Nanotube Array Electrode Research Articles

Photoeletrocatalytic Activity of a Cu2O-Loaded Self-Organized Highly Oriented TiO2 Nanotube Array Electrode for 4-Chlorophenol Degradation

Differently sized Cu2O nanoparticles have been assembled photocatalytically on the surface of self-organized highly oriented TiO2 nanotubes obtained by anodization of a Ti sheet in fluoride-containing electrolytes. X-ray diffraction analysis identifies an anatase structure and fine preferential orientation of (101) planes. The UV-vis absorption edge of the TiO2 nanotube arrays shift to lower energy after Cu2O loading. The composite array electrode exhibits a higher photovoltage response than the TiO2 powders directly deposited on a Ti sheet. The highest photoconversion efficiencies observed for the Cu2O-loaded electrode are 17.2% and 0.82% under UV light and visible light irradiation, respectively. Especially, the composite array electrode shows a higher efficiency than the nonloaded one for the photoelectrocatalytic decomposition of 4-chlorophenol. The improved photoeletrocatalytic activity of the TiO2/Cu2O composite array electrode is attributed to the synergistic effect of Cu2O nanoparticles and TiO2 nanotube arrays. The Cu2O nanoparticles could enhance the efficiency of photon harvesting and reduce the chances of electron-hole recombination by sending the electrons to the conduction band of TiO2 nanotubes. The accumulated electrons in the conduction band of TiO2 nanotubes would reduce oxygen to form peroxides for enhanced advanced oxidation. The byproducts were identified by high-performance liquid chromatography.

Aligned single-walled carbon nanotubes array electrode: Fabrication, characterization and application

In the presence of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS), carboxylic group-functionalized single-walled carbon nanotubes (SWNTs) were assembled vertically on the glassy carbon electrode using ethylenediamine as linking agent to fabricate an aligned electrode (SWNTE). The morphological characteristic was studied with atomic force microscope (AFM) and its electrochemical property was investigated using K 3[Fe(CN) 6] as probe. ssDNA had a sensitive voltammetric response at the SWNTE and the oxidative peak potentials of guanine base and adenine base were 0.608 V and 0.896 V, respectively. Under the optimal conditions, the DPV peak current of guanine base vs. the concentration of ssDNA was linear in the range of 5.4 μg/L–10.8 mg/L with a detection limit of 1 μg/L (S/N = 3).

Visible light photoelectrocatalysis with salicylic acid-modified TiO 2 nanotube array electrode for p-nitrophenol degradation

This research focused on immersion method synthesis of visible light active salicylic acid (SA)-modified TiO 2 nanotube array electrode and its photoelectrocatalytic (PEC) activity. The SA-modified TiO 2 nanotube array electrode was synthesized by immersing in SA solution with an anodized TiO 2 nanotube array electrode. Scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), infrared spectroscopy (IR), UV–vis diffuse reflectance spectrum (DRS), and Surface photovoltage (SPV) were used to characterize this electrode. It was found that SA-modified TiO 2 nanotube array electrode absorbed well into visible region and exhibited enhanced visible light PEC activity on the degradation of p-nitrophenol (PNP). The degradation efficiencies increased from 63 to 100% under UV light, and 79–100% under visible light ( λ > 400 nm), compared with TiO 2 nanotube array electrode. The enhanced PEC activity of SA-modified TiO 2 nanotube array electrode was attributed to the amount of surface hydroxyl groups introduced by SA-modification and the extension of absorption wavelength range.

Gold nanoparticles integrated in a nanotube array for electrochemical detection of glucose

An enzyme-free amperometric glucose sensor of gold nanoparticle-constituted nanotube array electrode is presented. The resulted gold nanotube array electrode with significantly enhanced surface roughness shows prominent catalytic activity toward the electrooxidation of glucose in a pH 7.4 phosphate buffer (PBS) solution and thus can be used to individually or simultaneously determine glucose and the common interfering molecule of ascorbic acid (AA). In the case of glucose detection, the amperometric responses show a linear relationship to glucose concentration in the range of 1 mM–42.5 mM with a detection limit down to 10 μM. The present non-enzymatic glucose electrochemical biosensor shows a good stability and reproducibility.

