PPy modified titanium foam electrode with high performance for supercapacitor

Pyrrole was polymerized on the surface of titanium foam using FeCl₃ as oxidant and the as-synthesized product could be directly used as electrode for supercapacitor. The globular polypyrrole (PPy) particles were firmly loaded on the substrate with high density. The morphology study of PPy film is observed in SEM images, the XRD, FTIR and UV–vis spectra reveal the structure and crystalline of PPy nanoparticles. The electrochemical properties of PPy modified electrode are investigated by cyclic voltammetry (CV), galvanostatic charge/discharge (GCD) and cycle life techniques. The electrochemical measurements showed such a PPy–Ti electrode had a wide working potential window, a high specific capacitance of 855 F g⁻¹ and excellent cycle stability at a discharge current density of 1 A g⁻¹.     

Zinc oxide nanoparticles-chitosan composite film for cholesterol biosensor

Zinc oxide nanoparticles (NanoZnO) uniformly dispersed in chitosan (CHIT) have been used to fabricate a hybrid nanocomposite film onto indium-tin-oxide (ITO) glass plate. Cholesterol oxidase (ChOx) has been immobilized onto this NanoZnO-CHIT composite film using physiosorption technique. Both NanoZnO-CHIT/ITO electrode and ChOx/NanoZnO-CHIT/ITO bioelectrode have been characterized using Fourier transform-infrared (FTIR), X-ray diffraction (XRD), cyclic voltammetry (CV), scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS) techniques, respectively. The ChOx/NanoZnO-CHIT/ITO bioelectrode exhibits linearity from 5 to 300 mg dl⁻¹ of cholesterol with detection limit as 5 mg dl⁻¹, sensitivity as 1.41 × 10⁻⁴ A mg dl⁻¹ and the value of Michaelis-Menten constant (K_m) as 8.63 mg dl⁻¹. This cholesterol biosensor can be used to estimate cholesterol in serum samples.     

Photoluminescence properties of BaMoO4 amorphous thin films

BaMoO₄ amorphous and crystalline thin films were prepared from polymeric precursors. The BaMoO₄ was deposited onto Si wafers by means of the spinning technique. The structure and optical properties of the resulting films were characterized by FTIR reflectance spectra, X-ray diffraction (XRD), atomic force microscopy (AFM) and optical reflectance. The bond Mo-O present in BaMoO₄ was confirmed by FTIR reflectance spectra. XRD characterization showed that thin films heat-treated at 600 and 200 °C presented the scheelite-type crystalline phase and amorphous, respectively. AFM analyses showed a considerable variation in surface morphology by comparing samples heat-treated at 200 and 600 °C. The reflectivity spectra showed two bands, positioned at 3.38 and 4.37 eV that were attributed to the excitonic state of Ba²⁺ and electronic transitions within MoO²⁻₄, respectively. The optical band gaps of BaMoO₄ were 3.38 and 2.19 eV, for crystalline (600 °C/2 h) and amorphous (200 °C/8 h) films, respectively. The room-temperature luminescence spectra revealed an intense single-emission band in the visible region. The PL intensity of these materials was increased upon heat-treatment. The excellent optical properties observed for BaMoO₄ amorphous thin films suggested that this material is a highly promising candidate for photoluminescent applications.     

Fabrication of Pt/polypyrrole hybrid hollow microspheres and their application in electrochemical biosensing towards hydrogen peroxide

Pt/polypyrrole (PPy) hybrid hollow microspheres were successfully prepared by wet chemical method via Fe₃O₄ template and evaluated as electrocatalysts for the reduction of hydrogen peroxide. The as-synthesized products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), X-ray diffraction (XRD), inductive coupled plasma emission spectrum (ICP) and Fourier-transform infrared spectra (FTIR) measurements. The results exhibited that ultra-high-density Pt nanoparticles (NPs) were well deposited on the PPy shell with the mean diameters of around 4.1 nm. Cyclic voltammetry (CV) results demonstrated that Pt/PPy hybrid hollow microspheres, as enzyme-less catalysts, exhibited good electrocatalytic activity towards the reduction of hydrogen peroxide in 0.1 M phosphate buffer solution (pH = 7.0). The composite had a fast response of less than 2 s with linear range of 1.0-8.0 mM and a relatively low detection limit of 1.2 μM (S/N = 3). The sensitivity of the sensor for H₂O₂ was 80.4 mA M⁻¹ cm⁻².     

