Preparation of a sodium alginate–poly(vinyl alcohol)–chitosan bipolar membrane and its application in the electrogeneration of ferrate(VI)

A sodium alginate (SA)–poly(vinyl alcohol) (PVA)–chitosan (CS) bipolar membrane (BPM) was prepared by a paste method with PVA, SA, and CS as starting materials and modified by Fe³⁺ and GA as a crosslinking agent. The morphology, functional groups, and physical properties of the film were studied by scanning electron microscopy, IR spectroscopy, and tensile testing, respectively. The SA–PVA–CS BPM was used as a separator in the electrolysis cell for electrogenerated ferrate(VI). The results show that the SA–PVA–CS BPM possessed reasonable physical and electrochemical properties. The SA–PVA–CS BPM not only prevented ferrate(VI) from diffusing into the cathode room but also played an important role in the supply of OH^? consumed during the electrogenerated ferrate(VI) process. Compared with the traditional method of preparing ferrate(VI), electrodialysis with the BPM (SA–PVA–CS) had the further advantage of lower alkali and energy consumption. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Photoredox processes in the Cr(VI)–Cr(III)–oxalate system and their environmental relevance

Irradiation of the [Cr(C₂O₄)₃]³⁻ complex or the chromate(VI)–oxalate mixture, or the ternary system composed of Cr(III), Cr(VI) and oxalate, leads to chromium photoreductions in consequence of the ligand to metal charge transfer (LMCT) excitations induced by artificial solar radiation. In the case of the Cr(III) complex, the photoreduction involves the innersphere electron transfer leading to the formation of the Cr(II) species and the C₂O₄⁻ radicals. On reacting with molecular oxygen, Cr(II) is oxidised to Cr(III) catalysing thereby the oxalate substitution reaction. Moreover, under specific conditions, Cr(II) can be also oxidised to Cr(VI). Chromate(VI) is not photoreducible, but in the presence of oxalate, or other sacrificial electron donor, the outersphere photoinduced electron transfer (PET) produces Cr(V) species and the C₂O₄⁻ radicals. This initiates a series of thermal reactions leading to the formation of Cr(III) and oxidized oxalate (CO₂). In the system composed of [Cr(C₂O₄)₃]³⁻ and chromate(VI), the acidic medium and anoxic conditions favour the Cr(VI) photoreduction, whereas alkaline oxygenated solutions assist the Cr(VI) photoproduction. When an approximately neutral solution equilibrated with the ambient air is irradiated intermittently, Cr(VI) is consumed and/or produced, accordingly to the time sequence of exposure and dark periods. The oscillations of Cr(VI) concentrations are accompanied by continuous oxidation of oxalate, playing the role of the sacrificial electron donor. The effects of solution pH, molecular oxygen, concentrations of reagents and cations on the reaction rates were investigated. The results of this paper revealed that the Cr(III)/Cr(VI) system under environmental conditions behaves as the photocatalytic one catalysing the oxidation of oxalate or other organic matter by molecular oxygen, contributing thereby to the abatement of pollution.     

Poly(sodium 4-styrenesulfonate)–metal ion interactions

The metal ion-binding properties of poly(sodium 4-styrenesulfonate) in conjunction with membrane filtration were investigated for Cu(II), Cd(II), Co(II), Cr(III), Hg(II), Ni(II), Pb(II), Zn(II), and Fe(II). Different experiments were carried out at different pH's, metal ion concentrations, polymer concentrations, and molecular weight fractions. Only Fe(II) and Cr(III) were retained at pH 1, which allows a selective separation of these metals from all the other metal ions. At pH 3 the retention ability of this polymer increased for all the metal ions. On the other hand, the metal ion-retention properties are dependent on the polymer/metal ratio. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 219–225, 1998     

Effects of surfactants on acrylonitrile polymerization initiated by a Cr(VI)–cyclohexanone redox system: A kinetic study

