Electrochemical synthesis and characterization of poly(m-phenylenediamine) films on copper for corrosion protection

Poly(m-phenylenediamine) (PMPD) films were electrosynthesized on copper by using cyclic voltammetry in near-neutral aqueous sodium oxalate medium. Attenuated Total Reflectance-Fourier Transform Infrared spectroscopy, scanning electron microscopy and atomic force microscopy were utilized to characterize the obtained PMPD films. Corrosion performances of uncoated and PMPD coated copper electrodes were investigated in 0.1 M H₂SO₄ by open circuit potential–time (E_ocp–t) curves, anodic polarization and electrochemical impedance spectroscopy techniques. Corrosion test results demonstrate that the PMPD coating appears to enhance protection of copper for considerable immersion periods. The percent protection efficiency value (E%) was found to be 80% even after 168 h immersion time in corrosive test solution.     

The photoelectrochemical behaviour of electrochemically deposited CdTe films

Cathodic photocurrents due to hydrogen evolution were observed at p-CdTe films deposited cathodically (?200 ≈ ?400 mV vs Ag/AgCl) from aqueous solution of pH = 1.4 containing 1 M CdSO₄ and 1 mM TeO₂ and it was demonstrated that the photocurrents were improved significantly by removing excess free Te metal and by increasing the crystalline size of CdTe.     

Electrochemical and in situ FTIR studies of biferrocene platinum(II) complex

Electron transfer mechanism during redox process of Pt(LSB)₂, a derivative of S-benzyl-N-(ferrocenyl-1-methyl-metylidene)-dithiocarbazate (HLSB), is studied by cyclic voltammetry, differential pulse voltammetry, digitally simulation and in situ FTIR spectroelectrochemistry. Electrochemistry results indicated the redox process of Pt(LSB)₂ involves two consecutive one-electron steps. Coordination of Pt to HLSB resulted in the increase of electron-withdrawing of the dithiocarbazate group, which is demonstrated by the positive shift of redox potentials of Pt(LSB)₂ compared with those of HLSB. The peak-peak separation of 129 mV revealed a strong degree of electronic communication between the two-ferrocene moieties in Pt(LSB)₂. The results of in situ FTIR indicated that electronic communication takes place through the skeleton chain of HLSB due to the extensive electron delocalization in the whole molecule.     

Synthesis,crystal structures and spectral characterization of trans-bisaquabis(o-vanillinato)copper(II), cis-aquabis(o-vanillinato)copper(II) and aqua[bis(o-vanillinato)-1,2-ethylenediimin]copper(II)

trans-Bisaquabis(o-vanillinato)copper(II) (I), cis-aquabis(o-vanillinato)copper(II) (II) and aqua[bis(o-vanillinato)-1,2-ethylenediimin]copper(II) (III) complexes were synthesized and characterized by means of elemental analysis, IR and UV–vis spectroscopy, thermal analysis and X-ray diffraction techniques. The coordination geometry around Cu(II) is a octahedral with coordination number of six for I and is a square-pyramidal with coordination number of five for both II and III. In all three compounds, a three-dimensional structure is formed via C–H⋯O hydrogen-bond interactions and intermolecular π–π and π-ring interactions. The compounds I and III have two-dimensional hydrogen-bonded step-chain structure in xz-plane, while compound II has a zigzag chain structure in xy-plane. On the basis of the first DTA_max of the anhydrous complexes of I and II, the thermal stability sequence is trans-isomer > cis-isomer. This fact should be related with the binding of the ligand.     

Electrochemical and photoelectrochemical behaviour of passivated niobium electrodes during hydrogen evolution

The electrochemical and photoelectrochemical behavior of niobium electrodes passivated in 0.5 M H₂SO₄ and 1 M HNO₃ has been investigated. High intensity pulse lasers were used as light sources. This technique allows photoelectrochemical measurements with light wavelengths smaller than the band gap of the semiconducting passive film. The donor concentration and the flat band potential of the passive films were calculated from capacity measurements. The effect of cathodic hydrogen evolution on the behaviour of the oxide film formed was found to depend on the time of the cathodic treatment of the electrode. The results showed that the behaviour of the passive film formed on niobium in nitric acid is different from that formed in sulphuric acid. The calculated donor concentrations and the extrapolated flat band potentials indicate that the nature of the passive film depends on the formation medium. The adsorption of hydrogen on the passivated Nb-electrode up to a time limit of 1 ms could be traced using photocharge measurements with excitation energies less than the band gap energy of the semiconducing oxide film.     

