Kinetics of Ion Exchange of Zr/Sn(IV) Phosphonate–Phosphate Hybrid Materials for Separation of Lanthanides from Oxidized Actinides

ABSTRACT

The kinetics of ion exchange of Zr/Sn(IV) phosphonate–phosphate hybrid ion exchange materials have been studied with several types of ions of specific interest to nuclear fuel recycling including Nd³⁺ at 4.5 and 43 mM and NpO₂⁺ at 2.9 mM spanning multiple HNO₃ concentrations. In most cases, the equilibrium was reached in less than 12 h. The ion exchange behavior followed that of pseudo first-order adsorption with rates ranging from 0.430–4.10 h^?1 to 0.290–0.435 h^?1 for Nd³⁺ and NpO₂⁺, respectively. A separation with both Nd³⁺ and NpO₂⁺ present was performed, resulting in separation factors of 1.9–12, 1.7–6.6, and 2.0–5.7 at 1 × 10^?1, 1 × 10^?2, and 1 × 10^?3 M HNO₃, respectively.     

Preparation and Properties of Water-Soluble PAA–PAS/SiO2 Hybrid Materials

Copolymers with different weight ratios of AA/PAS (acrylic acid/poly(DL-aspartic acid)) were synthesized and blended with sol-gel precursors to prepare water-soluble PAA–PAS/SiO₂ inorganic/organic hybrid materials. The PAS polymer or its copolymer in PAA–PAS/SiO₂ formed hydrogen bonds with SiO₂ and the amorphous structure of the hybrid material varied with the weight ratio of PAA. The hybrid materials exhibited enhanced thermal resistance over the copolymer alone. All hybrid materials were water-soluble and relatively insoluble in organic solvents.     

New Inorganic–Organic Hybrid Materials and Their Oxides for Removal of Heavy Metal Ions: Response Surface Methodology Approach

In this paper, Cu(II), Fe(III), Pb(II), and Zn(II) heavy metal ions were removed from their aqueous solutions by using novel inorganic–organic hybrid materials, Al-GPTS-H and Al-GPTS-NaOSiMe₃-H (hybrid material-1 and 2, respectively), and their oxides (calcined-1 and 2) as adsorbents. These ions removal by adsorption was optimized by using response surface methodology (RSM). Central composite design (CCD) method was used in order to investigate the effects of initial pH, initial metal concentration of solutions and adsorbent quantity on the adsorption efficiency (R, %). As a result of the experiments under optimum conditions, the maximum % R values were obtained by hybrid material-1 for Fe(III) (99.89%) and by calcined material-1 for Pb(II) (97.14%), respectively. These quite high adsorption efficiency values have shown that these hybrid materials and their oxides are suitable to use for heavy metal ions removal from aqueous solutions.     

Ladder-Like Versus Hexagonal Organic–Inorganic Hybrid Materials in the Extraction of Lead Ions

Meso-structured and ladder organic–inorganic hybrid materials functionalized with ammonium carboxylate groups were prepared. These materials were obtained by the sol–gel process starting from the cyanopropyltriethoxysilane precursor as a building block. Hydrolysis of CN to COOH groups followed by treatment with triethylamine gives rise to cationic exchange materials. These materials exhibit a high chelating capability towards cations and can be used for water treatment. Lead ion (Pb²⁺) was tested as example; and, some tests were made on the meso-structured and ladder material for further comparison in efficacy of extractions.     