Direct electrodeposition of Pt nanotube arrays and their enhanced electrocatalytic activities

Ordered Pt nanotube arrays have been fabricated by one-step electrodeposition utilizing nanochannel alumina templates. The electro-oxidation of ethanol on Pt nanotube arrays in acidic medium has been investigated by cyclic voltammetry. The oxidation peak currents on the Pt nanotube array electrode for ethanol oxidation are about 1.7 times those on the commercial PtRu/C electrode. The high electrocatalytic activities of the Pt nanotube array towards the oxidation of ethanol made it an excellent platform for direct ethanol fuel cell applications.

Synthesis of molecular imprinted polymer modified TiO 2 nanotube array electrode and their photoelectrocatalytic activity

A tetracycline hydrochloride (TC) molecularly imprinted polymer (MIP) modified TiO 2 nanotube array electrode was prepared via surface molecular imprinting. Its surface was structured with surface voids and the nanotubes were open at top end with an average diameter of approximately 50 nm. The MIP-modified TiO 2 nanotube array with anatase phase was identified by XRD and a distinguishable red shift in the absorption spectrum was observed. The MIP-modified electrode also exhibited a high adsorption capacity for TC due to its high surface area providing imprinted sites. Photocurrent was generated on the MIP-modified photoanode using the simulated solar spectrum and increased with the increase of positive bias potential. Under simulated solar light irradiation, the MIP-modified TiO 2 nanotube array electrode exhibited enhanced photoelectrocatalytic (PEC) activity with the apparent first-order rate constant being 1.2-fold of that with TiO 2 nanotube array electrode. The effect of the thickness of the MIP layer on the PEC activity was also evaluated.

A silicon-doped TiO 2 nanotube arrays electrode with enhanced photoelectrocatalytic activity

Silicon-doped titania nanotube arrays were fabricated by electrochemical anodization on a Ti sheet, followed by chemical vapor deposition (CVD) treatment using tetraethylorthosilicate as silicon source. The highly ordered nanotube arrays obtained by anodization kept its nanotube-like structural integrity after CVD treatment. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) results revealed that the introduced silicon might be incorporated into titania matrix. This incorporation helped to increase the thermal stability of titania, which was in favor of suppressing the phase transformation from anatase into rutile and also inhibiting the growth of anatase crystallite of titania at high calcination temperature. A significant blue-shift was observed in the spectrum of UV absorption. The surface of Si-doped TiO 2 nanotube arrays showed a super-hydrophilic behavior under UV illumination. For Si-doped TiO 2 nanotube electrode, the maximum photoconversion efficiencies of 31.8% under high-pressure mercury lamp irradiation and 16.5% using an optical filter (280–400 nm) under the same lamp irradiation were achieved, which were obviously higher than those of undoped one. The photoelectrocatalytic (PEC) activities were investigated using pentachlorophenol (PCP) as a probe substance. Compared with undoped TiO 2 nanotube electrode, the Si-doped TiO 2 showed better PEC capability in the degradation of PCP under high-pressure mercury lamp irradiation.

Ruthenium Porphyrin Functionalized Single-Walled Carbon Nanotube Arrays—A Step Toward Light Harvesting Antenna and Multibit Information Storage

Ruthenium porphyrin functionalized single-walled carbon nanotube arrays have been prepared using coordination of the axial position of the metal ion onto 4-aminopyridine preassembled single-walled carbon nanotubes directly anchored to a silicon(100) surface (SWCNTs-Si). The formation of these ruthenium porphyrin functionalized single-walled carbon nanotube array electrodes (RuTPP-SWCNTs-Si) has been monitored using infrared spectroscopy (IR), differential pulse voltammetry (DPV), atomic force microscopy (AFM), laser desorption time-of-flight mass spectroscopy (LDI-TOF-MS), UV-vis spectroscopy, fluorescence spectroscopy, and cyclic voltammetry. Electrochemical results show two successive one-electron reversible redox waves. The surface concentration of the ruthenium porphyrin molecules is 3.44 x 10 (-8) mol cm (-2). Optical results indicate that the immobilization of ruthenium porphyrin enhances the light absorption of SWCNTs-Si surfaces in the visible light region. Moreover mixed assembly of ferrocene/porphyrin onto carbon nanotube arrays has been achieved by altering the ratio of two redox-active species in the deposition solution. These results suggest the ruthenium porphyrin modified electrodes are excellent candidates for molecular memory devices and light harvesting antennae.

