Electrocatalysts on supports—III. Electrocatalytic and adsorption properties of microdeposits and thin films of platinum group metals

The adsorption and electrocatalytic properties of the microdeposits of rhodium on gold, palladium on niobium, ruthenium and osmium on titanium, and palladium thin films on glass carbon and nickel have been investigated. It is shown that hydrogen adsorption on rhodium and ruthenium microdeposits is characterized by a low binding energy and that on palladium films by a high binding energy. The cathodic hydrogen evolution rate on ruthenium microdeposits and palladium films on glass carbon and nickel is lower than that on the corresponding bulk metals. These results are consistent with the assumption of the predominant effect of the electronic interaction between microdeposits and thin films on the one hand and the supports on the other, which affects the hydrogen adsorption energy parameters.     

Impedance spectroscopic studies of sol–gel derived barium strontium titanate thin films

In the present work electroceramic thin films of barium strontium titanate (Ba_1?xSr_xTiO₃ – BST) were deposited on stainless steel substrates by sol–gel technique. Homogeneous Ba_0.6Sr_0.4TiO₃ thin films as well as spatially inhomogeneous BST thin films exhibiting artificial gradients in composition normal to the growth surface were deposited. Both up- and down-graded BST films were fabricated by depositing successive layers with Sr mole fraction x ranging from x = 0.5 to x = 0.3. In the present study the tool of impedance spectroscopy has been used to study the dielectric properties of BST thin films at room temperature. To analyze the impedance spectroscopy data the Nyquist (Z″ vs. Z′) plots as well as the simultaneous representation of the imaginary part of impedance and electrical modulus (Z″, M″) vs. frequency were used. Experimental data were fitted using the CNLS fitting method. Agreement between experimental and simulated data was established. The data indicated that the thin film samples fabricated can be represented by an equivalent circuit with two relaxation frequencies.     

Electrochemical absorption of hydrogen in transition metal oxides—II. Sorption of hydrogen in titanium monoxide TiO

The absorption of hydrogen in titanium “monoxide” was studied electrochemcially by potential-step and ac techniques. The absorption equilibrium obeys the Crandall—Faughnan—Armand isotherm and the chemical diffusion coefficient is a linear function of concentration. The heat of absorption is 80 kJ (g atom H)⁻¹ and the true diffusion coefficient D₀ is 4 × 10⁻¹³ cm²s⁻¹ at 20°C. The absorption occurs in oxygen vacancies.     

Electrochemical and in situ mössbauer studies of tin passivation

The tin passivation in borate buffer was studied using potentiodynamic curves recorded at high scanning rate (9 V min⁻¹, 3.6 V min⁻¹). The most important feature of these curves is the presence of a current peak at around — 1180 mV (vs sce) which had not been previously observed. The nature of the passive film formed in the vicinity of this potential was characterized using in situ Mössbauer measurements.On the basis of these results it was concluded that in borate buffer solution: (a) the passive film formed at more negative range of potentials (− 1180 to − 780 mV) is duplex, consisting of highly amorphous Sn(OH)₂ or hydrated stannous oxide and SnO₂ or Sn(OH)₄; (b) at more positive potentials, the passive layer consists only of Sn(IV) hydroxide or oxide which ensures a more efficient passivation.     

Infrared studies of so2 on carbons—I. Interaction of SO2 with carbon films

IR spectroscopic studies were carried out on the bond character of SO₂ molecules adsorbed on the surface of carbons. No spectroscopic evidence was found for the formation of any stable surface carbon-sulfur complexes after interaction of SO₂ with a carbon surface in the temperature range 25–600 Simultaneous adsorption of SO₂ and O₂ occurs with the participation of π electrons of condensed aromatic systems. It can be concluded from IR investigations that SO₂ retards the oxidation of carbon by O₂.     

