Synthesis and characterization of Ni–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composite coatings containing different forms of alumina

Electrodeposited Ni–Al₂O₃ composite coatings were prepared using alumina powders synthesized from solution combustion method, precipitation method and a commercial source. Solution combustion synthesized alumina powder yielded α-phase; precipitation method yielded purely γ-phase; commercial alumina powder was a mixture of α-, δ- and γ-phases. A nickel sulfamate bath was used for electro-codeposition. The current densities (0.23 A dm⁻² for 20 h, 0.77 A dm⁻² for 6 h, 1.55 A dm⁻² for 3 h and 3.1 A dm⁻² for 1.5 h) and bath agitation speeds (100, 200, 600 and 1000 rpm) were varied. The pH variations of the bath were higher during the electrodeposition of combustion synthesized alumina. The effect of different forms of alumina particles on the microhardness and microstructure of the nickel composite coating was studied. Composite coating containing combustion synthesized alumina particles was found to have higher microhardness (550 HK). It was found that at lower agitation speed (100 rpm), bigger particles were incorporated and at higher agitation speed (1000 rpm), smaller particles were incorporated. The area fraction of alumina particles incorporated in nickel matrix was highest for commercial alumina (24%). This study shows that it is not suffice to take just the current density and stirring speeds into account to explain the properties of the coatings but also to take into account the source of particles and their properties.     

Redox and transport behaviors of Cu(I) ions in TMHA-Tf<Subscript>2</Subscript>N ionic liquid solution

The redox and transport behavior of monovalent copper species in an ammonium imide-type ionic liquid, trimethyl-n-hexylammonium bis((trifluoromethyl)sulfonyl)amide (TMHA-Tf₂N) were examined with a micro-disc electrode to clarify its applicability to, for example, electroplating. It was found that the diffusion coefficient of Cu(I) ions in TMHA-Tf₂N containing 12 mmol dm⁻³ Cu(I) ions was 1.2 × 10⁻⁶ cm² s⁻¹ and the redox potential of Cu(I)/Cu was in the potential range 0.1–0.2 V vs. I ⁻/I ₃⁻ at 50 °C. The diffusion coefficient was one order smaller than that of Cu(II) ions in aqueous solution due to the high viscosity of the ionic liquid. The diffusion coefficient of Cu(I) ion increased with rising temperature and was 1.0 × 10⁻⁵ cm² s⁻¹ at 112 °C, which was comparable to that of Cu(II) ions in aqueous CuSO₄ solutions at ambient temperature. This is accounted for by the drastic decrease in the viscosity of the ionic liquid solution with increasing temperature. The activation energy of diffusion was estimated to be 39 kJ mol⁻¹ in the ionic liquid solution.     

Electropolymerization of benzotriazole in room temperature ionic liquid [bmim]PF<Subscript>6</Subscript>

The electropolymerization of benzotriazole on an Au electrode was investigated via cyclic voltammetry and chronoamperometry in a room temperature ionic liquid medium, 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim]PF₆) containing glacial acetic acid. The chronoamperometric investigation revealed that the instantaneous nucleation predominated the potentiostatic electropolymerization of benzotriazole at the oxidation peak potential. Scanning electron microscopy indicated that the polymer film was compact and relatively smooth and infrared spectroscopy suggested the polymer chains were formed mainly via coupling of the unsaturated nitrogen atoms. The polymer was found to be highly electroactive, showing a quasi-reversible and stable pair of redox peaks centering at 0.9 V versus Ag/AgCl in 0.1 mol L⁻¹ H₂SO₄.     

