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The glucose oxidase (GOD) modified polypyrrole/titania nanotube enzyme electrode is fabricated for electrochemical biosensing application. The titania nanotube array is grown directly on a titanium substrate through an anodic oxidation process. A thin film of polypyrrole is coated onto titania nanotube array to form polypyrrole/titania nanotube hybrid through a normal pulse voltammetry process. GOD-polypyrrole/titania nanotube enzyme electrode is prepared by the covalent immobilization of GOD onto polypyrrole/titania nanotube hybrid via the cross-linker of glutaraldehyde. The morphology and microstructure of nanotube electrodes are characterized by field emission scanning electron microscopy and Fourier transform infrared analysis. The biosensing properties of this nanotube enzyme electrode have been investigated by means of cyclic voltammetry and chronoamperometry. The hydrophilic polypyrrole/titania nanotube hybrid provides highly accessible nanochannels for GOD encapsulation, presenting good enzymatic affinity. As-formed GOD-polypyrrole/titania nanotube enzyme electrode well conducts bioelectrocatalytic oxidation of glucose, exhibiting a good biosensing performance with a high sensitivity, low detection limit and wide linear detection range., (© 2013 Elsevier B.V. All rights reserved.)

A bioelectrocatalysis system based on titania nanotube electrode has been developed for the quantitative detection application. Highly ordered titania nanotube array with inner diameter of 60 nm and total length of 540 nm was formed by anodizing titanium foils. The functionalization modification was achieved by embedding glucose oxidases inside tubule channels and electropolymerizing pyrrole for interfacial immobilization. Morphology and microstructure characterization, electrochemical properties and bioelectrocatalytic reactivities of this composite were fully investigated. The direct detection of hydrogen peroxide by electrocatalytic reduction reaction was fulfilled on pure titania nanotube array with a detection limit up to 2.0 x 10(-4)mM. A biosensor based on the glucose oxidase-titania/titanium electrode was constructed for amperometric detection and quantitative determination of glucose in a phosphate buffer solution (pH 6.8) under a potentiostatic condition (-0.4V versus SCE). The resulting glucose biosensor showed an excellent performance with a response time below 5.6s and a detection limit of 2.0 x 10(-3)mM. The corresponding detection sensitivity was 45.5 microA mM(-1)cm(-2). A good operational reliability was also achieved with relative standard deviations below 3.0%. This novel biosensor exhibited quite high response sensitivity and low detection limit for potential applications.

Titanium nitride modified lithium titanate nanotube array (TiN-Li 4 Ti 5 O 12 NTA) was designed as the electrode material of lithium-ion supercapacitor for electrochemical energy storage. Li 4 Ti 5 O 12 NTA was prepared through lithiation treatment of anodic TiO 2 NTA and then annealing treatment in argon. TiN-Li 4 Ti 5 O 12 NTA was formed through coating TiO 2 sol on the surface of Li 4 Ti 5 O 12 NTA and then full nitridation treatment in ammonia. Partially nitridized Li 4 Ti 5 O 12 (N-Li 4 Ti 5 O 12 ) NTA was also prepared through a controlled nitridation treatment of Li 4 Ti 5 O 12 NTA in ammonia. TiN-Li 4 Ti 5 O 12 NTA with full TiN coating layer exhibited higher conductivity than N-Li 4 Ti 5 O 12 NTA with partially incorporated TiN. The capacitance accordingly increased from 79.58 F g −1 for N-Li 4 Ti 5 O 12 to 143.83 F g −1 for TiN-Li 4 Ti 5 O 12 at 0.5 A g −1 in 0.5 M Li 2 SO 4 . The capacitance retention ratio also increased from 72.95% to 82.41% after 1000 cycles at 3.0 A g −1 . The all-solid-state supercapacitor was constructed using TiN-Li 4 Ti 5 O 12 NTA electrode and polyvinyl alcohol gel electrolyte containing Li 2 SO 4 , showing high capacitance of 40.45 F g −1 , energy density of 32.36 Wh kg −1 and power density of 0.6 kW kg −1 at the high output voltage of 2.4 V and current density of 0.5 A g −1 . Therefore, TiN-Li 4 Ti 5 O 12 NTA could act as a feasible electrode material of lithium-ion supercapacitor. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) and silver nanoparticles (Ag NPs) sequentially decorated nitrogen-doped titania nanotube array (N-TiO2 NTA) had been designed as visible-light-driven self-cleaning surface-enhanced Raman scattering (SERS) substrate for a recyclable SERS detection application. N-TiO2 NTA was fabricated by anodic oxidation and then doping nitrogen treatment in ammonia atmosphere, acting as a visible-light-driven photocatalyst and supporting substrate. Ag/GO/N-TiO2 NTA was prepared by decorating GO monolayer through an impregnation process and then depositing Ag NPs through a polyol process on the surface of N-TiO2 NTA, acting as the collection of organic molecule and Raman enhancement. The SERS activity of Ag/GO/N-TiO2 NTA was evaluated using methyl blue as an organic probe molecule, revealing the analytical enhancement factor of 4.54 × 104. Ag/GO/N-TiO2 NTA was applied as active SERS substrate to determine a low-affinity organic pollutant of bisphenol A, revealing the detection limit of as low as 5 × 10−7 m. Ag/GO/N-TiO2 NTA could also achieve self-cleaning function for a recycling utilization through visible-light-driven photocatalytic degradation of the adsorbed organic molecules. Ag/GO/N-TiO2 NTA has been successfully reused for five times without an obvious decay in accuracy and sensitivity for organic molecule detection. The unique properties of this SERS substrate enable it to have a promising application for the sensitive and recyclable SERS detection of low-affinity organic molecules. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

