High-sensitivity non-enzymatic glucose biosensor based on Cu(OH)2 nanoflower electrode covered with boron-doped nanocrystalline diamond layer

A non-enzymatic biosensor was developed using boron-doped nanocrystalline diamond (BDND) based on a Cu electrode with Cu(OH)₂ dendritic architecture. The Cu(OH)₂ nanoflower electrode was covered with a BDND layer using an electrostatic self-assembly seeding method with nanodiamond particles and hot-filament chemical vapor deposition. X-ray diffraction and Raman spectral analysis confirmed that the BDND nanoflower electrode was synthesized onto Cu(OH)₂ nanoflowers. Field-emission scanning electron microscope images showed that the fabricated electrodes were nanoflowers possessing large surface areas. From cyclic voltammetry, the peak currents of an BDND/Cu(OH)₂/Cu electrode was about 7, 6.2, and 5.9 times higher than that of the Cu foil, Cu(OH)₂/Cu, and BDND/Cu electrodes, respectively. A biosensor based on BDND/Cu(OH)₂/Cu exhibited excellent performance for glucose detection, and it had a linear detection range of 0 to 6 mM, a correlation coefficient of 0.9994, a low detection limit of 9 μM, and a high sensitivity of 2.1592 mA mM^− 1 cm^− 1.     

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.     

Flexible electrochemical biosensors based on O2 plasma functionalized MWCNT

A flexible glucose sensor is fabricated using O₂ plasma-functionalized multiwalled carbon nanotube (MWCNT) films on polydimethylsiloxane (PDMS) substrates and its performance is electrochemically characterized. After enzyme immobilization, the GOD/ MWCNT/Au/PDMS electrode exhibits a sensitivity of 18.15 μA mm^− 2mM^− 1 and a detection limit of 0.01 mM (signal to noise ratio was about 3). This high sensitivity may be attributed to a large enzyme loading and a higher electrocatalytic activity and electron transfer exhibited by O₂ plasma-functionalized CNTs than the pristine CNT, due to some oxygen-contained groups present on the O₂ plasma-functionalized CNT surface, which has been verified by XPS spectrum.     

Effect of Ti defects on electrochemical properties of highly-ordered titania nanotube arrays

In this paper, highly-ordered TiO₂ nanotube (TNT) electrodes fabricated by anodization at 20 V in 0.1 M F⁻-based solution were annealed in O₂, N₂ and CO respectively. The surface properties of the TiO₂ electrodes after annealing treatment by different gases were studied by means of photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical properties of the TNT electrodes were investigated by cyclic voltammetry, steady-state polarization and photocurrent response measurements. The results showed that Tiⁿ⁺ (n = 0-3) cations and oxygen vacancies existed in the TNT electrode after annealing in CO, leading to a very efficient electron transfer rate of 1.34 × 10^− 3 cm/s. Steady-state polarization measurement and photocurrent response demonstrated that the electrode potential of oxygen evolution reaction (OER) reduced by 20% and the photocurrent response increased by 50% for CO-annealed TNT electrode compared with O₂-annealed TNT electrode.     

Potentiodynamical co-deposited manganese oxide/carbon composite for high capacitance electrochemical capacitors

Manganese oxide/carbon composite materials were prepared by introducing the carbon powders into the potentiodynamical anodic co-deposited manganese oxide in 0.5 mol L^− 1 MnSO₄ and 0.5 mol L^− 1 H₂SO₄ mixed solution at 40 °C. The surface morphology and structure of the composite material were examined by scanning electron microscope and X-ray diffraction. Cyclic voltammetry tests and electrochemical impedance measurements were applied to investigate the performance of the composite electrodes with different ratios of manganese oxide and carbon. These composite materials with rough surface, which consisted of approximately amorphous manganese oxide, were confirmed to possess the ideal capacitive property. The highest specific capacitance of manganese oxide/carbon composite electrode was up to 410 F g^− 1 in 1.0 mol L^− 1 Na₂SO₄ electrolyte at the scan rate 10 mV s^− 1. The synthesized composite materials exhibited ideal capacitive behavior indicating a promising electrode material for electrochemical supercapacitors.     

