One-step Anodization Research Articles

Effect of irradiation intensity and initial pollutant concentration on gas phase photocatalytic activity of TiO2 nanotube arrays

Well-organized TiO2 nanotube arrays were fabricated via one-step anodization process. The as-prepared TiO2 nanotubes were characterized by X-ray powder diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy (DRS) and scanning electron microscopy (SEM). Photocatalytic activity of obtained photocatalyst was studied in reaction of toluene degradation in the gas phase using low powered and low cost light-emitting diodes (UV LEDs) as an irradiation source. The effect of irradiation intensity and initial pollutant concentration on gas phase photoactivity of TiO2 nanotubes was analyzed. Obtained TiO2 nanotubes were smooth and vertically oriented with a length of about 1.7±0.05μm. The inner diameter and the wall thickness were 65±2nm and 6±0.4 nm, respectively. The results showed that the initial toluene degradation rate increased (from 0.0062 up to 0.0567μmol/min) with raising initial toluene concentration (50–400ppm), while too high dose of irradiation (about 50mW/cm2) reduced photocatalytic toluene degradation rate. The best stability of TiO2 nanotubes in three subsequent irradiation cycles was observed for irradiation intensity of 38mW/cm2. Moreover, it was found that photocatalytic toluene degradation over TiO2 nanotubes showed first order kinetic behavior.

Characterization of arrangement and geometry of porous anodic alumina formed by one-step anodization of Al-1 wt% Si thin films

In the current work, porous anodic alumina (PAA) thin films have been fabricated from doped aluminum films, Al-1 wt% Si, using a one-step anodization method at room temperature. Two different electrolytes, namely, oxalic and phosphoric acids, have been utilized to obtain the PAA. A Fast Fourier transform based arrangement analysis for the obtained nanopores is reported. It is found that the nanoporous oxide layer is formed in Al-1 wt% Si with poor arrangement due to the poor spatial distribution of the nanopores, although they are in perfect circular shape. Moreover, the transient curves during the anodization, pore density, pore diameter, and interpore distance have been investigated.

Preparation of CuWO4@Cu2O film on copper mesh by anodization for oil/water separation and aqueous pollutant degradation

CuWO4@Cu2O film was prepared on copper mesh by a one-step electrochemical anodization method for efficiently separating oil/water mixtures and photodegrading organic pollutants in the water phase. The as-prepared mesh displayed superhydrophilicity and good underwater superoleophobicity due to the hierarchical cauliflower-like structure. The mesh possessed high separation efficiency up to 99.3% for oil/water separation. During the oil/water separation process, water passed through the mesh rapidly by gravity, while oils stayed above due to its underwater superoleophobicity. After the separation, the mesh could be used for degrading the aqueous pollutant in the separated water phase under visible light illumination, which significantly amplifies the utilization of solar energy. Methylene blue and rhodamine B were successfully photodegraded by the as-prepared mesh in the presence of Na2S2O8 with a maximum degradation efficiency of 96.4%.

Facile fabrication of wear-resistant multifunctional surfaces on titanium alloy substrate by one-step anodization and modification with silicon dioxide nanoparticles

This paper describes a simple, facile, low-cost method of fabricating a wear-resistant surface on titanium alloy substrates by single-step anodization and modification with silicon dioxide particles. The method produced a TiO2–SiO2 composite surface with micro- to nanohierarchical structure, which became multifunctional after fluoroalkylsilane modification. The surface not only showed excellent superhydrophobicity [contact angles (CAs) > 150°, sliding angles (SAs) ≤ 8°] but also exhibited better repellency of complex whole blood (CAs = 153° ± 2°, SAs = 9°). Furthermore, the wear resistance of the surface was investigated by sandpaper abrasion test. The results showed that the mechanical wear resistance of the TiO2–SiO2 composite surface was more than three times that of the surface prepared only by the electrochemical technique, and the surface still maintained the capacity of hydrophobicity even after 33.6 m of wear under conditions of 3400 Pa and 360# sandpaper. The method mentioned in this paper could be a candidate for the production of abrasion-resistant and super-repellent titanium alloy.

