Electrochemical deposition of mesoporous nickel hydroxide films from dilute surfactant solutions

A series of micelle-templated mesoporous nickel hydroxide films were prepared by electrochemical deposition from dilute surfactant solutions by using different types of template and by varying plating solvent composition. Lamellar mesostructured Ni(OH)2 films are obtained with only anionic surfactant sodium dodecyl sulfate (SDS) as the template. In particular, a unique cooperative assembly fashion, that is, the combination between Ni2+ and a complex composed of the primary template SDS and a cosurfactant, such as triblock poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) copolymers and poly(ethylene glycol), was explored, by which two-dimensional hexagonal mesoporous Ni(OH)2 films were electrodeposited. Meanwhile, the deposition medium also plays a crucial role in determining the mesostructure of Ni(OH)2 films. For the composite nickel hydroxide films deposited from aqueous solution or dilute aqueous solution of ethylene glycol (<20 wt %) in the presence of SDS or the SDS-poly(alkylene oxide) polymer complexes, a mixed lamellar phase with d(001) = 37.4 A and d(001) = 28.5 A was obtained. However, single lamellar phase with d(001) = 37.4 A was electrodeposited from concentrated aqueous solutions of ethylene glycol (> or = 20 wt %). Furthermore, such deposition baths have access to hexagonal mesoporous nickel hydroxide films with d(100) = 37.4 A at 70 degrees C with the SDS-poly(alkylene oxide) polymer complexes as the templates. Within the potential window for Ni(OH)2, the morphology and quality of mesostructured films are significantly dependent on the deposition potential, while the mesostructures of the composite films always remain unchanged.     

Electrodeposition of nickel from sulfate solutions in the presence of aminoacetic acid

Kinetics of nickel electrodeposition from sulfate electrolytes in the presence of aminoacetic acid at pH of 2.0 and 5.5 in the temperature range 20–50°C is considered.     

Electrocatalysis of copper deposition from acid sulphate solutions by sulphite and selenite ions

The effects of traces of chloride, sulphur, selenium and tellurium dioxide and the selenate and tellurate ions on the electrodeposition of copper from acid copper sulphate have been studied. Low concentrations of chloride have little effect on deposition kinetics but concentrations up to 20 ppm significantly affect nodule formation. Sulphur dioxide and selenium dioxide are true electrocatalysts for deposition, with SeO₂ the more effective. Molecules in solution immediately adjacent to the electrode appear to be the active catalyst. The catalytic mechanism may be a reduction oxidation cycle involving the elements in unstable forms. The chloride ion is adsorbed according to a Langmuir type isotherm. Adsorbed chloride inhibits catalysis by SO₂ and SeO₂. The electrocatalysts have been used to demonstrate the effect of overpotential on the structure of copper deposited at constant current density.     

Crystallographic and morphological characterization of thin pentacene films on polycrystalline copper surfaces

The degree of crystallinity, the structure and orientation of crystallites, and the morphology of thin pentacene films grown by vapor deposition in an ultrahigh vacuum environment on polycrystalline copper substrates have been investigated by x-ray diffraction and tapping-mode scanning force microscopy (TM-SFM). Depending on the substrate temperature during deposition, very different results are obtained: While at 77 K a long-range order is missing, the films become crystalline at elevated temperatures. From a high-resolution x-ray-diffraction profile analysis, the volume-weighted size of the crystallites perpendicular to the film surface could be determined. This size of the crystallites increases strongly upon changing temperature between room temperature and 333 K, at which point the size of individual crystallites typically exceeds 100 nm. In this temperature region, three different polymorphs are identified. The vast majority of crystallites have a fiber texture with the (001) net planes parallel to the substrate. In this geometry, the molecules are oriented standing up on the substrate (end-on arrangement). This alignment is remarkably different from that on single-crystalline metal surfaces, indicating that the growth is not epitaxial. Additionally, TM-SFM images show needlelike structures which suggest the presence of at least one additional orientation of crystallites (flat-on or edge-on). These results indicate that properties of thin crystalline pentacene films prepared on technologically relevant polycrystalline metal substrates for fast electronic applications may be compromised by the simultaneous presence of different local molecular aggregation states at all temperatures.     

Selective extraction and concentration of dispersed copper from dilute solutions of copper and zinc ions with weakly basic aminoanionites

The possibility of selective extraction and multiple concentration of copper in the form of ultrafine precipitate from dilute Cu²⁺-Zn²⁺ solutions by using a suitable sorbent and an effective mode of its regeneration was demonstrated. The extraction was performed in the dynamic mode in column-type reactors filled with an aminoanionite as a selective complexing sorbent, the regeneration of which was conducted by chemical reduction of Cu²⁺ in the ionite after its saturation. It was established that saturation-reduction cycles repeated many times result in the accumulation of metallic copper at the surface and in the bulk of the sorbent. The mechanism of the process includes the formation of complexes of copper and zinc with amino groups of the ionite and the subsequent displacement of Zn²⁺ ions from the anionite due to its higher affinity to Cu²⁺ ions followed by the conversion of Cu²⁺ ions to an unsorbable form (dispersed metallic copper). It was demonstrated that the presence of dispersed copper stimulates the additional sorption of Cu²⁺ ions via redox conproportionation. This method makes it possible to obtain a degree of concentration of copper ions in three cycles >300% higher than that attainable in the purely ion-exchange mode (without chemical reduction).     

