Development of modified inorganic adsorbents for radioactive iodine removal and biomolecule adsorption

Development and application of inorganic adsorbent materials have been continuously investigated due to their variability and versatility. This Master thesis has expanded the knowledge in the field of adsorption targeting radioactive iodine waste and proteins using modified inorganic materials. Industrial treatment of radioactive waste and safety disposal of nuclear waste is a constant concern around the world with the development of radioactive materials applications. To address the current problems, laminar titanate with large surface area (143 m2 g−1) was synthesized from inorganic titanium compounds by hydrothermal reactions at 433 K. Ag2O nanocrystals of particle size ranging from 5–30 nm were anchored on the titanate lamina surface which has crystallographic similarity to that of Ag2O nanocrystals. Therefore, the deposited Ag2O nanocrystals and titanate substrate could join together at these surfaces between which there forms a coherent interface. Such coherence between the two phases reduces the overall energy by minimizing surface energy and maintains the Ag2O nanocrystals firmly on the outer surface of the titanate structure. The combined adsorbent was then applied as efficient adsorbent to remove radioactive iodine from water (one gram adsorbent can capture up to 3.4 mmol of I- anions) and the composite adsorbent can be recovered easily for safe disposal. The structure changes of the titanate lamina and the composite adsorbent were characterized via various techniques. The isotherm and kinetics of iodine adsorption, competitive adsorption and column adsorption using the adsorbent were studied to determine the iodine removal abilities of the adsorbent. It is shown that the adsorbent exhibited excellent trapping ability towards iodine in the fix-bed column despite the presence of competitive ions. Hence, Ag2O deposited titanate lamina could serve as an effective adsorbent for removing iodine from radioactive waste. Surface hydroxyl group of the inorganic materials is widely applied for modification purposes and modification of inorganic materials for biomolecule adsorption can also be achieved. Specifically, γ-Al2O3 nanofibre material is converted via calcinations from boehmite precursor which is synthesised by hydrothermal chemical reactions under directing of surfactant. These γ-Al2O3 nanofibres possess large surface area (243 m2 g-1), good stability under extreme chemical conditions, good mechanical strength and rich surface hydroxyl groups making it an ideal candidate in industrialized separation column. The fibrous morphology of the adsorbent also guarantees facile recovery from aqueous solution under both centrifuge and sedimentation approaches. By chemically bonding the dyes molecules, the charge property of γ-Al2O3 is changed in the aim of selectively capturing of lysozyme from chicken egg white solution. The highest Lysozyme adsorption amount was obtained at around 600 mg/g and its proportion is elevated from around 5% to 69% in chicken egg white solution. It was found from the adsorption test under different solution pH that electrostatic force played the key role in the good selectivity and high adsorption rate of surface modified γ-Al2O3 nanofibre adsorbents. Overall, surface modified fibrous γ-Al2O3 could be applied potentially as an efficient adsorbent for capturing of various biomolecules.

Interfacial microstructure in Y1Ba2Cu3O7-δ high Tc superconductors

The microstructures of YBa2Cu3O7-δ ceramics prepared from freeze dried powders and containing an excess of CuO have been studied by analytical electron microscopy. Special attention has been paid to the interfacial microstructure. It was found that a liquid phase formed during sintering between 890°C and 920°C and this promoted grain growth and densification. Both clean grain boundaries and boundaries containing an amorphous intergranular film, which was rich in Cu, have been observed. Both CuO and BaCuO2 were present as secondary phases.