The polymerization of acrylonitrile (AN) was kinetically studied with a Cr(VI)–cyclohexanone (CH) redox system as an initiator from 25 to 45° C in the presence of a surfactant. The rate of polymerization and the percentage of the monomer conversion increased as the concentration of the anionic surfactant [sodium dodecyl sulfate (SDS)] increased above its critical micelle concentration. However, the cationic surfactant (cetyltrimethylammonium bromide) reduced the rate considerably at higher concentrations, whereas the nonionic surfactant (TX‐100) had no effect on the rate. The effects of the Cr(VI), CH, AN, and H⁺ concentrations and the ionic strength on the rates were also examined. The presence of 0.015M SDS reduced the overall activation energy of the polymerization by 5.55 kcal/mol with respect to that in the absence of the surfactant. With increasing SDS concentration, the viscosity‐average molecular weight also increased. A suitable mechanistic scheme was proposed for the polymerization process. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1147–1153, 2004     

Uranium(VI) and Ruthenium Extraction by Dialkyldithio-Phosphoric Acids

Abstract

Oxygen donors like dialkylphosphoric acids are good extractants for actinide ions, but little is known about their sulfur homologs. In this paper investigations of U(VI) and Ru extraction from various aqueous media are reported. This includes extraction of U(VI) from nitric, perchloric, and phosphoric acids by solutions of dialkyldithiophosphoric acids in dodecane or benzene. Extraction of U(VI) by synergistic mixtures, of which at least one of the components is a sulfur donor, has been investigated. The extracted species have been identified, and a comparison with the complexes obtained by extraction with the homologous oxygen donors is made. The sulful-actinide bond is weaker than the oxygen-actinide one, but in some synergistic extractions the dialkyldithlophosphonates are more efficient than the oxygen donors. In addition to size effects, this behavior could be attributed to the weakness of the hydrogen bonds of the SH groups, which allows a greater variety of the ligands to enter the coordination sphere of the metal. Ruthenium, like the d-transitiori elements, gives strong bonds with the sulfur donors. However, its extraction from nitric acid is slow. We investigated the influence of several parameters on the distribution coefficients and found that the presence of a reagent which destroys nitrous ions is necessary to achieve quantitative extraction. The role of RuNO groups is also discussed.     

Extraction Behavior of Uranium(VI) with Polyurethane Foam

Abstract

The extraction of uranium(VI) from aqueous solution with polyether-based polyurethane (PU) foam was studied. The effects of the kinds and concentrations of nitrate salts, uranium(VI) concentration, temperature, nitric acid concentration, pH, the content of poly(ethylene oxide) in the polyurethane foam, and the ratio of PU foam weight and solution volume on the extraction of uranium(VI) were investigated. The interferences of fluoride and carbonate ions on the extraction of uranium(VI) were also examined, and methods to overcome both interferences were suggested. It was found that no uranium was extracted in the absence of a nitrate salting-out agent, and the extraction behaviors of uranium(VI) with polyurethane foam could be explained in terms of an etherlike solvent extraction mechanism. In addition, the percentage extraction of a multiple stage was also estimated theoretically.     

Uranium (VI) Complexes of Some Tridentate Schiff Bases

Protonation constants (log K^H₁ and log K^H₂) of N-acetylacetoneanthranilic acid (abbr. H₂ AA), N-salicylideneanthranilic acid (abbr. H₂SA) and N, (2-hydroxy-1-naphthalidene) anthranilic acid (abbr. H₂ NA), and formation constants of their uranium (VI) complexes have been determined potentiometrically in 50% dioxan (vol/vol) solutions (μ = 0.1 M NaClO₄) at 30 ± 0.1°C. The stabilities of these complexes were found to be in the order: UO₂⁺²-H₂NA > UO₂⁺²-H₂SA > UO₂⁺²-H₂AA.     

Extraction of Uranium(VI) and Plutonium(IV) with Tetra-Alkylcarbamides

ABSTRACT

The use of tetra-alkylcarbamides as novel extractants for the separation of uranium(VI) and plutonium(IV) by solvent extraction from spent nuclear fuels is investigated in this study. Batch extraction experiments show that tetra-alkylcarbamides strongly extract U(VI) with high distribution ratios. Plutonium(IV) can be co-extracted with U(VI) at high nitric acid concentration, while high U(VI)/Pu(IV) selectivities can be reached at lower acidity. Loading capacity experiments with high uranium concentrations show that alkyl chains longer than butyl are necessary to avoid third phase formation. Nevertheless, the viscosity of uranium-loaded solvents gets too high with alkyl chains longer than pentyl. Overall, this study shows that with TPU extractant (with four pentyl chains), an efficient co-extraction of uranium and plutonium can be reached (D_U,Pu > 1) for a concentration of nitric acid higher than 4 mol?L^?1, while the partition between uranium(VI) and plutonium(IV) could be operated even at 2 mol?L^?1 nitric acid without redox chemistry.     