Study of electrochemical properties and the charge/discharge mechanism for Li<Subscript>4</Subscript>Mn<Subscript>5</Subscript>O<Subscript>12</Subscript>/MnO<Subscript>2</Subscript>-AC hybrid supercapacitor

Spinel Li₄Mn₅O₁₂ was prepared by a sol–gel method. The manganese oxide and activated carbon composite (MnO₂-AC) were prepared by a method in which KMnO₄ was reduced by activated carbon (AC). The products were characterized by XRD and FTIR. The hybrid supercapacitor was fabricated with Li₄Mn₅O₁₂ and MnO₂-AC, which were used as materials of the two electrodes. The pseudocapacitance performance of the Li₄Mn₅O₁₂/MnO₂-AC hybrid supercapacitor was studied in various aqueous electrolytes. Electrochemical properties of the Li₄Mn₅O₁₂/MnO₂-AC hybrid supercapacitor were studied by using cyclic voltammetry, electrochemical impedance measurement, and galvanostatic charge/discharge tests. The results show that the hybrid supercapacitor has electrochemical capacitance performance. The charge/discharge test showed that the specific capacitance of 51.3 F g⁻¹ was obtained within potential range of 0–1.3 V at a charge/discharge current density of 100 mA g⁻¹ in 1 mol L⁻¹ Li₂SO₄ solution. The charge/discharge mechanism of Li₄Mn₅O₁₂ and MnO₂-AC was discussed.     

Simultaneous absorption of CO<Subscript>2</Subscript> and SO<Subscript>2</Subscript> into aqueous AMP/NH<Subscript>3</Subscript> solutions in binary composite absorption system

To enhance the absorption rate for CO₂ and SO₂, aqueous ammonia (NH₃) solution was added to an aqueous 2-amino-2-methyl-1-propanol (AMP) solution. The simultaneous absorption rates of AMP and a blend of AMP+ NH₃ for CO₂ and SO₂ were measured by using a stirred-cell reactor at 303 K. The process operating parameters of interest in this study were the solvent and concentration, and the partial pressures of CO₂ and SO₂. As a result, the addition of NH₃ solution into aqueous AMP solution increased the reaction rate constants of CO₂ and SO₂ by 144 and 109%, respectively, compared to that of AMP solution alone. The simultaneous absorption rate of CO₂/SO₂ on the addition of 1 wt% NH₃ into 10 wt% AMP at a p _A1 of 15 kPa and p _A2 of 1 kPa was 5.50×10⁻⁶ kmol m⁻² s⁻¹, with an increase of 15.5% compared to 10 wt% AMP alone. Consequently, the addition of NH₃ solution into an aqueous AMP solution would be expected to be an excellent absorbent for the simultaneous removal of CO₂/SO₂ from the composition of flue gas emitted from thermoelectric power plants.     

Design of Efficient Ce<Subscript>x</Subscript>M<Subscript>1−x</Subscript>O<Subscript>2−δ</Subscript> (M = Zr,Hf, Tb and Pr) Nanosized Model Solid Solutions for CO Oxidation

Abstract  

Nanosized Ce_xM_1−xO_2−δ (M = Zr, Hf, Tb and Pr) solid solutions were prepared by a modified coprecipitation method and thermally treated at different temperatures from 773 to 1073 K in order to ascertain the thermal behavior. The structural and textural properties of the synthesized samples were investigated by means of X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), BET surface area, X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy (RS) techniques. The catalytic efficiency has been performed towards oxygen storage/release capacity (OSC) and CO oxidation activity. The characterization results indicated that the obtained solid solutions exhibit defective cubic fluorite structure. The solid solutions of ceria–hafnia, ceria–terbia and ceria–praseodymium exhibited good thermal stability up to 1073 K. A new Ce_0.6Zr_0.4O₂ phase along with Ce_0.75Zr_0.25O₂ was observed in the case of ceria–zirconia solid solution due to more Zr⁴⁺ incorporation in the ceria lattice at higher calcination temperatures. The reducibility of ceria has been increased upon doping with Zr⁴⁺, Hf⁴⁺, Tb^3+/4+ and Pr^3+/4+ cations. This enhancement is more in case of Hf⁴⁺ doped ceria. Among various solid solutions investigated, the ceria–hafnia combination exhibited better OSC and CO oxidation activity. The high efficiency of Ce–Hf solid solution was correlated with its superior bulk oxygen mobility and other physicochemical characteristics.     