(WO3)x–(TiO2)1−x nano-structured porous catalysts grown by micro-arc oxidation method: Characterization and formation mechanism

Very recently, we fabricated (WO₃)_x–(TiO₂)_1−x layers via micro-arc oxidation process under different applied voltages. Morphological and topographical studies, accomplished by SEM and AFM techniques, revealed that the pores size as well as the surface roughness increased with the voltage. Phase structure and chemical composition of the layers were also investigated by XRD and XPS and the results showed the grown layers consisted of titanium and tungsten oxides. It was found that WO₃ dispersed in the TiO₂ matrix and also doped into the TiO₂ lattice. In addition, optical properties of the synthesized layers were studied employing a UV–vis spectrophotometer. Band gap energy of the layers was approximately determined as 2.87 eV. Finally, methylene blue was selected as a model material and its degradation rate on the surface of the layers was measured to determine the photocatalytic efficiency. The degradation rate constants were measured as 2.2 × 10⁻² and 0.9 × 10⁻² min⁻¹ under ultraviolet and visible irradiations.     

Fabrication of TiO2 nanotube arrays by electrochemical anodization in an NH4F/H3PO4 electrolyte

Highly ordered TiO₂ nanotube arrays were fabricated by electrochemical anodization of titanium in an NH₄F/H₃PO₄ electrolyte. A TiO₂ crystal phase was identified by X-ray diffraction, and the morphology, length and pore diameter of the TiO₂ nanotube arrays were determined by field-emission scanning electron microscopy (FE-SEM). The anodization parameters including the rate of magnetic stirring, F⁻ concentration, calcination temperature, anodization voltage and anodization time were investigated in detail. The results show that the as-prepared TiO₂ nanotube arrays possessed good uniformity, a well-aligned morphology with a length of 750 nm and an average pore diameter of 62 nm at a 150 rpm rate of magnetic stirring for 120 min at 20 V in an electrolyte mixture of 0.2 M H₃PO₄ and 0.3 M NH₄F with a 500 °C calcination to obtain 100% anatase phase. The adsorption of N-719 dye at different tube lengths was determined by UV-vis analysis and found to increase with increasing tube length. We also discuss the formation mechanism of the TiO₂ nanotube arrays. The findings indicate that the formation of the TiO₂ nanotube arrays proceeds by the combined action of the electrochemical etching and chemical dissolution.     

Electrochemical behavior of ascorbate oxidase immobilized on graphite electrode modified with Au-nanoparticles

Direct electrochemistry of ascorbate oxidase was observed when immobilized on graphite modified with nano-sized gold structures. Au-structures were electrodeposited onto the graphite surface by means of cyclic voltammetry, then the enzyme was chemisorbed onto their surface. The electron transfer between the enzyme active center and the modified electrode surface was probed by square wave voltammetry (SWV) and cyclic voltammetry (CV). The dependence of the current maxima on the scan rate was found linear, suggesting that the redox process is controlled by surface chemistry. Bioelectrocatalytic oxidation of the enzyme substrate l-ascorbic acid was explored by constant potential amperometry over the potential range from 200 to 350 mV (vs. Ag/AgCl, 3 M KCl) at the рНs 5.6 and 7.0. At a potential as low as 200 mV, pH 7.0 and temperature 25 °C following operational parameters were determined for the enzyme electrode: a sensitivity: 1.54 μA mM⁻¹ mm⁻² (r² = 0.99₅), linear dynamic range up to 3.3 mМ, detection limit of 1.5 μМ, response time up to 20 s.     

