Preparation of a palladium alloy composite membrane supported in a porous stainless steel by vacuum electrodeposition

Pinhole-free palladium/nickel (Pd/Ni) alloy membranes deposited on a porous stainless steel (SUS) support have been fabricated. The deposition was made by vacuum electrodeposition technique which could produce the alloy film less than 1 μm thick. This technique allows for the Pd/Ni alloy by employing Pd/Ni complex reagent, and typical Pd/Ni plating had compositions of 78% Pd and 22% Ni. In order to make the surface smooth and enhance the adhesive bond between the top layer and the substrate, a nascent porous SUS disk was treated sequently with submicron nickel powder and CuCN solution. The important parameters that can affect deposition were pore size, defects, and surface roughness of substrate. The membranes were characterized by permeation experiments with hydrogen and nitrogen at temperatures ranging from 623 to 823 K and pressures from 10.3 to 51.7 cmHg. The composite membranes prepared in this technique yielded excellent separation performance for hydrogen: hydrogen permeance of 5.79×10⁻² cm³/cm² cmHg s and hydrogen/nitrogen (H₂/N₂) selectivity was 4700 at 823 K.     

Kinetics of the electrodeposition of palladium

The surface area changes which take place when Pd is deposited on Pd from chloro complexes are investigated electrochemically. A three-dimensional nucleation and growth model is used to evaluate the kinetics of the process.     

Indirect complexometric determination of palladium(II) using sodium nitrite as a selective masking reagent

A selective complexometric method is described for the determination of palladium, sodium nitrite being used as masking reagent. Palladium(II) in a given sample solution is initially cornplexed with an excess of EDTA and the surplus EDTA is titrated with zinc sulfate solution at pH 4.5–5.5 (acetic acid-sodium acetate buffer), using xylenol orange as indicator. An excess of sodium nitrite is then added, the mixture is shaken well and the EDTA released from the Pd-EDTA complex is titrated with a standard zinc sulfate solution. Results are obtained for 2.5–27.5 mg of Pd with relative errors 0.5% and standard deviations 0.05 mg. The interferences of various ions are studied. The method is applied for the determination of palladium(II) in alloys and complexes.     

Fabrication of a thin palladium membrane supported in a porous ceramic substrate by chemical vapor deposition

A thin, gas-tight palladium (Pd) membrane was prepared by the counter-diffusion chemical vapor deposition (CVD) process employing palladium chloride (PdCl₂) vapor and H₂ as Pd precursors. A disk-shaped, two-layer porous ceramic membrane consisting of a fine-pore γ-Al₂O₃ top layer and a coarse-pore -Al₂O₃ substrate was used as Pd membrane support. A 0.5–1 μm thick metallic membrane was deposited in the γ-Al₂O₃ top layer very close to its surface, as verified by XRD and SEM with a backscattered electron detector. The most important parameters that affected the CVD process were reaction temperature, reactants concentrations and top layer quality. Deposition of Pd in the γ-Al₂O₃ top layer resulted in a 100- to 1000-fold reduction in He permeance of the porous substrate. The H₂ permeation flux of these membranes was in the range 0.5–1.0 × 10⁻⁶ mol m⁻² s⁻¹ Pa⁻¹ at 350–450°C. The H₂ permeation data suggest that surface reaction steps are rate-limiting for H₂ transport through such thin membranes in the temperature range studied.     

An observation of palladium membrane formation on a porous stainless steel substrate by electroless deposition

The membranes made of palladium and its alloys are used for the extraction of high quality hydrogen from a mixture of gases. Most of recent research is focused on the development technologies for depositing a durable ultra-thin palladium membrane on a porous substrate in order to assure a good mechanical support and maximize the flux of hydrogen permeation. The formation of a palladium membrane deposited on a porous stainless steel substrate by an electroless process is recorded and described in this paper. The palladium deposition progress around the pore area at the surface of the substrate in the initial stages is illustrated. A bridge model is presented to describe the membrane formation around the pore area of the substrate. This model, together with the micrographs showing the deposition progress on the pore areas, will lead to the control of the deposition process for a membrane fabrication as well as the design and modification of a substrate.     