BACKGROUND The substrate materials of enzyme electrodes strongly affect bioelectrocatalytic activity. TiO2 nanotube arrays ( NTAs) show good affinity to glucose oxidase ( GOx) but low conductivity. TiN NTAs show good conductivity but low affinity to GOx. Nitrogen-doped TiO2 (N- TiO2) NTA with good hydrophilicity and conductivity was designed to prepare a GOx/N- TiO2 NTA enzyme electrode to promote bioelectrocatalytic performance. RESULTS N- TiO2 NTA had a well-ordered nanoarray structure with slightly distorted pore mouth and wrinkled nanotube wall. N- TiO2 NTA exhibited decreased charge transfer resistance and similar contact angle to TiO2 NTA, presenting high electrical conductivity and good hydrophilicity. GOx/N- TiO2 NTA exhibited highly increased current response at a potential of −0.45 V, presenting good bioelectrocatalysis towards glucose. A GOx/N- TiO2 NTA enzyme electrode was used to fabricate a glucose biosensor, showing a high sensitivity of 733.17 µA mM−1 cm−2 and a linear range of 0.05-0.85 mmol L−1 and low detection limit of 2.9 µmol L−1 for glucose determination. It exhibited high selectivity in the presence of common interfering substances and was used to determine glucose in serum. It also had good reproducibility and long-time storage stability. In addition, the GOx/N- TiO2 NTA enzyme electrode was used to fabricate a glucose fuel cell, showing maximum power density of 23.92 µW cm−2 as well as good bioelectrocatalytic stability. CONCLUSION High bioelectrocatalytic activity and stability of GOx/N- TiO2 NTA proved that N- TiO2 NTA could act as a reasonable supporting substrate material for enzyme electrodes for various bioelectrocatalytic applications. © 2015 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

The polypyrrole/titanium nitride/polyaniline (PPy/TiN/PANI) coaxial nanotube hybrid has been prepared as supercapacitor electrode material by stepwise loading of PPy and PANI into TiN nanotube array through normal pulse voltammetry and cyclic voltammetry electrodeposition process. P-type doping PPy and N-type doping PANI could be well incorporated into an integrated composite to act as an electroactive material. TiN nanotube array with highly ordered nanostructure and good electrical conductivity promoted the charge transfer capability of conducting polymers of PPy and PANI. PPy/TiN/PANI coaxial nanotube hybrid with P/N type doping properties exhibited high specific capacitance of 1471.9 F g −1 at a current density of 0.5 A g −1 and a potential window of 0.8 V in 1.0 M H 2 SO 4 solution. It could keep the capacitance of 1077.4 F g −1 at high current density of 10 A g −1 and capacitance retention of 78.0% after 200 cycles, presenting good rate capability and reasonable cycling stability. All-solid-state flexible supercapacitor was constructed using PPy/TiN/PANI electrode and H 2 SO 4 -included polyvinylalcohol gel electrolyte. It offered superior energy storage capacity with respect to specific capacitance of 288.4 F g −1 and energy density of 129.8 Wh kg −1 at high potential window of 1.8 V and current density of 1.0 A g −1 . PPy/TiN/PANI coaxial nanotube hybrid accordingly presented the promising application as supercapacitor electrode material for energy storage. [ABSTRACT FROM AUTHOR]