Highly efficient removal of phenol from aqueous solutions using graphene oxide/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composite membrane

To achieve superior separation performance in the phenol aqueous solutions treatment, a novel graphene oxide/Al₂O₃ composite membrane was prepared by a spin coating process. The microstructure measurement shows that the composite membrane has a multilayer structure and graphene oxide has been tightly coated on the surface of the Al₂O₃ membrane interlayer homogeneously. During the treatment of phenol aqueous solutions, the permeation flux and phenol rejection of the composite membrane were investigated. The results show the permeation flux of the membrane is about 1.153 L m^?2 h^?1 bar^?1 and the phenol rejection of the membrane increases to 99.9% when the phenol concentration is 0.01 g L^?1. The high phenol rejection of the composite membrane is mainly attributed to the physical sieving, the solution–diffusion effect and the hydrophobic nature of graphene oxide. All these results indicate the GO/Al₂O₃ composite membrane is a suitable material for the removal of phenol from aqueous solutions in environmental pollution management.     

Investigation of N<Subscript>2</Subscript>-fixation on polyaniline electrodes in methanol by electrochemical impedance spectroscopy

The ac response of polyaniline thin films on platinum electrodes was measured at different dc potentials during the N₂-fixation in methanol + LiClO₄ electrolyte with 0.03 mol L⁻¹ H₂SO₄ for the first time. The optimum film thickness was found to be 1.5 μm, N₂-pressure 50 bar and an optimum electrolysis potential of −0.12 V (NHE). The diffusion coefficients for N₂ into the polymer film was found to be (5 ± 2)×10⁻⁹ cm² s⁻¹.     

Electrochemical sensor for bisphenol A detection based on molecularly imprinted polymers and gold nanoparticles

A novel bisphenol A (BPA) sensor based on amperometric detection has been developed by using molecularly imprinted polymers (MIPs) and gold nanoparticles. The sensitive layer was prepared by electropolymerization of 2-aminothiophenol on a gold nanoparticles-modified glassy carbon electrode in the presence of BPA as a template. Cyclic voltammetry was used to monitor the process of electropolymerization. The properties of the layer were studied in the presence of Fe(CN)₆ ³⁻/Fe(CN)₆ ⁴⁻ redox couples. The template and the non-binding molecules were removed by washing with H₂SO₄ (0.65 mol L⁻¹) solution. The linear response range of the sensor was between 8.0 × 10⁻⁶–6.0 × 10⁻² mol L⁻¹, with a detection limit of 1.38 × 10⁻⁷ mol L⁻¹ (S/N = 3). The proposed MIPs sensor exhibited good selectivity for BPA. The stability and repeatability of the MIPs senor were found to be satisfactory. The results from real sample analysis confirmed the applicability of the MIPs sensor to quantitative analysis.     

Effects of antimony(III) on zinc electrodeposition from acidic sulfate electrolyte containing [BMIM]HSO<Subscript>4</Subscript>

The effect of antimony(III) on the cathodic current efficiency (CE), power consumption (PC), deposit morphology, and polarization behavior during electrodeposition of zinc from acidic sulfate solutions containing 1-butyl-3-methylimidazolium hydrogen sulfate-[BMIM]HSO₄ was investigated. The results indicated that the addition of Sb(III) alone decreased the CE, increased the PC, and deteriorated the quality of the zinc electrodeposits. However, the combined addition of Sb(III) and [BMIM]HSO₄ was found to be beneficial for zinc deposition and improved the surface morphology of the zinc electrodeposits. Maximum CE and minimum PC were obtained at the combined addition of 0.02 mg dm⁻³ Sb(III) and 5 mg dm⁻³ [BMIM]HSO₄. Depolarization of the cathode was noted in the presence of Sb(III) alone in the electrolyte whereas this effect was partly counteracted by the addition of [BMIM]HSO₄. Cathodic polarization curves were traced and analyzed to determine the electrokinetic parameters such as Tafel slope, transfer coefficient, and exchange current density so as to elucidate the nature of the electrode reactions. The data obtained from X-ray diffractogram revealed that the presence of Sb(III) did not change the structure of the electrodeposited zinc but affected the crystallographic orientation of the crystal planes.     

