Encapsulation of titanium (IV) silsesquioxane into the NH4USY zeolite: Preparation, characterization and application

This work describes the encapsulation of titanium (IV) silsesquioxane into the supercavities of NH₄USY ultra stabilized zeolite, after chemical treatment. The modified zeolite was characterized by Fourier transform infrared spectra, Nuclear magnetic resonance, scanning electronic microscopy, X-ray diffraction and thermogravity. This encapsulated titanium (IV) silsesquioxane can adsorb Azure A chloride after treatment with H₃PO₄, without modifier leaching problems. In an electrochemical study, the cyclic voltammograms of the graphite paste modified electrode, shows two redox couples with formal potential (E⁰′) −0.1 V and 0.21 V to I and II redox couples respectively (v=700 mV s−1; Britton Robinson buffer (B-R) solution, pH 3) versus SCE ascribed to a monomer and dimmer of azure. This paper shows the use of ultra stabilized zeolite in the electrochemical field as host for molecules with nanometric dimensions.     

A novel nanostructured composite formed by interaction of copper octa(3-aminopropyl)octasilsesquioxane with azide ligands: Preparation, characterization and a voltammetric application

This study presents the preparation, characterization and application of copper octa(3-aminopropyl)octasilsesquioxane following its subsequent reaction with azide ions (ASCA). The precursor (AC) and the novel compound (ASCA) were characterized by Fourier transform infrared spectra (FTIR), nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR), scanning electronic microscopy (SEM), X-ray diffraction (XRD), Thermogravimetric analyses and voltammetric technique. The cyclic voltammogram of the modified graphite paste electrode with ASCA (GPE-ASCA), showed one redox couple with formal potential () = 0.30 V and an irreversible process at 1.1 V (vs. Ag/AgCl; NaCl 1.0 M; v=20 mV s−1). The material is very sensitive to nitrite concentrations. The modified graphite paste electrode (GPE-ASCA) gives a linear range from 1.0 × 10⁻⁴ to 4.0 × 10⁻³ mol L⁻¹ for the determination of nitrite, with a detection limit of 2.1 × 10⁻⁴ mol L⁻¹ and the amperometric sensitivity of 8.04 mA/mol L⁻¹.     

Electropolymerization of Cu-(N,N′-bis(3-methoxysalicylidene)-2-aminobenzylamine) on platinum electrode: Application to the electrocatalytic reduction of hydrogen peroxide

The complex of copper (II) with N,N′-bis(3-methoxysalicylidene)-2-aminobenzylamine (H₂L) was synthesized and characterized by elemental analysis, magnetic susceptibility, UV–vis. and FT-IR spectroscopy. The results showed that the tetradentate ligand coordinated to the Cu(II) ion through the azomethine nitrogen and phenolic oxygen atoms. The prepared complex [CuL] was electropolymerized on platinum electrode surface in a 0.1 mol dm⁻³ solution of lithium perchlorate in acetonitrile by cyclic voltammetry between 0 and 1.6 V vs. Ag/Ag⁺. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), conductance measurements, FT-IR and SEM were used to characterize polymer film of Cu(II) complex. The reduction of hydrogen peroxide on poly[CuL] has been investigated mainly in phosphate buffer medium (pH 7.2), between 0 and −0.8 V versus Ag/Ag⁺ at a scan rate 0.1 V s⁻¹.     

High capacitive performance of nanostructured Mn-Ni-Co oxide composites for supercapacitor

Nanostructured Mn-Ni-Co oxide composites (MNCO) were prepared by thermal decomposition of the precursor obtained by chemical co-precipitation of Mn, Ni and Co salts. The chemical composition and morphology were characterized by X-ray diffraction (XRD), energy dispersive spectroscopy (EDS) and scanning electron microscopy (SEM). The electrochemical capacitance of MNCO electrode was examined by cyclic voltammetry, impedance and galvanostatic charge-discharge measurements. The results showed that MNCO electrode exhibited the good electrochemical characteristics. A maximum capacitance value of 1260 F g⁻¹ could be obtained within the potential range of −0.1 to 0.4 V versus saturated calomel electrode (SCE) in 6 mol L⁻¹ KOH electrolyte.     