Plasma surface graft of N,N-dimethylacrylamide onto porous polypropylene membrane

Plasma graft onto microporous polypropylene (PP) membranes was studied. PP substrates had 0.45 μ of average pore size and 80 to 150 μ thickness and monomer for graft was N,N-dimethylacrylamide. Even by short exposure to argon and hydrogen plasmas less than 10 s, post graft polymerization was very fast. Grafting layer could be distinguished from relatively less-grafted portion by electron microscopy. However, graft was, more or less, noticed to form over cross-section of substrate. Plasmas were excited by 13.56 MHz radio frequency source and the wattage less than 10 W was usually enough to prevent PP from heat damage. Grafting rate was dependent on plasma-exposure time. For argon plasma at 10 W, 0.1 Torr (13.3 Pa), grafting rate decreased after maximum rate was observed at 10 s exposure. Analysis by electron spin resonance (ESR) revealed that relationship between spin concentration and irradiation time was somewhat different from reported data on polyethylene substrate. Alkyl radicals showing an eight-line-signal on ESR spectra were rapidly converted to peroxy radicals in air at almost 100%-yield. Both kinds of radicals could initiate graft, and alkyl radicals were found more active. Apparent activation energies were estimated to be 14.2 and 7.9 kcal/mol for graft polymerizations initiated by peroxy and alkyl radicals, respectively. Thermal analysis and X-ray diffraction revealed that graft may exist not only inner and outer surfaces but also in bulk region of substrate. For substrates more than 1000% grafted, even crystalline region was destroyed completely. Diffusion or absorption of monomer into bulk may be an important factor to support growth of graft polymer.     

Preparation and properties of novel environment-sensitive membranes prepared by graft polymerization onto a porous membrane

The present work is concerned with the preparation and some properties of novel environment-sensitive membranes. A porous poly (vinylidene fluoride) membrane (pore size 0.22 μm) was pretreated by air plasma; subsequently, hydrophilic monomers were graft polymerized on the treated surface. Since the filtration characteristics of the obtained membranes reflect the configuration of the grafted chains, these can be changed reversibly from ultrafilter to microfilter and vice versa in response to the membrane environment such as pH, solvent composition and ionic species. Grafted chains act as a sensor and a valve to regulate filtration characteristics. The poly(acrylic acid) grafted membrane for example is very sensitive to environmental pH. In the pH region of 1 to 5, the filtration rate sharply decreased with increasing solution pH, the filtration rate at pH 1.4 being about ten times higher than at pH 5.2. Together with this decrease in filtration rate, the membrane gained the ability of ultrafiltration of macromolecular solutes such as dextran (M_w = 2,000,000) and albumin (M_w = 67,000). In the pH region of 5.2 to 7.5, filtration rate and solute rejection did not depend on pH. The pH sensitivity is reversible and reproducible. Because of characteristics such as the drastic alteration in filtration rate and solute separation properties and the quick response to solution conditions, the environment-sensitive membranes developed here may find applications in various areas of membrane technology.     

Indirect determination of Hg(II) based on reaction with metallic silver

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Thin-layer chromatographic separation of fluorescent amino acid derivatives of 5-isothiocyanato-1,3-dioxo-2-p-tolyl-2,3-dihydro-1H-benz[de]isoquinoline

Teile der Dissertationen von H. Görgen und J. Dörpinghaus, Med. Hochschule Hannover, 1978     

Polyethylene glycol in copper electrodeposition onto a rotating disk electrode

Many of the proprietary additive formulations that have been proposed to control the properties of metal electrodeposits include water soluble macromolecules. Among these are the hydrodynamically interesting polyethylene glycols ‘Polyox’. In the course of a rotating disk electrode study of the effects of additives in copper electrodeposition the present authors had cause to try the effects of low concentrations of Polyox in an acid copper sulphate plating solution. In the presence of an essential trace of chloride ion Polyox very strongly inhibited deposition below a critical overpotential at which current density rises extremely rapidly with increasing overpotential. These results suggest that below the critical overpotential chloride ions hold a film of Polyox onto the electrode surface and may also give the film some lateral cohesion. The film may be a Polyox-cuprous chloride complex. Striking spiral patterns form at the critical overpotential. Their characteristics are explained as the consequences of electrodeposition on a surface containing submicroscopic protrusions and depressions in conditions where current density increases very rapidly with potential.     

