Catalytic roughening of surface layers of BDD for various applications

The surface layers of BDD electrodes have been roughened through excavation by small Ni, Co and Pt particles in a flowing gas mixture of H₂(10%) and N₂(90%) between 800 °C and 1000 °C. The specific surface area of the BDD evaluated with the double layer capacitance was enhanced by the excavation of up to nearly 15 times as much pristine BDD electrode. The following potential applications for the surface-roughened BDD were proposed: (1) interlayer of the porous oxide catalyst layer and metal substrate of IrO₂-Ta₂O₅/(Ti or Nb) electrode, for instance, and (2) supporting material with large surface area for catalyst metal particles.     

The electrochemical behaviour of copper in alkaline solutions containing sodium sulphide

The electrochemical behaviour of copper in NaHCO₃ solution (pH 9) and NaOH solutions (pH 14) in the presence of sodium sulphide (10^–3 to 5×10^–2m) was investigated by using rotating disc electrode and rotating ring-disc techniques, triangular potential scanning voltammetry and potentiostatic steps. When the potential increases from –1.2V upwards, copper sulphide layers are firstly formed at potentials close to the equilibrium potentials of the Cu/Cu₂S and Cu/CuS reversible electrodes. When the potential exceeds 0.0 V (NHE), the copper oxide layer is electroformed. Pitting corrosion of copper is observed at potentials greater than –0.3 V. The charateristics of copper pitting are also determined through SEM optical microscopy and EDAX analysis. There are two main effects in the presence of sodium sulphide, namely, the delay in the cuprous oxide formation by the presence of the previously formed copper sulphide layer and the remarkable increase of copper electrodissolution when the potential exceeds the cuprous oxide electroformation threshold potential. These results are interpreted on the basis of a complex structured anodic sulphide layer and on a weakening of the metal-metal bond by the presence of adsorbed sulphur on the copper surface.     

A thermodynamic study of the effect of small-scale electrolytes on equilibrium redox potentials

Expressions are derived to calculate the equilibrium oxidation-reduction potentials for the Al⁺³/Al, Cu⁺²/Cu, and Zn⁺²/Zn systems in small-scale electrolytes. The geometrical system consists of a droplet of electrolyte resting on a flat metal plate, and the metal is considered to be immersed in a solution of its own ions. When the radius of the drop is allowed to vary, both the size of the electrolyte and the size of the active metal beneath the droplet change simultaneously. The total free energy change for the system consists of both electrochemical and surface chemical contributions. The interfacial free energy for the solid/liquid interface has been estimated from the Girifalco-Good expression or from spreading pressure considerations. When the droplet becomes sufficiently small in radius, the surface chemical contributions become significant, and the calculated redox potential changes from its normal value to more negative values as the size of the system decreases. The magnitude of this effect depends on the particular system. For 2 M Cu⁺², the calculated redox potential for a 0.8 nm radius droplet is 0.259 V more negative than for the bulk electrolyte. The effect is much smaller for aluminum and zinc. In all three systems, calculated redox potentials approach values for the bulk solution for droplet radii of about 10 nm.     

Electrocatalytic oxidation of ascorbic acid by [Fe(CN)6] redox couple electrostatically trapped in cationic N,N-dimethylaniline polymer film electropolymerized on diamond electrode