Adsorption of mercury cation on chemically modified clay

A montmorillonite clay (M) sample from the Amazon region, Brazil, was intercalated with pyridine (Py), dimethyl sulfoxide (DS) and 3-aminopropyltriethoxysilane (APS). The chemically modified montmorillonite (M_P/APS) sample showed modification of its physical-chemical properties including: specific area 41.39 m² g⁻¹ (M) to 198.45 m² g⁻¹ (M_P/APS). Solid-state ²⁹Si CPMAS/NMR of the silylated montmorillonite samples showed Q² and Q³ signals as well as T² and T³ signals. The appearance of T² and T³ signals can be attributed to the grafting of APS to the interlayer surface silanol groups. The natural and modified clays were used for mercury cation adsorption from aqueous solutions at room temperature and pH 3.0. The energetic effects (Δ_intH°, Δ_intG° and Δ_intS°) caused by mercury cation adsorption were determined through calorimetric titrations.     

A voltammetric and nanogravimetric study of ZnSe electrodeposition from an acid bath containing Zn(II) and Se(IV)

The negative potential sweep of a polycrystalline Au electrode in a solution containing 5 × 10^− 4 mol L^− 1 SeO₂, 0.2 mol L^− 1 Zn(ClO₄)₂ and 0.5 mol L^− 1 HClO₄ was analyzed at 0.05 V s^− 1. The simultaneously collected voltammetric and nanogravimetric responses allowed to analyze the several electrochemical processes occurring in the studied range of potential, finishing with the formation of a thin film of ZnSe. The association of results obtained using both techniques was applied to identify the species involved in the AuO reduction as (AuO)₂H₂SeO₃, which was desorbed during the oxide reduction with a mass variation much larger than that one observed in the supporting electrolyte. Initially, the Se(IV) reduction results in Se_ads coverage, followed by a further reduction to H₂Se, which is a gas and desorbs from the electrode surface. Finally, the Zn(II) reduction inhibits the H₂Se formation and generates a thin film of ZnSe, as the final coating. The strong dependence of the nature of reacting compound and the mass as well as the charge variations allowed to postulate a reaction mechanism.     

Effect of pH value on particle morphology and electrochemical properties of LiFePO4 by hydrothermal method

Lithium iron phosphate was prepared by hydrothermal synthesis using LiOH·H₂O, FeSO₄·7H₂O and H₃PO₄ as raw materials. The effects of pH value of reaction solution on particle morphology and electrochemical property were investigated. The pH value of the reaction solution was adjusted in the range of 2.5-8.8 by dilute sulfuric acid and ammonia water. The samples were characterized by field-emission scanning electronic microscope (FE-SEM), X-ray powder diffraction (XRD), constant-current charge/discharge cycling tests and chemical analysis. The results indicated that the particles exhibited acute angle diamond flake-like morphology at pH = 2.5, and as the pH value increased, the particle became hexagon flake-like, round flake-like and irregular flake-like morphology gradually. The optimal sample synthesized at pH = 6.4 exhibited discharge capacities of 151.8 mAh g⁻¹ at 0.2 C rate and 129.3 mAh g⁻¹ at 3 C rate. It was found that pH value affected the morphologies and properties of the product by means of different crystal growth rates.     

Preparation and characterization of nanostructured NiO/MnO2 composite electrode for electrochemical supercapacitors

Nanostructured nickel-manganese oxides composite was prepared by the sol-gel and the chemistry deposition combination new route. The surface morphology and structure of the composite were characterized by scanning electron microscope and X-ray diffraction. The as-synthesized NiO/MnO₂ samples exhibit higher surface area of 130-190 m² g⁻¹. Cyclic voltammetry and galvanostatic charge/discharge measurements were applied to investigate the electrochemical performance of the composite electrodes with different ratios of NiO/MnO₂. When the mass ratio of MnO₂ and NiO in composite material is 80:20, the specific capacitance value of NiO/MnO₂ calculated from the cyclic voltammetry curves is 453 F g⁻¹, for pure NiO and MnO₂ are 209, 330 F g⁻¹ in 6 mol L⁻¹ KOH electrolyte and at scan rate of 10 mV s⁻¹, respectively. The specific capacitance of NiO/MnO₂ electrode is much larger than that of each pristine component. Moreover, the composite electrodes showed high power density and stable electrochemical properties.     