Li ion diffusion in Li4Ti5O12 thin film electrode prepared by PVP sol-gel method

Li₄Ti₅O₁₂ thin films for rechargeable lithium batteries were prepared by a sol-gel method with poly(vinylpyrrolidone). Interfacial properties of lithium insertion into Li₄Ti₅O₁₂ thin film were examined by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and potentiostatic intermittent titration technique (PITT). Redox peaks in CV were very sharp even at a fast scan rate of 50 mV s⁻¹, indicating that Li₄Ti₅O₁₂ thin film had a fast electrochemical response, and that an apparent chemical diffusion coefficient of Li⁺ ion was estimated to be 6.8×10⁻¹¹ cm² s⁻¹ from a dependence of peak current on sweep rates. From EIS, it can be seen that Li⁺ ions become more mobile at 1.55 V vs. Li/Li⁺, corresponding to a two-phase region, and the chemical diffusion coefficients of Li⁺ ion ranged from 10⁻¹⁰ to 10⁻¹² cm² s⁻¹ at various potentials. The chemical diffusion coefficients of Li⁺ ion in Li₄Ti₅O₁₂ were also estimated from PITT. They were in a range of 10⁻¹¹-10⁻¹² cm² s⁻¹.     

Electrochemical analysis of methylparathion pesticide by a gemini surfactant-intercalated clay-modified electrode

In this study, an hybrid material obtained by the intercalation of a gemini surfactant between the layers of smectite-type clay, was fully characterized by X-ray diffraction (XRD), infrared spectroscopy (FTIR) and N₂ adsorption-desorption experiments (BET method). To ascertain the intercalation process of the starting clay by the dimeric surfactant, the permselectivity and ion exchange properties of the organoclay were investigated by ion exchange voltammetry using [Fe(CN)₆]³⁻ and [Ru(NH₃)₆]³⁺ as redox probes, by the means of a clay film-modified electrode. Due to its organophilic character, the surfactant-intercalated complex was evaluated as electrode modifier for the accumulation of methylparathion (MP) pesticide. The electroanalytical procedure involves two steps: preconcentration under open-circuit followed by voltammetric detection by square wave voltammetry: the peak current obtained (after 5 min preconcentration in 4 × 10⁻⁵ mol L⁻¹ MP) on a glassy carbon electrode coated by a thin film of the modified clay was more than five times higher than that exhibited by the same substrate covered by a film of the pristine clay. This opens the way to the development of a sensitive method for the detection of the pesticide. Many parameters that can affect the stripping response (surfactant loading of the hybrid material, film composition, pH of the detection medium, preconcentration time, electrolysis potential and duration as well as some other instrumental parameters) were systematically investigated to optimize the sensitivity of the organoclay-modified electrode. After optimization, a linear calibration curve for MP was obtained in the concentration range from 4 × 10⁻⁷ to 8.5 × 10⁻⁶ mol L⁻¹ in acetate buffer (pH 5), with a detection limit of 7 × 10⁻⁸ mol L⁻¹ (signal-to-noise ratio equal to 3). The interference effect of various inorganic ions likely to influence the stripping determination of the pesticide was also examined, and the described method was applied to spring water analysis.     