Multinegatively charged metal complex, hexacyanoferrate ([Fe(CN)₆]⁴⁻), was electrostatically trapped in the cationic polymer film of N,N-dimethylaniline (PDMA) which was electrochemically deposited on the boron-doped diamond (BDD) electrode by controlled-potential electro-oxidation of the monomer. This ferrocyanide-trapped PDMA film was used to catalyze the oxidation of ascorbic acid (AA). Increase in the oxidation current response with a negative shift of the anodic peak potential was observed at the cationic PDMA film-coated BDD (PDMA|BDD) electrode, compared with that at the bare BDD electrode. A more drastic enhancement in the oxidation peak current as well as more negative shift of oxidation potential was found at the ferrocyanide-trapped PDMA film-coated BDD ([Fe(CN)₆]^3−/4−|PDMA|BDD) electrode. This [Fe(CN)₆]^3−/4−|PDMA|BDD electrode can be used as an amperometric sensor of AA. Ferrocyanide, electrostatically trapped in the polymer film shows more electrocatalytic activity than that coordinatively attached to the polymer film or dissolved in the solution phase. The electrocatalytic current depends on the surface coverage of ferricyanide, Γ_Fe, within the polymer film. Diffusion coefficient (D) of AA in the solution was estimated by rotating disk electrode voltammetry: D = (5.8 ± 0.3) × 10⁻⁶ cm² s⁻¹. The second-order rate constant for the catalytic oxidation of AA by ferricyanide was also estimated to be 9.0 × 10⁴ M⁻¹ s⁻¹. In the hydrodynamic amperometry using the [Fe(CN)₆]^3−/4−|PDMA|BDD electrode, a successive addition of 1 μM AA caused the successive increase in current response with equal amplitude and the sensitivity was calculated as 0.233 μA cm⁻² μM⁻¹.     

Effect of cations in solution on the oxidation of methanol on the surface of platinum electrode

The effect of metal cations in solution on the oxidation of methanol on the electrode surface of platinum is a neglected aspect to direct methanol fuel cell (DMFC). In this paper, a smooth platinum electrode absorbing metal cations as the working electrode was applied to investigate the methanol oxidation with the cyclic voltammetry (CV) in 1.0 mol L⁻¹ H₂SO₄. From the analysis of experiment, it is found that the cations, Li⁺, Ce⁴⁺, Mn²⁺, Ni²⁺, Cu²⁺, have some negative effect on the catalytic oxidation of methanol on the surface of platinum. The degree of the effect from different cations was analyzed.     

Controllable electrode activities of nano-carbon films while maintaining surface flatness by electrochemical pretreatment

A carbon film consisting nanocrystallites with mixed sp² and sp³ bonds formed by using the electron cyclotron resonance (ECR) sputtering method was studied with respect to the changes in characteristics caused by electrochemical pretreatment (ECP). Unlike glassy carbon, our sputtered nanocrystalline carbon film deposited at an acceleration voltage of 75 V (ECR-75 nano-carbon film) largely retained its surface flatness after the ECP. This robust surface could be caused by an increase of 42% in the sp³ carbon realized by increasing the acceleration voltage during sputtering. The electrode activity of ECR-75 nano-carbon film was improved for surface sensitive species including Fe^3+/2+ unlike the boron doped diamond (BDD) electrode. This is because a sufficient quantity of surface sp² bonds remained and because the introduction of surface oxygen-containing groups is more efficient than with the BDD electrode. With pretreated ECR-75 nano-carbon film, the peak potential of glutathione was reduced solely due to the increase in the surface hydrophilicity with a sufficient quantity of surface sp² bonds, thus achieving the lowest detection limit (0.4 μM) ever obtained with carbon electrodes. We also achieved the stable measurement of 30 μM of serotonin (20 times) without the electrode surface fouling found with other electrodes.     

Nanostructured CuO thin film electrodes prepared by spray pyrolysis: a simple method for enhancing the electrochemical performance of CuO in lithium cells

Nanostructured CuO thin films were prepared by using a spray pyrolysis method, copper acetate as precursor and stainless steel as substrate. The textural and structural properties of the films were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The SEM images revealed thorough coating of the substrate and thickness of 450-1250 nm; the average particle size as determined from the AFM images ranged from 30 to 160 nm. The XRD patterns revealed the formation of CuO alone and the XPS spectra confirmed the presence of Cu²⁺ as the main oxidation state on the surface. The films were tested as electrodes in lithium cells and their electrochemical properties evaluated from galvanostatic and step potential electrochemical spectroscopy (SPES) measurements. The discharge STEP curves exhibited various peaks consistent with the processes CuO ⇔ Cu₂O ⇔ Cu and with decomposition of the electrolyte, a reversible process in the light of the AFM images. The best electrode exhibited capacity values of 625 Ah kg⁻¹ over more than 100 cycles. This value, which involves a CuO ⇔ Cu reversible global reaction, is ca. 50% higher than that reported for bulk CuO. The nanosize of the particles and the good adherence of the active material to the substrate are thought to be the key factors accounting for the enhanced electrochemical activity found.     