Carbon Nanotube Array Electrodes based Supercapacitors with 3.5V Working Voltage

Carbon Nanotube Array Electrodes based Supercapacitors with 3.5V Working Voltage

Preparation and photoelectrochemical properties of a hybrid electrode composed of polypyrrole encapsulated in highly ordered titanium dioxide nanotube array

We demonstrated in this paper that polypyrrole encapsulated in highly ordered TiO 2 nanotubes array (PPy/TiO 2 NTs) electrode could be obtained via two steps: (1) electrosynthesis of TiO 2 nanotube array in HF solution by anodization method; (2) followed by electropolymerization of pyrrole encapsulated in the TiO 2 nanotubes array. The morphological characteristics and structures of PPy/TiO 2 NTs electrode were examined by field-emission scanning electron microscopy, X-ray diffraction, and energy dispersive X-ray spectroscopy. The photoelectrochemical properties were studied in a three-electrode cell with 0.5 M Na 2SO 4 solution as supporting electrolyte. The photocurrent was dramatically enhanced on the PPy/TiO 2 NTs electrode, comparing with that on bare TiO 2 NTs electrode. A photocurrent density of 1.52 mA cm − 2 and the incident photon to electron conversion efficiency of 73.21% were obtained under an UV illumination of 10 mW cm − 2 .

Preparation and photoelectrocatalytic activity of ZnO nanorods embedded in highly ordered TiO 2 nanotube arrays electrode for azo dye degradation

In this article, the ZnO nanorods embedded in highly ordered TiO 2 nanotube arrays (ZnO/TiO 2 NR/Ts) electrodes were fabricated through two steps: (1) electrosynthesis of TiO 2 nanotube arrays (TiO 2 NTs) in HF solution by anodization method; (2) followed by cathodic electrodeposition of ZnO embedded in the TiO 2 nanotube arrays. The morphological characteristics and structures of ZnO/TiO 2 NR/Ts electrodes were examined by field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray (EDX) spectroscopy, X-ray diffraction (XRD) analysis, and UV–vis spectra. The linear-sweep photovoltammetry response on the ZnO/TiO 2 NR/Ts electrode was presented and the photocurrent was dramatically enhanced on the ZnO/TiO 2 NR/Ts electrode, comparing with that on bare TiO 2 NTs electrode. The photocatalytic and photoelectrocatalytic activity of ZnO/TiO 2 NR/Ts electrode was evaluated in degradation of methyl orange (MO) in aqueous solution.

Fabrication and characterization of carbon nanotube array electrodes with gold nanoparticle tips

Abstract In this work we fabricated 8 mm long aligned multi-walled carbon nanotube array electrodes and electrochemically deposited gold nanoparticles in a controlled manner onto the nanotube tips at the top of the array. A soldering technique was also developed to provide reliable electrical contact between the carbon nanotubes at the bottom of the array and copper on a patterned printed circuit board. The top surfaces of the nanotube tower electrodes were activated using a reactive ion etcher prior to gold deposition. Electrodeposition of Au particles on the plasma-treated tower electrodes was performed over a range of deposition times and potentials. Cyclic voltammetry and electrochemical impedance spectroscopy analyses showed that the Au-deposited carbon nanotube array electrodes were successfully fabricated. The new electrodes will be the foundation for further biosensor development using self-assembled monolayers and bio-conjugation of antibodies for novel label-free immunosensing.