Photodeposition of Pt nanoparticles on TiO2-carbon xerogel composites

Carbon xerogels synthesized from polycondensation of resorcinol with formaldehyde, having specific surface areas in the range 650 to 990 m² g⁻¹ and variable degrees of surface oxidation, are used to prepare TiO₂-carbon xerogel composites by sol-gel methods. These composite materials are used to support Pt nanoparticles (5 wt.%) by the photodeposition technique. After a high temperature reduction treatment at 773 K, the obtained materials were characterized in order to assess the interactions between the phases Pt, TiO₂ and carbon xerogel. It is observed that the carbon xerogel acts as an adhesive agent of the TiO₂ and Pt particles, enhancing the interaction between the metal and the composite support.     

Transparent nanoporous tin-oxide film electrode fabricated by anodization

A transparent nanoporous tin oxide film electrode was fabricated by anodizing a tin film on a fluorine-doped tin oxide (FTO) film electrode. The resulting anodized nanoporous tin oxide (ANPTO) film has columnar-type pore channels with around 50 nm in diameter and is optically transparent. Electrochemical measurements with Fe(CN)₆³⁻ as a redox probe clearly revealed that the ANPTO film could be used for a working electrode with a large internal surface area. Moreover, it was found that ANPTO film had a wider anodic potential window (> ca. 2.0 V) than conventional metal oxide electrodes, such as FTO and indium tin oxide film electrodes (> ca. 1.3 V). The wide anodic potential window improves applicability of a transparent metal oxide electrode for various electrochemical oxidation reactions, which are often interfered by oxygen evolution in water. These results conclude that the ANPTO film can be used as an advanced transparent nanoporous film electrode.     

Dye-sensitized solar cells with TiO2 nanocrystalline films prepared by conventional and rapid thermal annealing processes

Titanium oxide (TiO₂) thin films are prepared by the sol-gel method and annealed at 600 °C by conventional (CTA) and rapid thermal annealing (RTA) processes on fluorine-doped tin oxide -coated glass substrates for application as the work electrode for the dye-sensitized solar cells (DSSC). TiO₂ thin films are crystallized using a conventional furnace and the proposed RTA process at annealing rates of 5 °Cmin⁻¹ and 600 °Cmin⁻¹, respectively. The TiO₂ thin films are characterized by X-ray diffraction, scanning electron microscopy and Brunauer-Emmett-Teller analysis. Based on the results, the TiO₂ films crystallized by RTA show better crystallization, higher porosity and larger surface area than those of CTA. The short-circuit photocurrent and open-circuit voltage values increased from 5.2 mAcm⁻² and 0.6 V for the DSSC with the CTA-derived TiO₂ films to 8.3 mAcm⁻² and 0.68 V, respectively, for the DSSC containing RTA-derived TiO₂ films.     

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.     

Synthesis and characterization of polythiophene-modified TiO<Subscript>2</Subscript> nanotube arrays

The highly ordered and uniform TiO₂ nanotube arrays were fabricated by anodic oxidation method and PTh(polythiophene)/TiO₂ nanotube arrays electrode were obtained by electrochemical polymerization. X-ray powder diffraction (XRD) analysis confirmed the formation of TiO₂ phase. The morphologies and optical characteristics of the TiO₂ nanotube arrays were studied by scanning electron microscope (SEM), UV-Vis absorption spectra and Raman spectra. The results demonstrate that the PTh/TiO₂ electrode could enlarge the visible light absorption region and increase the photocurrent in visible region. The modified TiO₂ electrode with light-to-electric energy conversion efficiency of 1·46%, the short-circuit current density of 4·52 mAcm^− 2, open-circuit voltage of 0·74 V and fill factor of 0·44, were obtained.     

Enhanced photoelectrochemical properties and photocatalytic activity of porous TiO2 films with highly dispersed small Au nanoparticles

