabenzimidazoles and Its Dinuclear Zinc Complex Bridged by a Carboxylate Group for the Hydrolysis of 2-Hydroxypropyl-p-nitrophenyl phosphate

A dinuclear zinc(II) complex with the ligand bis{tris[2-(1-methylbenzimidazole-2-yl)ethyl]-methylamine}nitrilotriacetic acid sodium salt, L, was synthesized and characterized. Complex formation of L with Zn²⁺ in aqueous acetone was studied by Zn²⁺ titration using ¹H NMR and UV–vis spectroscopies. Analysis of the titration data indicates the formation of a dizinc complex. The ν_as(COO⁻) and ν_s(COO⁻) stretches were observed at 1572 and 1450 cm⁻¹, respectively. The low separation of the stretches, Δ_exp = 115 cm⁻¹, is an indication of chelating coordination of the carboxylate group between the two zinc(II) ions. The catalytic activity of [LZn₂]³⁺ 1, as a model for phosphatase that catalyze chemical transformation of phosphate ester, in the hydrolysis of the RNA model, 2-hydroxypropyl p-nitrophenyl phosphate, was examined in aqueous acetone buffer solution, pH 7.0–9.5. The mechanism of the catalytic hydrolysis suggests that the rate of acceleration is due to what is called double Lewis acid activation.     

Behavior of acrylic acid–itaconic acid hydrogels in swelling,shrinking, and uptakes of some metal ions from aqueous solution

An experimental research of the absorption properties of metal ions onto synthetic hydrogel obtained by solution polymerization of acrylic acid and itaconic acid in presence of N,N′‐methylenebisacrylamide as crosslinking agent was carried out. The swelling behavior in aqueous salt solutions was studied as a function of divalent cation concentration (Cu²⁺, Zn²⁺, Ni²⁺, Co²⁺, Cd²⁺, Pb²⁺, Hg²⁺) in the external solution ranging from 10^?5 to 1M, at 25°C. The ability of these hydrogels to bind cations was measured at different pH values and metal ion concentrations. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 530–536, 2003     

Binding of heavy metal ions by formaldehyde-polymerized peanut skins

Peanut skin, when treated with formaldehyde to polymerize tannins, is a highly efficient substrate for removal of many heavy metal ions from aqueous waste solutions. The ions Ag¹⁺, Cd²⁺, Cr⁶⁺, Cu²⁺, Hg²⁺, Ni²⁺, Pb²⁺, Zn²⁺, as well as Ca²⁺ and Mg²⁺, were contacted with formaldehyde-treated peanut skin. Quantitative removal could be achieved with Ag¹⁺, Cd²⁺, Cu²⁺, Hg²⁺, Pb²⁺, and Zn²⁺. Capacity of the substrate for ions was promising for Pb²⁺ (2.1 meq/g substrate), Cu²⁺ (3.0 meq/g), and Cd²⁺ (1.3 meq/g). Sorption from a solution containing Cd²⁺, Cu²⁺, Hg²⁺, Ni²⁺, Pb²⁺, Zn²⁺, on a packed column of formaldehyde-treated peanut skin indicated that Hg²⁺, Pb²⁺, and Cu²⁺ were rapidly and completely bound to the packing, while Cd²⁺, Ni²⁺, and Zn²⁺ were poorly bound until the preferred ions had been removed from solution.     

Gold supported on well-ordered ceria films: nucleation, growth and morphology in CO oxidation reaction

Structure of gold nanoparticles formed by physical vapor deposition onto thin ceria films was studied by scanning tunneling microscopy (STM). Gold preferentially nucleates on point defects present on the terraces of the well-ordered, fully oxidized films to a low density. The nucleation expands to the terrace step edges, providing a large variety of low-coordinated sites. Only at high coverage, the Au particles grow homogeneously on the oxygen-terminated CeO₂(111) terraces. The morphology of Au particles was further examined by STM in situ and ex situ at elevated (up to 20 mbar) pressures of O₂, CO, and CO + O₂ at 300 K. The particles are found to be stable in O₂ ambient up to 10 mbar, meanwhile gold sintering emerges at CO pressures above ∼1 mbar. Sintering of the Au particles, which mainly proceeds along the step edges of the CeO₂(111) support, is observed in CO + O₂ (1:1) mixture at much lower pressure (∼10⁻³ mbar), thus indicating that the structural stability of the Au/ceria catalysts is intimately connected with its reactivity in the CO oxidation reaction.     

A Comparative Study on Characterization of Aluminium Tungstate and Surfactant-Based Aluminium Tungstate Cation-Exchangers: Analytical Applications for the Separation of Toxic Metal Ions

Two cation-exchange materials, aluminium tungstate (AT) and sodium dodecyl sulphate–aluminium tungstate (SDS–AT), were synthesized. Both samples were characterized by Fourier transform infrared spectroscopy, X-ray diffraction analysis and scanning electron microscopy. The distribution coefficients for various metal ions on SDS–AT cation-exchange material were performed in different solvent systems. On the basis of distribution coefficient values, the SDS–AT cation-exchange material was found to be selective for the very toxic metal ion, Cr³⁺. The hybrid cation-exchange material offered a variety of technological opportunities for quantitative determination and separation of Cr³⁺ from synthetic mixtures of metal ions. Some binary and ternary separations of metal ions; viz., Cd²⁺–Cr³⁺, Zn²⁺–Cr³⁺, Cu²⁺–Cr³⁺, Pb²⁺–Cr³⁺, Mg²⁺–Pb²⁺–Cr³⁺ and Mg²⁺–Cd²⁺–Cr³⁺, were performed using a packed column of this material.     