Polymorphism and crystallization in poly(vinylidene fluoride)/ poly(ϵ‐caprolactone)–block–poly(dimethylsiloxane)–block–poly(ϵ‐caprolactone) blends

The miscibility, crystallization kinetics and crystalline morphology of a new system of poly(vinylidene fluoride)/poly(?‐caprolactone)‐block‐poly(dimethylsiloxane)‐block‐poly(?‐caprolactone) (PVDF/PCL‐b‐PDMS‐b‐PCL) triblock copolymer were investigated by a variety of techniques. The miscibility and phase behaviour of PVDF/PCL‐b‐PDMS‐b‐PCL were studied by determination of the melting point temperature, crystallization kinetics and Fourier transform infrared (FTIR) mapping. Chemical imaging was used as a new technique to characterize the interaction of polymer blends in crystalline morphology. The results demonstrate the existence of characteristic peaks of both PVDF and PCL in the chosen crystalline area. The crystalline structures of PVDF were affected by the PCL‐b‐PDMS‐b‐PCL triblock copolymer and facilitate the formation of the β polymorph which was illustrated by FTIR analysis. The β crystal phase fraction increases significantly on increasing the composition of the PCL‐b‐PDMS‐b‐PCL triblock copolymer. In addition, confined crystallization of PCL within PVDF inter‐lamellar and/or inter‐fibrillar regions was confirmed through polarizing optical microscopy, wide‐angle X‐ray diffraction and small‐angle X‐ray scattering analysis. © 2019 Society of Chemical Industry     

Hydronium Copper(II)‐tris(5‐nitrotetrazolate) Trihydrate – A Primary Explosive

The long‐time elusive structure of the acid copper(II) salt intermediate in the production of DBX‐1 is presented. The single‐crystal X‐ray shows infinite chains of copper(II) ions complexed by six 5‐nitrotetrazolate anions are aligned along the sixfold axis. Hydronium ions are located on the threefold axis with additional neutral water molecules.     

The Solvent Extraction of Uranium(VI) by N-m-Tolyl-o-methoxybenzohydroxamic Acid

Abstract

A simple and rapid spectrophotometric determination of uranium(VI) is described. The uranium(VI) N-m-tolyl-o-methoxybenzohydroxamic acid complex is extracted with chloroform at pH 5.3 to 5.5 from aqueous solution. Maximum absorption of orange-red extract occurs at 510 nm. The colored complex obeys Beer's law over the range 0.3 to 20 ppm of uranium. The effect of acidity, reagent concentration, and diverse ions on the visible absorption of extracted complex has been studied.     

Rapid Solvent Extraction of Uranium(VI) with N-Phenylbenzohydroxamic Acid

Abstract

A rapid method for the simultaneous solvent extraction and spectrophotometric determination of macro-amounts of hexavalent uranium with N-phenyl-benzohydroxamic acid is described. The intense blood-red colored complex thus extracted from chloroform at pH ～ 4 absorbs at around 510 nm. A clean-cut separation from many commonly occurring metal ions is easily accomplished. Effects of acidity, reagent concentration, and diverse ions on the visible absorption of the extracted complex have also been investigated.     

A study of Cu(I)‐ethylene complexation for olefin–paraffin separation

The current cryogenic distillation technology used for olefin–paraffin separation incurs extensive capital and operating costs. An alternative olefin–paraffin separation process, based on reactive absorption, could yield significant cost reductions. The research efforts described herein explored the structural characteristics of an NMP‐CuCl‐aniline absorption solution with ethylene to aid future development of olefin–paraffin separation systems. Solution IR and ¹H NMR spectroscopy suggested weak and labile Cu(I)‐ethylene and Cu(I)‐aniline coordination, which point to the coexistence of multiple structures in solution. Experiments also revealed solvent‐dependent and temperature‐dependent coordination. The agreement of the collected spectral data with literature implied single ethylene coordination, whereas the Cl^? ion likely remained coordinated with Cu(I). Solvent interference prohibited detailed investigation of IR spectra, but ¹H NMR spectroscopy showed more promise as an analytical technique for the NMP‐CuCl‐aniline‐ethylene system. Finally, a tradeoff appears to exist between ethylene capacity and complex stability, and thus, an optimal ligand must be found that balances these two competing needs. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Bending of poly(vinyl alcohol)–poly(sodium acrylate) composite hydrogel in electric fields