Tunable synthesis of nanoporous tin oxide structures on metallic tin by one-step electrochemical anodization

Nanoporous tin oxide structures were synthesized by electrochemical anodization of tin substrates at various anodizing conditions, including electrolyte species and concentration, anodizing potential, anodizing temperature and duration of the process. The influences of anodizing conditions on the structure features of anodized oxide films were investigated in detail. It is worth stressing that the correlation of the morphologies and current density virtue time curves (i-t curves) was analyzed in our work. The structure features of as-prepared tin oxide layers were found to be strongly related to anodizing conditions. Significant increases of average pore diameter occurred with the increase of anodizing potential, temperature and time. In addition, it is noteworthy that strong linear dependences between average steady-state current density and electrolyte concentration, anodizing potential as well as temperature were observed. It indicates the anodizing process is limited by mass transfer in electrolyte. Moreover, growth mechanisms in both kinetics and thermodynamics were established to elaborate the growth process of porous structures during anodization.

Photoinduced deposition of gold nanoparticles on TiO2–WO3 nanotube films as efficient photoanodes for solar water splitting

Gold-modified TiO2–WO3 nanotubes with different amounts of gold were obtained by two methods; photoassisted deposition and one-step electrochemical anodizing method. The morphology, crystallinity and elemental composition were studied by FE-SEM, XRD and EDX. The photoelectrochemical performance was examined under Xe light illumination in 1 M NaOH electrolyte. Characterization of the as-prepared TiO2–WO3 samples indicated that sodium tungstate concentration in anodizing solution significantly influenced the morphology and photoelectrochemical activity of fabricated films. Also, photoelectrochemical characterizations show that the photocatalytic activity of Au/TiO2–WO3 nanotubes was improved as compared with that of bare TiO2–WO3 nanotubes. The experimental results showed that the photocatalytic activities of Au/TiO2–WO3 were significantly affected by the amount of Au nanoparticles. The amount of gold nanoparticles was effectively controlled by time of photoreduction of the chloroauric acid solution. These new photoanodes showed enhanced high photocurrent density with good stability and are a highly promising photoanodes for photocatalytic hydrogen production.

Novel visible-light-responsive photo-catalysts based on palladium decorated nanotube films fabricated on titanium substrates

A novel visible-light-responsive photo-catalyst was synthesized for the photo-degradation of methylene blue. Highly ordered and uniformly distributed titanium dioxide-tungsten trioxide nanotubes on pure titanium substrates were successfully fabricated by one-step electrochemical anodizing and palladium deposited on these nanotubes by photo-reduction method. The resulting samples were characterized by X-ray diffraction, field emission scanning electron microscope, ultraviolet–visible spectroscopy and energy dispersive X-ray spectrometer methods. The degradation of methylene blue (MB) was used as a model reaction to evaluate the photo-catalytic activity of the obtained samples. After irradiated under visible light for 60min, degradation ratio of Pd-deposited nanotubes was improved as compared with that of bare titanium dioxide-tungsten trioxide nanotubes. Under the same condition, no obvious photo-degradation of methylene blue was found for bare TiO2 nanotubes. Kinetic research showed that photo-degradation process followed the first-order reaction; the apparent reaction rate constant of Pd-based nanotubes was approximately 2.19 times higher than that on the unmodified nanotubes. The catalysts prepared in this study exhibit industrially relevant interests due to the low cost and high photo-catalytic activity.

Anodization of bismuth doped TiO2 nanotubes composite for photocatalytic degradation of phenol in visible light

Bismuth doped TiO2 photocatalyst was synthesized in a one-step electrochemical anodization method. Bismuth nitrate Bi(NO3)3 was used as a bismuth source. The obtained samples were characterized by FE-SEM, XRD, EDX and XPS. The optimum synthesis conditions for bismuth doping were 1.0M bismuth nitrate in an ethylene glycol electrolyte with anodization at 40V for 2h. Compared with undoped TiO2 nanotubes, bismuth doped TiO2 photocatalyst showed a higher photocatalytic activity by a factor of 4.0 for phenol degradation under visible light irradiation. The optimum phenol degradation using a photoelectrocatalytic method was observed at a 0.5V external bias, and this degradation rate was 5.2 times faster than that observed for undoped TiO2 nanotubes. The doped bismuth TiO2 nanotubes are favorable for the separation of photo-induced electrons and holes, reducing the recombination of charges, and promoting the formation of hydroxyl radicals and superoxides that degrade phenol.