Membrane extraction and electrodeposition of silver(I) in systems with di(2-ethylhexyl) hydrogen phosphate

Extraction of silver(I) from nitric acid solution by electrodialysis with liquid membranes containing di(2-ethylhexyl) hydrogen phosphate with addition of tri-n-octylamine in 1,2-dichloroethane is studied. The effects of the composition of aqueous solutions and liquid membranes as well as of the basic parameters of electrodialysis on the Ag(I) transport and electrodeposition rates are examined, and the process conditions are optimized.     

The influence of poly(ethylene oxide) and illumination on the copper electrodeposition process onto n-Si(100)

In this study, we examined the influence of illumination and the presence of poly(ethylene oxide) (PEO) as an additive for the copper electrodeposition process onto n-Si(100). The study was carried out by means of cyclic voltammetry (CV) and the potential steps method, from which the corresponding nucleation and growth mechanism (NGM) were determined. Likewise, a morphologic analysis of the deposits obtained at different potential values by means of atomic force microscopy (AFM) was carried out. In a first stage, Mott-Schottky measurements so as to characterize the energetics of the semiconductor/electrolyte interface were made. Also, parallel capacity measurements were carried out in order to determine the surface state density of the substrate. It was found that when PEO concentration is increased, the number of these surface states decreases. The CV results indicated that the presence of PEO inhibits the photoelectrochemical reaction of oxide formation on the surface of the semiconductor. This allows a decrease in the overpotential associated with the electrodeposition process. The analysis of the j/t transients shows that the NGM corresponds to progressive three-dimensional (3D) diffusional controlled (PN3D(Diff)), which was confirmed by the AFM technique. Neither illumination nor the presence of PEO changes the mechanisms. Their influence is in that they diminish the size of the nuclei and the speed with which these are formed, which produces a more homogeneous electrodeposit.     

Fast electrodeposition of zinc onto single zinc nanoparticles

The zinc deposition reaction onto metallic zinc has been investigated at the single particle level through the electrode-particle collision method in neutral solutions, and in respect of its dependence on the applied potential and the ionic strength of a sulphate-containing solution. Depending on the concentration of sulphate ions in solution, different amounts of metallic zinc were deposited on the single Zn nanoparticles. Specifically, insights into the electron transfer kinetics at the single particles were obtained, indicating an electrically early reactant-like transition state, which is consistent with the rate-determining partial de-hydration/de-complexation process. Such information on the reaction kinetics at the nanoscale is of vital importance for the development of more efficient and long-lasting nanostructured Zn-based negative electrodes for Zn-ion battery applications.

     

Selective electrodeposition of ZnO onto Cu2O

The co-deposition of cuprous oxide (Cu₂O) and zinc oxide (ZnO) on indium tin oxide (ITO) substrate was executed by two different electrochemical methods and the formation mechanism of ZnO onto Cu₂O was investigated by ex-situ SEM, XRD, and XPS. The single galvanostatic electrodeposition step in a mixed nitrate electrolyte offered a useful method in preparing ZnO onto triangular Cu₂O islands formed. On the other hand, hexagonal shaped ZnO phase was electrodeposited on ITO substrate as well as on Cu₂O islands when two steps of the galvanostatic and potentiostatic process were applied.     

Determination of silver in solution with a piezoelectric detector after electrodeposition

Silver in solution is determined in situ by frequency change of a piezoelectric quartz crystal due to electrodeposition on the electrode of the crystal immersed in the solution. A test solution containing EDTA for masking other metal ions flows through a thermostated cell which contains the crystal with platinum-plated electrodes. The frequency change is proportional to the silver concentration in the range 10^?6?3 × 10^?5 M after electrodeposition for 10 min, and 2 × 10^?7?1 × 10^?6 M for 1 h.     