Synthesis of Indium Nanowires by Galvanic Displacement and Their Optical Properties

Single crystalline indium nanowires were prepared on Zn substrate which had been treated in concentrated sulphuric acid by galvanic displacement in the 0.002 mol L⁻¹ In₂(SO₄)₃-0.002 mol L⁻¹ SeO₂-0.02 mol L⁻¹ SDS-0.01 mol L⁻¹ citric acid aqueous solution. The typical diameter of indium nanowires is 30 nm and most of the nanowires are over 30 μm in length. XRD, HRTEM, SAED and structural simulation clearly demonstrate that indium nanowires are single-crystalline with the tetragonal structure, the growth direction of the nanowires is along [100] facet. The UV-Vis absorption spectra showed that indium nanowires display typical transverse resonance of SPR properties. The surfactant (SDS) and the pretreatment of Zn substrate play an important role in the growth process. The mechanism of indium nanowires growth is the synergic effect of treated Zn substrate (hard template) and SDS (soft template).     

Determination of cadmium (II) using H<Subscript>2</Subscript>O<Subscript>2</Subscript>-oxidized activated carbon modified electrode

Pristine activated carbon (AcC) was oxidized by H₂O₂ under ultrasonic conditions. Compared with pristine AcC, the H₂O₂-oxidized AC possesses higher accumulation ability to trace levels of Cd²⁺. Based on this, a highly sensitive, simple and rapid electrochemical method was developed for the determination of Cd²⁺. In 0.01 mol L⁻¹ HClO₄ solution, Cd²⁺ was effectively accumulated at the surface of H₂O₂-oxidized AcC modified paste electrode, and then reduced to Cd under −1.10 V. During the following potential sweep from −1.10 to −0.50 V, reduced Cd was oxidized and a sensitive stripping peak appears at −0.77 V. The stripping peak current of Cd²⁺ changes linearly with concentration over the range 5.0 × 10⁻⁸ to 5.0 × 10⁻⁶ mol L⁻¹. The limit of detection was found to be 3.0 × 10⁻⁸ mol L⁻¹ for 2-min accumulation. Finally, this new sensing method was successfully used to detect Cd²⁺ in waste water samples.     

Electrochemical study of the codeposition of Mg–Li–Al alloys from LiCl–KCl–MgCl<Subscript>2</Subscript>–AlCl<Subscript>3</Subscript> melts

This work presents a novel electrochemical study on the codeposition of Mg, Li and Al on a molybdenum electrode in LiCl–KCl–MgCl₂–AlCl₃ melts at 943 K to form Mg–Li–Al alloys. Cyclic voltammograms (CVs) showed that the underpotential deposition (UPD) of magnesium on pre-deposited aluminum leads to the formation of a liquid Mg–Al solution, and the succeeding underpotential deposition of lithium on pre-deposited Mg–Al leads to the formation of a liquid Mg–Li–Al solution. Chronopotentiometric measurements indicated that the codeposition of Mg, Li and Al occurs at current densities lower than −0.47 A cm⁻² in LiCl–KCl–MgCl₂ (0.525 mol kg⁻¹) melts containing 0.075 mol kg⁻¹ AlCl₃. Chronoamperograms demonstrated that the onset potential for the codeposition of Mg, Li and Al is −2.100 V, and the codeposition of Mg, Li and Al is formed when the applied potentials are more negative than −2.100 V. The diffusion coefficient of aluminum ions in the melts was determined by different electrochemical techniques. X-ray diffraction and inductively coupled plasma analysis indicated that α, α + β and β Mg–Li–Al alloys with different lithium and aluminum contents were obtained via potentiostatic and galvanostatic electrolysis.     

Effects of temperature and current density on zinc electrodeposition from acidic sulfate electrolyte with [BMIM]HSO<Subscript>4</Subscript> as additive

The effects of temperature and current density on cathodic current efficiency, specific energy consumption, and zinc deposit morphology during zinc electrodeposition from sulfate electrolyte in the presence of 1-butyl-3-methylimidazolium hydrogen sulfate ([BMIM]HSO₄) as additive were investigated. The highest current efficiency (93.7%) and lowest specific energy consumption (2,486 kWh t⁻¹) were achieved at 400 A m⁻² and 313 K with addition of 5 mg dm⁻³ [BMIM]HSO₄. In addition, the temperature dependence of some kinetic parameters for the zinc electrodeposition reaction was experimentally determined. Potentiodynamic polarization sweeps were carried out to obtain the expression for each parameter as a function of temperature. In the condition studied, the exchange current density depended on temperature as ln(i ₀) = −a/T + b and the charge transfer coefficient was constant. Moreover, the adsorption of the additive on cathodic surface obeyed the Langmuir adsorption isotherm. The associated thermodynamic parameters indicated the adsorption to be chemical.     

