Electrochemical study of β-diketonatobis(triphenylphosphite)rhodium(I) complexes

The electrochemical behaviour of the series of ten [Rh(RCOCHCOR′)(P(OPh)₃)₂] complexes with R, R′ = CF₃, CF₃ (1), CF₃, CH₃ (2), CF₃, Ph (C₆H₅) (3), CF₃, Fc (ferrocenyl = (C₅H₅)Fe(C₅H₄)) (4), CH₃, Ph (5), CH₃, CH₃ (6), Ph, Ph (7), Fc, CH₃ (8), Fc, Ph (9) and Fc, Fc (10) were studied in acetonitrile containing 0.100 mol dm⁻³ tetra-n-butylammonium hexafluorophosphate as supporting electrolyte utilizing a glassy carbon working electrode. Results are consistent with Rh(I) being first oxidized in an electrochemically irreversible two-electron transfer process at peak anodic potentials ranging E_pa(Rh) = 0.124–0.881 V vs. Fc/Fc⁺. For the ferrocene-containing complexes (4), and (8)–(10) the rhodium oxidation was followed by the electrochemically reversible oxidation of the ferrocenyl group in a one-electron transfer process at a slightly more positive potential. Relationships were established between the electrochemical quantity E_pa(Rh) and kinetic parameter log k₂ as well the sum of experimental group electronegativities (Gordy Scale) of the R and R′ groups (χ_R + χ_R′), the Hammett σ values (σ_R + σ_R′) and the Lever ligand parameter E_L for the [Rh(RCOCHCOR′)(P(OPh)₃)₂] complexes: E_pa(Rh) (vs. Fc/Fc⁺/V) = 0.31 (χ_R + χ_R′)–1.09 = 0.56 (σ_R + σ_R′) + 0.28 = S_M (ΣE_L) + (I_M − 0.66 V) = −0.23 log k₂ − 0.03 (k₂ = second order rate constant for the oxidative addition of methyl iodide to rhodium). A profound shift of E_pa(Rh) to a more positive potential was observed for Rh(I) substrates containing β-diketonato ligands with increasing electronegative substituents R and R′. An exponential dependence of E_pa(Rh) on the pK_a of the β-diketone was obtained.     

Chitosan–Fe3O4 nanocomposite based electrochemical sensors for the determination of bisphenol A

This paper reports the application of chitosan–Fe₃O₄ (CS–Fe₃O₄) nanocomposite modified glassy carbon electrodes for the amperometric determination of bisphenol A (BPA). We observed that the CS–Fe₃O₄ nanocomposite could remarkably enhance the current response and decrease its oxidation overpotential in the electrochemical detection. Experimental parameters, such as the amount of the CS–Fe₃O₄, the accumulation potential and time, the pH value of buffer solution etc. were optimized. Under the optimized conditions, the oxidation peak current was proportional to BPA concentration in the range between 5.0 × 10⁻⁸ and 3.0 × 10⁻⁵ mol dm⁻³ with the correlation coefficient of 0.9992 and the limit of detection of 8.0 × 10⁻⁹ mol dm⁻³ (S/N = 3). The proposed sensors were successfully employed to determine BPA in real plastic products and the recoveries were between 92.0% and 06.2%. This strategy might open more opportunities for the electrochemical determination of BPA in practical applications. Additionally, the leaching studies of BPA on incubation time using the as-prepared modified electrode were successfully carried out.     

Combustion synthesis and characterization of Cu-Sm co-doped CeO2 electrolytes

Nano-sized CSO (Ce_0.80Sm_0.20O_2−δ) and CSCO (Ce_0.79Sm_0.20Cu_0.01O_2−δ) were synthesized by the PVA assisted combustion method, and then characterized by the structure of PVA-cation complexes and nano-powders, as well as mechanical and electrical performance after sintering. The results indicate that the PVA-cation complexes (PVA-(Ce³⁺,Sm³⁺) and PVA-(Ce³⁺,Sm³⁺,Cu²⁺)) were formed by coordinating metal cations to hydroxyl groups, as well as the COO⁻¹ group derived from the oxidation of PVA with NO₃⁻¹. Low temperatures (around 200 °C) caused intense combustion reactions, resulting in the direct crystallization of cubic fluorite nano-CSO (10-20 nm) and nano-CSCO (10-15 nm) crystals with homogeneous element distribution. This slight compositional modification of CSO by co-doping with 1 mol% CuO resulted in a significantly lowered densification temperature, as well as enhanced mechanical and electrical property. The strength improvement can be ascribed to the dense and fine-grained microstructure without normal grain coarsening, resulting in a transgranular-dominant fracture mode during strength testing.     