Direct electrochemistry and electrocatalysis of hemoglobin in gelatine film modified glassy carbon electrode

Direct electrochemical and electrocatalytic behavior of hemoglobin (Hb) immobilized on glass carbon electrode (GCE) containing gelatine (Gel) films was investigated. The characteristics of Hb/Gel film modified GC electrode were performed by using SEM microscopy, UV-vis spectroscopy and electrochemical methods. The immobilized Hb showed a couple of quasi-reversible redox peak with a formal potential of −0.38 V (versus SCE) in 0.1 M pH 7.0 PBS. The formal potential changed linearly from pH 4.03 to 8.41 with a slope value of −52.0 mV pH⁻¹, which suggested that a proton transfer was accompanied with each electron transfer (ET) in the electrochemical reaction. The Hb/gelatine/GCE displayed a rapid amperometric response to the reduction of H₂O₂ and nitrite.     

Photovoltammetric behavior and photoelectrochemical determination of p-phenylenediamine on CdS quantum dots and graphene hybrid film

A photoelectroactive film composed of CdS quantum dots and graphene sheets (GS) was coated on F-doped SnO₂ (FTO) conducting glass for studying the electrochemical response of p-phenylenediamine (PPD) under photoirradiation. The result indicated that the cyclic voltammogram of PPD on CdS–GS hybrid film became sigmoidal in shape after exposed under visible light, due to the photoelectrocatalytic reaction. Such a photovoltammetric response was used to rapidly optimize the photoelectrocatalytic activity of hybrid films composed of different ratios of CdS to GS toward PPD. The influences of scan rate and pH on the photovoltammetric behavior of PPD on CdS–GS film revealed that although the controlled step for electrochemical process was not changed under photoirradiation, more electrons than protons might participate the photoelectrocatalytic process. Furthermore, the photoelectroactive CdS–GS hybrid film was explored for PPD determination based on the photocurrent response of film toward PPD. Under optimal conditions, the photocurrent signal on CdS–GS film was linearly proportional to the concentration of PPD ranging from 1.0 × 10⁻⁷ to 3.0 × 10⁻⁶ mol L⁻¹, with a detection limit (3S/N) of 4.3 × 10⁻⁸ mol L⁻¹. Our work based on CdS–GS hybrid film not only demonstrated a new facile photovoltammetric way to study the photoinduced electron transfer process of PPD, but also developed a sensitive photoelectrochemical strategy for PPD determination.     

Amorphous carbon nitride as an alternative electrode material in electroanalysis: Simultaneous determination of dopamine and ascorbic acid

Boron-doped diamond (BDD) films are excellent electrode materials, whose electrochemical activity for some analytes can be tuned by controlling their surface termination, most commonly either to predominantly hydrogen or oxygen. This tuning can be accomplished by e.g. suitable cathodic or anodic electrochemical pretreatments. Recently, it has been shown that amorphous carbon nitride (a-CN_x) films may present electrochemical characteristics similar to those of BDD, including the influence of surface termination on their electrochemical activity toward some analytes. In this work, we report for the first time a complete electroanalytical method using an a-CN_x electrode. Thus, an a-CN_x film deposited on a stainless steel foil by DC magnetron sputtering is proposed as an alternative electrode for the simultaneous determination of dopamine (DA) and ascorbic acid (AA) in synthetic biological samples by square-wave voltammetry. The obtained results are compared with those attained using a BDD electrode. For both electrodes, a same anodic pretreatment in 0.1 mol L⁻¹ KOH was necessary to attain an adequate and equivalent separation of the DA and AA oxidation potential peaks of about 330 mV. The detection limits obtained for the simultaneous determination of these analytes using the a-CN_x electrode were 0.0656 μmol L⁻¹ for DA and 1.05 μmol L⁻¹ for AA, whereas with the BDD electrode these values were 0.283 μmol L⁻¹ and 0.968 μmol L⁻¹, respectively. Furthermore, the results obtained in the analysis of the analytes in synthetic biological samples were satisfactory, attesting the potential application of the a-CN_x electrode in electroanalysis.     

