Titania Arrays Research Articles

Electrocatalytic activities of electrochemically reduced tubular titania arrays loaded with cobalt ions in flow-through processes

This study examines the electrocatalytic activity of disordered titania nanotube arrays modified with Co2+ for the oxidation of (in)organic substrates and inactivation of E. coli in a flow-through electrochemical device. As-anodized TiO2 nanotubes (TNTs) on perforated Ti foils are electrochemically reduced to create Ti3+ states and oxygen vacancies. The electrochemically reduced TNTs (r-TNTs) are capable of adsorbing Co2+ in ~7 times larger amounts than the bare TNTs. Among the bare and modified TNT samples (TNTs, r-TNTs, Co-TNTs, and Co-r-TNTs), Co-r-TNTs exhibit the lowest interfacial charge-transfer resistance and fastest internal charge-transfer kinetics. The electron spin resonance analysis further reveals an enhanced production of OOH radicals in Co-r-TNTs. The combined effect of the excellent charge-transfer behavior and the radical production of Co-r-TNTs leads to faster decomposition of N,N-dimethyl-p-nitrosoaniline, higher current efficiency in the oxidation of iodide to triiodide, and greater inactivation of E. coli as compared to r-TNTs. Details on the surface characterization of the bare and modified TNTs samples are presented and the role of the adsorbed Co2+ is discussed.

Erratum to: Easy Formation and Dye-Sensitized Solar Cell Application of Highly-Ordered 3D Titania Arrays Using Photodynamic Polymer

Three-dimensional (3D) periodic TiO2 relief structures were created by simple heat-treatment of alternatively spin-coated TiO2 colloidal nanoparticles on surface relief gratings using photodynamic polymers. The structure of the 3D arrays formed by this method was confirmed with optical properties and scanning electron microscopy. Dye-sensitized solar cells using 3D TiO2 relief patterns were fabricated, and their photovoltaic application was assessed.

Easy formation and dye-sensitized solar cell application of highly-ordered 3D titania arrays using photodynamic polymer

Easy formation and dye-sensitized solar cell application of highly-ordered 3D titania arrays using photodynamic polymer

Fast charge transport of titania nanotube arrays in dye-sensitized solar cells

Abstract Vertically oriented nanotubular titania arrays with a length of ca. 12 μm were fabricated by anodisation of titanium foils. Rietveld refinements of grazing incidence and wide angle XRD patterns for the annealed nanotube titania array showed that they consist of anatase crystals with a pronounced size anisotropy and a moderate preferred orientation. The energy conversion efficiency of dye sensitized solar cells based on the annealed nanotubular anatase array exceeds 6% under standard AM1.5 100 mW/cm2 irradiance and thus outperforms solar cells based on anatase nanoparticles when comparing analogous back illumination cell designs. Electrochemical impedance spectroscopy was employed to clarify the origin of the improved short circuit current and conversion efficiency. It was found that the effective diffusion length in the nanotube cells reaches >100 μm and no longer limits the onversion efficiency. The faster electron transport can be traced back to the larger crystallite size and the reduced intergrain orientation mismatch in the titania nanotubes.

The rapid growth of 3 µm long titania nanotubes by anodization of titanium in a neutral electrochemicalbath

The length of titania nanotubes formed by anodization of 0.1 mm thicktitanium foil was found to be a strong function of the pH of the electrolyte.The longest nanotubes were formed by using an electrolyte consisting of 1 MNa2SO4 plus5 wt% NH4F with pH 7. At this pH, after 30 min of anodization, 3 µm length nanotubular titania arrays with top diameters of∼50 nm and bottom diameters of 100 nm were produced. No acid was added to this electrolyte. Theformation of titania nanotubes in neutral pH systems was therefore successful due to the excessNH4F in the electrolyte which increases the chemical dissolution process at the metal/oxideinterface. Since the pH of the electrolyte at the top part of the nanotubes is kept veryhigh, the dissolution of the nanotubes at the surface is minimal. However, theamount is adequate to remove the initial barrier layer, forming a rather well-definednanoporous structure. All anodized foils were weakly crystalline and the transformationto anatase phase was achieved by heat treatment at temperatures from 200 to500 °C for 1 h in air. Annealing at temperatures above500 °C induce rutile phase formation and annealing at higher temperatures accelerates the diffusion ofTi4+ leading to excessive growth and the nanotubular structure diminishes.