Fabrication of nickel oxide-embedded titania nanotube array for redox capacitance application

Titania nanotube array with an enlarged tube diameter of 110 nm and length of 700 nm was grown on titanium metal by a potentiostatic anodization in hydrofluoric acid–phosphoric acid–ethenyl glycol electrolyte. Nickel hydroxide was introduced into this titania nanotubes by either an electrodeposition–oxidation or hydrothermal process. Nickel oxide–titania composite was finally formed by heating treatment at 300 °C. Such a well-defined nanocomposite supported on titanium substrate was designed as a functional nanotube array electrode for the redox capacitance application. The morphology, microstructure and electrochemical properties of the nanocomposites were investigated by field emission scanning electron microscope, X-ray diffraction, energy dispersive X-ray diffraction and cyclic voltammetry measurements. It was found that nickel oxide could be embedded in titania nanotubes and extend from inner wall to top layer with an open pore mouth. The entire tube lengths were approx. 770 nm and 710 nm, meanwhile nickel-to-titanium atom ratios were determined as 9.6 at% and 36.4 at% for nickel oxide-embedded titania by an electrochemical and hydrothermal synthesis, respectively. The corresponding specific redox capacitance was also increased from 26 mF cm −2 to 85 mF cm −2 with highly reversible charge–discharge stability. Such an improvement was mostly ascribed to more accessible reaction interface of electroactive nickel oxide through its higher loading and a uniform dispersion on titania nanotubes. The capacitance was further increased up to 128 mF cm −2 for 36.4 at% nickel-containing nickel oxide–titania/titanium electrode when a porous graphite carbon instead of a platinum sheet was used as a cathode.

Comparison Between Electrochemical Properties of Aligned Carbon Nanotube Array and Entangled Carbon Nanotube Electrodes

Carbon nanotubes (CNTs) are promising electrochemical double-layer capacitor electrode materials because they have excellent conductivity and mesopores dominated pore structures. Electrochemical properties of an ultralong aligned carbon nanotube array (ACNTA) electrode and an entangled CNT (ECNT) electrode in ionic liquid electrolyte were studied by cyclic voltammetry, galvanostatic charge/discharge, and ac impedance. The ACNTA electrode obtains higher specific capacitance, lower equivalent series resistance, and better rate capability than the ECNT electrode. The reason is that ACNTA electrode possesses larger pore size and more regular pore structure and conductive paths, which are revealed by adsorption and scanning electron microscopy results, than ECNT electrode.

Fabrication of MgO-coated TiO2 nanotubes and application to dye-sensitized solar cells

Dye-sensitized solar cells (DSCs) are more spotlighted than conventional photovoltaic devices due to their relatively low cost, easy fabrication and high efficiency. However, there are limitations to increase the conversion efficiency of DSCs. The limiting factors are the quantity of dye adsorption and charge recombination between TiO2 electrode and electrolyte. Coating other materials such as high energy band gap insulators or semiconductors on the TiO2 electrode enhances dye adsorption and reduces charge recombination. We fabricated DSCs based on bare TiO2 nanotube arrays and 0.02 and 0.04 M MgO coated TiO2 nanotube arrays. MgO layer increased the photovoltage and photocurrent. The overall conversion efficiency of DSCs using 0.02 M MgO coated TiO2 nanotubes was 1.61%. MgO formed insulating layers between TiO2 nanotube array electrode and electrolyte. Charge recombination was inhibited at the interfaces of TiO2 nanotube array electrode and electrolyte by MgO insulating layers. MgO coating also improved dye adsorption because iso-electric point (IEP) of MgO was larger than TiO2. When the IEP of coating material is larger than TiO2, the chemical attraction between the electrode surface and Ru-based dye molecule is increased.

Photoelectrochemical oxidation behavior of methanol on highly ordered TiO2 nanotube array electrodes

The highly ordered titanium dioxide nanotube array (HOTDNA) electrodes were prepared in hydrofluoric acid solution by electrochemical anodic oxidation technique on a pure titanium sheet. The HOTDNA electrodes were characterized by X-ray diffraction, SEM microscopy, and UV–vis spectra. It has shown high density, well ordered and uniform titanium dioxide nanotube array film covered on these electrodes and the TiO2 structure depending on the heating condition, the anatase phase of TiO2 appeared when heating to 500 °C. The photoelectrochemical characteristics of methanol in 0.5 M Na2SO4 on the HOTDNA electrodes were investigated. The cyclic voltammetry, photocurrent-time and open-circuit photopotential response of methanol on the HOTDNA electrode were represented and significant photogenerated current was observed upon illumination in the UV regions with the light of 253.7 nm central wavelength. The effect of variables such as light intensity, applied potential, and methanol concentration on the photoelectrochemical response was investigated. It was found that the photocurrent was greatly influenced by these factors.