The porous CuO electrode fabricated by hydrogen bubble evolution and its application to highly sensitive non-enzymatic glucose detection

The porous Cu film was deposited on a Pt/Ti/Si substrate by electrochemical deposition accompanied by hydrogen evolution at very high current densities. CuO films with similar morphologies were obtained by subsequent annealing of the porous copper films. The morphology, composition and structure of the porous Cu and porous CuO were investigated by FE-SEM, EDS and XRD methods. The complete transformation of Cu to CuO after annealing was indicated. The sensing performances of the porous CuO film were evaluated in alkaline solution with the porous CuO film showing a wide linearity range from 1 μM to 2.5 mM with sensitivity of 2.9 mA cm⁻² mM⁻¹, and detection limit of 0.14 μM. The sensor showed good selectivity to conventional intermediates such as AA and UA and long term stability.     

Electrosyntheses of free-standing poly(dibenzo-18-crown-6) films in boron trifluoride diethyl etherate on stainless steel electrode

High-quality free-standing poly(dibenzo-18-crown-6) (PDBC) films with a conductivity of 4.1 × 10⁻² S cm⁻¹ and good thermal stability were synthesized electrochemically on stainless steel electrode by direct anodic oxidation of dibenzo-18-crown-6 (DBC) in pure boron trifluoride diethyl etherate (BFEE). In this medium, the oxidation potential onset of DBC was measured to be only 0.98 V vs. SCE, which was much lower than that in acetonitrile + 0.1 mol L⁻¹ Bu₄NBF₄ (1.45 V vs. SCE). PDBC films obtained from this medium showed good redox activity and stability in BFEE. The structural characterization of PDBC was performed using UV-vis, FTIR spectroscopy. The results of quantum chemistry calculations of DBC monomer and FTIR spectroscopy of PDBC films indicated that the polymerization mainly occurred at C₍₄₎ and C₍₅₎ positions). Fluorescent spectral studies indicated that PDBC was a blue light emitter. To the best of our knowledge, this is the first report on the electrodeposition of free-standing PDBC films.     

Rapid DNA electrochemical biosensing platform for label-free potentiometric detection of DNA hybridization

This paper described a novel electrochemical DNA biosensor for rapid specific detection of nucleic acids based on the sulfonated polyaniline (SPAN) nanofibre and cysteamine-capped gold nanoparticle (CA-G_NP) layer-by-layer films. A precursor film of 3-mercaptopropionic acid (MPA) was firstly self-assembled on the Au electrode surface. CA-G_NP was covalently deposited on the Au/MPA electrode to obtain a stable substrate. SPAN nanofibre and CA-G_NP were alternately layer-by-layer assembled on the stable substrate by electrostatic force. Cyclic voltammetry was used to monitor the consecutive growth of the multilayer films by utilizing [Fe(CN)₆]^3−/4− as the redox indicator. The (CA-G_NP/SPAN)_n films showed satisfactory ability of electron transfer and excellent redox activity in neutral media. Negatively charged probe ssDNA was immobilized on the outer layer of the multilayer film (CA-G_NP) through electrostatic affinity. Chronopotentiometry and electrochemical impedance spectroscopy were employed to obtain the direct electrochemical readout for probe ssDNA immobilization and hybridization using [Fe(CN)₆]^3−/4− in solution as the mediator. While electrochemical impedance spectroscopy led to the characterization of the electron-transfer resistance at the electrode, chronopotentiometry provided the total resistance at the interfaces of the modified electrodes. A good correlation between the total electrode resistances and the electron-transfer resistances at the conducting supports was found. Chronopotentiometry was suggested as a rapid transduction means (a few seconds). Based on the (CA-G_NP/SPAN)_n films, the target DNA with 20-base could be detected up to 2.13 × 10⁻¹³ mol/L, and the feasibility for the detection of base-mismatched DNA was also demonstrated.     