Properties of amorphous Si thin film anodes prepared by pulsed laser deposition

Amorphous Si (a-Si) thin film anodes were prepared by pulsed laser deposition (PLD) at room temperature. Structures and properties of the thin films were investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and electrochemical measurements. Galvanostatic charge/discharge tests of half cells using lithium counter electrode were conducted at a constant current density of 100 μA/cm² in different voltage windows. Cyclic voltammetry (CV) was obtained between 0 and 1.5 V at various scan rates from 0.1 to 2 mV/s. The apparent diffusion coefficient (D_Li) calculated from the CV measurements was about ∼10⁻¹³ cm²/s. The Si thin film anode was also successfully coupled with LiCoO₂ thin film cathode. The a-Si/LiCoO₂ full cell showed stable cycle performance between 1 and 4 V.     

Voltammetric detection of bisphenol a by a chitosan-graphene composite modified carbon ionic liquid electrode

In this paper 1-ethyl-3-methylimidazolium tetrafluoroborate based carbon ionic liquid electrode (CILE) was fabricated and further modified with chitosan (CTS) and graphene (GR) composite film. The fabricated CTS-GR/CILE was further used for the investigation on the electrochemical behavior of bisphenol A (BPA) by cyclic voltammetry and differential pulse voltammetry. A well-defined anodic peak appeared at 0.436 V in 0.1 mol/L pH 8.0 Britton-Robinson buffer solution, which was attributed to the electrooxidation of BPA on the modified electrode. The electrochemical parameters of BPA on the modified electrode were calculated with the results of the charge transfer coefficient (α) as 0.662 and the apparent heterogeneous electron transfer rate constant (k_s) as 1.36 s^− 1. Under the optimal conditions, a linear relationship between the oxidation peak current of BPA and its concentration can be obtained in the range from 0.1 μmol/L to 800.0 μmol/L with the limit of detection as 2.64 × 10^− 8 mol/L (3σ). The CTS-GR/CILE was applied to the detection of BPA content in plastic products with satisfactory results.     

Preparation of flower-like CuO by a simple chemical precipitation method and their application as electrode materials for capacitor

A novel CuO electrode material with flower-like nanostructures was fabricated at a low temperature (80 °C) by a simple chemical precipitation method. Scanning electron microscopy (SEM) results showed that CuO with spherical and flower-like structure can be formed under a weak alkali (C₆H₁₂N₄), and CuO with sheets structure can be obtained under a strong alkali (NaOH). A possible growth mechanism of CuO nanocrystals was discussed. The flower-like CuO electrode exhibited a higher specific capacitance (133.6 Fg⁻¹) and an excellent cycle performance at a high current density of 10 mA/cm². Specific capacitance of flower-like CuO was 405.3% higher than globular CuO (26.44 Fg⁻¹) at 2 mA/cm².     

Preparation and electrochemical properties of lamellar MnO2 for supercapacitors

Lamellar birnessite-type MnO₂ materials were prepared by changing the pH of the initial reaction system via hydrothermal synthesis. The interlayer spacing of MnO₂ with a layered structure increased gradually when the initial pH value varied from 12.43 to 2.81, while the MnO₂, composed of α-MnO₂ and γ-MnO₂, had a rod-like structure at pH 0.63. Electrochemical studies indicated that the specific capacitance of birnessite-type MnO₂ was much higher than that of rod-like MnO₂ at high discharge current densities due to the lamellar structure with fast intercalation/deintercalation of protons and high utilization of MnO₂. The initial specific capacitance of MnO₂ prepared at pH 2.81 was 242.1 F g⁻¹ at 2 mA cm⁻² in 2 mol L⁻¹ (NH₄)₂SO₄ aqueous electrolyte. The capacitance increased by about 8.1% of initial capacitance after 200 cycles at a current density of 100 mA cm⁻².     