The polypyrrole/titania/polyaniline (PPy/TiO 2 /PANI) coaxial nanotube hybrid has been prepared through a stepwise electrodeposition process for an electrochemical energy storage. Independent TiO 2 nanotube array was used as the framework, which was formed by anodizing titanium foil at 30 V in fluoride-containing water and ethylene glycol mixture solution. The PPy was selectively coated on the outer surface of TiO 2 nanotube walls to form PPy/TiO 2 through a normal pulse voltammetry electrodeposition process. The PANI was then coated on the inner surface of TiO 2 nanotube walls to form PPy/TiO 2 /PANI coaxial nanotube hybrid through a photoassisted cyclic voltammetry electrodeposition process. The morphology and microstructure feature of PPy/TiO 2 /PANI were characterized by field-emission scanning electron microscopy and Raman spectrum. The capacitance performance was conducted by cyclic voltammetry and galvanostatic charge–discharge measurements. PPy/TiO 2 /PANI coaxial nanotube hybrid with P/N-type doping properties exhibited a high specific capacitance of 497 F g −1 at a current density of 0.5 A g −1 and a potential window of −0.2 to 0.8 V in 1.0 M H 2 SO 4 solution. The capacitance declined from 267.9 to 193.7 F g −1 after 500 cycles at a high current density of 2.0 A g −1 , showing 72.3% capacitance retention and a good cycle stability for the promising supercapacitor application. [ABSTRACT FROM AUTHOR]

We report on a new nanocomposite material for electrochemical sensing of hydrogen peroxide using a titanium dioxide nanotube arrays modified with reduced graphene oxide onto which silver nanoparticles (AgNPs) were chemically deposited. Transmission electron microscopy, scanning electron microscopy, X-ray diffraction, and energy-dispersive X-ray and Raman spectroscopy were used to characterize its microstructure and morphology. The results demonstrated that the AgNPs were uniformly dispersed on the surface of the modified electrode which was investigated with respect to capability for sensing hydrogen peroxide (HO). Under optimized experimental condition, the electrode responds to HO with a sensitivity of 1152 μA mM cm at a working potential of −0.6 V. The current response is linearly related to the concentration of HO in the range from 50 to 15.5 mM (with a correlation coefficient of 0.9997), and the detection limit is 2.2 μM. The sensor exhibits good stability and excellent selectivity for HO. By immobilizing glucose oxidase on the surface of this electrode, a glucose biosensor was obtained that responds to glucose in the 0.5 to 50 mM concentration range. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Abstract: The manganese dioxide-titanium nitride (MnO2-TiN) nanotube hybrid has been designed to improve its electroactivity and conductivity for a supercapacitor application. Titanium nitride (TiN) nanotube array was prepared by an anodization process of titanium in ethylene glycol (EG) solution containing ammonium fluoride, subsequent calcination process in an air atmosphere, and final nitridation process in an ammonia atmosphere. Electroactive MnO2 was then loaded into well-aligned TiN nanotubes to form MnO2-TiN nanotube hybrid with well-designed shell layer of MnO2 through a controlled cyclic voltammetry electrodeposition process, which was directly supported on ultra thin and supple titanium foil to establish a bendable electrode. The morphology and microstructure of MnO2-TiN nanotube hybrid were characterized by scanning electron microscopy and X-ray diffraction. The electrochemical capacitance was investigated by cyclic voltammetry and galvanostatic charge/discharge measurements. The villiform MnO2 thin shell layer was fully covered on TiN nanotube walls to form a coaxial heterogeneous structure. Superior electrical conductivity and accessible nanochannels of TiN contributed to a high capacitance performance of MnO2. The specific capacitance of MnO2-TiN was determined to be 853.3Fg−1 (or 213.2mFcm−2) at a current density of 1.0Ag−1 (or 0.25mAcm−2). All-solid-state flexible supercapacitor was constructed using two symmetric film electrodes of MnO2-TiN nanotube hybrid and a polyvinyl alcohol gel electrolyte of KOH-KI-EG. The volume specific capacitance, energy and power density were determined to be 4.01Fcm−3, 1.81mWhcm−3 and 32.8mWcm−3 at a high potential window of 1.8V and a current density of 2.0mAcm−2. Such MnO2-TiN nanotube hybrid electrode material exhibited effective energy storage in flexible supercapacitor application. [Copyright &y& Elsevier]