Direct electrodeposition of porous platinum honeycomb structures

Honeycomb platinum was electrodeposited from an aqueous solution of K₂PtCl₄ and H₂SO₄ in a simple one step procedure using hydrogen bubbles as a dynamic template. SEM studies revealed the structure to consist of interconnecting pores with sizes from 5 to 10 μm, with fine structure consisting of nodules of 100 to 200 nm with sharp extrusions that exhibited excellent electrocatalytic activity for methanol oxidation. The simplicity of the method and the quality of the surfaces prepared suggest applications in catalysis where a convenient method to prepare high surface area platinum in one step is desirable.     

Dynamics of copper electrodeposition onto fibrous carbon electrodes

Distribution of copper electrodeposited from a sulfuric acid solution onto fibrous carbon electrodes, copper deposition rate, and current efficiency by the metal were studied in relation to the electrolysis duration, electrical conductivity of the electrode, geometric current density, and solution flow rate. The variation of the electrode thickness on which copper ions discharge at the limiting diffusion current at various solution flow rates and the electrode thickness on which the whole amount of oxygen dissolved in the electrolyte is reduced were calculated in relation to the solution flow rate and geometric current density. The main factors governing the distribution of copper across the electrode thickness and the electrolysis parameters from the beginning of the process till ??clogging?? of a part of the electrode by the metal were determined.     

Investigation of structural and biological properties of N-heterocyclic carbene silver(I) and palladium(II) complexes

abstract

Computational investigations were done on bis(1-allyl-3-benzyl-2,3-dihydro-1H-benzo[d]imidazol-2-yl)silver(I), bis(1-benzyl-3-butyl-2,3-dihydro-1H-benzo[d]imidazol-2-yl)silver(I), bis(1-allyl-3-benzyl-2,3-dihydro-1H-benzo[d]imidazol-2-yl)dibromidepalladium(II), and bis(1-benzyl-3-butyl-2,3-dihydro-1H-benzo[d]imidazol-2-yl)dibromidepalladium(II) complexes. Related complexes were optimized at different six calculation levels which are HF/6-31G(LANL2DZ), HF/6-31G(d,p)(LANL2DZ), B3LYP/6-31G(LANL2DZ), B3LYP/6-31G(d,p)(LANL2DZ), M062X/6-31G(LANL2DZ) and M062X/6-31G(d,p)(LANL2DZ) levels in vacuo. IR and NMR spectrum are calculated and examined in detail. Energy diagram of molecular orbitals, contour diagram of frontier molecular orbitals, molecular electrostatic potential maps and the harmonic surface of related molecules are examined in detail. Finally, interactions between mentioned complexes and related proteins (1BNA, 1JNX, and 2ING) are investigated in detail. As a result, it is found that biological and anti-cancer properties of silver N-heterocyclic carbene complexes are higher than those of palladium complexes.     

Sorption of aqueous palladium onto synthetic hydroxyapatite

The sorption of Pd(II) on hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) has been studied at 25 °C as a function of pH, in 0.01 M NaClO₄, and 0.01 and 0.025 M Ca(ClO₄)₂ aqueous background electrolytes and Pd(II) concentration (9.3 to 47 ??M), trying to minimize some types of reactions, such as solid dissolution of and metal precipitation. The radiotracer palladium, ¹⁰⁹Pd, obtained by neutron irradiation, has been used to calculate the palladium??s distribution coefficients K _d between aqueous and solid phase. A mathematical treatment of results has been made by ion-exchange theory in order to interpret palladium sorption onto treated solid. For this, we take into account the existence of active sites at the hydroxyapatite surface, and the aqueous solution chemistry of palladium as well as the effect of phosphate anions from solid dissolution. The results can be explained as evidence of sorption of the species PdOH⁺, and of a mixed hydroxo complex of Pd²⁺ like (XCaO^?)?CPdOH⁺·nH₂O fixed onto {??Ca?COH} surface sites of the hydroxyapatite.     

Influence of base electrolytes on the electrodeposition of iron onto a silicon surface

Comparative electrodeposition of iron onto the surface of silicon was investigated at large overpotential in the presence of some base electrolytes. The nanostructure of the iron electrodeposits was analyzed with SEM and FE-SEM measurements. The results highlight the influences of ion specificity on the rate of hydrogen evolution and of selective ion adsorption on the morphology of the iron electrodeposits.