Titania nanotube arrays for light sensor and UV photometer

Titania nanotube arrays were fabricated by anodic oxidation of titanium foil. The speed of electron transfer between the titania arrays and solution was measured by electrochemical impedance spectroscopy. High conductivity has been achieved by annealing the TNT arrays in air, much better than previously reported. The photocurrent performances in exposure to a simulated sunlight, tungsten lamp and fluorescent lamp have been investigated under 0 bias, indicating ∼ms response with advantages of high sensitivity and excellent heat stability. The device can effectively detect a trace UV light change and prevent from infrared/thermal influence in exposure to any light source containing UV, which promises a new type light sensor/switch for common light source including sunlight. In addition, the linear plot of photocurrent versus the incident light intensity (UV and simulated sunlight) indicates that the nanotube arrays can be used as a sensitive and stable UV photometer.

Block Copolymer Morphologies in Dye-Sensitized Solar Cells: Probing the Photovoltaic Structure−Function Relation

We integrate mesostructured titania arrays into dye-sensitized solar cells by replicating ordered, oriented one-dimensional (1D) columnar and three-dimensional (3D) bicontinuous gyroid block copolymer phases. The solar cell performance, charge transport, and recombination are investigated. We observe faster charge transport in 1D "wires" than through 3D gyroid arrays. However, owing to their structural instability, the surface area of the wire arrays is low, inhibiting the solar cell performance. The gyroid morphology, on the other hand, outperforms the current state-of-the-art mesoporous nanoparticle films.

In situ templated synthesis of anatase single-crystal nanotube arrays

Anatase single-crystal nanotubes were obtained using an in situ templated method.First, highly ordered titania arrays were formed through an anodization process inH3PO4 electrolytes containing 0.5 wt% HF. Under optimized conditions titaniananotubes with a diameter of up to 100 nm and a length of up to1.1 µm were prepared. Second, the crystallization and stability of the titaniananotubes were studied in air at elevated temperatures. Anatasesingle-crystal nanotubes were fabricated after annealing the sample in air at450 °C. The anatase single-crystal structure was verified by selected area diffraction pattern andHRTEM images.

Theoretical bandgap modeling of two-dimensional square photonic crystals fabricated by the interference of three noncoplanar laser beams

We have investigated numerically the photonic bandgap (PBG) and spectral properties of two-dimensional (2-D) square structures fabricated by holographic lithography. Based on the block-iterative frequency-domain method and on the nonorthogonal finite-difference time-domain method, we have calculated band structure as a function of intensity threshold and shown that the PBG of 2-D titania arrays opens only for TM polarization and that directional PBGs can be obtained simultaneously for TE- and TM-polarized waves. In addition, we have shown that symmetry reduction of the atom introduced by holographic lithography can lift the band degeneracies and create an absolute PBG for a square lattice of dielectric rods in air.

Low Cost Integrated Sensors Utilizing Patterned Nano-Structured Titania Arrays Fabricated Using a Simple Process

ABSTRACTUsing a novel low-temperature process, we demonstrate the facile integration of crack-free nanostructured titania (NST) as sensing elements in microsystems. Unlike conventional sol-gel methods, NST layers of interconnected nano-walls and nano-wires were formed by reacting Ti surfaces with aqueous hydrogen peroxide solution. Cracks were observed in NST layers formed on blanket Ti films but absent on arrays of patterned Ti pads below a threshold dimension. Analyses using TEM, high resolution SEM, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) reveal that NST consists of anatase TiO2 nano-crystals. NST pads were found able to detect oxygen gas of a few ppm. NST pad arrays were integrated on rigid and flexible substrates with potential applications in low cost and wearable sensing systems.

Theoretical bandgap modeling of two-dimensional triangular photonic crystals formed by interference technique of three-noncoplanar beams

Using the block-iterative frequency domain method and the nonorthogonal FDTD method, the photonic band gap (PBG) and spectral properties are investigated for a new class of two-dimensional (2-D) trigonal structures with an approximately circular or exagonal "atom" shape formed by holographic lithography. Calculations of band structures as a function of the intensity threshold show that the PBG of 2-D titania arrays opens only for TM polarization, and directional PBG can open for TE and TM polarization simultaneously. In addition, up to four sizeable full PBGs can open for an inverted GaAs triangular structure.

Direct fabrication of two-dimensional titania arrays using interference photolithography

Two-dimensional (2D) titania arrays with periods of 0.8–2.0 μm were fabricated by polymerization of a photosensitive titanium-containing monomer film using interference photolithography. The 2D precursor arrays were prepared by exposing a mixture of methacrylic acid, ethyleneglycol dimethacrylate, and titanium ethoxide doped with photoinitiator to 355 nm, 15 ns pulses from a Nd-Yttrium–aluminum–garnet laser and then rinsing with methanol. Pure titania arrays were obtained from the precursor arrays by subsequent calcination at 575 °C. The structure of the arrays fabricated by this method was confirmed with optical microscopy and scanning electron microscopy.