The Preparation of Core–Shell P(St-MMA)–SiO2 Hybrid Nanoparticles and Filling in the Styrene/n-butyl Acrylate Adhesive

In this study, core–shell poly(styrene-methyl methacrylate) (P(St-MMA))–SiO₂ hybrid nanoparticles were prepared successfully by emulsion polymerization. Firstly, nanosilica particles were modified by oleic acid (OA) in order to introduce the polymerization active vinyl groups and hydrophobic groups onto the nanosilica. This was followed by graft copolymerization onto the modified nanosilica particles to obtain P(St-MMA)–SiO₂ hybrid nanoparticles. The hybrid nanoparticles were characterized by: transmission electron microscope (TEM); Fourier transform infrared spectroscopy (FT-IR); dynamic light scattering (DLS); and thermal gravimetric analysis (TGA). The results indicate that the hybrid particles had a regular spherical morphology with a diameter ranging from 50 to 80 nm. A reasonable mechanism for the preparation of the core–shell hybrid nanocomposites was presented. The obtained hybrid nanoparticles were subsequently (incorporated into) filled in the poly(styrene-n-butyl acrylate) (PSBA) latex. The effect of (hybrid nanoparticle concentration) filling content on the physicochemical properties of PSBA latex and the resulting node strength per monofilanment of the fibre glass gridding cloth was investigated. The results indicated that the node strength/monofilanment of the fibre glass gridding cloth coated with the PBSA latex filled with 1.0 wt% hybrid nanoparticles demonstrated greatest improvement among all the investigated PSBA latex. This result is related to the rheological properties of the latex. Moreover, the water-resistance property of PSBA composite film was found to be enhanced when compared with that of unfilled PSBA film.     

Nanoarchitectonics of Enzyme/Metal–Organic Framework Composites for Wastewater Treatment

Journal of Inorganic and Organometallic Polymers and Materials - Metal–organic frameworks (MOFs) provide advantages as supporting materials for the immobilization of enzymes due to their...     

Preparation of Pt–Co alloy catalysts by electrodeposition for oxygen reduction in PEMFC

Direct current (DC) and pulse current (PC) electrodeposition of Pt–Co alloy onto pretreated electrodes has been conducted to fabricate catalyst electrodes for oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFC). The effect of plating mode and pulse plating parameters on the Pt–Co alloy catalyst structure, composition and electroactivity for the ORR in PEMFC has been investigated. The electrodeposited Pt–Co alloy catalyst indicates higher electrocatalytic activity towards the ORR than the electrodeposited Pt catalyst. The activity of the electrodeposited Pt–Co catalysts is further improved by applying the current in a pulse waveform pattern. The electrodeposition mode and the pulse plating parameters do not have the significant effect on the Pt:Co composition of deposited catalysts, but show the substantial effect on the deposit structures produced. The Pt–Co catalysts prepared by PC electrodeposition have finer structures and contain smaller Pt–Co catalyst particles compared to that produced by DC electrodeposition. By varying the Pt concentration in deposition solution, the Pt:Co composition of the electrodeposited catalyst that exhibits the highest activity is found. The Pt–Co alloy catalyst with the Pt:Co composition of 82:18 obtained at the charge density of 2 C cm⁻², the pulse current density of 200 mA cm⁻², 5% duty cycle and 1 Hz was found to yield the best electrocatalytic activity towards the ORR in PEMFC.     

Hybrid sol–gel coatings for corrosion protection of galvanized steel in simulated concrete pore solution

The aim of this experimental research was to study the electrochemical behavior of organic–inorganic hybrid (OIH) coatings for corrosion protection of hot-dip galvanized steel (HDGS) in the first instants of immersion in simulated concrete pore solution (SCPS) (pH > 12.5). The electrochemical performance of the OIH coatings was assessed by electrochemical impedance spectroscopy, potentiodynamic polarization curves, macrocell current density, and polarization resistance. The OIH coatings were prepared via the sol–gel method and were deposited on HDGS surfaces by dip-coating using one or three dip steps. The electrochemical results obtained for HDGS samples coated with OIH matrices in SCPS showed higher corrosion resistance than bare HDGS; as the molecular weight (MW) of Jeffamine^® increased the barrier protection of the coating decreased. The lowest protection efficiency was found for HDGS samples synthesized with oligopolymers with an MW of 2000. Coatings produced with an oligopolymer of 230 MW conferred the highest protection. The surface morphology of the OIH coatings deposited on HDGS surfaces was studied by atomic force microscopy. The results show that the roughness of the OIH films depends on the MW of Jeffamine^® and on the number of dip-coating steps used. Thermogravimetry results show that the Jeffamine^® MW affected the thermal properties of the prepared OIH samples. The prepared OIH materials are thermally stable within the range of 20–80°C.     