Electropolymerization of high quality electrochromic poly(3-alkyl-thiophene)s via a room temperature ionic liquid

Electrochemical polymerization in a room temperature ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF₆), has been used to prepare electrochromic poly(3-methylthiophene) (PMeT) and its more attractive derivatives: poly(3-hexylthiophene) (PHexT) and poly(3-octylthiophene) (POcT). Spectroelectrochemistry and electrochromic properties of the resulting polymers were characterized using various experiment techniques in [BMIM]PF₆/CH₃CN (1:1, v/v) solution. The thin films were bright red, orange red and orange yellow at its fully reduced state for PMeT, PHexT and POcT, respectively. After oxidization of these undoped polymers, the films underwent reversible change to the bright blue, blue or black blue form. These poly(3-alkylthiophene)s (PMeT, PHexT and POcT) films exhibit high chromatic contrast (46, 45 or 39%), comparative switching times (1.1, 1.4 or 1.9 s), great electrochromic efficiency (250, 220 and 230 cm² C⁻¹) and long-term switching stability. High quality electrochromic polymers were provided for the use of commercially available thiophene monomers, avoiding the use of other custom synthesized monomers.     

A wormhole-structured mesoporous carbon with superior adsorption for dyes

A series of large-pore mesoporous carbon materials with a three-dimensional wormhole framework structure were synthesized by nanocasting using mesoporous silica as a hard template. Samples of hard-template mesoporous silica with pore diameters from 3.08 to 6.43 nm, pore volumes from 0.59 to 1.02 cm³ g⁻¹ and surface areas from 832 to 579 m² g⁻¹ were prepared from tetraethyl orthosilicate as the silica source and ionic liquid 1-butyl-3-methylimidazolium bromide as structure-directing agent through hydrothermal treatment at different temperatures (110–150 °C) followed by calcining at 550 °C. Subsequently, carbon materials with large pore diameters (2.76–6.70 nm), pore volumes (0.74–2.10 cm³ g⁻¹) and high surface areas (1074–1276 m² g⁻¹) were synthesized using the various mesoporous silicas synthesized at the different hydrothermal temperatures as a hard-template. The carbon material obtained at a hydrothermal temperature of 150 °C possesses outstanding adsorbility for amaranth and methylene blue dyes.     

Effects of synthetic route on structure and electrochemical performance of Li3V2(PO4)3/C cathode materials

Three different synthetic routes, including solid-state reaction, sol–gel and hydrothermal methods are successfully used for preparation of Li₃V₂(PO₄)₃/C. Ascorbic acid is used as a reducing agent and/or as a chelating agent. The Li₃V₂(PO₄)₃/C synthesized by hydrothermal method with fine particles exhibits lower impedance and smaller potential difference values between oxidation and reduction peaks than those by solid-state reaction and sol–gel methods. Thus as cathode material for Li-ion batteries, the Li₃V₂(PO₄)₃/C synthesized by hydrothermal method shows higher discharge capacity, better rate capability and cyclic performance. Even at a high charge–discharge rate of 10 C, it still can deliver a discharge capacity of 101.4 mAh g⁻¹ and 106.6 mAh g⁻¹ in the potential range of 3.0–4.3 V and 3.0–4.8 V, respectively. The hydrothermal synthesis has been considered to be a competitive process to prepare Li₃V₂(PO₄)₃/C cathode materials with excellent electrochemical performances.     