Comparative study of LiMn2O4 thin film cathode grown at high, medium and low temperatures by pulsed laser deposition

LiMn₂O₄ thin films with different crystallizations were respectively grown at high, medium and low temperatures by pulsed laser deposition (PLD). Structures, morphologies and electrochemical properties of these three types of thin films were comparatively studied. Films grown at high temperature (?873 K) possessed flat and smooth surfaces and were highly crystallized with different textures and crystal sizes depending on the deposition pressure of oxygen. However, films deposited at low temperature (473 K) had rough surfaces with amorphous characteristics. At medium temperature (673 K), the film was found to consist mainly of nano-crystals less than 100 nm with relatively loose and rough surfaces, but very dense as observed from the cross-section. The film deposited at 873 K and 100 mTorr of oxygen showed an initial discharge capacity of 54.3 μAh/cm² μm and decayed at 0.28% per cycle, while the amorphous film had an initial discharge capacity of 20.2 μAh/cm² μm and a loss rate of 0.29% per cycle. Compared with the highly crystallized and the amorphous films, nano-crystalline film exhibited higher potential, more capacity and much better cycling stability. As high as 61 μAh/cm² μm of discharge capacity can be achieved with an average decaying rate of only 0.032% per cycle up to 500 cycles. The excellent performance of nano-crystalline film was correlated to its microstructures in the present study.     

A novel amperometric biosensor for the detection of nitrophenol

We report on a novel amperometric biosensor for detecting phenolic compounds based on the co-immobilization of horseradish-peroxidase (HRP) and methylene blue (MB) with chitosan on Au-modified TiO₂ nanotube arrays. The titania nanotube arrays were directly grown on a Ti substrate using anodic oxidation first; a gold thin film was then coated onto the TiO₂ nanotubes by an argon plasma technique. The morphology and composition of the fabricated Au-modified TiO₂ nanotube arrays were characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). Cyclic voltammetry and amperometry were used to study the proposed electrochemical biosensor. The effect of pH, applied electrode potential and the concentration of H₂O₂ on the sensitivity of the biosensor have been systemically investigated. The performance of the proposed biosensor was tested using seven different phenolic compounds, showing very high sensitivity; in particular, the linearity of the biosensor for the detection of 3-nitrophenol was observed from 3 × 10⁻⁷ to 1.2 × 10⁻⁴ M with a detection limit of 9 × 10⁻⁸ M (based on the S/N = 3).     

Growth and characterization of molybdenum oxide thin films prepared by photochemical metal–organic deposition (PMOD)

Molybdenum oxide thin films have been successfully prepared by direct UV irradiation of amorphous films of a molybdenum dioxide acetylacetonate complex on Si(1 0 0) substrates. Photodeposited films were characterized by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) and the surface morphology examined by Atomic Force Microscopy (AFM). It was found that as-photodeposited films are uniform and smooth, with thickness of 350 nm, with rms surface roughness of 28 nm and contain non-stoichiometric oxides (MoO_3−x). The results of XRD analysis showed that post-annealing of the films in air at 450 °C transforms the sub-oxides to α-MoO₃ phase with a much rougher surface morphology (rms = 144 nm). The as-photodeposited MoO_3−x films are amorphous, and exhibit better optical quality than annealed films.     

Influence of hole mobility on the response characteristics of p-type nickel oxide thin film based glucose biosensor

RF sputtered p-type nickel oxide (NiO) thin film exhibiting tunable semiconductor character which in turns enhanced its functional properties. NiO thin film with high hole mobility is developed as a potential matrix for the realization of glucose biosensor. NiO thin film prepared under the optimized deposition conditions offer good electrical conductivity (1.5 × 10⁻³ Ω⁻¹-cm⁻¹) with high hole mobility (2.8 cm² V⁻¹ s⁻¹). The bioelectrode (GO_x/NiO/ITO/glass) exhibits a low value of Michaelis–Menten constant (K_m = 1.05 mM), indicating high affinity of the immobilized GO_x toward the analyte (glucose). Due to the high surface coverage (2.32 × 10⁻⁷ mol cm⁻²) of the immobilized enzyme on to the NiO matrix and its high electrocatalytic activity, the prepared biosensor exhibits a high sensitivity of 0.1 mA (mM⁻¹-cm⁻²) and a good linearity from 25 to 300 mg dL⁻¹ of glucose concentration with fast response time of 5 s. Various functional properties of the material (mobility, crystallinity and stress) are found to influence the charge communication feature of NiO thin film matrix to a great extent, resulting in enhanced sensing response characteristics.     

