Porous Titania Layer Research Articles

Enhancing corrosion stability and shelf life of nanoscale zero-valent iron via encapsulation in porous Ze-TiO2 matrix: An interface for simultaneous oxidation and adsorption of As(III)

The potential of Nanoscale zero-valent iron (nZVI) for arsenic removal is immense, however its stability is still a concern, as it forms aggregates and is quickly oxidized in groundwater. The focus of the present work is to enhance the shelf life of nZVI and simultaneously using it to develop a material with high rate of adsorption (i.e. 10 mg g−1 in 60 min) for As(III) in ultra-low concentrations (100−1000 μg L−1). The composite was prepared by growing nano-titania on zeolite (Ze) surface in multilayers, and doping it with nZVI. Characterization of the composite was done using SEM, TEM, FT-IR, BET and XPS studies. The porous titania layer imparts a hydrophilic character to an otherwise hydrophobic substrate of zeolite, enhancing rate of As(III) adsorption. Nano TiO2 in the composite plays an important role by preventing nZVI against corrosion, besides oxidizing As(III) to less toxic As(V) which is then removed by adsorption and subsequent complexation with nZVI. The design of the proposed composite structure resulted in a remarkable increase in the shelf life of nZVI upto six months and showed corrosion stability even after numerous adsorption-desorption cycles. The As(III) adsorption mechanism has been proposed using kinetics and isotherm study. Additionally, the ease of magnetic separation and recyclability substantiates the potential utilization of the composite for treatment of As(III) contaminated drinking water.

Fructose dehydration to hydroxyl-methylfurfural in an immobilized catalytic microreactor

In this paper we report a microfluidic platform that allows for high temperature, high pressure conversion with inline spectroscopic measurement for a fast and accurate determination of both reaction rate constant and activation energy. The dehydration of fructose to hydroxyl-methylfurfural has been performed in this immobilized microreactor with both dense zirconia and porous titania layers, as a starting point to probe the potential of abundant metal oxide catalysts.

Corrosion resistance and in vitro bioactivity of dense and porous titania coatings deposited on 316L SS by spraying method

Titania coatings were deposited on 316L SS by the spraying method. It was found that the hardness, corrosion resistance and in vitro bioactivity of the titania coatings depends strongly on their particle size and the deposition rate. A small particle size and lower deposition rate promote the formation of a flat and more compact coating, which improves the corrosion resistance and hardness. However, a rough and porous structure obtained with a high deposition rate is required for the nucleation and growth of hydroxyapatite. Therefore, hard and corrosion resistant coatings with good bioactive properties can be achieved by the deposition of two layers, firstly depositing a dense layer and then a porous titania layer.

The Role of Titanium Surface Nanostructuring on Preosteoblast Morphology, Adhesion, and Migration.

Surface structuring of titanium-based implants is known to modulate the behavior of adherent cells, but the influence of different nanotopographies is poorly understood. The aim is to investigate preosteoblast proliferation, adhesion, morphology, and migration on surfaces with similar surface chemistry but distinct nanotopographical features. Sonochemical treatment and anodic oxidation are employed to fabricate disordered, mesoporous titania (TMS) and ordered titania nanotubular (TNT) topographies on titanium, respectively. Morphological evaluation reveals that cells are polygonal and well-spread on TMS, but display an elongated, fibroblast-like morphology on TNT surfaces, while they are much flatter on glass. Both nanostructured surfaces impair cell adhesion, but TMS is more favorable for cell growth due to its support of cell attachment and spreading in contrast to TNT. A quantitative wound healing assay in combination with live-cell imaging reveals that cell migration on TMS surfaces has a more collective character than on other surfaces, probably due to a closer proximity between neighboring migrating cells on TMS. The results indicate distinctly different cell adhesion and migration on ordered and disordered titania nanotopographies, providing important information that can be used in optimizing titanium-based scaffold design to foster bone tissue growth and repair while allowing for the encapsulation of drugs into porous titania layer.