Electrochemical synthesis and surface characterization of hexagonal Cu–ZnO nano-funnel tube films

An electrochemical deposition technique was used to synthesis hexagonal nano-funnel tube films on zinc foil, utilizing an electrolyte of ZnCl₂+H₂O₂ under ambient conditions. The structures, morphologies, chemical compositions, and optical properties of the synthesized films were characterized using X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–visible diffuse reflectance spectrometry (UV-vis-DRS), photoluminescence (PL) spectrometry, and energy-dispersive X-ray spectrometry (EDS) techniques. The XRD pattern showed a set of diffraction peaks that were indexed to the ZnO, Zn(OH)₂, and Cu phases. The SEM observations revealed a cauliflower-like morphology consisting of branches in the form of nano-funnel tubes. The TEM results demonstrated that the synthesized film was comprised of several branches. The EDS studies confirmed the presence of only Cu, Zn, and O atoms. The UV-vis-DRS spectrum showed the onset of the band gap absorption peak at ～375 nm. The PL studies evaluated various emission bands that originated from different defect mechanisms. In addition, the hexagonal nano-funnel tube film showed a good superhydrophobicity, with a water contact angle of ～153°.     

Electrochemical synthesis of glyoxylic acid from glyoxal—III. influence of the adatoms on the yields of the reaction on platinum and vitreous carbon electrodes

The addition in a cell of small amounts of adatoms like Ag, Sn, Bi, Tl or Au increases the yield of glyoxylic acid prepared by electrochemical oxidation of glyoxal on a platinum anode. The chemical yields reach values of 67 and 69% at 20 and 50°C respectively when they were of 58 and 62% in the same experimental conditions on bright platinum. The glyoxal is almost completely eliminated.     

Reactive extraction of d,l-phenylalanine with trioctyl-methyl-ammonium chloride (TOMAC) as a carrier—III. Equilibrium and mass transfer investigations

The partition coefficient and the equilibrium constants are evaluated for the reactive extraction of d, l-phenylalanine from the aqueous phase into xylene/TOMAC (liquid ion exchanger) at different amino acid and carrier concentration. Also, the interfacial mass transport of the reactive extraction process is investigated, and the mass transfer coefficients of the components are identified. The influence of coextraction of buffer- and/or OH⁻-ions is discussed.     

Infrared studies of SO2 on carbons—II. the SO2 species adsorbed on carbon films

IR spectroscopic studies were carried out on the character of interactions between adsorbed molecules of SO₂ and O₂, H₂O or H₂S on the surface of carbons. The character of bonding between adsorbed molecules and the carbon films depends on the chemical structure of the surface functional groups. Weakly adsorbed SO₂ gives rise to the bands at 1330 and 1140 cm⁻¹. Strongly held SO₂ is indicated by the band around 1045 cm⁻¹. Catalytic activity of carbon films in the oxidation of aqueous sulfur dioxide solution has been studied. The results suggest that Superoxide ions take part in the adsortion of acids on the surface of carbon as well as in the catalytic oxidation of aqueous SO₂ solution by O₂.     

Equilibrium,kinetics and thermodynamic studies for the removal of organophosphorus pesticide using Amberlyst-15 resin: Quantitative analysis by liquid chromatography–mass spectrometry

In the present paper, Amberlyst-15 resin was used for the removal of malathion. Various experimental parameters such as effect of pH, contact time, resin dose, initial malathion concentration and temperature were studied to find the optimum conditions for malathion removal. The removal rate of malathion by Amberlyst-15 was rapid and equilibrium was established within 30 min. Kinetic studies showed better applicability for pseudo-second-order model and equilibrium data was best fitted to Freundlich isotherm model. The thermodynamic parameters showed that the adsorption of malathion was feasible, endothermic and spontaneous. The concentration of malathion was determined using ultra-performance liquid chromatography–tandem mass spectrometry.     