Preparation of LiFePO4/C composite powders by ultrasonic spray pyrolysis followed by heat treatment and their electrochemical properties

LiFePO₄ powders could be successfully prepared from a precursor solution, which was composed of Li(HCOO)·H₂O, FeCl₂·4H₂O and H₃PO₄ stoichiometrically dissolved in distilled water, by ultrasonic spray pyrolysis at 500 °C followed by heat treatment at sintering temperatures ranging from 500 to 800 °C in N₂ + 3% H₂ gas atmosphere. Raman spectroscopy revealed that α-Fe₂O₃ thin layers were formed on the surface of as-prepared LiFePO₄ powders during spray pyrolysis, and they disappeared after sintering above 600 °C. The LiFePO₄ powders prepared at 500 °C and then sintered at 600 °C exhibited a first discharge capacity of 100 mAh g⁻¹ at a 0.1 C charge-discharge rate. To improve the electrochemical properties of the LiFePO₄ powders, LiFePO₄/C composite powders with various amounts of citric acid added were prepared by the present method. The LiFePO₄/C (1.87 wt.%) composite powders prepared at 500 °C and then sintered at 800 °C exhibited first-discharge capacities of 140 mAh g⁻¹ at 0.1 C and 84 mAh g⁻¹ at 5 C with excellent cycle performance. In this study, the optimum amount of carbon for the LiFePO₄/C composite powders was 1.87 wt.%. From the cyclic voltammetry (CV) and AC impedance spectroscopy measurements, the effects of carbon addition on the electrochemical properties of LiFePO₄ powders were also discussed.     

Unique properties of polyaniline in the presence of applied magnetic field and ferric chloride

Fe-contained polyaniline (abbreviated as PANI–Fe) was prepared by chemical oxidation of aniline with ammonium peroxydisulfate oxidant in 0.5 mol dm⁻³ HCl and an adequate content of FeCl₃·6H₂O solution in the presence of an applied magnetic field at room temperature. The X-ray photoelectron spectroscopy (XPS) and UV–vis and FTIR spectra suggest that there is an interaction between FeCl₃ and PANI chains, but PANI–Fe backbone is essentially identical with that of parent polyaniline. The electron paramagnetic resonance (EPR) spectrum shows that there were unpaired electrons in PANI–Fe synthesized in the presence of an applied magnetic field, the spin density and the conductivity of which are 7.308 × 10²⁰ spins g⁻¹ and 0.891 S cm⁻¹, respectively. The plot of magnetization (M) vs. the applied magnetic field (H) displays that the PANI–Fe possesses soft ferromagnetic behavior at room temperature. The results of cyclic voltammogram show that the PANI–Fe film is of excellent electrochemical activity.     

Amperometric hydrogen peroxide biosensor based on cobalt ferrite-chitosan nanocomposite

A novel H₂O₂ biosensor based on horseradish peroxidase (HRP) immobilized into CoFe₂O₄-chitosan nanocomposite has been developed for the detection of hydrogen peroxide. The nanocomposite films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). HRP has been entrapped into CoFe₂O₄-chitosan nanocomposite film and the immobilized enzyme could retain its bioactivity. This biosensor exhibited a fast amperometric response to hydrogen peroxide. The linear range for H₂O₂ determination was from 3 × 10^− 2 to 8 mM, with a detection limit of 2 × 10^− 3 mM based on S/N = 3. The response time of the biosensor was 4 s. The effects of the pH and the temperature of the immobilized HRP electrode were also studied.     

Investigation on passivity of titanium under steady-state conditions in acidic solutions

The passivity of titanium was studied using potentiostatic polarization combined with Mott–Schottky analysis in acidic solutions. The oxide layer was characterized as an n-type semiconducting, oxygen deficient oxide (TiO_{1.993–1.996}) with a donor density in the range of 10¹⁹–10²⁰ cm⁻³ depending on electrode potential and electrolyte pH. The calculated thickness for the inner oxide layer was in the range of 1–4 nm, increasing linearly with applied potential and exponentially with electrolyte pH. The potential- and pH-dependence of the inner oxide thickness was interpreted by a modified point defect model for the migration-controlled oxide growth, in which the rate-determining step in the passive film growth processes was assumed to be the donor lattice migration.     

