Cu/SiO2 thin film on TiO2 nanotubes on Ti15Mo alloy: surface and antibacterial evaluation

The aim of this work is to investigate wettability and antibacterial properties of the well-ordered titanium dioxide (TiO2) nanotube (TNTs) surfaces on new-generation titanium–15 molybdenum (Ti15Mo) alloys for dental and orthopedic implant applications. Thus, the well-ordered TNTs and flat oxide surfaces were fabricated at various potentials such as 20, 40 and 60 V on Ti15Mo alloy by anodic oxidation (AO) technique. Uniform elemental distributions were obtained across all surfaces. In particular, the nanotube surfaces produced at 60 V showed hydrophilic behavior, whereas the flat and nanotube surfaces produced at 20 and 40 V were hydrophobic, respectively. The in vitro antibacterial activity of all surfaces against Escherichia coli (gram-negative) and Staphylococcus aureus (gram-positive) bacteria was investigated in detail. Compared with bare Ti15Mo alloys, the flat and TNTs surfaces showed antibacterial activity. Furthermore, the antibacterial efficiency of TNTs produced on titanium–15 molybdenum alloy improved with increasing AO potential values.

Enhanced efficiency of dye-sensitized solar cells through TiCl4-treated, nanoporous-layer-covered TiO2 nanotube arrays

The inter–relationships of alloy composition, film composition and ionic transport for formation of amorphous anodic oxide films are addressed quantitatively through systematic study of sputter–deposited Al–Ta alloys containing up to 39 at.% Ta. The work reveals the dependence of electric field, ionic transport number, incorporation of species into the anodic film at the alloy–film interface and mobility and distribution of species within the anodic film on alloy composition. Anodic oxidation, at high current efficiency, of alloys containing 2.8, 15, 32 and 39 at.% tantalum results in formation of two–layered anodic films by migration of cations outwards and by migration of anions inwards: an outer layer, 20% or less of the total film thickness, composed of relatively pure alumina and an inner layer containing units of Al2O3 and Ta2O5 distributed relatively homogeneously. Two–layered films develop due to the slower migration rate of Ta5+ ions relative to A13+ ions in the inner layer of the growing anodic films, which changes progressively from about 0.6 for dilute alloys to about 0.9 for Al–39 at. per cent Ta. The average nm V−1 ratios, total transport numbers of cations and average Pilling–Bedworth ratios for the films change almost linearly with alloy composition between the values for anodic alumina and anodic tantala. A tantalum–enriched layer, about 1 nm thick, is formed in the Al–2.8 at.% Ta and Al–15 at.% Ta alloys just beneath the anodic film, indicating prior oxidation of aluminium in the initial stages of anodizing. In contrast, aluminium and tantalum in the alloys containing more than 30 at.% tantalum are immediately incorporated into anodic films in their alloy proportions, without development of a tantalum–enriched layer, at the available resolution. Boron species, incorporated from the electrolyte into the outer parts of the films, are immobile in films on alloys up to 15 at.% Ta but migrate outwards in other films, possibly due to the increased Lorentz field. Though the inter–relationships between film parameters and alloy composition are established for Al–Ta alloys specifically, the findings are considered to be equally relevant to amorphous anodic oxides formed on alloys and semiconductors generally.