Preparation of blend polyethersulfone/cellulose acetate/polyethylene glycol asymmetric membranes for oil–water separation

Blend PES/CA hydrophilic membranes were prepared via a phase-inversion process for oil–water separation. PEG-400 was introduced into the polymer solution in order to enhance phase-inversion and produce high permeability membranes. A gas permeation test was conducted to estimate mean pore size and surface porosity of the membranes. The membranes were characterized in terms of morphology, overall porosity, water contact angle, water flux and hydraulic resistance. A cross-flow separation system was used to evaluate oil–water separation performance of the membranes. From FESEM examination, the prepared PES/CA membrane presented thinner outer skin layer, higher surface porosity with larger pore sizes. The outer surface water contact angle of the prepared membrane significantly decreased when CA was added into the polymer solution. The higher water flux of the PES/CA membrane was related to the higher hydrophilicity and larger pore sizes of the membrane. From oil–water separation test, the PES/CA membrane showed stable oil rejection of 88 % and water flux of 27 l/m² s after 150 min of the operation. In conclusion, by controlling fabrication parameters a developed membrane structure with high hydrophilicity, high surface porosity and low resistance can be achieved to improve oil rejection and water productivity.     

Preparation,Characterization, and Properties of Novel Polyimide–SiO2 Hybrid Composites Based on Bipyridine for Low Dielectric Applications

Novel low dielectric polyimide–SiO₂ hybrid materials containing bipyridine were prepared with three-step sol–gel process from poly(amic acid)s. (3-Aminopropyl)triethoxysilane as coupling agent was used to increase the intrachain chemical bonding between the polyimide and SiO₂ groups. The thermal, dielectric, and physical properties of the hybrid materials were investigated and correlated with the porous structure. The glass transition temperatures of all the hybrids were found to be higher than polyimides. The effect of SiO₂ groups on the porous structure and dielectric properties was investigated. The dielectric constant of the hybrid materials was observed a decrease from 3.30 to 2.15 with increased SiO₂ amount.     

Preparation of Ti/Pt/SnO2–Sb2O4 electrodes for anodic oxidation of pharmaceutical drugs

Ti/Pt/SnO₂–Sb₂O₄ electrodes were prepared by alternating Sn and Sb electrodepositions, repeated 4 or 16 times, onto a platinized titanium foil by a thermo-electrochemical method. Chemical, electrochemical, and structural tests have been used for the characterization of Ti/Pt/SnO₂–Sb₂O₄ electrodes. Anodic oxidation of the aqueous solution contaminated by amoxicillin, clofibric acid, diclofenac, and ibuprofen having a concentration of 100 mg L^?1 and 0.035 M of Na₂SO₄ have been applied using Ti/Pt/SnO₂–Sb₂O₄ electrodes at a current density of 10 and 30 mA cm^?2. The chemical oxygen demand removals increased with current density and except for diclofenac, the Ti/Pt/SnO₂–Sb₂O₄ electrode with 4 electrodeposition repetitions gave the best results. The combustion efficiencies for diclofenac and ibuprofen were higher than those obtained with similar electrode material, prepared without platinization, especially in the assay run with Ti/Pt/SnO₂–Sb₂O₄ (16 electrodeposition repetitions).     

The Effect of Si Substitution for SiC on SHS in the Ti–Si–C System

Investigated was the effect of Si substitution for SiC on SHS in the Ti–Si–C system. Starting powders were intermixed to obtain 3Ti–SiC–C and 3Ti–Si–2C green mixtures and then green compacts by uniaxial pressing. The influence of heating rate, reactor temperature, and replacement of SiC by Si was studied by XRD, SEM, and TEM. In combustion products obtained in optimized conditions, Ti₃SiC₂ was found to be predominant. In comparison with conventional methods, our products obtained in a one-step low-temperature process contained minimal amounts of undesired impurities and required no finishing processes such as chemical purification.     