The competitive heavy metal removal by hydroxyethyl cellulose-g-poly(acrylic acid) copolymer and its sodium salt: The effect of copper content on the adsorption capacity

Summary Crosslinked hydroxyethyl cellulose-g-poly(acrylic acid) (HEC-g-pAA) graft copolymer was prepared by grafting of acrylic acid (AA) onto hydroxyethyl cellulose (HEC) using [Ce(NH₄)₂(NO₃)₆]/HNO₃ initiator system in the presence of poly(ethyleneglycol diacrylate) (PEGDA) crosslinking agent in 1:1 (v/v) mixture of methanol and water at 30 °C. Carboxyl content of copolymer was determined by neutralization of –COOH groups with NaOH solution and sodium salt of copolymer (HEC-g-pAANa) was swelled in distilled water in order to determine the equilibrium swelling value of copolymer. Both dry HEC-g-pAA and swollen HEC-g-pAANa copolymers were used in the heavy metal ion removal from three different aqueous ion solutions as follows: a binary ion solution with equal molar contents of Pb²⁺and Cd²⁺, a triple ion solution with equal molar contents of Pb²⁺, Cu²⁺ and Cd²⁺, and a triple ion solution with twice Cu²⁺molar contents of Pb²⁺and Cd²⁺. Higher removal values on swollen HEC-g-pAANa were observed in comparison to those on dry polymer. The presence of Cu²⁺decreased the adsorption values for Pb²⁺ and Cd²⁺ ions on both types of HEC copolymer. However, with further increase in Cu²⁺ content both dry and swollen copolymers became apparently selective to Cu²⁺ removal and Cu²⁺ removal values exceeded the sum of adsorption values for Pb²⁺ and Cd²⁺. Maximum metal ion removal capacities were 1.79 and 0.85 mmol Me²⁺/g_polymer on swollen HEC-g-pAANa and dry HEC-g-pAA, respectively.     

Selective Facilitated Transport of Uranium(VI) Across a Bulk Liquid Membrane Containing Benzoyltrifluoroacetone as Extractant-Carrier

Abstract

A study has been made on carrier-mediated transport of uranium(VI) using a bulk liquid membrane prepared by dissolving benzoyltrifluoroacetone (HBTA) in carbon tetrachloride. The source phase comprised of a solution of UO₂ ²⁺ or its binary mixture with other cations such as Th⁴⁺, Hf⁴⁺, Zr⁴⁺, Fe³⁺, La³⁺, Cu²⁺, Co²⁺, Mn²⁺, Ni²⁺, and Zn²⁺ in aqueous solutions of pH 6.0, while 0.1 M hydrochloric acid was serving as a stripping agent in the receiving compartment. The interference from Th⁴⁺ and a few other cations could be eliminated by using trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid (DCTA) as a proper masking agent in the feed solution. Various factors influencing the transport process have been studied and an uphill transport (>99%) of uranium(VI) from the source phase could be accomplished under optimum conditions.     

Electrochemical oxidation of <Emphasis Type="Italic">p</Emphasis>-sulfonated calix[8]arene

The water-soluble p-sulfonated sodium salt of calix[8]arene (III) was synthesized. The product was characterized by FT-IR, NMR and UV–Vis spectra.Then the electrochemical behaviors of p-sulfonated sodium salt of calix[8]arene in NaAc+HAc (pH = 4) buffer solution was studied. In aqueous solution, p-sulfonated calix[8]arene can be oxidized when the potential is more than 0.7 V vs SCE. It was confirmed that the reaction was a two-electron irreversible electrochemical reaction. The transfer coefficient, α, was measured as 0.7. At 25°, the diffusion coefficient of p-sulfonated calix[8]arene was determined as 8.6 × 10⁻⁷ cm² s⁻¹. The diffusion activation energy of p-sulfonated calix[8]arene was 18.9 kJ mol⁻¹ at pH = 4.     

Dissolution of alumina ceramics in HCl aqueous solution

Dissolution of a cold isostatically pressed high purity alumina ceramics in aqueous HCl solutions was studied as a function of immersion time and acid concentration. From the amounts of Al³⁺, Mg²⁺, Ca²⁺, Na⁺, Si⁴⁺ and Fe³⁺ ions released in the corrosive solution, a degree of dissolution χ_i for each component was calculated according to the equation χ_i = A/B, where A and B are respectively the amount of the element released in the corrosive solution and the amount of the element in the untreated material. The determination of the amounts of ions released in the corrosive solutions was carried out by means of atomic absorption spectrometry (AAS). The corrosion of alumina ceramics in the HCl aqueous solution is determined by the solubility of alumina and the solubility of grain-boundary impurities. Very low dissolution values of Al³⁺, Mg²⁺, Ca²⁺, Na⁺, Si⁴⁺ and Fe³⁺ ions after the corrosion test of alumina ceramics showed a very good corrosion resistance in the HCl aqueous solution.