Small Au nanoparticles (NPs) with mean diameter of 4.1 nm were highly deposited on TiO₂ films via a simple electrostatic self-assembly method. The physically separated Au NPs, with a high surface density of 6.3 × 10¹¹ NPs/cm², were mainly distributed on the top layer of porous TiO₂ films. The deposition of Au NPs induced a negative shift (~ 100 mV) of the apparent flat band potential of Au-TiO₂ electrodes. The charge separation efficiency of the TiO₂ electrode increased from 72.1% to 88.5% by dispersing Au NPs. Whatever redox species were present in the electrolyte, the Au-TiO₂ electrode had higher photovoltage than the TiO₂ electrode. The photovoltage was very sensitive to added redox species such as O₂, O₃, and methanol, and the effect of adsorbed redox species on electron accumulation was discussed. The electrochemical impedance spectroscopic measurements revealed that the charge transfer resistance (R_ct) of Au-TiO₂ films was reduced to 16% of bare TiO₂ electrode, and the decreased R_ct corresponded to the increased photocatalytic activity of Au-TiO₂ films. The beneficial role of uniformly dispersed small Au NPs on the charge separation was discussed. By modifying TiO₂ films with small Au NPs, the photocatalytic activity of TiO₂ films for formaldehyde degradation increased about 2.5 times.     

Copper underpotential deposition on TiO2 electrodes: A voltammetric and electrochemical quartz crystal nanobalance study

In this work, the electrogravimetric behavior of copper electrodeposition on TiO₂ electrodes was analyzed. Copper electrodeposition was carried out in 0.1 mol L^− 1 H₂SO₄ using several concentrations of CuSO₄. The voltammetric curve displays a redox processes. The first redox process occurs in the region of − 0.30 at 0.1 V (vs. saturated calomel electrode, SCE) and it is related to bulk Cu electrodeposition and stripping. For this cathodic process, it was observed that the mass gain increases both as the sweep rate decreases and as the concentration of copper increases. The second redox process, which occurs between − 0.1 V and 0.35 V (vs. SCE), the stripping charge (and mass) are independent of both sweep rate and CuSO₄ concentration and, finally, there is a saturation charge (and saturation mass) as the deposition time is increased. From the saturated mass, obtained using an electrochemical quartz crystal nanobalance, for this electrodeposition process (248 ng cm^− 2) a roughness factor of 1.8 was calculated for the TiO₂ film.     

Inexpensive synthesis of anatase TiO2 nanowires by a novel method and its electrochemical characterization

We demonstrate a simple, rapid, inexpensive and novel approach for the synthesis of a kind of anatase TiO₂ nanowires. The method is based on a hydrothermal method under normal atmosphere without using the complex Teflon-lined autoclave, high concentrations NaOH solution and long reaction time. The as-prepared materials are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical measurements. The obtained anatase TiO₂ nanowires show excellent performance. The initial Li insertion/extraction capacity is 260 and 224 mA h g^− 1 at 20 mA g^− 1, respectively. In the 20th cycle, the reversible capacity still remains about 216 mA h g^− 1, exhibiting excellent cycling stability. The discharging capacity is about 159 mA h g^− 1 in the 20th cycle at 200 mA g^− 1, demonstrating a good high-rate performance. Anatase TiO₂ nanowires might be a promising anode material for lithium-ion batteries.     

Electrochemical impedance immunosensor for the detection of cardiac biomarker Myogobin (Mb) in aqueous solution

A label-free, electrochemical impedance immunosensor based on surface modified thin flat gold wire electrode is reported for the quantitative detection of cardiac biomarker Myoglobin in aqueous solution. The protein antibody, ab-Mb, was covalently immobilized through a self assembled monolayer of 11-mercaptoundecanoic acid (MUA) and 3-mercapto propionic acid (MPA) via carbodiimide coupling reaction using N-(3-dimethylaminopropyl)-N′-ethyl carbodiimide hydrochloride (EDC) and N-Hydroxy Succinamide (NHS). The immunosensor (ab-Mb/MUA-MPA/Au) was characterized by electrochemical techniques. The electrochemical performance of the immunosensor was studied by electrochemical impedance spectroscopy. The immunosensor showed an increased electrontransfer resistance on coupling with biomarker protein antigen, ag-Mb, in the presence of a redox probe [Fe (CN)₆]^3−/4−. The modified Au electrode immunosensor exhibits an electrochemical impedance response to antigen, ag-Mb concentrations in a linear range from 10 ng to 650 ng mL⁻¹ with a lowest detection limit of 5.2 ng mL⁻¹.     