Facile Solvothermal Synthesis Ni(OH)<Subscript>2</Subscript> Nanostructure for Electrochemical Capacitors

Nickel hydroxide nanosheets were successfully synthesized by facile solvothermal method without any template. The structure and morphology of the as-prepared sample were characterized by X-ray diffraction, Fourier transform infrared spectroscopy and transmission electron microscopy. The observations revealed the formation of hexagonal phase β-Ni(OH)₂ nanosheets with an average diameter of about 100–120 nm. Electrochemical studies were carried out using cyclic voltammetry and galvanostatic charge–discharge tests, respectively. A maximum specific capacitance of 2,342 F g⁻¹, which is the highest reported for a β-Ni(OH)₂ electrode, could be achieved in 6 mol L⁻¹ KOH electrolyte within the potential range of 0–0.50 V (vs. SCE) for the obtained β-Ni(OH)₂ electrode at 0.4 A g⁻¹, suggesting its potential application in the electrode material for electrochemical capacitors.     

Chemical and electrochemical characterization of TiO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> atomic layer depositions on AZ-31 magnesium alloy

In this study, innovative TiO₂/Al₂O₃ mono/multilayers were applied by atomic layer depositions (ALD) on ASTM-AZ-31 magnesium/aluminum alloy to enhance its well-known scarce corrosion resistance. Four different configurations of ALD layers were tested: single TiO₂ layer, single Al₂O₃ layer, Al₂O₃/TiO₂ bilayer and Al₂O₃/TiO₂/Al₂O₃/TiO₂ multilayer deposited using Al[(CH₃)]₃ (trimethylaluminum, TMA), and TiCl₄ and H₂O precursors. All depositions were performed at 120°C to obtain an amorphous-like structure of both oxide layers. The four coatings were then investigated using different techniques, such as scanning electron microscope (SEM), stylus profilometer, glow discharge optical emission spectrometry (GDOES) and polarization curves in 0.05-M NaCl solution. The thickness of all the coatings was around 100 nm. The layers compositions were successfully investigated by the GDOES technique, although obtained data seem to be affected by substrate roughness and differences in sputtering rates between ceramic oxides and metallic magnesium alloy. Corrosion resistance showed to be strongly enhanced by the nanometric coatings, giving lower corrosion current densities in 0.05-M NaCl media with respect to the uncoated substrate (from 10⁻⁴ to 10⁻⁶ A/cm² for the single layers and from 10⁻⁴ to 10⁻⁸ A/cm² for the bi- and multilayers). All polarization curves on coated samples also showed a passive region, wider for the bi-layer (from −0.58 to −0.43 V with respect to Ag/AgCl) and multilayer (from −0.53 to −0.38 V with respect to Ag/AgCl) structures.     

Role of Mo<Superscript>6+</Superscript> during nickel electrodeposition from sulfate solutions

The effect of Mo⁶⁺ on the current efficiency, deposit quality, surface morphology, crystallographic orientations and polarisation behaviour of the cathode during electrodeposition of nickel from sulfate solutions was investigated. Mo⁶⁺ did not have a significant effect on current efficiency over the concentration range 2–100 mg dm⁻³. However; a decrease in current efficiency by a magnitude of more than 20% was seen at 500 mg dm⁻³. The quality of the nickel deposit with reference to the visual appearance and contamination level varied with varying concentration of Mo⁶⁺; this was also reflected in the morphology and crystallographic orientations of the deposits. Addition of Mo⁶⁺ to the electrolyte introduced two new crystal planes i.e., (220) and (311). Depolarisation of the cathode was noted at lower concentrations of Mo⁶⁺ (2–40 mg dm⁻³) whereas polarisation of the cathode was observed at Mo⁶⁺ concentration >40 mg dm⁻³ .The effect of Mo⁶⁺ on parameters such as Tafel slope (b), transfer coefficient (α) and exchange current density (i ₀) were also determined.     