Preliminary investigations on the anodic oxidation of Ti–13Nb–13Zr alloy in a solution containing calcium and phosphorus

Investigations on the surface modification of Ti–13Nb–13Zr alloy by anodic oxidation are reported here. The oxidation process was carried out in a solution containing 4 mol dm⁻³ H₃PO₄ and 100 g dm⁻³ Ca(H₂PO₂)₂. The anodising was realised at voltages of 80 V and 150 V. Moreover, a portion of the samples that had been oxidised at 150 V were held at a temperature of 500 °C. It was found that the morphology of the sample surface did not change during the oxidation of the alloy at 80 V. An application of 150 V led to the incorporation of calcium and phosphorus into the formed oxide layer and to significant modification of the surface morphology. The electrochemical characteristics of the modified alloy was also determined in Ringer's solution. It was shown that the electropolishing and anodising result in a considerable increase in the corrosion resistance of the Ti–13Nb–13Zr alloy.     

Neutral state colorless electrochromic polymer networks: Spacer effect on electrochromic performance

A series of carbazole-based monomers and their corresponding polymers with various spacer units were synthesized and coated onto ITO-glass surface via an electrochemical cross-linking process. All carbazole-based polymers exhibited multi-electrochromic behavior thanks to two separate oxidation processes. All materials were characterized by FT-IR, ¹H NMR, GPC, DSC, UV–vis, Florescence and CV. In addition, electrochromic properties of the cross-linked polymer films were investigated via spectro-electrochemical measurements. The colorless films were converted to yellowish green and greenish blue colors at the anodic regime. The results indicate that the spacer unit between the carbazole unit and the polymer backbone has a great impact on the optical and electrochemical properties and also on the electrochromic performance of these polymers. PVBEC with benzyloxy based spacer exhibits a high contrast ratio (ΔT% = 55 at 690 nm), a faster response time of about 2.1 s, a higher coloration efficiency (331 cm² C⁻¹) and a better stability (retains its performance by 94.3% even after 1000 cycles).     

Electrochemical performance of Li3V2(PO4)3/C cathode materials using stearic acid as a carbon source

The Li₃V₂(PO₄)₃/C cathode materials are synthesized by a simple solid-state reaction process using stearic acid as both reduction agent and carbon source. Scanning electron microscopy and transmission electron microscopy observations show that the Li₃V₂(PO₄)₃/C composite synthesized at 700 °C has uniform particle size distribution and fine carbon coating. The Li₃V₂(PO₄)₃/C shows a high initial discharge capacity of 130.6 and 124.4 mAh g⁻¹ between 3.0 and 4.3 V, and 185.9 and 140.9 mAh g⁻¹ between 3.0 and 4.8 V at 0.1 and 5 C, respectively. Even at a charge–discharge rate of 15 C, the Li₃V₂(PO₄)₃/C still can deliver a discharge capacity of 103.3 and 112.1 mAh g⁻¹ in the potential region of 3.0–4.3 V and 3.0–4.8 V, respectively. Based on the analysis of cyclic voltammograms and electrochemical impedance spectra, the apparent diffusion coefficients of Li ions in the composites are in the region of 1.09 × 10⁻⁹ and 4.95 × 10⁻⁸ cm² s⁻¹.     

‘One-pot’ synthesis of two molybdenum/tungsten (VI)–copper(I) mixed metal clusters under catalysis of 1,10-phenathroline

Under the catalysis of 1,10-phenathroline (phen), (NH₄)₂ M'S₄ (M’ = Mo,W) reacts with CuSCN and dppm in mixed solvent MeCN/DMF (1:1) to yield two saddle-shaped clusters [WS₄Cu₄(SCN)₂ (dppm)₃]·3DMF·2CH₃CN (1) and [MoS₄Cu₄(SCN)₂ (dppm)₃]·4DMF (2) (dppm = bis (diphenylphosphino) methane). Compounds 1–2 were characterized by elemental analysis, IR, UV–Vis, ¹H NMR, ³¹P NMR, and single-crystal X-ray diffraction. Each [M'S₄]²⁻ (M’ = Mo, W) anion coordinates to four Cu atoms through four bridging S atoms, and all S atoms are coordinated with two Cu atoms. In each cluster the four Cu atoms are almost in one plane, and the M’ atom is above the plane. Cluster 1 was characterized by luminescent with the λ_em = 545 nm. The possible catalysis mechanism of phenathroline is discussed.     