Bending of poly(vinyl alcohol) hydrogel mixed with poly(sodium acrylate) chains, PVA–PAA gel, under the influence of dc electric fields was studied. The PVA–PAA gel was prepared by repeatedly freezing and thawing a mixture of PVA and polyacrylic acid aqueous solutions. The PVA–PAA gel was a hydrogel with the PAA chains, which were entangled with the PVA polymer network and were fixed in the gel. The PVA–PAA gel bent toward the negative electrode in electrolyte solutions under dc electric fields as did the polyelectrolyte gel with negatively charged polyions. The PVA gel, free of PAA, was insensitive to dc electric fields. The deflection of the bending and the bending speed were influenced by the filed intensity, the concentration of the polyion in the gel, and the thickness of the gel. The bending of the PVA–PAA gel was qualitatively explained by a bending theory of polyelectrolyte gel, based upon the change of the osmotic pressure due to the ion concentration difference between the inside and the outside of the gel.     

Synthesis of poly(sodium acrylate‐co‐sodium 1‐(acryloyloxy) propan‐2‐yl phosphate) and comparative study on its swelling properties with poly(sodium acrylate) and poly(sodium acrylate‐co‐2‐hydroxypropyl acrylate)

A new superabsorbent copolymer, poly(sodium acrylate‐co‐sodium 1‐(acryloyloxy) propan‐2‐yl phosphate) [P(SA‐co‐SAPP)], was synthesized by a novel prepared monomer, 1‐(acryloyloxy) propan‐2‐yl phosphoryl dichloride. The swelling properties of the superabsorbent were investigated by comparison with poly(sodium acrylate) (PSA) and the copolymer of poly(sodium acrylate‐co‐2‐hydroxypropyl acrylate) [P(SA‐co‐HPA)]. The results showed that (1) the superabsorbent containing sodium 1‐(acryloyloxy) propan‐2‐yl phosphate had higher water absorbency at general testing conditions; (2) the swelling properties of P(SA‐co‐SAPP) and PSA were obviously influenced by pH of solutions, which were different from that of P(SA‐co‐HPA); (3) the swelling process and the saturated water absorbency of all superabsorbents were remarkably affected by cations, especially multivalent ones, while barely affected by anions. POLYM. ENG. SCI., 47:728–737, 2007. © 2007 Society of Plastics Engineers.     

Preparation and characterization of crosslinked poly(methylmethacrylate‐acrylic acid sodium salt)‐modified bone cement

Bone cement is used as load‐distributing filler between the prosthesis and the bone as well as a method to anchor prosthesis in orthopedic implants. In this study, crosslinked poly(methylmethacrylate‐acrylic acid sodium salt), denoted as poly(MMA‐AAS‐AMA), was applied to bone cement. Allylmethacrylate (AMA) was used as a crosslinking agent. It was demonstrated by FTIR that the wavenumbers of the asymmetrical and symmetrical stretching vibrations for carboxylate anion of poly(MMA‐AAS‐AMA) were 1586 and 1407 cm⁻¹, respectively. The poly(MMA‐AAS‐AMA)‐modified bone cement was prepared and characterized using tensile and compressive test. An excess of poly(MMA‐AAS‐AMA) in bone cement caused poor mechanical properties of the modified bone cement, because poly(MMA‐AAS‐AMA) absorbed water. In dynamic mechanical analysis, the excessive content of poly(MMA‐AAS‐AMA) lowered the stiffness of the modified bone cement, because of water existed in poly(MMA‐AAS‐AMA). The glass transition temperature of the bone cement shifted to higher temperature at higher frequency because of viscoelasticity. Based on swelling measurement, the modified bone cement was able to swell in controlled manner, and the swelling rate of the modified bone cement was improved. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010