Polysulfone Membranes. III. Performance Evaluation of Polyethersulfone—PVP Membranes

Abstract

The performance of membranes produced from casting solutions consisting of polyethersulfone (PES), poly-(N-vinyl-pyrrolidone) (PVP), and N-methyl-2-pyrrolidinone (NMP) were systematically studied. Zero-shear casting solution viscosities for these polymer solutions were determined as a function of PES and PVP concentrations. Ultrafiltration membranes were then cast using the phase inversion technique and characterized by separation experiments using polyethylene glycols of various molecular weights as test solutes. A pore flow model was fitted to the resulting separation data to provide estimates of the average pore radius and membrane porosity. These parameters were used to compare laboratory results for this membrane casting solution system with performance data for commercially available polyethersulfone membranes.     

I.R. studies of carbons—VII. The pyrolysis of a phenol-formaldehyde resin

Infrared spectra were recorded of the chars produced by pyrolyzing a Novolac phenol-formaldehyde resin in vacuum and in nitrogen, using photothermal beam deflection spectroscopy. The two pyrolysis techniques led to the same results. Thermal branching and cross-linking occurred near 350°C, with the formation of diphenyl ether structures. These reactions continued at higher temperatures when aryl-aryl ethers were formed. Autooxidation is not an important degradation pathway. Although some changes occur, the polymer network remains essentially intact until 500°C, the aromatic systems being held apart and stabilized by aliphatic bridges. In the 500–560°C range, however, drastic changes occur in that the network collapses, aliphatic bridges are destroyed, hydrocarbonaceous residues are eliminated and those remaining are altered, polyaromatic domains form, and the resulting char is much like other intermediate temperature chars.     

Microcalorimetric and infrared spectroscopic studies ofγ-Al2O3 modified by tin oxides

Microcalorimetric and infrared spectroscopic studies of ammonia and carbon dioxide adsorption have been used to study the effects on the acid/base properties of adding tin oxide to-Al₂O₃. The addition of SnO₂ to-Al₂O₃ decreases the number of strong acid sites (heats of ammonia adsorption higher than 140 kJ/mol), increases the number of weaker acid sites (heats from 110 to 130 kJ/mol), and decreases slightly the number of basic sites (heats of carbon dioxide adsorption from 70 to 150 kJ/mol). In contrast, the presence of SnO on-Al₂O₃ decreases the total number of acid sites (heats of ammonia adsorption higher than 70 kJ/mol) and eliminates most of the basic sites. Infrared spectroscopy of adsorbed ammonia reveals interactions between aluminum cations and stannous ions, leading to a decrease in the strength of the Lewis acid sites associated with aluminum cations.     

Electrochemical synthesis of polypyrrole (PPy) and PPyǀmetal composites on copper electrode and investigation of their anticorrosive properties

This study reports corrosion protection behaviour of various metal cations electrodeposited onto polypyrrole (PPy) coated copper (Cu) electrode. Before electropolymerization of pyrrole, the Cu electrode was passivated in 0.1 M oxalic acid via cyclic voltammetry method. After the coating process, metal cation electrodeposition onto PPy coating was carried out in 10⁻² M CuCl₂, ZnCl₂, FeCl₂ and NiCl₂ solutions. Corrosion behaviour of uncoated, PPy and PPy|metal coated Cu electrodes was studied in 0.1 M H₂SO₄ solution by using potentiodynamic polarization, chronoamperometric and impedance spectroscopic measurements. Surface morphologies were examined by scanning electron microscope (SEM). All the electrochemical measurements were in good agreement showing that metal electrodeposited PPy coated Cu electrodes have a higher corrosion resistance. Furthermore, SEM results show that while all the samples have a homogeneous distribution of metal cations, zinc and nickel have a much better homogeneous distribution compared to copper and iron. It was found that the best corrosion protection is provided by PPy|Zn and PPy|Ni coatings and there is a significant increase in their polarization resistance with increasing amounts of electrodeposited cations.     