Electrochemical behaviour of copper in neutral aerated chloride solution. II. Impedance investigation

A.c. and EHD impedance measurements were performed on a Cu rotating disc electrode immersed in neutral aerated NaCl and the results were compared with simulated curves according to the kinetic model developed in Part I. The agreement is good over the whole anodic range and at the corrosion potential. A slowing down of the mass transport rate is explained by diffusion through a surface layer (Cu₂O) at the corrosion potential and for the close anodic range. It is confirmed that, on the cathodic plateau, the interface may be considered as uniformly accessible for the cathodic partial reaction of oxygen reduction. However, at less cathodic potential a surface layer effect due to CuCl must also be taken into account. Diffusion coefficients for both O₂ and CuCl ₂ ^– were determined by EHD impedance.     

Electrochemical preparation and characterization of poly(1-amino-9,10-anthraquinone) films

Poly(1-amino-9,10-anthraquinone), PAAQ, films were prepared by electrochemical oxidation of the monomer, AAQ, in acetonitrile using LiClO₄ as supporting electrolyte. The influence of scan repetition, scan rate and monomer concentration on the formation of polymer film was studied. The electrochemical behavior of the formed polymer films was investigated in both non-aqueous and aqueous media. The prepared films were found to be more stable in organic solvents than in aqueous solutions. The investigated organic solvents are methanol, ethanol, acetone, carbon tetrachloride, benzene, and chloroform. The polymer film shows electrochemical response in both non-aqueous and aqueous media. In non-aqueous solutions it has a wide potential range of electroactivity (from −1.5 to +1.3 V). In aqueous media the polymer film shows electrochemical response in the potential range between −0.3 and +1.3 V only. The presence of quinone units suggests potential applications in diverse areas such as electrocatalytic processes and lithium ion batteries.     

Electrochemical and photoelectrochemical behaviour of passivated Ti and Nb electrodes in nitric acid solutions

Ti and Nb electrodes were passivated galvanostatically in nitric acid solutions. The electrochemical and photoelectrochemical behaviour of these electrodes was studied and compared with the behaviour of similar electrodes passivated in sulphuric acid solutions under the same conditions. The flatband potential and donor concentration of the passive films were obtained from the corresponding Mott-Schottky plots. The photoelectrochemical investigations were carried out using a pulsed laser which rendered measurements with photon energies smaller than the band gap. The results showed that the behaviour of passivated titanium in nitric acid was differing from its behaviour in sulphuric acid. The behaviour of the passivated niobium was not much affected by the exchange of the two acids.     

Electrochemical copper (II) sensor based on chitosan covered gold nanoparticles

This study outlines a new sensing platform based on glassy carbon electrodes modified by gold nanoparticles (AuNPs) for the determination of heavy metal. A glassy carbon electrode was modified by chitosan stabilized AuNPs. AuNPs were prepared by reducing gold salt with a polysaccharide chitosan. Here, chitosan acted as a reducing/stabilizing agent. The AuNPs were characterized with UV–Visible absorption spectroscopy, Fourier transform infrared spectroscopy, and transmission electron microscopy. Chitosan covered AuNPs were immobilized on the glassy carbon electrode for the determination of Cu (II) in aqueous solutions. The electrochemical determination of Cu (II) ions was performed using the differential pulse voltammetry technique. Some parameters for Cu (II) determination, such as pH, preconcentration time and electrolysis potential of Cu (II), were optimized. The detection limit was calculated as 5 × 10^?9 mol L^?1 by means of the 3:1 current-to-noise ratio. The interference of Cr(III), Fe(II), Ni(II), Pb(II), Mg(II), Zn(II), Ba(II) ions was investigated and showed a negligible effect on the electrode response. Recovery studies were carried out using tap water.     

In situ synthesis and dielectric properties of copper(II) and nickel(II) chiral Schiff base complexes

Two chiral Schiff base-containing complexes, [Cu(L¹)](ClO₄)₂·H₂O (1, L¹ = (S,S)-N1,N2-bis((1H-imidazol-4-yl)methylene)cyclohexane-1,2-diamine) and [Ni(L²)₂](ClO₄)₂ (2, L² = (S,S)-N1-((1H-imidazol-4-yl)methylene)cyclohexane-1,2-diamine) were synthesized from the reaction mixture of 1H-imidazole-4-carbaldehyde, (S,S)-1,2-diaminocyclohexane and Cu(ClO₄)₂·6H₂O or Ni(ClO₄)₂·6H₂O in methanol. Single-crystal X-ray diffraction analyses reveal that the in situ generated chiral Schiff base ligands L¹ and L² are bisubstituted and monosubstituted, respectively, corresponding to the different metal ions Cu^II and Ni^II. Variable-frequency and -temperature dielectric properties of 1 and 2 have been studied.     