YBCO thin films on Yttria stabilized Zirconia and LaAlO3-growth and properties

Laser deposition was used to deposit YBaCuO thin films on Yttria-stabilized Zirconia substrates, at substrate holder temperatures of 710-765 °C. We observed a transition from singlecrystalline to polycrystalline growth at a temperature of ∼750 °C. All films were highly c-axis oriented and had critical temperatures between 89.5 and 92 K. In the twinned singlecrystalline films, the lowest measured microwave surface resistance was 0.37 mΩ at 4.2 K and 21.5 GHz, and the highest critical current 5×106 A/cm2 at 77 K. The polycrystalline films had up to a factor of 50 higher surface resistance and a factor of 10 lower critical current. A meander line resonator made of a film on a LaAlO3 substrate, showed a microwave surface resistance of 5μΩ at 4.2 K and 2.5 GHz. © 1991.

Comments on the phase diagrams and crystallisation paths of Y-Ba-Cu-O materials

Our micro structural characterisation of Y-Ba-Cu-O quenched partial melts shows that the BaCuO2 (BC1) phase is crystalline at temperatures as high as 1100°C, and that the partial melt self-establishes a micro structural gradient from the surface towards the interior of the samples, which can be associated with a gradient in an equivalent partial pressure of O2 (pO2). The extension of the Y2BaCuO5-YBa2Cu3O7-x (Y211-Y123) tie-line intersects the primary crystallisation field of BC1 first. The actual peritectic reaction that takes place is Y2BaCuO5(s) + BaCuO2(s) + 2BaCu2O2(L) + 1/2O2 → 2YBa2Cu3O6(s). Two schematic representations which allow an analysis of the pO2 dependence are given. The gradient in micro structure self-established by the sample acts as a driving force for texturing. With this new perspective gained about the actual peritectic reaction and mechanisms of melt-texturing of Y123, it is possible to explain most of the aspects about partial melt-texturing. In addition, it seems possible to devise heat treatments that may allow for the production of well-oriented single domains with very large diameters. © 1999 Elsevier Science B.V.

Observation of exsolution textures within Ba-Cu-O-rich solidified melts of Y-Ba-Cu-O materials and their relationship to Y123 nucleation and texturing

Layers (about 60-100 μm thick) of almost pure BaCuO2 (BC1), as determined using X-ray diffractometry (XRD) and scanning electron microscopy (SEM), coat the surfaces of YBa2Cu3O7-x (Y123) samples partial melt processed using a single-zone vertical furnace. The actual Cu/Ba ratio of the BC1 phase is 1.2-1.3 as determined using energy dispersive X-ray spectrometry (EDS). The nominally BC1 phase displays an exsolution of BC1.5 or BC2 in the form of thin plates (about 50-100 nm thick) along {100}-type cleavage planes or facets. The exsolved phase also fills cracks within the BC1 layer that require it to be in a molten state at some stage of processing. The samples were influenced by Pt contamination from the supporting wire, which may have stabilised the BC1.5 phase. Many of the Y123 grains have the same morphology as the exsolution domains, and run nearly parallel to the thin plates of the exsolved phases, strongly indicating that Y123 nucleation took place at the interface between the BC1 and the BC1.5 or BC2 exsolved phases. The network of nearly parallel exsolved 'channels' provides a matrix and a mechanism through which a high degree of local texture can be initiated in the material.

Phase composition of the rapidly quenched melt of YBa2Cu3O7-y+20 mol% Y2BaCuO5

Samples of YBa2Cu3O7-y+20 mol% Y2BaCuO5, with thicknesses ranging between 50-250 μm, have been melt processed and rapidly quenched from temperatures between 985 and 1100°C by immersing them in liquid nitrogen. The phase composition and microstructures of these samples have been characterised using a combination of X-ray diffractometry, optical microscopy and scanning electron microscopy with energy dispersive X-ray spectroscopy. The quenched melt of samples quenched from temperatures greater than 985°C appears relatively homogeneous but consists of Ba2Cu3Ox (BC1.5) and BaCu2O2 (BC2) regions. At about 985°C, BaCuO2 (BC1) crystallises from the melt and most of the BC1.5 decomposes into BC1 and CuO or into BC1 and BC2. The crystallisation of BC1 induces segregation of elements in the melt and this is very significant for the melt texturing of YBCO.