A reddish orange stoichiometric phosphor LiEu(PO3)4 for white light-emitting diodes

Stoichiometric phosphors LiGd_1−xEu_x(PO₃)₄(x=0, 0.2, 0.4, 0.6, 0.8, 1.0) were synthesized via traditional solid state reactions. The X-ray powder diffraction measurements show that all prepared samples are isostructural with LiNd(PO₃)₄. Eu³⁺ doped phosphors can emit intense reddish orange light under the excitation of near ultraviolet light from 370 to 410 nm. The strongest two at 591 and 613 nm can be attributed to the transitions from excited state ⁵D₀ to ground states ⁷F₁ and ⁷F₂, respectively. The typical chromaticity coordinates (x=0.620, y=0.368) of Eu³⁺ doped phosphors are in red area. The recorded absorbance spectra indicate that there is effective absorbance in the near UV region for all Eu³⁺ doped samples. Present research indicates that LiGd_1–xEu_x(PO₃)₄ is a promising phosphor for white light-emitting diodes.     

Electrochemical behavior of catechol, resorcinol and hydroquinone at graphene–chitosan composite film modified glassy carbon electrode and their simultaneous determination in water samples

Graphene–chitosan composite film modified glassy carbon electrode was prepared and characterized. The fabricated electrode showed excellent electrochemical catalytic activities towards the oxidation of catechol (CT), resorcinol (RS) and hydroquinone (HQ). The oxidation overpotentials of CT, RS and HQ decreased significantly and the corresponding oxidation currents increased remarkably compared with those obtained at the bare GCE and chitosan modified GCE. Some kinetic parameters, such as the electron transfer number (n), proton transfer number (m), charge transfer coefficient (α) and the apparent heterogeneous electron transfer rate constant (k_s), were calculated. Differential pulse voltammetry was used for the simultaneous determination of CT, RS and HQ in their ternary mixture. The peak-to-peak potential separations between CT and RS, RS and HQ, and HQ and CT were 0.388, 0.484 and 0.096 V, respectively. The calibration curves for CT, RS and HQ were obtained in the range of 1 × 10⁻⁶ to 4 × 10⁻⁴, 1 × 10⁻⁶ to 5.5 × 10⁻⁴ and 1 × 10⁻⁶ to 3 × 10⁻⁴ mol L⁻¹, respectively. The detection limits were 7.5 × 10⁻⁷ mol L⁻¹ (S/N = 3).     

Kinetic investigations of the electrochemical bromination of peracetylated d-glucal in organic solvents

Cyclic voltammetry and ultramicroelectrodes were used to investigate the kinetic aspects of the electrochemical bromination of 3,4,6-tri-O-acetyl-d-glucal (1) in acetonitrile (AN), dichloromethane (DCM), and dimethylsulfoxide (DMSO). Qualitative and quantitative results, determined notably from the kinetic parameter [glucal]/v representing the competition between glucal concentration and time, clearly showed that glucal bromination depended on the nature of both the solvent and the in situ electrogenerated reactive brominated species (Br₂ or Br₃⁻) obtained from the oxidation of a bromide salt. It was especially shown that Br₂ reacted more rapidly than Br₃⁻ towards (1). On the other hand, the reactivity of both brominated species appeared to follow the solvent polarity order since the highest reactivity was obtained in DMSO whereas the lowest one was found in DCM.     

A new carbon nanotubes (CNTs)–poly acrylonitrile (PAN) composite electrolyte for solid state dye sensitized solar cells

A new carbon nanotube (CNTs)–poly acrylonitrile (PAN) composite electrolyte was prepared by the thermal polymerization of acrylonitrile (AN) with CNTs for solid-state dye sensitized solar cells (DSSCs). It was found that the uniform CNT–PAN composite was formed due to the thermal polymerization of AN on CNTs. The strong bonding between CNTs and PAN could be confirmed by the characterization of XPS and Raman spectroscopy, resulting in the lowering of crystallinity and the increasing the ionic conductivity of composite electrolytes. On comparison with bare CNTs and the other composite electrolytes, the formation of triiodide (I₃⁻) ions in CNT–PAN composite electrolytes was drastically increased which was expected from the high ionic conductivity of electrolyte via I₃⁻/I⁻ redox couple. DSSCs fabricated with CNT–PAN composite electrolytes achieved relatively high conversion efficiency of 3.9% with an open circuit voltage (V_OC) of 0.57 V, short circuit current density (J_SC) of 10.9 mA/cm² and fill factor of 63.6%, which attributed to supply the higher extent of I₃⁻ ions from CNT–PAN composite electrolyte during the charge transport process.     