Adsorption studies of cesium on potassium copper nickel hexacyanoferrate(II) from aqueous solutions

Adsorption of cesium from aqueous solutions on potassium copper nickel hexacyanoferrate(II) (KCNF) has been investigated in batch experiments and optimized as a function of concentration of acids, salts and adsorbate using a radiotracer technique. The results are presented in terms of distribution coefficient, K_d (ml·g^–1). The uptake of cesium obeys a Freundlich adsorption isotherm over the concentration range of 3.7 to 37 mmol·l^–1 with b values of 0.77, 0.68 and 0.56 at temperatures of 293, 313, 333 K, respectively. The Langmuir adsorption isotherm is followed in the concentration range of 15 to 75 mmol·l^–1 in the same temperature range. The values of limiting adsorption concentration (C_m) have been found to be 2.58, 2.44 and 2.32 mmol·g^–1. The heat of adsorption was calculated as 26.43 kJ·mol^–1. The influence of a number of anions and cations on cesium retention has also been studied. Column experiments have been performed and breakthrough have been obtained under different operating conditions. The low cesium capacity of 1.1 mmol·g^–1 has been obtained under dynamic conditions as compared to batch experiments. Desorption of cesium from the column has been achieved (45.4%) by nitric acid solution of 8M concentration at a flow rate of 0.5 ml·min^–1.     

Ion activities and copper electrode reactions in magnesium sulphate solutions

Thermodynamic and kinetic studies have revealed conventional mean-ion and convenient single-ion activity coefficients for copper(II), magnesium and sulphate ions and standard exchange rates for either step of the liquid Cu(Hg)/Cu(II) electrode and of the solid Cu/Cu(II) electrode, all in 0.005 mol kg^?1 CuSO₄+0.005 mol kg^?1 H₂SO₄+(x?0.01) mol kg^?1MgSO₄ (for x=0.2 to 3) at 25°C. With increasing x, the sulphate activity coefficient steadily falls, the copper(II) and magnesium activity coefficients go through a minimum near x=1, and the standard rates fall. The kinetic changes with x reveal some information on double-layer and ligand effects.     

Electrodeposition of mercury on gold from very dilute mercury(II) solution

Flameless atomic absorption spectrometry (flameless a.a.s.) was applied to study the state of mercury deposited on a gold plate electrode from very dilute mercury(II) solution by controlled-potential electrolysis. A stable monolayer is formed on the gold electrode by the electrolysis at a potential about 200 mV more positive than the reversible Nernst potential for the reduction of mercury(II) to mercury(0). After the monolayer formation, bulk mercury is deposited on the monolayer at the reversible potential and an adatom layer is also found. The difference of activation free energies between the evaporation of mercury from the monolayer and that from bulk mercury corresponds to the underpotential shift for the electrodeposition of mercury on the gold electrode.     

Electrodialysis performance when recycling dilute nickel solutions directly into a plating bath

This work was performed to determine membrane performance characteristics when using low current electrodialysis to recover and recycle nickel (salts) from dilute waste waters. Results showed that nickel at typical plating rinse concentrations (3000 p.p.m.) can be transferred electrically across commercially available membranes, and directly into a concentrated Watt's nickel plating bath (72,000 p.p.m.). Recovery at approximately 90% current efficiency was possible at current densities as low as 3.0 mA/cm². Nickel and co-transported water were routinely recycled as a relatively concentrated solution which would not cause dilution, since it was well above plating bath strength at all but the lowest current densities.     

Crystallization of isotactic polystyrene from dilute solutions

The overall rate of crystallization of isotactic polystyrene from dilute solutions, 1% by weight, in trans-decalin and benzyl alcohol was studied as a function of temperature using dilatometry. These solvents were chosen because the dissolution temperatures of crystalline isotactic polystyrene are practically the same in both solvents. The overall rate of crystallization as a function of crystallization temperature showed a maximum in both solvents at about 50°C. At lower crystallization temperatures the rate of crystallization is much lower. The overall rate of crystallization of isotactic polystyrene in benzyl alcohol is far larger than in trans-decalin at the same undercooling throughout the temperature range, which is in apparent contradiction to present crystallization theories. At very large undercooling (T_c lower than about 0°C) the solutions of isotactic polystyrene in both solvents quickly become “rigid” gels. Surface replicas of freeze-etched gels indicate that a fringed micelle type of crystallization takes place at these low temperatures. The transition from folded chain crystallization to fringed micelle crystallization may be due to a stiffening of the polymer chain below about 50°C, with a reduced rotational mobility of the phenyl groups on the chain. If very dilute solutions, below 0.5% by weight, are crystallized at these low temperatures no gels were formed but fibrous crystals are produced which could be observed under the polarizing microscope.     