Deposition of a titania layer on spherical porous silica particles and their nanostructure-induced vapor sensing properties

A titania-stearic acid hybrid layer was deposited onto well-defined silica-hexadecyltrimethylammonium hybrid spherical particles with 854 nm size to obtain nanoporous particles with a useful hierarchical core-shell structure. The deposition of a 35 nm-thick titania layer was confirmed by transmission electron microscopy. The core-shell particles were washed with acidic ethanol (solvent extraction) and calcined at 550 °C for 5 h to remove the template, resulting in the formation of nanoporous titania coated nanoporous silica spherical particles, which have a bimodal pore size distribution attributed to the hierarchical porous core and porous shell structure. The nanoporous titania coated particles exhibited an unusual crystal phase transition; only anatase was present even after the calcination at 1000 °C for 1 h. This would be due to the interfacial bonding between the core silica and the shell titania, preventing the crystal phase transition from anatase to rutile. On the other hand, the direct calcination of the titania-stearic acid coated particles without solvent extraction led to a shell composed of both anatase and rutile. The transformation to rutile could be caused by the strong exothermic reaction during the oxidative decomposition of the occluded stearic acid. Furthermore, the intense exothermic reaction induced the formation of a yolk-shell structure, which played a role in the sensitive/selective sensing properties for acetic acid when the yolk-shell particles were coated onto a nanomechanical Membrane-type Surface stress Sensor (MSS).

Control of Titania Layer of Dye-Sensitized Solar Cell (DSC)

In recent days, green technology that is based on solar cell is highly focused for sustainable society. So, the efficiency of Si type of solar cell is drastically improved. On the other hand, dye-sensitized solar cell (DSC) is also highly focused because of flexibility and design in spite of low efficiency. To clear the low efficiency problem, many studies on the development of dye and titania were carried out. Because the dye was developed, then the absorbed wavelength became broad and the absorption ratio on each wavelength was increased. Due to the study on titania, unique shapes of titania were suggested and the absorption characteristics were improved. In spite that many studies on chemical view were carried out, few studies on fabrication process were carried out. So, we focused on fabrication of titania layer of DSC. Usually, the titania layer was fabricated by the doctor blade method or the screen print method. The inside of the fabricated titania layer utilizing the ordinary method had little porous. In the case that the porous titania layer was formed, then the flow of electricity was increased due to the increased surface of titania layer. We applied the electrostatic inkjet method for fabrication of the titania layer because the porous layer was formed due to evaporation effect utilizing the electrostatice inkjet method. We already formed porous titania layer and achieved the efficiency improvement. In this paper, we investigated the fundamental characteristics on fabrication of porous titania layer utilizing the evaporation effect. The experimental set-up to investigate the characteristics was shown as follows. Titania paste was filled with the ink tank. Nozzle was installed at the end of the tank. FTO glass electrode was set on the XY linear stage and the rotation stage. When the high voltage was applied between the nozzle and the glass electrode, small droplets were ejected because the electrostatic inkjet method was took place. Formation and ejection of the small droplets were observed with a high-speed camera and a light. The evaluation of the porous titania layer was carried out with the SEM and XRR. We investigated the characteristics of the porous titania layer in case that the rotation speed was changed.

Semi-transparent ordered TiO2 nanostructures prepared by anodization of titanium thin films deposited onto the FTO substrate

In a significant amount of cases, the highly ordered TiO2 nanotube arrays grow through anodic oxidation of a titanium metal plate immersed in electrolyte containing fluoride ions. However, for some practical applications, e.g. solar cells or electrochromic windows, the semi-transparent TiO2 formed directly on the transparent, conductive substrate is very much desired. This work shows that high-quality Ti coating could be formed at room temperature using an industrial magnetron sputtering system within 50min. Under optimized conditions, the anodization process was performed on 2μm titanium films deposited onto the FTO (fluorine-tin-oxide) support. Depending on the electrolyte type, highly ordered tubular or porous titania layers were obtained. The fabricated samples, after their thermal annealing, were investigated using scanning electron microscopy, Raman spectroscopy and UV–vis spectroscopy in order to investigate their morphology, crystallinity and absorbance ability. The photocurrent response curves indicate that materials are resistant to the photocorrosion process and their activity is strongly connected to optical properties. The most transparent TiO2 films were fabricated when Ti was anodized in water electrolyte, whereas the highest photocurrent densities (12μAcm−2) were registered for titania received after Ti anodization in ethylene glycol solution. The obtained results are of significant importance in the production of thin, semi-transparent titania nanostructures on a commercial scale.