Sintering of glass-added BaZn1/3Nb2/3O3 ceramics

The complex perovskite oxide Ba(Zn_1/3Nb_2/3)O₃ (BZN) has been studied for its attractive dielectric properties which place this material interesting for applications as multilayer ceramics capacitors or hyperfrequency resonators. This material is sinterable at low temperature with combined glass phase–lithium salt additions, and exhibits, at 1 MHz very low dielectric losses combined with relatively high dielectric constant and a good stability of this later versus temperature. The 2 wt.% of ZnO–SiO₂–B₂O₃ glass phase and 1 wt.% of LiF-added BZN sample sintered at 900 °C exhibits a relative density higher than 95% and attractive dielectric properties: a dielectric constant ?_r of 39, low dielectrics losses (tan(δ) < 10⁻³) and a temperature coefficient of permittivity τ_? of 45 ppm/°C⁻¹. The 2 wt.% ZnO–SiO₂–B₂O₃ glass phase and 1 wt.% of B₂O₃-added BZN sintered at 930 °C exhibits also attractive dielectric properties (?_r = 38, tan(δ) < 10⁻³) and it is more interesting in terms of temperature coefficient of the permittivity (τ_? = −5 ppm/°C). Their good dielectric properties and their compatibility with Ag electrodes, make these ceramics suitable for L.T.C.C applications.     

Transparent Al–In–Zn–O Oxide semiconducting films with various in composition for thin-film transistor applications

Al–In–Zn–O thin-film transistors were fabricated. To examine the effect of In composition, we adopted a co-sputtering method using Al–Zn–O and In₂O₃ targets. The sputtering power of In₂O₃ was varied to 200, 150, and 50 W. The mobility and turn-on voltage of each device were 27.8 cm²V⁻¹ s⁻¹ and −4.2 V, 4.5 cm²V⁻¹ s⁻¹ and −3.5 V, 0.7 cm²V⁻¹ s⁻¹ and −3 V, respectively. We also investigated instabilities under negative gate bias stress (NBS) and negative bias illumination stress (NBIS). While the NBS was not influenced by the In contents, the NBIS characteristics were optimized for the device with In₂O₃ sputtering at 150 W.     

A novel platform of hemoglobin on core–shell structurally Fe3O4@Au nanoparticles and its direct electrochemistry

A novel platform, which hemoglobin (Hb) was immobilized on core–shell structurally Fe₃O₄/Au nanoparticles (simplified as Fe₃O₄@Au NPs) modified glassy carbon electrode (GCE), has been developed for fabricating the third biosensors. Fe₃O₄@Au NPs, characterized using transmission electron microscope (TEM), scanning electron microscope (SEM) and energy dispersive spectra (EDS), were coated onto GCE mediated by chitosan so as to provide larger surface area for anchoring Hb. The thermodynamics, dynamics and catalysis properties of Hb immobilized on Fe₃O₄@Au NPs were discussed by UV–visible spectrum (UV–vis), electrochemical impedance spectroscopy (EIS), electrochemical quartz crystal microbalance technique (EQCM) and cyclic voltammetry (CV). The electrochemical parameters of Hb on Fe₃O₄@Au NPs modified GCE were further carefully calculated with the results of the effective working area as 3.61 cm², the surface coverage concentration (Γ) as 1.07 × 10⁻¹² mol cm⁻², the electron-transfer rate constant (K_s) as 1.03 s⁻¹, the number of electron transferred (n) as 1.20 and the standard entropy of the immobilized Hb (ΔS⁰′) as calculated to be −104.1 J mol⁻¹ K⁻¹. The electrocatalytic behaviors of the immobilized Hb on Fe₃O₄@Au NPs were applied for the determination of hydrogen peroxide (H₂O₂), oxygen (O₂) and trichloroacetic acid (TCA). The possible functions of Fe₃O₄ core and Au shell as a novel platform for achieving Hb direct electrochemistry were discussed, respectively.     