A glucose biosensor has been fabricated by immobilizing glucose oxidase (GOx) on unhybridized titanium dioxide nanotube arrays using an optimized cross-linking technique. The TiO nanotube arrays were synthesized directly on a titanium substrate by anodic oxidation. The structure and morphology of electrode material were characterized by X-ray diffraction and scanning electron microscopy. The electrochemical performances of the glucose biosensor were conducted by cyclic voltammetry and chronoamperometry measurements. It gives a linear response to glucose in the 0.05 to 0.65 mM concentration range, with a correlation coefficient of 0.9981, a sensitivity of 199.6 μA mM cm, and a detection limit as low as 3.8 µM. This glucose biosensor exhibited high selectivity for glucose determination in the presence of ascorbic acid, sucrose and other common interfering substances. This glucose biosensor also performed good reproducibility and long-time storage stability. This optimized cross-linking technique could open a new avenue for other enzyme biosensors fabrication. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A polyaniline/titanium nitride (PANI/TiN) nanotube hybrid was prepared and used for an electrochemical supercapacitor application. Firstly, the well-aligned TiN nanotube array was prepared by anodization of titanium foil and subsequent nitridation through ammonia annealing. Then, PANI was deposited into TiN nanotube through the electrochemical polymerization process. The obtained PANI/TiN nanotube hybrid had an ordered porous structure. A high specific capacitance of 1,066 F g was obtained at the charge-discharge current density of 1 A g when only the mass of PANI was considered. The specific capacitance can even achieve 864 F g at 10 A g and still keep 93 % of the initial capacity after 200 cycles. An aqueous supercapacitor, consisting of two symmetric PANI/TiN nanotube hybrid electrodes and 1.0 M HSO electrolyte solution, showed the specific capacitance of 194.8 F g, energy density of 9.74 Wh kg, and power density of 0.3 kW kg. [ABSTRACT FROM AUTHOR]

In this study, the polypyrrole-titania nanotube hybrid has been synthesized for an electrochemical supercapacitor application. The highly ordered and independent titania nanotube array is fabricated by an electro-oxidation of titanium sheet through an electrochemical anodization process in an aqueous solution containing ammonium fluoride, phosphoric acid and ethylene glycol. The polypyrrole-titania nanotube hybrid is then prepared by electrodepositing the conducting polypyrrole into well-aligned titania nanotubes through a normal pulse voltammetry deposition process in an organic acetonitrile solution containing pyrrole monomer and lithium perchlorate. The morphology and microstructure of polypyrrole-titania nanotube hybrid are characterized by scanning electron microscopy, infrared spectroscopy and Raman spectroscopy. The electrochemical capacitance performance is determined by cyclic voltammetry and charge/discharge measurement. It indicates that the polypyrrole film can been uniformly deposited on both surfaces of titania nanotube walls, demonstrating a heterogeneous coaxial nanotube structure. The specific capacitance of polypyrrole-titania nanotube hybrid is determined to be 179 F g based on the polypyrrole mass. The specific energy and specific power are 7.8 Wh kg and 2.8 kW kg at a constant charge/discharge current of 1.85 mA cm, respectively. The retained specific capacitance still keeps 85% of the initial capacity even after 200 cycle numbers. This result demonstrates the satisfying stability and durability of PPy-TiO nanotube hybrid electrode in a cyclic charge/discharge process. Such a composite electrode material with highly ordered and coaxial nanotube hybrid structure can contribute high energy storage for supercapacitor applications. [ABSTRACT FROM AUTHOR]