Enhanced Efficiency of Nanoporous-layer-covered TiO2 NanotubeArrays for Front Illuminated Dye-sensitized Solar Cells

Nanoporous-layer-covered TiO2 nanotube arrays (Type II TNTs) were fabricated by two-step electrochemical anodization. For comparison, conventional TiO2 nanotube arrays (Type I TNTs) were also prepared by one-step electrochemical anodization. Types I and II TNTs were detached by selective etching and then transferred successfully to a transparent F-doped SnO2 (FTO) substrate by a sol-gel process. Both FTO/Types I and II TNTs allowed front side illumination to exhibit incident photon-to-current efficiencies (IPCEs) in the long wavelength region of 300 to 750 nm without the absorption of light by the iodine-containing electrolyte. The Type II TNT exhibited longer electron lifetime and faster charge transfer than the Type I TNT because of its relatively fewer defect states. These beneficial effects lead to a high overall energy conversion efficiency (5.32 %) of the resulting dye-sensitized solar cell. Keywords: dye-sensitized solar cell, nanotube array, electron lifetime, charge transfer, front side illumination

Enhanced Efficiency of Nanoporous-layer-covered TiO2NanotubeArrays for Front Illuminated Dye-sensitized Solar Cells

ABSTRACT Nanoporous-layer-covered TiO 2 nanotube arrays (Type II TNTs) were fabricated by two-step electrochemical anodization.For comparison, conventional TiO 2 nanotube arrays (Type I TNTs) were also prepared by one-step electrochemical anod-ization. Types I and II TNTs were detached by selective etching and then transferred successfully to a transparent F-dopedSnO 2 (FTO) substrate by a sol-gel process. Both FTO/Types I and II TNTs allowed front side illumination to exhibit inci-dent photon-to-current efficiencies (IPCEs) in the long wavelength region of 300 to 750 nm without the absorption of lightby the iodine-containing electrolyte. The Type II TNT exhibited longer electron lifetime and faster charge transfer than theType I TNT because of its relatively fewer defect states. These beneficial effects lead to a high overall energy conversionefficiency (5.32 %) of the resulting dye-sensitized solar cell.Keywords : dye-sensitized solar cell, nanotube array, electron lifetime, charge transfer, front side illumination

Novel simple method for preparing tailored polymer-titania nanotubes hybrid materials

A novel method for preparing hybrid polymer-titania nanotube (TNT) arrays with promising optical, catalytic and filtration applications is reported. The procedure is based on a one-step rapid galvanostatic anodization followed by the transfer of the TNT arrays to a polymer support by applying heat and pressure. The fraction of open-ended tubes can be controlled by changing the intensity of the current at the end of the anodization step. For example, completely open-ended or close-ended TNT arrays can be obtained by applying high or low current intensity, respectively at the end of the anodization process. The reported procedure allows the one-step simple and rapid preparation of flexible hybrid polymer-TNT materials which have great potential for photonic flow-through membranes.

Fabrication, characterization and photocatalytic properties of Au/TiO2-WO3 nanotubular composite synthesized by photo-assisted deposition and electrochemical anodizing methods

A photo-assisted deposition (PAD) technique was adopted to construct highly dispersed gold nanoparticles on TiO2-WO3 nanotubular composite electrodes prepared by one-step electrochemical anodizing. The morphology, crystallinity, elemental composition and light absorption capability of samples were distinguished based on various characterizations. The degradation of methylene blue (MB) was used as a model reaction to evaluate the photocatalytic activity of the obtained samples. Characterization of the as-prepared TiO2-WO3 samples indicated that dopant concentration in anodizing solution significantly influenced the morphology and photocatalytic activity of fabricated films. It was found that the degradation ratio of Au/TiO2-WO3 nanotubes was improved as compared with that of bare TiO2-WO3 nanotubes. The experimental results showed that the photocatalytic activities of Au/TiO2-WO3 were significantly affected by the amount of Au nanoparticles. This work provides an insight into designing and synthesizing new TiO2-WO3 nanotubes-based hybrid materials for effective visible light-activated photocatalysis.

Preparation of TiO2 and WO3–TiO2 nanotubes decorated with PbO nanoparticles by chemical bath deposition process: A stable and efficient photo catalyst