Preparation and characterization of CeO2–TiO2 support for Ru catalysts: Application in CWAO of p-hydroxybenzoic acid

The catalytic wet air oxidation of aqueous solutions of p-hydroxybenzoic acid has been carried out over CeO₂–TiO₂ supported ruthenium catalysts (Ru/Ce–Ti) at 140 °C and 50 bar of air. High activity of ruthenium supported catalysts was observed. It was found that the decrease of the molar ratio Ce/Ti from 3 to 1/3, improves the activity of Ru catalysts. The activity of the samples decreases in the following order: Ru/Ce–Ti (1/3) > Ru/CeO₂ ≈ Ru/TiO₂ > Ru/TiO₂DT51. Characterization of samples was performed by means of N₂ adsorption–desorption, XRD, UV–visible, TPR, SEM and TEM.     

Preparation and application of epoxy–chitosan/alginate support in the immobilization of microbial lipases by covalent attachment

The aim of this work was the preparation and application of highly hydrophobic epoxy–chitosan/alginate as a support to immobilize microbial lipases from Thermomyces lanuginosus commercially available as Lipolase® (TLL1) and Lipex® 100L (TLL2) and Pseudomonas fluorescens (PFL). The catalytic properties of the biocatalysts were assayed in olive oil hydrolysis and butyl butyrate synthesis. The results indicated that 12 h was enough for TLL1 to be immobilized on the support. Covalent attachment of TLL1 turned biocatalysts highly active and around 6-fold more stable than free lipase. Based on the results, a time of incubation of 24 h was selected for further studies about the maximum immobilized protein amount and butyl butyrate synthesis. Maximum protein loading immobilized was found to be 25.4 mg g^?1 support for TLL1, followed by TLL2 (20.5 mg g^?1) and PFL (15.5 mg g^?1) offering 80 mg protein g^?1 support. The immobilization of TLL1 and TLL2 resulted in highly active biocatalysts (around 1300 IU g^?1 gel), almost fivefold higher than PFL (272.4 IU g^?1 gel). In butyl butyrate synthesis, PFL showed similar activity to TLL1 and TLL2 derivatives, up to 60 mmol L^?1. The biocatalysts displayed high activity after five successive cycles, retaining around 95% of the initial activity.     

The role of zinc oxide in Cu/ZnO catalysts for methanol synthesis and the water–gas shift reaction

All commercial catalysts for methanol synthesis and for the water–gas shift reaction in the low temperature region contain zinc oxide in addition to the main active component, copper. The varied benefits of zinc oxide are analysed here. The formation of zincian malachite and other copper/zinc hydroxy carbonates is essential in the production of small, stable copper crystallites in the final catalyst. Further, the regular distribution of copper crystallites on the zinc oxide phase ensures long catalyst life. Zinc oxide also increases catalyst life in the water–gas shift process by absorbing sulphur poisons but it is not effective against chloride poisons. In methanol synthesis, zinc oxide (as a base) removes acidic sites on the alumina phase which would otherwise convert methanol to dimethyl ether. Although bulk reduction of zinc oxide to metallic zinc does not take place, reduction to copper–zinc alloy (brass) can occur, sometimes as a surface phase only. A new interpretation of conflicting measurements of adsorbed oxygen on the copper surfaces of methanol synthesis catalysts is based on the formation of Cu–O–Zn sites, in addition to oxygen adsorbed on copper alone. The possible role of zinc oxide as well as copper in the mechanisms of methanol synthesis is still the subject of controversy. It is proposed that, only under conditions of deficiency of adsorbed hydrogen on the copper phase, hydrogen dissociation on zinc oxide, followed by hydrogen spillover to copper, is significant. This revised version was published online in June 2006 with corrections to the Cover Date.