TheLangmuir-Freundlich equation in adsorption from dilute solutions on solids

Correlation between parameters obtained from the signle-solute and bisolute adsorption data by means of theLangmuir-Freundlich equation has been studied.     

Electrodeposition of copper on metal-filled composite support

When a metal is deposited onto low-conductive supports, the metal deposit propagates from the contact site over the electrode surface. In the work, a mathematic model of variation in the overvoltage in the course of galvanostatic growth of copper deposit is proposed. The model takes into account the kinetic parameters of electrodeposition and geometric characteristics of growing deposit, which were obtained by using independent measurements. The chronopotentiograms, which were calculated by the model, agree satisfactorily with the experimental data. This allows one to apply the model proposed for estimating the tangential growth rate by the kinetic parameters of electrodeposition and structural characteristics of deposit.     

Buried interfacial layer of highly oriented molecules in copper phthalocyanine thin films on polycrystalline gold

The growth of copper phthalocyanine thin films evaporated on polycrystalline gold is examined in detail using near edge x-ray absorption fine structure spectroscopy and surface sensitive x-ray photoemission spectroscopy. The combination of both methods allows distinguishing between the uppermost layers and buried interface layers in films up to approximately 3 nm thickness. An interfacial layer of approximately 3 ML of molecules with an orientation parallel to the substrate surface was found, whereas the subsequent molecules are perpendicular to the metal surface. It was shown that even if the preferred molecular orientation in thin films is perpendicular, the buried interfacial layer can be oriented differently.     

Electrodeposition of mercury on glassy carbon electrode from very dilute mercury(II) solution

Flameless atomic absorption sepctrometry (AAS) has been applied to the investigation of the electroreduction of mercury at the glassy carbon (GC) electrode in dilute mercury(II) solution. The atomic mercury which is produced by electrolysis is found both in the electrolyte solution and on the electrode. The evaporation experiment combined with the flameless AAS clearly shows that mercury(0) deposits on the GC electrode as metallic mercury and adatoms depending strongly on the concentration of mercury(II) in the solution. The monolayer formation and underpotential deposition cannot be observed in the mercury(II)/GC electrode system.     

Electrodeposition of Mo-Se thin films from a sulfamatic electrolyte

Mo-Se thin films have been electrodeposited on conducting tin oxide (SnO₂) coated glass substrates from a sulfamatic solution containing Na₂MoO₄ and H₂SeO₃ under potentiostatic conditions. The deposition potential varied from –0.6 V to –0.9 V, at a deposition temperature of 20–40 °C and pH 6.5. X-ray diffraction analysis revealed that the overall composition of the films deposited is consistent with the formation of MoO₂ and MoSe₂. The lattice parameters of the as-deposited MoSe₂ are a=b=3.2340 Å and c=13.2859 Å, which fits a hexagonal structure.     

Electrodeposition of cobalt oxide films from carbonate solutions containing Co(II)–tartrate complexes

An electrochemical procedure of anodic deposition of cobalt oxyhydroxide film on a glassy carbon substrate in an alkaline medium (i.e. pH 11.6) is described. The electrodeposited film was obtained either by voltage cycling or by potentiostatic conditions using non-deaerated 0.1 M Na₂CO₃ solutions containing 40 mM tartrate ions and 4 mM CoCl₂. The effects on the film formation and growth, such as tartrate–cobalt ratio, pH, applied potential, etc. were widely evaluated. The electrodeposition process, under anodic conditions and moderately alkaline solutions, most likely involves a redox transition Co(II)→Co(III)/Co(IV) with destruction of the tartrate complex and formation of insoluble oxide/hydroxide cobalt species on the glassy carbon surface. The resulting cobalt oxyhydroxide films were characterised by cyclic voltammetry (CV) in 0.1 M NaOH solutions and by scanning electron microscopy (SEM) analysis after different strategies of preparation and various electrochemical treatments. The electrochemical activity of the deposited films was checked using various organic molecules as model compounds.     

Adsorption of polypropylene from dilute solutions on a zeolite column packing

Faujasite type zeolite CBV-780 was tested as adsorbent for isotactic polypropylene by liquid chromatography. When cyclohexane, cyclohexanol, n-decanol, n-dodecanol, diphenylmethane, or methylcyclohexane was used as mobile phase, polypropylene was fully or partially retained within the column packing. This is the first series of sorbent-solvent systems to show a pronounced retention of isotactic polypropylene. According to the hydrodynamic volumes of polypropylene in solution, macromolecules of polypropylene should be fully excluded from the pore volume of the sorbent. Sizes of polypropylene macromolecules in linear conformations, however, correlate with the pore size of the column packing used. It is presumed that the polypropylene chains partially penetrate into the pores and are retained due to the high adsorption potential in the narrow pores.