Poly(BCB)/Au-nanoparticles hybrid film modified electrode: Preparation, characterization and its application as a non-enzymatic sensor

We report electrochemical preparation and characterization of poly-brilliant cresyl blue (Poly(BCB))/gold nanoparticles (Au-NPs) modified electrode. The Poly(BCB)/Au-NPs modified electrode has been used as an electrochemical sensor for the detection of hydrogen peroxide (H₂O₂) at lower potential (− 0.2 V). The Poly(BCB)/Au-NPs film was characterized by scanning electron microscopy, Uv-visible spectroscopy (Uv-vis) and cyclic voltammetry. We have observed that, Au-NPs attached glassy carbon electrode (Au-NPs/GCE) significantly enhanced the polymerization of BCB compared to bare GCE. The Poly(BCB) film was irreversibly attached onto the Au-NPs modified electrode, the resulting hybrid film modified electrode was electrochemically active in the pH range from 2 to 11. Attachment of Poly(BCB)/Au-NPs hybrid film on the electrode surface was confirmed by Uv-vis spectra. In addition, electrocatalytic properties of the Poly(BCB)/Au-NPs/GCE towards reduction of H₂O₂ have been investigated, and it was found that the sensitivity, reduction potential as well as the corresponding detection limit were improved as compared to the voltammetric response of the Poly(BCB)/GCE and Au-NPs/GCE. Based on this study, a non-enzymatic electrochemical sensor for the determination of H₂O₂ has been reported. Moreover, analysis of commercial H₂O₂ samples was performed using the proposed method and satisfactory results were obtained.     

Electrochemical characterization of polyaniline electrode in ammonium citrate containing electrolyte

Polyaniline electrode (PANI) was formed electrochemically at graphite electrode. Electrochemical polymerization was performed at constant current density of 2.0 mA cm⁻² from aqueous solution of 1.0 mol dm⁻³ HCl with addition of 0.25 mol dm⁻³ aniline monomer. Electrochemical characterization of the PANI electrode in chloride and chloride/citrate electrolyte was performed using cyclic voltammetry and galvanostatic measurement in order to study the influence of citrate ions on charge/discharge capability and cycling efficiency. It was observed that, for anodic potential 0.32 V, higher electrode capacity of PANI electrode in chloride/citrate electrolyte was obtained, comparing to chloride electrolyte, indicating positive effect of citrate ions on cycling characteristics. On the other hand, for higher anodic potential limit of 0.50 V, faster decrease of the electrode capacity in chloride/citrate electrolyte was observed. It was suggested that influence of both chloride and citrate anions had exhibited influence on electrochemical behavior of PANI electrode in citrate containing electrolyte.     

Study on preparation of NiOOH by a new catalytic electrolysis method

The present paper reports a new catalytic electrolysis method to prepare NiOOH. KMnO₄ is proposed as a catalyst to play the role of electron-transfer medium in the electrolysis preparation of NiOOH for the first time. Through the self-redox reaction of KMnO₄, the highly efficient electron-transfer process between the electrolyte and the electrode of the spherical Ni(OH)₂ is realized, thus resulting in a high electrolytic efficiency and short electrolysis time. The mechanism of catalytic electrolysis is preliminarily discussed. The experimental results show that the electrode prepared with the NiOOH powders by catalytic electrolysis offers a discharge capacity of 267 mAh g⁻¹ at a current density of 120 mA g⁻¹ and exhibits good cycling performance.     

Surfactant-free synthesis and electrochemical properties of chrysanthemum-like InVO4 hierarchical microstructures

Novel chrysanthemum-like hierarchical microstructures of orthorhombic InVO₄ were synthesized via a hydrothermal route without assistance of any template or organic additive. The chrysanthemum-like InVO₄ microstructures are built up of numerous nanobelts radially aligned around the spherical surface. Based on the structural feature of orthorhombic InVO₄ and the key role of the pH value, a probable mechanism of the etching-splitting growth process induced by H⁺ ions was proposed to explain the formation of InVO₄ microstructures. Furthermore, the chrysanthemum-like InVO₄ sample shows a high discharge capacity of 608.6 mAh g⁻¹ and acceptable capacity retention when used as an electrode material in lithium ion batteries. The pure orthorhombic phase and unique porous morphology play basic roles in the structural requirement to serve as transport paths for lithium ion.