1. Introduction Dye-sensitized solar cells (DSSCs) based on nanocrystalline semiconductor oxides are a low-cost alternative to conventional solid-state photovoltaic devices [1-6]. However, as one of the major way of enhancing light absorption, light scattering plays an important role in improving DSSC efficiency. Both theoretical and experimental studies have demonstrated that a light-scatting structure can increase the optical length within a film and enhance the light absorption of porous film, resulting in improved conversion efficiency of DSSC [3,4]. Metal nanoparticles can contribute to the effective light absorption of solar cells, both by local field enhancement through the localized surface plasmon resonance and by light scattering leading to prolonged optical-path lengths [5]. Many researchers demonstrated that the size of the metal nanoparticles is a key factor for determining the plasmonic phenomena, and especially, light scattering occurs more dominantly than light absorption as the size of the metal nanoparticles increases [6]. In this study, the synthesis of anatase TiO2 nanotube (TNT) arrays with Ag nanoparticles by anodic oxidation has been proposed. The influence of the length of the TNT arrays on the photovoltaic characteristics of the prepared devices was also examined. DSSCs based on TiO2 nanotube arrays with Ag nanoparticles showed significantly enhanced performance than DSSCs consisting of bare TiO2nanotube arrays. 2. Experimental Ti foils (0.25 mm thickness, 99.7 wt% purity) were degreased by sonication in acetone, deionized (DI) water, and ethanol for 20 min, to remove surface impurities, and finally to dried in a nitrogen stream. Electrochemical anodic oxidation of the Ti foils was carried out in a two-electrode cell, with platinum (Pt) as the counter electrode at room temperature. The electrolyte for anodic oxidation was prepared with anhydrous ethylene glycol (EG) with NH4F (0.25 wt%) and H2O (3 vol%) mixture solution was stirred for 1h. The voltage was supplied by a DC power supply with a condition of 30/40/50 V at RT for 1h. After anodic oxidation, the samples were rinsed in ethanol and dried in air, followed by heat treatment at 450°C in N2 for 2h to produce TiO2 nanotube arrays. Ag nanoparticles was carried out by immersing the as-prepared TiO2 nanotube in an aqueous electrolyte composed of 0.2 M Silver nitrate (AgNO3) solution and 0.15 M Sodium borohydride (NaBH4) for 5 min at room temperature. The TiO2 nanotube arrays with Ag nanoparticles were then rinsed with DI water and dried in vacuum at 50°C overnight. To fabricate DSSCs, TiO2 nanotube arrays with or without Ag modifications were soaked with N719 dye was added tert-butanol and acetonitrile solution, such mixing ratio 1:1 to prepare a concentration of 5 × 10-4 M dye solution. The DSSCs were finally packed by sealing the dye-coated electrode with a thermally platinized FTO counter electrode through a thin thermal plastic film (Surlyn, 25 ƒÝm, Solaronix). An electrolyte composed of 0.1 M N-methyl benzimidiazoium, 0.6 M 1-propyl-3-methylimidiazolium iodide, 0.05 M I2, 0.1 M guanidinium thiocyanate, and 0.2 M NaI in 3-methoxypropionitrile was introduced into the cell through a pre-drilled hole in the counter electrode. The hole was subsequently sealed with a microscope slip using Surlyn film. 3. Results and Discussion Fig. 1 XRD patterns of TNT arrays by anodic oxidation at 30 V (a) without Ag nanoparticles, (b) with Ag nanoparticles, (c) TNTs peak, and (d) Ag peak.Fig. 2 I-V characteristic curves of DSSCs with and without Ag nanoparticles by anodic oxidation at different voltage. 4. Conclusions In conclusion, anatase TiO2 nanotube arrays with Ag nanoparticles were synthesized by anodic oxidation. At the deposition voltage of 30 V and Ag-coated TiO2 nanotube arrays, the η, Jsc, and FF all reached the maximum. Compared with the conventional DSSCs Jsc, Voc, and η were increased from 7.28 to 8.45 mA/cm2, 0.7 to 0.72 V, and 4.03 to 4.81%. It is expected that the proposed approach for the synthesis of high-quality TiO2nanotube arrays with Ag nanoparticles might open up potential applications for solid or liquid DSSCs and nanostructure devices in the near future.