BF<Subscript>3</Subscript>OEt<Subscript>2</Subscript>-coinitiated cationic polymerization of cyclopentadiene in the presence of water at room temperature

The cationic polymerization of cyclopentadiene (CPD) with 1-(4-methoxyphenyl)ethanol (1)/BF₃OEt₂ initiating system in CH₂Cl₂:CH₃CN 4:1 (v/v) mixture at room temperature and in the presence of water ([H₂O]/[BF₃OEt₂] up to 8) is reported. The number-average molecular weights of obtained polymers increased in direct proportion to monomer conversion or initial monomer concentration (M _n ≤ 4,000 g mol⁻¹) in agreement with calculated values, and were inversely proportional to initiator concentration. Polymer MWDs were relatively narrow (M _w/M _n = 1.4–1.7) up to 60% of monomer conversion. It was also shown that regioselectivity of CPD polymerization with 1/BF₃OEt₂ initiating system did not depend significantly on water, monomer, or initiator concentration (1,4-structures content was nearly 60% in all cases).     

Photoelectrochemical characterization of the synthetic crednerite CuMnO<Subscript>2</Subscript>

High quality crednerite CuMnO₂ was prepared by solid state reaction at 950 °C under argon flow. The oxide crystallizes in a monoclinically distorted delafossite structure associated to the static Jahn–Teller (J–T) effect of Mn³⁺ ion. Thermal analysis showed that it converts reversibly to spinel Cu _x Mn_3−x O₄ at ~420 °C in air and further heating reform the crednerite above 940 °C. CuMnO₂ is p-type, narrow semiconductor band gap with a direct optical gap of 1.31 eV. It exhibits a long-term chemical stability in basic medium (KOH 0.5 M), the semi logarithmic plot gave an exchange current density of 0.2 μA cm⁻² and a corrosion potential of ~−0.1 V_SCE. The electrochemical oxygen insertion/desinsertion is evidenced from the intensity–potential characteristics. The flat band potential (V _fb = −0.26 V_SCE) and the holes density (N _A  = 5.12 × 10¹⁸ cm⁻³) were determined, respectively, by extrapolating the curve C ⁻² versus the potential to the intersection with C ⁻²  = 0 and from the slope of the Mott–Schottky plot. From photoelectrochemical measurements, the valence band formed from Cu-3d wave function is positioned at 5.24 ± 0.02 eV below vacuum. The Nyquist representation shows straight line in the high frequency range with an angle of 65° ascribed to Warburg impedance originating from oxygen intercalation and compatible with a system under mass transfer control. The electrochemical junction is modeled by an equivalent electrical circuit thanks to the Randles model.     

Electrochemical oxidation of an acid dye by active chlorine generated using Ti/Sn<Subscript>(1−<Emphasis Type="Italic">x</Emphasis>)</Subscript>Ir<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript> electrodes

The generation of active chlorine on Ti/Sn_(1−x)Ir _x O₂ anodes, with different compositions of Ir (x = 0.01, 0.05, 0.10 and 0.30 ), was investigated by controlled current density electrolysis. Using a low concentration of chloride ions (0.05 mol L⁻¹) and a low current density (5 mA cm⁻²) it was possible to produce up to 60 mg L⁻¹ of active chlorine on a Ti/Sn_0.99Ir_0.01O₂ anode. The feasibility of the discoloration of a textile acid azo dye, acid red 29 dye (C.I. 16570), was also investigated with in situ electrogenerated active chlorine on Ti/Sn_(1−x)Ir _x O₂ anodes. The best conditions for 100% discoloration and maximum degradation (70% TOC reduction) were found to be: NaCl pH 4, 25 mA cm⁻² and 6 h of electrolysis. It is suggested that active chlorine generation and/or powerful oxidants such as chlorine radicals and hydroxyl radicals are responsible for promoting faster dye degradation. Rate constants calculated from color decay versus time reveal a zero order reaction at dye concentrations up to 1.0 × 10⁻⁴ mol L⁻¹. Effects of other electrolytes, dye concentration and applied density currents also have been investigated and are discussed.