Electroactive polyimide with oligoaniline in the main chain via oxidative coupling polymerization

By oxidative coupling polymerization of the imidic macromonomer of oligoaniline and p-phenylenediamine we have prepared an electroactive polyimide, exhibiting exciting molecular structure, electrochemical properties and excellent thermal stability. The polymerization characteristics and structure of the electroactive polyimide were systematically studied by Fourier-transform infrared (FTIR) spectra and X-ray powder diffraction (XRD). Electrochemical activity of the polyimide was tested in 1.0 M H₂SO₄ aqueous solution and it shows two redox peaks, which is the same as that of polyaniline. Moreover, the thermal properties of the polyimide were evaluated by thermogravimetric analysis (TGA). Its electrical conductivity is about 8.87 × 10⁻⁶ S cm⁻¹ at room temperature upon preliminarily protonic-doped experiment.     

A label-free electrochemical immunoassay for IgG detection based on the electron transfer

In this study, a highly selective, label-free electrochemical immunoassay strategy based on the charge transport through the multilayer films associated with the electrocatalytic reduction of [Fe(CN)₆]³⁻ is proposed using human immunoglobulin G (human IgG) as the model analyte. The antibody-antigen complex formed on the sensing interface can efficiently induce change of the surface charge characteristics, the conductivity of multilayer film and/or electron transfer distance, resulting in an immunoreaction signal. The current reduction is proportional to the amount of analyte. Under the optimized experimental conditions, the proposed sensing strategy provides a linear dynamic range from 10 to 10⁴ ng mL⁻¹ and a detection limit of 3 ng mL⁻¹, indicating an improved analytical performance. This possibly makes it a potential alternative in bioanalysis of proteins and other molecules.     

Electrodepositions and capacitive properties of hybrid films of polyaniline and manganese dioxide with fibrous morphologies

Electrocodepositions were conducted in solutions of aniline and MnSO₄ through potential cycling to afford hybrid films of polyaniline (PANI) and manganese dioxide (PANI/MnO₂). The films obtained displayed characteristic redox peaks of PANI on cyclic voltammograms in acidic aqueous solution. While in 1.0 M NaNO₃ at pH 1, the films showed pseudocapacitive behaviors from 0 to 0.65 V vs. SCE. MnO₂ was detected through XRD and XPS measurements on the films. The codeposition of PANI with MnO₂ had dramatic effects on morphologies of the obtained hybrid films that displayed fibrous morphologies instead of granular one of PANI. Hybrid film PM50 obtained in the presence of 50 mM Mn²⁺ displayed a specific capacitance of 532 F g⁻¹ at 2.4 mA cm⁻² discharging current, 26% higher than that of similarly prepared PANI. It showed a coulombic efficiency (η) of 97.5% over 1200 cycles with 76% specific capacitance maintained.     

Microfabricated ISEs: critical comparison of inherently conducting polymer and hydrogel based inner contacts

A rigorous side by side comparison of miniature planar potassium-selective electrodes with hydrogel and potassium hexacyanoferrate(II)/(III) doped polypyrrole (PPy/FeCN) based inner contacts is presented. The planar electrodes were manufactured by screen printing as four- and five-site arrays on ceramic substrates. These electrode arrays were incorporated into a flow-through cell, which could accommodate nine electrode sites. Two identical flow cells were connected in series and the effect of the inner contacts on the analytical performance of the respective electrodes has been critically evaluated. The time necessary to reach steady state conditions has been determined and the effect of experimental parameters (temperature, ambient light intensity, CO₂, and O₂ concentration of the sample) on the potential stability of the electrodes was analyzed. At controlled temperature, the drift of the planar potassium electrodes with hydrogel and PPy/FeCN solid contact were 0.11±0.02 mV h⁻¹ and 0.03±0.007 mV h⁻¹, respectively. The experimental data proved that there is no aqueous film formation between the PPy/FeCN film and the potassium-selective solvent polymeric membrane.