Super paramagnetism, as one of the most fascinating magnetic phenomena, has been widely used in electronics, magnetic imaging, cell separation, drug delivery and cancer therapy. Super paramagnetism typically appears in a sufficient small magnetic nanoparticle, where the magnetic moment flips randomly with the thermal fluctuations. Once the size of the particle increasing, resulting in the magnetic domain merging and domain wall motion, the magnetic property undergoes a transition from the super paramagnetism to the ferromagnetism. Therefore, preparation of super paramagnetic thin films and nanostructure, instead of particles, would be a challenge since the film structure favors the formation of the large ferromagnetic domains in high-energy growth modes [1-2]. This results in a large grain size and magnetic domain. Atomic layer deposition (ALD), featured with self-limiting surface reaction, is used to synthesize the thin films and nanostructures due to its precise control of the thickness at monolayer atomic level and conformal deposition with low energy. Most of ALD deposited oxide thin films are found to be polycrystalline or amorphous with very small grain size, which is ideal for the preparation of super paramagnetic thin films and nano-structure. One of the key challenges in realizing super paramagnetism is to find a low-energy growth way to create sufficient small grains and magnetic domains which allow the magnetization randomly and rapidly reverse. In this work, well-defined super paramagnetic and ferrimagnetic Fe 3 O 4 thin films and well-ordered Fe 3 O 4 nanootube arrays are successfully grown using atomic layer deposition (ALD) technique by finely optimizing the growth condition and post-annealing process. As-grown Fe 3 O 4 thin films and nanotube arrays exhibit a conformal surface and nanocrystalline nature with the average grain size just few nanometers, resulting in a super paramagnetic behavior with a blocking temperature of 210 K (figure 1b). The in-situ grown iron oxide thin films exhibit a well-controlled morphology with the grain size less than 5 nm. The well-defined super paramagnetic loops are observed showing a near zero coercive field for the Fe 3 O 4 thin films (figure 1a). Super paramagnetic Fe 3 O 4 nanotube arrays (figure 1d-e) are in situ obtained by finely tuning the growth condition and the level of oxidization. The evolution of super papramagnetism is related to the atom-by-atom growth at a low temperature results in a very small grain size. After post-annealing the thin films in H 2 /Ar mixture atmosphere at 400 °C, the magnetic ordering of the magnetite films and nanotube arrays undergoes a transition from superparamagnetism to ferrimagnetism, exhibiting a distinct magnetic anisotropy.(figure 1c) Atomic layer deposition of magnetite thin films and well-ordered nanotube arrays with well-controlled morphology and magnetic properties provides great opportunities for integrating with other order parameters to realize magnetic nano-devices with potential applications in spintronics, electronics, and bio-applications.[3-4]

Synthesis and characterization of TiO2/ZrO2 coaxial core–shell composite nanotubes for photocatalytic applications