Synthesis,crystal structure and nonlinear optical property of cadmium(II) and copper(II) complexes with novel chiral ligand

Two novel metal-organic frameworks (MOFs) [Cd(3-MPCA)₂ · H₂O] · 5.5H₂O (1) and [Cu(3-MPCA)₂ · H₂O] · 4H₂O (2) [3-MPCA⁻ = (1R, 3S)-1,2,2-trimethyl-3-(pyridin-3-ylmethylcarbamoyl)cyclopentanecarboxylate] were hydrothermally synthesized and characterized by X-ray crystallography. Complexes 1 and 2 are homochiral and have similar one-dimensional (1D) chain structure, which are further linked by strong hydrogen bonds to give 3D architectures. There are oxygen hexmers and heptamers from water molecules and carbonyl group in 1 with O⋯O distances and O–O–O angles comparable to the corresponding values in ice. Nonlinear optical measurements on powdered sample of 1 and 2 revealed that they display second-harmonic-generation (SHG) response of 0.8 and 0.3 times of that for urea, respectively.     

Combined effects of sucrose and copper(II) ions on the growth and copper(II) bioaccumulation properties of Candida sp

A microbiological process using Candida sp was developed for the removal of copper(II) ions in the presence of molasses as nutrient. The combined effects of sucrose (in molasses) and copper(II) ions on the growth and copper(II) bioaccumulation properties of adapted Candida cells was tested under laboratory conditions as a function of initial pH and single‐sucrose and dual‐sucrose and copper(II) ion concentrations. The optimum pH value for maximum growth and metal ion accumulation was determined as 4.0 for the microorganism. At a constant copper(II) concentration, growth and copper(II) bioaccumulation increased with increasing concentrations of molasses sucrose up to 15 gdm⁻³. Although increased initial copper(II) concentration increased the copper(II) uptake capacity of the microorganism, inhibition by copper(II) ions of the growth of Candida sp was observed at all the concentrations of copper(II) at all the sucrose concentrations studied. The non‐competitive inhibition kinetics (assuming copper(II) ions as the toxic inhibitory component) were used to define the relationship between the specific growth rate and molasses sucrose and copper(II) concentrations and model parameters were determined by using experimental data. © 2000 Society of Chemical Industry     

Electrochemical formation and characterization of porous titania (TiO2) films on Ti

Galvanostatically and potentiostatically formed surface oxide films on titanium in H₂O₂ free and H₂O₂ containing H₂SO₄ solutions were investigated. Conventional electrochemical techniques, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy, were used. In the absence of H₂O₂, the impedance response indicated a stable thin oxide film which depends on the mode of anodization of the metal. However, in the presence of H₂O₂ the film characteristics were changed. A significant decrease in the corrosion resistance of the surface film was recorded. The film characteristics were also found to be affected by the mode of oxide film growth and polarization time. The EIS results and the impedance data fitting to equivalent circuit models have shown that the oxide film consists of two layers. The electrochemical characteristics of the anodic films formed under different conditions have been discussed.     

Electrochemical behaviour of tetraazamacrocyclic nickel(II) complexes functionalized with crown ethers

Tetraazamacrocyclic nickel(II) complexes linked by the system of conjugated double bonds with one or two benzo-15-crown-5 moieties (2Ni and 3Ni) were synthesized and characterized. The CV of these complexes in acetonitrile (ACN) solution exhibited reversible Ni^II/III redox process. At more positive potentials oxidation of the bezno-15-crown-5 ether (B15C5) moiety was found. In complexes 2Ni and 3Ni redox potential of Ni^II/III did not change after the interactions of alkali and alkaline earth metal cations with B15C5 unit. However, the presence of guest cations caused a significant change of B15C5 oxidation potential. Complexation of two Cl⁻ anions to the coordinated Ni^II in 2Ni and 3Ni resulted in an appreciable shift of both Ni^II/III and B15C5 redox processes after addition of metal cations. Behaviour of complexes 2Ni and 3Ni was compared with behaviour of similar Cu^II complexes.     

Growth and photoelectrochemical behaviour of electrodeposited ZnO thin films for solar cells

Thin zinc oxide films were deposited potentiostatically from zinc nitrate aqueous solutions on ITO substrates. The influence of experimental parameters (temperature, electrolyte concentration, deposition potential) on structure and morphology of films was investigated. Deposited films were generally polycrystalline in structure, even if growth according to preferential planes occurs in certain conditions. The effect of thermal treatments in air at 150 and 350 °C was also studied. In some cases, Cl species were incorporated into deposit by adding zinc chloride to the electrolyte. A photoelectrochemical investigation, performed in neutral solution before and after thermal treatment, gives more information on film structure and reveals improvement of n-type semiconducting properties after annealing, suggesting diminution of defects and traps originated from the disordered regions of the oxide. In fact, after thermal treatment, the optical gap of the films decreases towards the value reported for the crystalline oxide. No apparent benefits in the semiconducting properties of the films were observed after incorporation of Cl species into the films.     