We present a new method for synthesizing Pb/TNTs and Pb/WTNTs composite with good photo catalytic activity. TiO2 nanotube (TNTs) and WO3–TiO2 nanotubes (WTNTs) were prepared by one-step electrochemical anodizing method and lead has been successfully deposited on these nanotubes by chemical bath deposition process. The morphology, crystal structure, elemental composition and light absorption capability of the prepared samples were evaluated using various characterization techniques. Results showed that the fabricated films have highly ordered nanotube morphology. Diffuse reflectance spectra showed an increase in the visible absorption relative to bare samples. The degradation of methylene blue was used as a model reaction to evaluate the photo catalytic activity of these novel visible-light-responsive photo catalysts. Results showed that the photo catalytic activity of bare WTNTs samples is higher than that with undoped TNTs sample. Compared with unmodified TNTs and WTNTs, the Pb/TNTs and Pb/WTNTs samples exhibited enhanced photo catalytic activity in the degradation of methylene blue. The sample Pb/WTNTs exhibited better photo catalytic activity than other samples. Also prepared photo catalysts showed good stability and could be recycled several times without significant loss of their activity. This work provides an insight in designing and synthesizing new WTNTs-based hybrid materials for effective visible light-activated photo catalysis. Since Pb/TNTs and Pb/WTNTs electrodes can be easily removed and replaced after the photo catalytic reaction, avoiding the filtration step after photoreaction or the immobilizing process required for photo catalyst particles, the operation in the photo-reactor becomes much easier from an engineering point of view. The catalysts prepared in this study exhibit industrially relevant interests due to the low cost and high photo catalytic activity.

Nanoporous tin oxides synthesized via electrochemical anodization in oxalic acid and their photoelectrochemical activity

Nanoporous tin oxide layers were obtained by one-step potentiostatic anodization carried out in 0.3M H2C2O4 followed by thermal annealing at temperatures in the range of 200–700°C. The morphology and crystallinity of as obtained oxide layers were characterized by SEM, and XRD, respectively. It was confirmed, that after 10min of anodic oxidation at the potential of 8V, anodic tin oxide consists of a dense array of randomly distributed nanopores with an average diameter of about 50–60nm. Moreover, such kind of porous structures is maintained during annealing at temperatures up to 500°C. On the contrary, for higher annealing temperatures a transformation of nanoporous layers into particle-like structures was evident. A gradual increase of the crystallite size with increasing annealing temperature was also confirmed. Finally, photoelectrochemical properties of anodic tin oxide layers, annealed at temperatures in the range of 400–700°C, were extensively investigated. The best photoelectrochemical performance with the maximum photocurrent densities of above 25μAcm−2 and conversion efficiency of about 30% was observed for sample annealed at 500°C. Higher annealing temperatures result in a gradual decrease in photocurrent densities that can be attributed to the change in the sample morphology and decrease in electrochemical reaction sites. Optical band gap energies were determined on the basis of UV–vis reflectance spectra and photocurrent measurements, and a gradual increase in the band gap energy with increasing annealing temperature was confirmed.

Preparation of cobalt coated TiO2 and WO3–TiO2 nanotube films via photo-assisted deposition with enhanced photocatalytic activity under visible light illumination

Highly ordered TiO2 and WO3–TiO2 nanotubes were prepared by one-step electrochemical anodizing method and cobalt has been successfully deposited on these nanotubes by photo-assisted deposition process. The morphology, crystal structure, elemental composition and light absorption capability of samples were characterized by field emission scanning electron microscope, X-ray diffraction, energy dispersive X-ray spectrometer and ultraviolet–visible spectroscopy methods. All cobalt loaded samples show an appearance of red shift relative to the unloaded samples. The degradation of methylene blue was used as a model reaction to evaluate the photocatalytic activity of these novel visible-light-responsive photocatalysts. Results showed that the photocatalytic activity of bare WO3–TiO2 samples is higher than that with undoped TiO2 sample. Compared with unmodified TiO2 and WO3–TiO2, the Co/TiO2 and Co/WO3–TiO2 samples exhibited enhanced photocatalytic activity in the degradation of methylene blue. Kinetic research showed that the reaction rate constant of Co/WO3–TiO2 is approximately 2.26 times higher than the apparent reaction rate constant of bare WO3–TiO2. This work provides an insight into designing and synthesizing new TiO2–WO3 nanotubes-based hybrid materials for effective visible light-activated photocatalysis. The catalysts prepared in this study exhibit industrially relevant interests due to the low cost and high photocatalytic activity.

Efficient solar water-splitting using Cu/WO3-TiO2 photoanodes prepared by anodizing and photoassisted deposition method

WO3-TiO2 nanotube films on pure titanium substrates were successfully fabricated by one-step electrochemical anodizing and copper deposited on these nanotubes by photo-assisted deposition method. The morphology, structure and composition of synthesized films were characterized by SEM, XRD, EDX and UV-vis, respectively. Results showed that the films have the ordered nanotubes with average pore diameter of 70–100 nm and wall thickness of 20–25 nm. Diffuse reflectance spectra showed an increase in the visible absorption relative to bare WO3-TiO2 nanotubes. Photocatalytic activity of samples was evaluated by testing the solar water splitting. After irradiated under xenon light illumination for 360 min, the total amount of H2 evolved on the Cu/WO3-TiO2 sample was 55 mL/cm2, which is approximately 6.9 times higher than that on the bare WO3-TiO2 (8 mL/cm2). The catalysts prepared in this study exhibit industrially relevant interests due to the low cost and high photocatalytic activity.