Fabrication of Boron-Doped TiO2 Nanotube Array Electrode and Investigation of Its Photoelectrochemical Capability

Boron-doped TiO2 nanotube arrays were produced by forming a nanotube-like TiO2 film in an anodization process on a Ti sheet, followed by chemical vapor deposition treatment using trimethyl borate as the boron source with N2 as the carrier gas, and were characterized by ESEM, XPS, XRD, and UV−vis methods. The highly ordered vertically oriented nanotube arrays were obtained, and the nanotubes were open at the top end with an average diameter of approximately 80 nm. Analysis by XPS indicated that the introduced boron was probably incorporated into TiO2 and that the chemical environmental surrounding boron might be Ti−B−O. The boron-doped sample with a mixture of anatase and rutile was identified by X-ray diffraction. A shift of the absorption edge to a lower energy in the spectrum of the UV−vis absorption was observed. Under both UV and 400−620 nm visible light irradiation, the B-doped TiO2 nanotube array electrode exhibited a higher photoconversion efficiency than the non-doped one, a notable photoconversion efficiency of 31.5% was achieved under high-pressure mercury lamp irradiation, and a photoconversion efficiency of 15.1% on the B-doped electrode was obtained under λ > 290 nm light irradiation. The photoelectrocatalytic activity of the prepared electrode was evaluated using pentachlorophenol as a test substance under UV and visible light irradiation.

Photoelectrocatalytic Activity of Highly Ordered TiO2 Nanotube Arrays Electrode for Azo Dye Degradation

A highly ordered titanium dioxide nanotube arrays (HOTDNA) electrode was prepared in hydrofluoric acid solution by electrochemical anodization technique on a pure titanium sheet. The HOTDNA electrode was characterized by FE-SEM microscopy, X-ray diffraction, and UV-vis spectra. The linear-sweep photovoltammetry response on the HOTDNA electrode is presented in this work. The photogenerated current of 0.3 mA/cm2 was observed significantly upon illumination with applied potential of 0.5 V in the UV regions at the central wavelength of 253.7 nm. Photoelectrocatalytic (PEC) and photocatalytic (PC) activities of the HOTDNA electrode were evaluated in the degradation of methyl orange (MeO) in aqueous solution. A set of optimized conditions such as anodic potential, calcinations temperature, and MeO concentration on the PEC activity was investigated. The PEC and PC activities of HOTDNA electrode were compared. We concluded that the HOTDNA electrode was an effective photoelectrode for achieving an enhanced MeO degradation.

Fabrication and Catalytic Properties of Co−Ag−Pt Nanoparticle-Decorated Titania Nanotube Arrays

Highly ordered titania nanotube arrays are fabricated by anodic oxidation of titanium in a fluoride-ion-containing electrolyte. In this work Co−Ag−Pt nanoparticles, approximately 20 nm in diameter, are electrochemically deposited inside the nanotubes and the catalytic properties of the resultant architecture examined using Mn2+/Mn3+ as the probe. The effect of Co, Ag, and Pt loading content on the catalytic activity is investigated. In comparison to a Pt electrode, the oxidation potential of the Co−Ag−Pt/titania nanotube array electrode is negatively shifted by 93 mV and the peak current increased by a factor of 9.

Electrochemical Double-Layer Capacitance of MoS[sub 2] Nanowall Films

Edge-oriented MoS 2 films synthesized by single source precursor chemical vapor deposition exhibit a high density of nanowalls, which can potentially exhibit excellent electrochemical charge storage properties. The electrochemical double-layer capacitance of layered, nanowalled MoS 2 film has been investigated in this work using electrochemical impedance spectroscopy. We show that edge-oriented MoS 2 thin films can behave as a supercapacitor at alternating current frequencies up to 100 Hz. The supercapacitor performance is comparable to that of carbon nanotube array electrodes. In addition to double-layer capacitance, diffusion of the ions into the films at slow scan rates gives rise to faradaic capacitance, which enhances the capacitance significantly. The real and imaginary part of the capacitance of the MoS 2 films was analyzed as a function of frequency, in order to obtain information on the relaxation time constant and frequency dependence of the supercapacitor properties.