Abstract: Highly ordered TiO2 nanotube array with inner diameter of 120nm was formed by anodizing titanium foils and was further modified for enzyme immobilization and biosensing. AuNPs sized in 8–12nm were uniformly electrodeposited on TiO2 nanotube arrays by pulsed method. Glucose oxidase (GOD) was covalently immobilized on the surface of gold nanoparticles (AuNPs) modified TiO2 nanotube array electrode for the first time. Results demonstrate that the modified TiO2 nanotube array electrode exhibits good electrocatalytic performance and high sensitivity without any electron mediator. The covalently fabricated glucose biosensor shows higher immobilized ratio of GOD, good reproducibility and stability. These indicate AuNPs modified TiO2 nanotube array is an attractive material for using in the fabrication of biosensors because of its excellent biocompatibility, high specific surface area, unique nanostructure, and effective immobilization of biomolecules. This facile modification approach could be extended to prepare various TiO2 nanotube array based biosensors. [ABSTRACT FROM AUTHOR]

Abstract: Highly-ordered and well-separated titania nanotube array was prepared by a potentiostatic anodization process. The desired nickel oxide–titania (NiO–TiO2) nanocomposites were constructed through incorporating nickel hydroxide into titania nanotubes by a one-cycle or multi-cycle alternate electrodeposition–oxidation and then a thermal dehydration process. By means of the microstructure promotion from particulate to flower-like NiO–TiO2 nanocomposite, specific capacitances were accordingly increased from 26.9 to 46.3mFcm−2 and energy densities were also improved from 13.1 to 33.3 for mwscm−2 in a redox supercapacitor application at a potential window of 1.2V. The flower-like nanocomposite could keep 92.3% of initial capacitance even after 1000 cycles, presenting high operation stability in a continuous charge–discharge process. The superior energy-storage performance of flower-like nanocomposite was mostly attributed to its highly accessible redox reaction sites of three-dimensional NiO on TiO2 nanotubes. [Copyright &y& Elsevier]

Surface nanocrystallization of titanium metal is processed by a high-energy shot peening treatment for drastic subdivision of bulk crystalline grains. Titania nanotube array directly grown on the nanocrystalline titanium substrate is achieved by a controlled anodization process. Field emission scanning electron microscopy, X-ray diffraction, and impedance spectroscopy analysis are conducted to investigate surface morphology, crystal phase, and electrical conductivity, respectively. The photoelectrochemical performance of the tailored titania nanotubes/titanium nanocrystallites has been investigated under UV light illumination. When the microstructure of the titanium substrate is modified from bulk crystals to nanocrystallites, the obtained titania nanotube array exhibits an independent structure with enlarged pore size and thinned tube wall, which is ascribed to the intensified anodic oxidation of ultrafine titanium crystallites along intergranular boundaries. Owing to the promoted interfacial electron transfer of the titania/nanocrystalline titanium, the complex impedance predominated by the charge transfer resistance has been significantly decreased in the electrochemical process. Both photocurrent and photovoltage responses have accordingly enhanced as well in the photoelectrochemical process. [ABSTRACT FROM AUTHOR]

Abstract: Titania nanotube array with an enlarged tube diameter of 110nm and length of 700nm 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. 770nm and 710nm, meanwhile nickel-to-titanium atom ratios were determined as 9.6at% and 36.4at% for nickel oxide-embedded titania by an electrochemical and hydrothermal synthesis, respectively. The corresponding specific redox capacitance was also increased from 26mFcm−2 to 85mFcm−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 128mFcm−2 for 36.4at% nickel-containing nickel oxide–titania/titanium electrode when a porous graphite carbon instead of a platinum sheet was used as a cathode. [Copyright &y& Elsevier]

Abstract: Titania/titanium (TiO2/Ti) electrodes with tailored surface structure have been fabricated by galvanostatic–potentiostatic anodization process. Highly ordered titania nanotubes array can be prepared by electrolyzing titanium foil at 20V for 40min in HF–H3PO4 electrolyte. Comparatively, micro-structured and crystallized TiO2 multiporous film can be prepared at 20–40V for 6h in H2SO4–H3PO4–H2O2–HF electrolyte. The morphological characteristics and crystal behaviors of both nanotubular and micro-structured TiO2 films are investigated by field emission scanning electron microscopy and X-ray diffraction measurement. Photoelectrochemical properties of TiO2/Ti film electrodes are examined by anodic photocurrent response and cyclic voltammetry measurement. Photocatalytic and photoelectrocatalytic application are investigated by using either nanotubular TiO2/Ti thin-film or micro-structured TiO2/Ti thick-film electrodes as photoanodes for recalcitrant organic pollutant degradation. [Copyright &y& Elsevier]