Synthesis and characterization of Cu-doped ceria nanopowders

Nanopowdered solid solution Ce_1−xCu_xO_2−γ samples (0 ≤ x ≤ 0.15) were synthesized by self-propagating room temperature synthesis (SPRT). Raman spectroscopy and XRD at room temperature were used to study the vibration properties of these materials as well as the Cu solubility in ceria lattice. The solubility limit of Cu²⁺ in CeO₂ lattice was found to be lower than published in the literature. Results show that obtained powders with low dopant concentration are solid solutions with a fluorite-type crystal structure. However, with Cu content higher than 7.5 mass%, the phase separation was observed and two oxide phases, CeO₂ and CuO, coexist. All powders were nanometric in size with high specific surface area.     

Adsorption capacity and removal efficiency of heavy metal ions by Moso and Ma bamboo activated carbons

In order to understand the adsorption capacity and removal efficiency of heavy metal ions by Moso and Ma bamboo activated carbons, the carbon yield, specific surface area, micropore area, zeta potential, and the effects of pH value, soaking time and dosage of bamboo activated carbon were investigated in this study. In comparison with once-activated bamboo carbons, lower carbon yields, larger specific surface area and micropore volume were found for the twice-activated bamboo carbons. The optimum pH values for adsorption capacity and removal efficiency of heavy metal ions were 5.81–7.86 and 7.10–9.82 by Moso and Ma bamboo activated carbons, respectively. The optimum soaking time was 2–4 h for Pb²⁺, 4–8 h for Cu²⁺ and Cd²⁺, and 4 h for Cr³⁺ by Moso bamboo activated carbons, and 1 h for the tested heavy metal ions by Ma bamboo activated carbons. The adsorption capacity and removal efficiency of heavy metal ions of the various bamboo activated carbons decreased in the order: twice-activated Ma bamboo carbons > once-activated Ma bamboo carbons > twice-activated Moso bamboo carbons > once-activated Moso bamboo carbons. The Ma bamboo activated carbons had a lower zeta potential and effectively attracted positively charged metal ions. The removal efficiency of heavy metal ions by the various bamboo activated carbons decreased in the order: Pb²⁺ > Cu²⁺ > Cr³⁺ > Cd²⁺.     

Electrochemical properties of Cu2O/Cu composite particles prepared by a novel and facile method

Cu₂O/Cu composite particles were synthesized by a novel and facile chemical reduction method without any template or surfactant. X-ray diffraction (XRD) results showed that the product mainly consisted of the Cu₂O phase coexisting with a few Cu phases. Typical FE-SEM images indicated that the particles with an octahedral shape were Cu₂O. In addition, the electrochemical performance of the Cu₂O/Cu particles as the working electrode material in alkaline solution was systematically investigated. The particles showed a maximum discharge capacity of 222.9 mAh g⁻¹ at a discharge current density of 60 mA g⁻¹ and a high value of 109.1 mAh g⁻¹ after 50 charge–discharge cycles. The results of cyclic voltammetry demonstrated that the reaction between Cu₂O and Cu is the major electrochemical reaction during the charging and discharging process. The results of electrochemical impedance spectroscopy indicated that the formation of Cu₂O on the surface of Cu particles significantly increased the contact resistance and the charge transfer resistance of the electrode during the discharging process.     