Fabrication of new photoanodes for solar-water-splitting photoelectrochemical cells: synergistic effect between platinum and nanocomposite photocatalysts

Platinum nanoparticles deposited on titanium dioxide–tungsten trioxide (Pt/TW) were prepared by one-step electrochemical anodizing and UV light photoreduction method. The characterizations of such prepared catalysts were studied by field emission scanning electron microscopy, X-ray diffraction and energy dispersive X-ray spectroscopy. Diffuse reflectance spectra showed an increase in the visible absorption relative to bare TW nanotubes. Compared with the unmodified TW, Pt/TW samples exhibited obviously enhanced photocatalytic activity in the solar water splitting. After irradiated under xenon light illumination for 360 min, the total amount of H2 evolved on the Pt/TW sample was approximately 2.0 times higher than that on the bare TW and 8.0 times higher than that on the bare TiO2. Under irradiation, electron-hole pairs are formed on the Pt nanoparticles due to surface plasmon resonance and the introduction of Pt can form the Schottky barrier between TW and Pt nanoparticles which inhibit the photogen-erated charge carrier recombination and promoting the interfacial charge transfer.

The effect of anodizing voltage on morphology and photocatalytic activity of tantalum oxide nanostructure

In this study, tantalum oxide nanostructure films with different morphology were prepared by one-step anodizing of tantalum foil in aqueous electrolytes consisting of sulfuric acid and hydrofluoric acid. The effects of anodizing voltage on the morphology and photocatalytic activity of prepared tantalum oxide films were investigated. The morphology and structure were characterized by FE-SEM, XRD and EDX. SEM results show that films morphology can be varied by controlling anodizing voltage and under optimized electrochemical conditions, Ta2O5 nanotube layers can be grown up to thickness of 2 μm. Photocatalytic activity of the Ta2O5 films was evaluated in terms of the degradation of methylene blue under UV light. The results showed that Ta2O5 nanotube film exhibited higher photocatalytic activity than the Ta2O5 nanoporous films. The reason of this enhanced photocatalytic property can be attributed to high specific surface areas and the nanotube structures of this sample.

Cobalt modified tungsten–titania nanotube composite photoanodes for photoelectrochemical solar water splitting

Cobalt modified tungsten–titania nanotubes (Co/WTNs) with different amounts of cobalt were prepared by two methods; photo-assisted deposition and one-step electrochemical anodizing method. The morphology, crystallinity, elemental composition and light absorption capability of samples were characterized by field emission scanning electron microscope, X-ray diffraction, energy dispersive X-ray spectrometer and ultraviolet–visible spectroscopy methods. All cobalt loaded samples show a red shift relative to the unloaded samples. The photo-catalytic water splitting was used as a model reaction to evaluate the photo-catalytic activity of the obtained samples. The photo-catalytic performance was examined under xenon lamp irradiation in 1 M NaOH electrolyte. All cobalt modified samples showed photo-catalytic properties better than that for the bare WTNs and bare TiO2 samples. The total amount of H2 evolved on the Co/WTNs2 sample was 1.9 times higher than that on the bare TiO2 sample. The catalysts prepared in this study exhibit industrially relevant interests due to the low cost and high photocatalytic activity. These new photoanodes are highly promising photoanodes for photo-catalytic hydrogen production.

Solar water-splitting using palladium modified tungsten trioxide-titania nanotube photocatalysts

Palladium modified tungsten trioxide-titania nanotubes (WOTNs) with different amounts of palladium were prepared by two methods; photo-assisted deposition and one-step electrochemical anodizing method. The resulting samples were characterized by X-ray diffraction, field emission scanning electron microscope, ultraviolet–visible spectroscopy and energy dispersive X-ray spectrometer methods. The photocatalytic water splitting was used as a model reaction to evaluate the photocatalytic activity of the obtained samples. The photocatalytic performance was examined under xenon lamp irradiation in 1 M NaOH electrolyte. All palladium modified samples showed photocatalytic properties superior to that for the bare WOTNs sample. The total amount of H2 evolved on the Pd/WOTNs2 sample was 2.5 times higher than that on the bare WOTNs sample. These new photoanodes showed enhanced high photocurrent density with good stability and are highly promising photoanodes for photocatalytic hydrogen production.