Electrochemical construction of a bio-inspired micro/nano-textured structure with cell-sized microhole arrays on biomedical titanium to enhance bioactivity

Biomimetic surface design of medical implants is vitally crucial to improve cellular responses and the integration of tissue onto materials. In this study, a novel hierarchical cell-sized microhole array combined with a nano-network structure was fabricated on a medical titanium surface to mimic multi-level bone structure. A three-step procedure was developed as follows: 1) electrochemical self-organization of etching on titanium substrate to create highly ordered cell-sized microhole arrays, 2) suitable dual acid etching to increase the roughness of the microholes, and then 3) electrochemical anodization in a NaOH electrolyte to construct a nano-network porous titania layer on the above micro-roughened surface. The bio-inspired micro/nano-textured structure presented the enhanced wettability and superhydrophilicity. The ability of in vitro biomineralization and corrosion resistance of the bio-inspired micro/nano-textured structure were enhanced after annealing treatment. More importantly, the bio-inspired micro/nano-textured structure on the titanium surface possessed a favourable interfacial environment to enhance attachment and proliferation of human osteoblast-like MG63 cells. All of the results demonstrated that such a bio-inspired surface of micro/nano-textured porous TiO2 is a most promising candidate for the next generation of titanium implants.

Fundamental Characteristics on Nano Porous Titania Layer of Dye-Sensitized Solar Cell (DSC) Utilizing Electrostatic 3D Printer

Fundamental Characteristics on Nano Porous Titania Layer of Dye-Sensitized Solar Cell (DSC) Utilizing Electrostatic 3D Printer

Control of Charge Dynamics through a Charge‐Separation Interface for All‐Solid Perovskite‐Sensitized Solar Cells

The relationship between the structure of the charge-separation interface and the photovoltaic performance of all-solid dye-sensitized solar cells is reported. This cell is composed of porous a TiO2/perovskite (CH3NH3PbI(x)Cl(3-x))/p-type organic conductor. The porous titania layer was passivated with Al2O3 or Y2O3 to remove surface traps of the porous titania layer. Both passivations were effective in increasing the efficiency of the solar cell. Especially, the effect of Y2O3 passivation was remarkable. After passivation, the efficiency increased from 6.59 to 7.5%. The increase in the efficiency was discussed in terms of the electron lifetime in TiO2, the thermally stimulated current, the measurement of the microwave refractive carrier lifetime, and transition absorption spectroscopy. It was proven that surface passivation resulted in retardation of charge recombination between the electrons in the porous titania layers and the holes in the p-type organic conductors.

Adsorption and photodegradation of methylene blue using a bulk Ti material with porous titania layer prepared by chemical oxidation

In this study, a chemical oxidation method was adopted to prepare a porous titania network on Ti bulk for dye adsorption and photodegradation. The prepared titania layer was characterized by SEM, AFM, ATR-FTIR, XRD, and zeta potential. Using a longer oxidation time (90min), a thicker titania layer (≈4μm) with pHpzc (pH of the point of zero charge) of ca. 2.2 and larger fraction of anatase phase could be formed. The prepared titania layer exhibited a better adsorption capability for MB (methylene blue) at various pH values than the commercial P25 TiO2 nanoparticles (pHpzc=6.0–6.8). Moreover, the effect of surface roughness on dye photodegradation was investigated. With UV irradiation, it took 6h to completely decompose MB using the titania layer prepared from the polished surface, whereas only half time was required by that abraded via #240 sandpaper. An improved dye photodegradation efficiency was achieved by a rougher surface for providing a larger surface area.