Yttrium barium copper oxide thin films on yttria-stabilized zirconia: growth and properties

Y Ba Cu oxide thin films were grown epitaxially on single cryst. yttria-stabilized zirconia substrates by laser deposition. [on SciFinder(R)]

Very thin yttrium barium copper oxide films made by coevaporation

Superconducting YBa2Cu3O7 thin films with various thicknesses from 100 Å to 5000 Å were deposited on (100) SrTiO3 substrates with std. BaF2 coevaporation process. The films had crit. temps. of up to 93 K. The best crit. currents were 1 × 106 A/cm2 at 77 K and 3 × 107 A/cm2 at 4.2 K. The crit. current was generally higher for thinner films. Two different etching methods were used to pattern the films for jc measurements: Ar ion etching and EDTA wet etching. The wet etching was found to work well for thicker films (>1000 Å). For the thinner films, the ion etching process was preferred because of the reduced film surface degrdn. [on SciFinder(R)]

Production of metal oxide nanoparticles

Particles having at least regions of at least one metal oxide having nano-sized grains are produced by providing particles of a material having an initial, nonequiaxed particle shape, prepg. a mixt. of these particles and at last one metal oxide precursor, and treating the mixt. such that the precursor reacts with the particles. The process can be a co-pptn. process, sol-gel synthesis, micro-emulsion method, surfactant-based process, or a process that uses polymers. Complex metal oxide nanoparticles are produced by (a) prepg. a soln. contg. metal cations, (b) mixing the soln. with a surfactant to form micelles within the soln., and (c) heating the micellar liq. to form metal oxide and to remove the surfactant. The formed metal oxide particles have essentially the same morphol. (particle size and shape) as the initial morphol. of the material particles provided. [on SciFinder(R)]

Electrocrystallization of phase I, CuTCNQ (TCNQ= 7, 7, 8, 8-tetracyanoquinodimethane), on indium tin oxide and boron-doped diamond electrodes

The electrochemical reduction of TCNQ to TCNQ•- in acetonitrile in the presence of [Cu(MeCN)4]+ has been undertaken at boron-doped diamond (BDD) and indium tin oxide (ITO) electrodes. The nucleation and growth process at BDD is similar to that reported previously at metal electrodes. At an ITO electrode, the electrocrystallization of more strongly adhered, larger, branched, needle-shaped phase I CuTCNQ crystals is detected under potential step conditions and also when the potential is cycled over the potential range of 0.7 to −0.1 V versus Ag/AgCl (3 M KCl). Video imaging can be used at optically transparent ITO electrodes to monitor the growth stage of the very large branched crystals formed during the course of electrochemical experiments. Both in situ video imaging and ex situ X-ray diffraction and scanning electron microscopy (SEM) data are consistent with the nucleation of CuTCNQ taking place at a discrete number of preferred sites on the ITO surface. At BDD electrodes, ex situ optical images show that the preferential growth of CuTCNQ occurs at the more highly conducting boron-rich areas of the electrode, within which there are preferred sites for CuTCNQ formation.

Investigation of mediated oxidation of ascorbic acid by ferrocenemethanol using large-amplitude fourier transformed ac voltammetry under quasi-reversible electron-transfer conditions at an indium tin oxide electrode