1. Introduction Dye-sensitized solar cells (DSSCs) are considered as a new generation of solar cells due to their low cost and high performance [1-4]. DSSCs based on a TiO2 nanoparticle (TiO2 NP) network with air mass (AM) 1.5 solar efficiencies of more than 10% have been demonstrated. However, further enhancement in power conversion efficiency (PCE) has been difficult to achieve partly due to charge recombination and a reduced electron transport rate through the nanocrystalline photoanodes. Metal nanoparticles can contribute to the effective light absorption of solar cells, both by local field enhancement through the localized surface plasmon resonance and by light scattering leading to prolonged optical-path lengths [5]. Many researchers demonstrated that the size of the metal nanoparticles is a key factor for determining the plasmonic phenomena, and especially, light scattering occurs more dominantly than light absorption as the size of the metal nanoparticles increases [6]. In this work, TiO2 nanotubes (TNs) array synthesized by anodization method had a much organized standing nanotubes and tubes with uniform length, thickness, and diameter. The anodic oxidation process was carried out at 30 V, 25°C, 0.3 wt% NH4F + 3 vol% H2O as electrolyte and an anodization time of 1 h. The DSSC with TNs array as working electrode had fill-factor of 77.94%, Voc of 0.69 V, Isc of 6.85 mA/cm2, and 3.68% of efficiency. Since TNs array had roughly 1.2% higher efficiency than randomly stacked TNs, I have decided to further enhance the TNs array with gold nanoparticles. The DSSC with gold-lined TNs array as working electrode had fill-factor of 81.09%, Voc of 0.72 V, Isc of 7.54 mA/cm2, and finally an efficiency of 4.40%. 2. Experimental Once the Ti plate was cleaned thoroughly, apply Teflon® tape at the back of the plate to avoid oxidation on the back of the Ti plate. Clamp the plate with positive (anode) charge. The buffer solution used for the anodization is a mixture of 0.25 wt% NH4F plus 3 vol% H2O in ethyl glycol, stirred for one hour. The optimized voltage, setting temperature, and oxidation time are 30 V, 25°C, and one hour, respectively. After anodization, the Ti plate is immersed in ethanol and place in an ultrasonic bath to remove any excess contaminations, and then dried in room temperature overnight. Synthesize TNs array using optimized parameter setting, after annealing process, dipped the Ti foil into 1 mM of AuCl4 solution for 5 min, rinsed with deionized water, then dipped the foil into 0.15 M NaBH4 solution for another 5 min.To fabricate DSSCs, TiO2 nanotube arrays with or without Au modifications were soaked with N719 dye was added tert-butanol and acetonitrile solution, such mixing ratio 1:1 to prepare a concentration of 5 × 10-4 M dye solution. The DSSCs were finally packed by sealing the dye-coated electrode with a thermally platinized FTO counter electrode through a thin thermal plastic film (Surlyn, 25 ƒÝm, Solaronix). An electrolyte composed of 0.1 M N-methyl benzimidiazoium, 0.6 M 1-propyl-3-methylimidiazolium iodide, 0.05 M I2, 0.1 M guanidinium thiocyanate, and 0.2 M NaI in 3-methoxypropionitrile was introduced into the cell through a pre-drilled hole in the counter electrode. The hole was subsequently sealed with a microscope slip using Surlyn film. 3. Results and Discussion Fig. 1 Gold nanoparticles within TNs array.Fig. 2 I-V characteristic curves of DSSCs with Au nanoparticles by anodic oxidation at different voltage. 4. Conclusions In conclusion, anatase TiO2 nanotube arrays with Au nanoparticles was synthesized by anodic oxidation. At the deposition voltage of 30 V and Au-doped TiO2 nanotube arrays, the η, Jsc, and FF all reached the maximum. Compared with the conventional DSSCs Jsc, Voc, and η are 7.54 mA/cm2, 0.72 V, and 4.4%. Au-doped DSSCs has evident adsorption peak in visible range, indicating that Au-doped TiO2nanotubes are hopeful to become visible light photocatalyst.

In this article, we present recent advances that we have achieved toward improving the properties of anodically formed semiconducting TiO2 nanotubes as well as nanowire arrays as electrodes for oxidative photoelectrochemistry. The morphology, crystallinity, composition, and illumination geometry of nanotube or nanowire arrays are critical factors in their performance as photoelectrodes. We discuss the key aspects relating to each factor and the advances achieved in improving each. With respect to the more fully investigated nanotube arrays, the ability to control the morphological parameters such as pore size, tube length, and wall thickness of the nanotube architecture has enabled high performance in applications such as water photoelectrolysis, photocatalysis, dye-sensitized solar cells, and heterojunction TiO2−polymer hybrid solar cells. We begin by reviewing the photoelectrochemical performance of state-of-the-art nanotube arrays fabricated on planar substrates. We then present more recent results related to the growth of TiO2 nanotube arrays on nonplanar substrates designed in such a way that reflected light normally lost to free space is instead directed to a different point on the device, in turn improving overall photoconversion efficiency. Insofar as the crystallinity of the nanotubes is concerned, the use of a high-temperature oxygen or air-ambient anneal to crystallize the nanotube arrays is disadvantageous, since it results in a thick barrier layer where recombination losses occur and also because it precludes compatibility with polymeric substrates. In this regard, we discovered a two-step fabrication process for synthesis of crystallized nanotube arrays at low-temperatures. The photoelectrochemical applications of TiO2 are limited by its large electronic band gap. We briefly review the cationic and anionic doping approaches popularly used to modify the TiO2 band gap. We consider the use of ternary oxide systems containing titania as both a structural support and corrosion-inhibitor, in particular fabrication and performance of n-type Ti−Fe−O nanotubes and p-type copper-rich Cu−Ti−O nanotubes, with a note on our recent synthesis of iron oxide nanotube arrays by anodic oxidation of iron. Fabrication and photoelectrochemical properties of CdS−TiO2 and CdTe−TiO2 nanotube array heterojunction photoelectrodes are discussed. The article concludes by examining low temperature synthesis, and resulting properties, of single crystal vertically oriented TiO2 nanowire arrays on transparent conductive glass substrates; preliminary investigation of these nanowire array photoelectrodes for water photolysis reveals them to have low series resistance and provide excellent separation of photogenerated charges.