Construction of micro–nano network structure on titanium surface for improving bioactivity

A novel hierarchical micro–nano structured titania layer was constructed on Ti surface to mimic the multi-level bone structure. The Ti substrate was subjected to a suitable acid etching and subsequent anodization in NaOH electrolyte to form a micro–nano porous titania layer. It was indicated that this microporous/nano-network (micro/nano-network) structured surface presented the enhanced wettability and superhydrophilic property. The polarization curve measurements showed that the as-prepared micro/nano-network structured TiO2 surface was of better corrosion resistance compared to the blank Ti surface, according to its corrosion current decreased, corrosion potential shifted positively and polarization resistance increased in Hank's solution. Meanwhile, the Mott–Schottky plots revealed that less oxygen vacancies existed in the micro/nano-network structured TiO2 film in contrast to the natural oxide film on blank Ti surface. Moreover, it was observed that the micro/nano-network structured surface was completely covered by a homogeneous apatite layer when immersed in simulated body fluid (SBF) for 14 days, exhibiting an excellent ability of biomineration. Furthermore, the superior cell adhesion and viability were discerned on such hierarchically structured surface, through a comparison of MG63 cell behaviors on blank Ti surface, nano-network structured surface and micro/nano-network structured surface. All results suggest our construction of micro–nano porous TiO2 surface is a promising strategy for improving the bioactivity of titanium implants.

Superhydrophilicity on microstructured titanium surfaces via a superficial titania layer with interconnected nanoscale pores

Microstructured titanium (Ti) surfaces often suffer from poor hydrophilicity which makes the realization of open microfluidic devices difficult. Here, we investigate the effect of a superficial porous titania (TiO2) layer on the hydrophilicity of microstructured surfaces. High aspect ratio Ti micropillars were micromachined from bulk Ti sheets. Porous TiO2 was subsequently grown on Ti micropillars by a wet oxidation route followed by thermal annealing. Porous TiO2 was characterized using atomic force microscopy, x-ray diffraction and x-ray photoelectron spectroscopy. Detailed morphology study and pore size analysis were carried using focused ion beam machining coupled with scanning electron microscopy. Static contact angle and dynamic spreading studies clearly demonstrate enhanced hydrophilicity of microstructured Ti surfaces with a superficial porous TiO2 layer. Such enhancement promises interesting applications in the microfluidics and microsystems fields.

RGB organic electrochromic cells

In this work we present three novel viologen-type electrochromic compounds, which turn into red, green and blue (RGB) upon electrochemical reduction on porous titania surface. The synthesis of the three compounds involved attaching benzyl group with phosphonic acid residue as an anchor to 4,4′-bipyridine, 3,3′-dimethyl-4,4′-bipyridine and 4,4′,4″,4′″-thieno-2,3,4,5-tetrayltetrapyridine. The sterically demanding benzyl groups help to decrease the strong propensity of the colored radical cations to aggregation. The electrochromic derivatives were adsorbed on the surface of porous titania layers prepared by electrophoretic deposition onto a fluorine-doped tin oxide (FTO) glass followed by mechanical compression. Finally the electrodes with the grafted electrochromic derivatives were glued to a second FTO glass to form a closed cell, which operates with two electrodes. The electrochromic windows exhibited high contrast, fast response and low current consumption (∼1mA) when relatively low voltage (∼5V) was applied.

Preparation, characterization, in vitro bioactivity, and osteoblast adhesion of multi‐level porous titania layer on titanium by two‐step anodization treatment

To combine the advantages of different electrolytes in anodic oxidation, pure titanium samples were anodized in CH(3) COOH electrolyte according to a novel anodizing treatment regime and then in H(2) SO(4) electrolyte in potentialstatic mode. The in vitro bioactivity of the as-prepared titanium samples was evaluated by simulated body fluid (SBF) test. In addition, MG63 osteoblast-like cells were cultured on surfaces of the as-prepared titanium samples to evaluate osteoblast adhesion ability. The titanium samples after the two-step anodization treatment were covered by titania layers of anatase and/or rutile with several micrometres thickness and presented a multi-level porous surface morphology consisting of interlaced grooves about 20-μm wide overlaid with submicron scale pores. The SBF test results showed that the crystal titania layers prepared at appropriate conditions were able to induce apatite-forming in 7 days, indicating that the abundance of surface Ti-OH groups and (101)-oriented rutile structure both played important roles in in vitro bioactivity of titania layers. The cell experiment results showed that the macroscopic grooves could effectively promote osteoblast adhesion and growth and submicron scale pores might be beneficial to osteoblast adhesion. The two-step anodization treatment might be a promising candidate for surface modification of titanium implant.