The ability of the technique of large-amplitude Fourier transformed (FT) ac voltammetry to facilitate the quantitative evaluation of electrode processes involving electron transfer and catalytically coupled chemical reactions has been evaluated. Predictions derived on the basis of detailed simulations imply that the rate of electron transfer is crucial, as confirmed by studies on the ferrocenemethanol (FcMeOH)-mediated electrocatalytic oxidation of ascorbic acid. Thus, at glassy carbon, gold, and boron-doped diamond electrodes, the introduction of the coupled electrocatalytic reaction, while producing significantly enhanced dc currents, does not affect the ac harmonics. This outcome is as expected if the FcMeOH (0/+) process remains fully reversible in the presence of ascorbic acid. In contrast, the ac harmonic components available from FT-ac voltammetry are predicted to be highly sensitive to the homogeneous kinetics when an electrocatalytic reaction is coupled to a quasi-reversible electron-transfer process. The required quasi-reversible scenario is available at an indium tin oxide electrode. Consequently, reversible potential, heterogeneous charge-transfer rate constant, and charge-transfer coefficient values of 0.19 V vs Ag/AgCl, 0.006 cm s (-1) and 0.55, respectively, along with a second-order homogeneous chemical rate constant of 2500 M (-1) s (-1) for the rate-determining step in the catalytic reaction were determined by comparison of simulated responses and experimental voltammograms derived from the dc and first to fourth ac harmonic components generated at an indium tin oxide electrode. The theoretical concepts derived for large-amplitude FT ac voltammetry are believed to be applicable to a wide range of important solution-based mediated electrocatalytic reactions.

Formation of nanostructured porous Cu-Au surfaces : the influence of cationic sites on (electro)-catalysis

The fabrication of nanostructured bimetallic materials through electrochemical routes offers the ability to control the composition and shape of the final material that can then be effectively applied as (electro)-catalysts. In this work a clean and transitory hydrogen bubble templating method is employed to generate porous Cu–Au materials with a highly anisotropic nanostructured interior. Significantly, the co-electrodeposition of copper and gold promotes the formation of a mixed bimetallic oxide surface which does not occur at the individually electrodeposited materials. Interestingly, the surface is dominated by Au(I) oxide species incorporated within a Cu2O matrix which is extremely effective for the industrially important (electro)-catalytic reduction of 4-nitrophenol. It is proposed that an aurophilic type of interaction takes place between both oxidized gold and copper species which stabilizes the surface against further oxidation and facilitates the binding of 4-nitrophenol to the surface and increases the rate of reaction. An added benefit is that very low gold loadings are required typically less than 2 wt% for a significant enhancement in performance to be observed. Therefore the ability to create a partially oxidized Cu–Au surface through a facile electrochemical route that uses a clean template consisting of only hydrogen bubbles should be of benefit for many more important reactions.

Fabrication of metal-nanoparticle-modified semiconducting copper--and silver--TCNQ materials as substrates for the reduction of chromium (VI) using thiosulfate ions at ambient temperature

The formation of readily recoverable and reusable organic semiconducting Cu- and AgTCNQ (TCNQ=7,7,8,8-tetracyanoquinodimethane) microstructures decorated with Pt and Pd metallic nanoparticles is described for the effective reduction of CrVI ions in aqueous solution at room temperature using both formic acid and an environmentally friendly thiosulfate reductant. The M-TCNQ (M=metal) materials were formed by electrocrystallisation onto a glassy carbon surface followed by galvanic replacement in the presence of H2PtCl6 or PdCl2 to form the composite material. It was found that loading of the surface with nanoparticles could easily be controlled by changing the metal salt concentration. Significantly, the M-TCNQ substrates facilitated the formation of well-isolated metal nanoparticles on their surfaces under appropriate galvanic replacement conditions. The semiconductor–metal nanoparticle combination was also found to be critical to the catalyst performance, wherein the best-performing material was CuTCNQ modified by well-isolated Pt nanoparticles with both formic acid and thiosulfate ions as the reductant.

Improved adhesion of active electrode materials to metal electrode substrates

A battery electrode for a lithium ion battery comprising an elec. conductive substrate having an electrode layer applied thereto, characterized in that the electrode layer includes an org. material having high alky., or an org. material which can be dissolved in org. solvents, or an org. material having an imide group(s) and aminoacetal group(s), or an org. material that chelates with or bonds with a metal substrate or that chelates with or bonds with an active material in the electrode layer. The org. material may be guanidine carbonate. [on SciFinder(R)]