Meldola blue immobilized on a new SiO2/TiO2/graphite composite for electrocatalytic oxidation of NADH

Meldola blue immobilized on a new SiO₂/TiO₂/graphite composite was applied in the electrocatalytic oxidation of NADH. The materials were prepared by the sol-gel processing method and characterized by several techniques including scanning electronic microscopy coupled to energy dispersive spectroscopy (SEM-EDS), X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electronic microscopy (HRTEM). Si and Ti mapping profiles on the surface showed a homogeneous distribution of the components. Ti2p binding energy peaks indicate that the formation of Si-O-Ti linkage is presumably the responsible for the high rigidity of the matrices. The good electrical conductivity presented by the composites (5 and 11 S cm⁻¹) can be related to a homogeneous distribution of graphite particles observed by TEM. After the materials characterization, a SiO₂/TiO₂/graphite electrode was prepared and some chemical modifications were performed on its surface to promote the adsorption of meldola blue. The resulting system presented electrocatalytic properties toward the oxidation of NADH, decreasing the oxidation potential to −120 mV. The proposed sensor showed a wide linear response range from 0.018 to 7.29 mmol l⁻¹ and limit of detection of 0.008 mmol l⁻¹. SiO₂/TiO₂/graphite has shown to be a promising material to be used as a suitable support in the construction of new electrochemical sensors.     

Electrochemical investigation of the dimeric oxo-bridged ruthenium complex in aqueous solution and its incorporation within a cation-exchange polymeric film on the electrode surface for electrocatalytic activity of hydrogen peroxide oxidation

Electrochemical behavior of oxo-bridged dinuclear ruthenium(III) complex ([(bpy)2(H₂O)Ru^III-O-Ru^III(H₂O)(bpy)2]⁴⁺) has been studied in aqueous solution (KCl 0.5 mol L⁻¹) by both cyclic and rotating disk electrode (RDE) voltammetry in order to identify and elucidate the reaction mechanism. Modified electrode containing the oxo-bridged ruthenium complex incorporated into a cation-exchange polymeric film deposited onto platinum electrode surface was studied. Cyclic voltammetry at the modified electrode in KCl solution showed a single-electron reduction/oxidation of the couple Ru^III-O-Ru^III/Ru^III-O-Ru^IV. The modified electrode exhibited electrocatalytic property toward hydrogen peroxide oxidation in KCl solution with a decrease of the overpotential of 340 mV compared with the platinum electrode. The Tafel plot analyses have been used to elucidate the kinetics and mechanism of the hydrogen peroxide oxidation. The first at low overpotential region there is no significant change in the Tafel slope (∼0.130 V dec⁻¹) with varying peroxide concentration. The second region at higher overpotential the slope values (0.91–0.47 V dec⁻¹) were depended on the peroxide concentration. The apparent reaction order for H₂O₂ varies from 0.16 to 0.50 in function of the applied potential. The apparent reaction order (at constant potential) with respect to H⁺ concentration of 10⁻⁵ to 10⁻¹ mol L⁻¹ was 0.25. A plot of the anodic current vs. the H₂O₂ concentration for chronoamperometry (potential fixed = +0.61 V) at the modified electrode was linear in the 1.0 × 10⁻⁵ to 2.5 × 10⁻⁴ mol L⁻¹ concentration range.     

Electrosynthesis of polyaniline–molybdate coating on steel and its corrosion protection performance

Electrosynthesis of polyaniline–molybdate (PANI–MoO₄²⁻) on mild steel was achieved in oxalic acid medium using cyclic voltammetry technique. Adherent and homogeneous PANI–MoO₄²⁻ coating was obtained. The corrosion behavior of steel with PANI–MoO₄²⁻ coatings in 1% NaCl solutions was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy techniques. The coating was characterized by SEM, XPS, EDAX and FTIR. The self-healing ability of PANI–MoO₄²⁻ coating was confirmed by SVET technique. It has been found that the PANI–MoO₄²⁻ coating is able to offer higher corrosion protection in comparison to that of pure PANI coating due to inhibitive nature of molybdate ions.