Discharge behaviour of copper(II) halide cathodes with molten nitrate electrolytes

This paper describes the discharge behaviour between 150 and 220°C of cells using copper(II) halide as the cathode material and molten nitrate as the electrolyte for a reserve battery of high energy density running at medium temperatures. At these temperatures a lithium–aluminium alloy/copper(II) chloride cell can be discharged at a current density of 50mAcm–2. The open-circuit potentials are 3.45V (against 20wt% lithium–aluminium alloy). Discharge results on the combination LiAl/LiNO3–KNO3/CuCl2 cells show a capacity of 1343Cg–1 to zero voltage at a current density of 50mAcm–2 at 230°C. In practice, this is equivalent to a specific energy output of 356Whkg–1 of cathode to a 70% voltage cut-off. The compatibility of copper(II) chloride with nitrate electrolytes has been investigated. Copper(II) chloride appears to be compatible with nitrate up to about 260°C. The performance of the LiAl/NO3/CuF2 cell was very poor giving a capacity of 50Cg–1.     

Electrochemical and photoelectrochemical response of electrodes coated with LB films of an azopolymer

This paper describes the electrochemical and photoelectrochemical behaviour of electrodes coated with Langmuir-Blodgett (LB) films of an azopolymer. The coating material used is a pyridine azopolymer (PAzPy) obtained by free radical polymerization of 6-[2-(4-pyridyazo)phenoxy]hexyl methacrylate (AzPy). Cyclic voltammetry experiments of LB films deposited at several transference surface pressures were performed to analyze the effect of the molecular packing on the electrochemical response. The influence of the pH of the electrolytic solution was also considered. AFM images have helped in the interpretation of the molecular architecture influence on the redox activity of the films. From the experimental results it was concluded that PAzPy is situated with the nitrogen from the pyridine group close to the ITO electrode surface in the LB films, which allows a direct electron transfer between the electrode surface and the azobenzene group leading to a quick electrochemical response of the films. The azobenzene electrochemical activity and the kinetics of the process are also highly dependent on the proton transfer process between the electrolytic solution and the azobenzene unit. The efficiency of the proton transfer process is determined by the pH of the electrolytic solution as well as by the molecular architecture of the film. The results presented in this paper show that, under optimal conditions, both the percentage of electroactive azobenzene chromophores and the standard heterogeneous rate constant of electron transfer are higher for PAzPy arranged in LB films compared with the values so far reported for azobenzenes of lower molecular weight.     

Electrochemical and spectroscopic characterization of poly(1,8-diaminocarbazole): Part II. Electrochemical, in situ vis/NIR and Raman studies of redox reaction of PDACz in protic and aprotic media

Electrochemical redox reactions of poly(1,8-diaminocarbazole) (PDACz) films in aqueous (0.1 M HClO₄) and nonaqueous (0.1 M LiClO₄ in acetonitrile) solutions were studied by cyclic voltammetry, in situ vis/NIR and Raman spectroscopy. It has been demonstrated that spectroelectrochemical behavior of the polymer is strongly dependent on the nature of the solution used for doping-undoping but not on the medium used for electropolymerization. A redox couples Fe²⁺/Fe³⁺, Fe(CN)₆^4−/3− and tertrathiafulvalene were used as the probes for the studies of electroactivity of the oxidized polymer films. The results were discussed in terms of different mechanism of deprotonation process of the polymer in aqueous solution of 0.1 M HClO₄ and in 0.1 M LiClO₄ solution in aprotic acetonitrile and the reaction schemes in the two media are proposed.     

Mn(II), Co(II) and Ni(II) complexes of 4-(2-thiazolylazo)resorcinol: Syntheses, characterization, catalase-like activity, thermal and electrochemical behaviour

Manganese(II), cobalt(II) and nickel(II) acetates react with the ligand, 4-(2-thiazolylazo)resorcinol, to form complexes of general formula [ML₂] for MCo(II), Ni(II) and [ML₂]·2H₂O for MMn(II). Each of the azo complexes was characterized using elemental analysis, electrolytic conductance, UV–visible spectroscopy and magnetic susceptibility. An octahedral structure is proposed for all complexes prepared, which molar conductance data revealed to be non-electrolytes. IR spectra reveal that the ligand is coordinated to the metal ions in a tridentate manner via the resorcinol OH, azo N and thiazole N groups as donor sites. The electrochemical behaviour of the ligand and its complexes were obtained by cyclic voltammetry. Thermal decomposition studies were undertaken to secure additional information on the structure of the investigated compounds. The manganese(II) complex catalysed the disproportionation of hydrogen peroxide in the presence of imidazole.