Equilibrium and kinetics of heavy metal ion exchange

Ion exchange has a great potential to remove heavy metals from industrial wastewaters or heavy metal-containing sludge. In order to design and operate heavy metal removal processes, the equilibrium relationship between ions and resin must be known a prior. A series of ion-exchange equilibrium tests of Cu²⁺/H⁺, Zn²⁺/H⁺, and Cd²⁺/H⁺ systems using Amberlite IR-120 were performed. The equilibrium data were analyzed by the Langmuir isotherm, Freundlich isotherm, and selectivity coefficient approaches. The thermodynamic parameters such as Gibbs free energy change, enthalpy change, and entropy change were calculated. By comparison of the selectivity coefficients, the affinity sequence to IR-120 is Cu²⁺ > Zn²⁺ > Cd²⁺ > H⁺. Moreover, in order to understand the heavy metal extraction kinetics in the presence of Amberlite IR-120, the ion-exchange kinetics was also studied. The ion-exchange kinetic data were regressed by the pseudo first-order, second-order models, and a reversible reaction model. The activation energies calculated from the rate coefficients at different temperatures are 15.41, 7.04, and 17.01 kJ/mol for copper, zinc, and cadmium, respectively. Although the pseudo first- and second-order models are easier to use for data analysis, the resultant model parameters depend on operating conditions. The reversible reaction model is capable to predict the effects of resin to solution ratio, initial heavy metal concentration, and temperature on the ion-exchange kinetic curves.     

Evaluation of the electrochemical properties of 3-hydroxyflavone using voltammetric methods

Electrochemical behavior of ring C of 3-hydroxyflavone (3-HF) has been investigated by cyclic and differential pulse voltammetry, using a glassy carbon electrode (GCE) in different buffer systems. It exhibited a sensitive diffusion controlled anodic peak at 0.70 V (vs Ag/AgCl) in a buffer system at pH 2.0. At higher pH, 8.0, while the peak at 0.70 V shifted to 0.41 V, a new peak at 0.8 V appeared. Moreover, electrochemical method was applied to investigate the antioxidant effect and metal chelating properties of 3-HF with Cd²⁺, Cu²⁺, Hg²⁺ and Pb²⁺ as they could have possible toxicological effects, for which fluorescence technique were also applied. Antioxidant effect was determined in terms of trolox equivalent antioxidant capacity (TEAC) using the peak areas of cyclic voltammetry (CV), which indicated that 1.0 mM 3-HF is equivalent to 0.2 mM of trolox. Such a result might be another indication of the importance of hydroxyl groups on the other rings of flavones. Electrochemical and fluorescence spectroscopic methods revealed that the best interactions of the cations could be obtained depending on the pH of the medium. Selective interactions of Cd²⁺ and Cu²⁺ at pH 2 and 7, respectively, were observed.     

Hollow mesoporous silica capsules loaded with copper,silver, and zinc oxide nanoclusters for sustained antibacterial efficacy

Intensive and overuse of antibiotics during the last years has triggered a distinct rise in antibiotic resistance worldwide. In addition to the newly developed antimicrobials, there is a high demand for alternative treatment options against persistent bacterial infections. The biocidal impact of metal ions like copper (Cu²⁺), silver (Ag⁺), and zinc (Zn²⁺), also known as the oligodynamic effect has been used for ages to kill or inhibit the growth of microorganisms and to employ long-term prevention strategies against their biological antagonists. Herein, we report on the synthesis of Cu, Ag, and Zn metal and corresponding oxide nanoparticles immobilized on hollow mesoporous silica capsules (HMSCs) obtained by a hard-template assisted sol-gel synthesis followed by reduction of appropriate metal salts in the presence of HMSCs. Compartmentalization of nanosized metal and oxide clusters in Ag@HMSCs, Cu@HMSCs, and ZnO@HMSCs particles prevented their agglomeration and offered high release kinetics of metal ions between 2.0 and 3.7 mM during 24 h, as monitored by UV-vis analyses. The distribution and morphology of pristine and metal functionalized HMSCs were evaluated by transmission electron microscopy analysis revealing the successful synthesis of Ag, Cu, and ZnO nanoparticles supported on HMSCs. X-ray photoelectron spectroscopy revealed that mainly Cu(II), Ag(0), and Zn(II) species were present in the modified HMSCs. In addition to the surface attachment of preformed metal (Ag and Cu) and metal oxide (ZnO) cluster, nucleation of metal nanoparticles inside the void of HMSCs provided an internal reservoir which allowed for a time-dependent release of metal ions through slower dissolution rates leading to a long-term and sustained bacterial inhibition over several hours. The high antimicrobial efficiency of Ag@HMSCs, Cu@HMSCs, and ZnO@HMSCs particles was investigated toward both Gram-positive (Bacillus subtilis) and Gram-negative (Escherichia coli) bacteria by INT assays showing a complete growth inhibition for both bacteria types after 24 h. While Ag@HMSCs and Cu@HMSCs showed a higher susceptibility against Gram-negative bacteria, ZnO@HMSCs showed a higher susceptibility against Gram-positive bacteria. This demonstrates the promise of metal-loaded capsules as antibacterial delivery vehicles with dual-mode time-release profiles being potential alternatives for antibiotic drugs.     