IR studies of carbons—VI. The effects of KHCO3 on cellulose pyrolysis and char oxidation

The pyrolysis in vacuum of cellulose containing 5 wt. % of KHCO₃ (KHC) was followed by IR photothermal beam deflection spectroscopy, and compared with observations made with pure cellulose (PC) [Carbon 21, 283(1983)]. The KHCO₃, and KOH and K₂CO₃ formed from it, drastically altered the cellulose carbonization and the subsequent oxidation of the KHC chars. KHC became charred at 140 °C and the cellulose disrupted at 220 °C. The surface layer was a mixture of weak acid K salts. K₂CO₃ was not formed until 310 °C and persisted until about 500 °C, when metallic K was evolved. Unlike PC, the surface layer contained no aromatic CH structures. The carbonization of KHC proceeded more rapidly and to a greater extent than with PC. The oxidation of KHC chars was also markedly affected; burn-off occurred at much lower temperatures, and the gasification temperature range was narrower, than with PC chars.     

Microcalorimetric, reaction kinetics and DFT studies of Pt–Zn/X-zeolite for isobutane dehydrogenation

Microcalorimetric measurements of the adsorption of H₂ and C₂H₄ were carried out at 300 K on a Pt–Zn/X-zeolite catalyst (Pt:Zn atomic ratio equal to 1:1). The initial heats of H₂ and C₂H₄ adsorption were equal to 75 and 122 kJ/mol, respectively, and these values are weaker than the values of 90 and 155 kJ/mol typically observed for supported Pt catalysts. Reaction kinetics measurements for isobutane dehydrogenation over the Pt–Zn/X-zeolite catalyst were carried out at temperatures from 673 to 773 K, at isobutane pressures from 0.01 to 0.04 atm, and at hydrogen pressures from 0.1 to 0.7 atm. The catalyst shows high activity and selectivity for dehydrogenation of isobutane to isobutylene. The reaction kinetics can be described with a Horiuti–Polanyi reaction scheme. DFT calculations were carried out for the adsorption of ethylene on slabs of Pt(111), Pt₃Zn(111) and PtZn(011). Results from these calculations indicate that addition of Zn to Pt weakens the binding energies of -bonded ethylene, di--bonded ethylene, and ethylidyne species on atop, bridged, and three-fold Pt sites, respectively. These effects are most significant for the bonding of ethylidyne species, and they are least significant for -bonded ethylene species. Results from DFT calculations for the adsorption of formaldehyde show that addition of Zn to Pt weakens the di--bonding at Pt–Pt sites; however, this weakening effect of Zn on formaldehyde adsorption is less significant than the effect on ethylene adsorption. Moreover, the preferred location for adsorption of formaldehyde on PtZn(011) is a Pt–Zn site, whereas the preferred location for adsorption of ethylene is a Pt–Pt site. Thus, formaldehyde is adsorbed more strongly by 53 kJ/mol on PtZn(011) compared to the di--adsorption of ethylene, whereas formaldehyde and ethylene adsorb in the di--forms with comparable energies on Pt(111). This preferred adsorption of formaldehyde compared to ethylene on PtZn(011) may be at least partially responsible for the enhanced selectivity of Pt–Zn-based catalysts for hydrogenation of C=O groups compared to C=C bonds in ,-unsaturated aldehydes.     

Electrochemical generation of reactive nitrogen species—VIII. Anodic N,N-coupling of N-aminophthalimides

Anodic N,N-coupling of N-aminophthalimides (1) was investigated in dry acetonitrile by cyclic voltammetry and preparative electrolysis. The compound 1 showed mainly three anodic peaks in the voltammogram. Anodic oxidation of 1 at the first peak potential provided 1,4-diphthalyltetrazane (3) together with 1,4-diphthalyltetrazene (4) and phthalimide (5), whereas the oxidation at the second peak potential gave 4 and 5. It was found that 3 could be anodically converted into 4 in a high current efficiency and a reasonable yield. On the basis of the results, N,N-coupling mechanism was discussed.