In-situ preparation of multi-layer TiO2 nanotube array thin films by anodic oxidation method

The multi-layer TiO₂ nanotube array thin films have been formed by anodic oxidation method via adjusting the outer voltage during oxidation process in glycerol electrolyte containing 0.3% NH₄HF₂. The diameter of the nanotube array increases with the outer voltage, and the length of nanotube in every layer increases with the anodic oxidation time. These multi-layers bring new possibilities to tailor the properties of the TiO₂ nanotube array thin films formed via anodic oxidation method. Further, such multi-layer structure provide a new approach to evaluate the growth rate of TiO₂ nanotube, which will help us to understand more deeply the formation mechanism of the TiO₂ nanotubes. The growth rate of TiO₂ nanotube array is respectively 1.2 and 3.6 μm/h under the anodic voltage of 30 V and 60 V. These multi-layer TiO₂ nanotube array thin films may exhibit lots of potential applications in photoelectrochemical fields.     

Single-walled carbon nanotubes modified carbon ionic liquid electrode for sensitive electrochemical detection of rutin

The single-walled carbon nanotubes (SWCNTs) modified carbon ionic liquid electrode (CILE) was designed and further used for the voltammetric detection of rutin in this paper. CILE was prepared by mixing graphite powder with ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate and liquid paraffin together. Based on the interaction of SWCNTs with IL present on the electrode surface, a stable SWCNTs film was formed on the CILE to get a modified electrode denoted as SWCNTs/CILE. The characteristics of SWCNTs/CILE were recorded by different methods including cyclic voltammetry, electrochemical impedance spectroscopy and scanning electron microscopy. The electrochemical behaviors of rutin on the SWCNTs/CILE were investigated by cyclic voltammetry and differential pulse voltammetry. Due to the specific interface provided by the SWCNTs-IL film, the electrochemical response of rutin was greatly enhanced with a pair of well-defined redox peaks appeared in pH 2.5 phosphate buffer solution. The oxidation peak currents showed good linear relationship with the rutin concentration in the range from 1.0 × 10^− 7 to 8.0 × 10^− 4 mol/L with the detection limit as 7.0 × 10^− 8 mol/L (3σ). The SWCNTs/CILE showed the advantages such as excellent selectivity, improved performance, good stability and it was further applied to the rutin tablets sample detection with satisfactory results.     

Experimental design in the electrodeposition process of porous composite Ni–P + TiO2 coatings

In this paper, an environmentally friendly electroplating process of the composite Ni–P + TiO₂ coatings was developed. Such coatings were prepared by in situ codeposition of Ni–P with TiO₂ powder (anatase) on a polycrystalline copper substrate from the nickel-plating bath in which titanium dioxide particles were held in suspension. The codeposition was carried out under galvanostatic conditions on a rotating disc electrode. To optimize the production conditions of the Ni–P coatings modified with TiO₂ by the method of mathematical statistics, the Hartley's polyselective quasi D optimum plan of experiments was used. The relationship between the percentage content in the electrodeposited composite Ni–P + TiO₂ coatings (z) and the electrodeposition parameters like cathodic current density (j_dep), bath temperature (T) as well as content of TiO₂ powder suspended in the galvanic bath (c), has been described by the adequate cubic polynomial equation and illustrated graphically. Based on the Hartley's plan it can be stated that the maximal TiO₂ content of 28.7 at.% in the Ni–P + TiO₂ coating can be obtained for the following optimal parameters of the electrodeposition process: j_dep = 0.05 A cm⁻², c = 99 g dm⁻³ and T = 40 °C. The chemical and physical characteristics of the coating obtained under such optimum conditions, have been presented. The deposit exhibits the presence of TiO₂ particles embedded into the amorphous Ni–P matrix. It has been ascertained that embedding of TiO₂ powder to the amorphous Ni–P matrix leads to the production of deposits with large surface area. Such electrochemical codeposition method may be a good alternative in the field of porous composite coatings used in gas evolution.