Cu2+, Fe2+ and Fe3+ analysis of bioleaching solutions using chronoamperometry and BDD electrode

In this work, a boron-doped diamond (BDD) electrode was evaluated for the electroanalytical determination of millimolar concentrations of Cu²⁺, Fe²⁺ and Fe³⁺ using chronoamperometry. The interfering role that each ion plays on the quantitative determination of other metal ion concentrations was also assessed. No interference from other metal ions was observed when Fe³⁺ and Fe²⁺ were analysed. By contrast, reduction of Fe³⁺ took place at the same potential where [Cu²⁺] was measured causing a minor interference to the Cu²⁺ signal. A multiple linear regression (MLR) calibration model was made for each analyte using real bioleaching samples, which demonstrated high coefficients of determination and adequate standard errors. The methods developed were used to monitor bioleaching of chalcopyrite for 4 months. The electroanalytical methods are particularly well-suited for analysing Cu²⁺, Fe³⁺ and Fe²⁺ concentration in acidic mine drainage (AMD) and bioleaching environments.     

Effective MgO surface doping of Cu/Zn/Al oxides as water–gas shift catalysts

Trace amounts of MgO were doped on Cu/ZnO/Al₂O₃ catalysts with the Cu/Zn/Al molar ratio of 45/45/10 and tested for the water–gas shift (WGS) reaction. A mixture of Zn(Cu)–Al hydrotalcite (HT) and Cu/Zn aurichalcite was prepared by co-precipitation (cp) of the metal nitrates and calcined at 300 °C to form the catalyst precursor. When the precursor was dispersed in an aqueous solution of Mg(II) nitrate, HT was reconstituted by the “memory effect.” During this procedure, the catalyst particle surface was modified by MgO-doping, leading to a high sustainability. Contrarily, cp-Mg/Cu/Zn/Al prepared by Mg²⁺, Cu²⁺, Zn²⁺ and Al³⁺ co-precipitation as a control exhibited high activity but low sustainability. Mg²⁺ ions were enriched in the surface layer of m-Mg–Cu/Zn/Al, whereas Mg²⁺ ions were homogeneously distributed throughout the particles of cp-Mg/Cu/Zn/Al. CuO particles were significantly sintered on the m-catalyst during the dispersion, whereas CuO particles were highly dispersed on the cp-catalyst. However, the m-catalyst was more sustainable against sintering than the cp-catalyst. Judging from TOF, the surface doping of MgO more efficiently enhanced an intrinsic activity of the m-catalyst than the cp-catalyst. Trace amounts of MgO on the catalyst surface were enough to enhance both activity and sustainability of the m-catalyst by accelerating the reduction–oxidation between Cu⁰ and Cu⁺ and by suppressing Cu⁰ (or Cu⁺) oxidation to Cu²⁺.     