Surface characterization of TiO2 nanotube arrays produced on Ti6Al4V alloy by anodic oxidation

All‐Solid‐State Cable‐Type Supercapacitors with Ultrahigh Rate Capability

This paper focused on the influence of various oxidation parameters such as electrolyte composition, reaction time, calcination temperature and current change on the morphology and structure of TiO2 nanotube arrays. It was found that ammonium fluoride with a high viscosity reduced the diffusion rate of fluoride ions and significantly increased the length of TiO2 nanotubes, creating nanotubes with ordered arrays and uniform diameters. Meanwhile, the time of anodic oxidation determined the length of TiO2 nanotube arrays. Well-aligned nanotube arrays could be obtained after 0.5-2.5 h of oxidation. In addition, when the oxidation temperature was about 30 °C, the TiO2 nanotube arrays achieved the optimal uniformity and the maximum length-diameter aspect ratio. The morphology and quality of the TiO2 nanotubes fabricated were estimated through current as a function of reaction time. Consequently, formation mechanism of TiO2 nanotube arrays was investigated undergoing three major periods. The findings of this study can shed some light on the optimal conditions for preparing well-aligned TiO2 nanotube arrays with high length-diameter aspect ratio.

Nano zero-valent iron impregnated on titanium dioxide nanotube array film for both oxidation and reduction of methyl orange

CdS nanoparticle-sensitized TiO2 (CdS-TiO2) nanotube arrays are synthesized with a facile one-step electrodeposition technique. In these composited nanostructures, CdS nanoparticles uniformly distribute in the TiO2 nanotubes and partially embed in the shell of TiO2 nanotubes. These structures effectively prevent CdS nanoparticles assembling or clogging the nanotubes and improve the contact area between CdS nanoparticles and the TiO2 shells. Furthermore, the size and distribution density of CdS nanoparticles can be tuned easily by controlling the concentration of electrolyte. Coupling TiO2 nanotubes with CdS nanoparticles extends the optical absorption from ultraviolet into the visible-light region up to 580 nm. An 11-fold enhancement in photoelectrochemical (PEC) activity is observed for CdS-TiO2 nanotube arrays compared with plain TiO2 nanotube arrays. This unique method is also suitable for the synthesis of other narrow band gap semiconductor-sensitized TiO2 nanotubes.

Controlled synthesis of octahedral Cu 2O on TiO 2 nanotube arrays by electrochemical deposition

In recent years, it was demonstrated that Ti-Mo alloys are promising to be use as orthopedic implants. The presence of TiO2 nanotubes can increase the bioactivity and improve the osseointegration of Ti and its alloys implants, although this modification could lead to a reduction in the dynamic mechanical properties. In this context, the purpose of the present study was to obtain self-organized nanotubes on the surface of biomedical Ti-15Mo alloy and verify whether the fatigue performance was significantly changed. Organized nanotubes were obtained by anodic oxidation using ethylene glycol + NH4F solution. The axial fatigue behavior was characterized by stepwise increases of the applied load in air and in physiological media at 37°C. The results was compared with the as-polished samples in order to compare if the Ti-15Mo alloy fatigue behavior was affected by the surface modification, and it was found that the mechanical performance of the Ti-15Mo alloy was affected by the surface modification, in that specific experimental conditions used to obtain the nanotubes.