Contributions of water dipoles to double layer properties: A three-state water model

Differences between various two state water models in the literature are elucidated. A model is proposed which involves an equilibrium between dimers and monomers on the electrode surface. An approximate consideration of the waterwater and watermetal interactions on the surface indicates (θ_dimer/θ_monomer) ?2 at 25°C.Application of the model to a calculation of the surface potential g^s(dipole) of water in the mercury-solution interface as a function of electrode-charge yields +0.03 V at the pzc. The calculated g^s(dipole) varies from +0.16 V to ?0.10 V when the electrode charge is varied from +16 to?16 υC cm^?2.Evaluation of the dipole capacitance as a function of electrode charge shows a water contribution to the capacitance which would not effect the observed value, ie there would be no water-derived capacitance hump.     

Electrochemical detection of copper ion using a modified copolythiophene electrode

This paper studies the detection of copper ions by using an iminodiacetatic acid (IDA) modified conducting copolymer electrode. The copolymer film comprising 3-methyl thiophene (3MT) and 3-thiophene acetic acid (3TA) was chosen as the selective metal cation sensing electrode. The carboxylic group of the copolymer was modified to produce IDA group for metal ion capture. The modified electrode was used for the electrochemical analysis of trace copper ions by square wave voltammetry (SWV) technique. The electrode was found to be highly selective to Cu²⁺ in the range of 0.1-10 μM. The modified electrode offered an excellent way, with a high stability and reusability, for selective determination of Cu²⁺ in a solution of mixed metal ions.     

Novel application of boron-doped diamond and related material to electrochemical generation of functional water

The performances of the electrogeneration of ClO⁻ on the different electrode materials, such as boron-doped diamond (BDD), Pt/BDD and Pt, were investigated at constant voltages of 10, 20 and 30 V as well as constant currents of 25, 50 and 75 mA. The BDD and Pt/BDD electrodes showed superior to platinum electrode for the ClO⁻ generation at both constant voltage and constant current conditions under respective room temperature (RT) and low temperature (LT) (2-5 °C). Both BDD and Pt/BDD electrodes exhibited high stability used under high voltage and current conditions.     

Accumulation of Cu(II) cations in poly(3,4-ethylenedioxythiophene) films doped by hexacyanoferrate anions and its application in Cu-selective electrodes with PVC based membranes

Electrochemical properties of poly(3,4-ethylenedioxythiophene) doped with hexacyanoferrate(II,III) ions (PEDOT(HCF)) were studied in the presence of Cu²⁺ ions. Voltammetric and EDAX studies revealed retention of hexacyanoferrate anions in the polymer film and accumulation of Cu(II) cations, as well as formation of solid copper hexacyanoferrate near the polymer surface.Accumulation of Cu²⁺ ions was found to be advantageous from the point of view of PEDOT(HCF) applications as a solid contact (ion-to-electron transducer) in all-solid-state Cu²⁺-selective electrodes with solvent polymeric polyvinyl chloride (PVC) based membrane, containing Cu²⁺-selective ionophore. Binding of Cu²⁺ ions in the conducting polymer layer results in analyte ions flux into the transducer phase. Thus, pronounced enhancement of selectivity of the all-solid-state Cu²⁺-selective electrode or lower detection limit of the potentiometric response range was achieved, reaching under optimised conditions 10⁻⁷ M CuSO₄.     

Cationic conjugated polyelectrolyte-based fluorometric detection of copper(II) ions in aqueous solution

A series of water-soluble cationic polyfluorene copolymer containing 2,2′-bipyridine moieties (PFP-P_1-3) in the backbone were designed and synthesized as the fluorescent probes for Cu²⁺ ions. In the absence of the Cu²⁺ ion, the PFP-P₂ exhibits strong fluorescence emission in aqueous solution. Upon adding the Cu²⁺ ion, the PFP-P₂ coordinates to Cu²⁺ ions through weak N?Cu interactions, and its fluorescence is efficiently quenched by the Cu²⁺ ion with a Stern-Volmer constant (K_sv) of 1.44 × 10⁷ M⁻¹. The new method has high sensitivity with a detection limit of 20 nM. The minor interference from other heavy metal ions clearly shows that the PFP-P₂ can be used as the Cu²⁺ ion probe with good selectivity.