Fabrication of Electron Passes in Nano-TiO2 Layer by High-Velocity Oxy-Fuel Method for Dye-Sensitized Solar Cells

Necking among titania nanoparticles in porous titania layers of dye-sensitized solar cells (DSC) was carried out by the collision of nanoparticles in a very fast gas flow of more than 1000–1500 m/s. where the substrate was held in an ambient atmosphere. The rapid gas flow was obtained by a high velocity oxy-fuel method (HVOF) operated at an intermediate temperature. The photovoltaic performance of a cell prepared by the HVOF method was slightly lower than that of DSCs fabricated by a conventional method involving coating-baking processes. The slightly low efficiency was explained by the small dye load and slightly lower electron diffusion coefficient in a porous titania layer. The time needed for fabricating a nanoporous titania layer (10 ×10 cm2) by the HVOF method was only a few minutes and was extremely shortened from the 2 h needed in the case of conventional coating and heating processes, which demonstrates that the HVOF method is useful for necking titania nanoparticles within an extremely short time.

フッ素ドープ酸化スズ透明立体電極を用いた色素増感太陽電池における電子収集の改善

The collection of injected electrons for dye-sensitized solar cells (DSSCs) was improved by two studies of three dimensional fluorine doped SnO2 transparent electrodes (3D FTO). One of the studies conducted here involved making textured glass substrates of silica sphere particles and low resistance FTO films. The other study involved a transparent 3D FTO electrode incorporated into the porous titania layer. In order to suppress back reactions between I3- ions and FTO, the FTO film surfaces in the DSSCs had to be covered with compact titania films prepared by using titanyl nitrate solutions. We confirmed the time constants for the recombination and collection of the injected electrons by using optical modulation techniques. It was found that these 3D configurations contributed to the improvement in the performance of the DSSCs.

Transparent Conductive Oxide Layer-Less Three Dimensional Dye Sensitized Solar Cells: Fabrication of Ionic Path in Three Dimensional Ti Electrode

A transparent conductive oxide-less dye-sensitized solar cell (TCO-less DSC) consisting of a thick and porous Ti electrode is reported. The Ti electrode was contacted with the back of a stained porous titania layer. A thick Ti electrode prepared by conventional sputtering prevented ionic diffusions through the Ti electrode and decreased photovoltaic performance. Tetrapod-shaped ZnO crystals were used to prepare straight and continuous nanopores in the Ti electrode to maintain the ionic diffusion. 8% efficiency of the TCO-less DSC is also reported.

A Dual-Layer Titania Film with Enhanced Photocatalytic Activity

A dual-layer titania film consisting of a sol−gel anatase layer over an interconnected porous anatase one was fabricated and its photoelectrochemical behavior as well as photocatalytic ability were studied in detail. The porous layer was fabricated through direct oxidation of a metallic Ti substrate with an aqueous hydrogen peroxide at 80 °C for 1 h. The Ti substrate with the porous titania layer was then subjected to a sol−gel spin-coating to deposit the upper titania layer. The dual-layer titania film as a whole was phase pure anatase after a subsequent thermal treatment at 450 °C. The UV−vis diffuse reflectance spectra and ambient photoluminescence spectra indicated that the porous anatase possessed a band gap width narrower than that of the sol−gel derived anatase, which was attributed to the relatively larger amounts of surface oxygen deficiency. Under UV illumination, both the saturated photocurrent and the activity to assist photodegradation of rhodamine B in water were nearly double that of the si...

Preparation of Double Dye-Layer Structure of Dye-Sensitized Solar Cells from Cocktail Solutions for Harvesting Light in Wide Range of Wavelengths

Dye-sensitized solar cells (DSCs) consisting of a double dye-layer structure of Ru dye (Z907) and organic dye (NK3705) were prepared by dipping porous titania substrates into dye mixture solutions. Dye structures such as NK3705 were crucial for realizing the double layer structure. A porous titania layer adsorbed NK3705 predominantly in the dye mixture. The adsorbed NK3705 was then replaced by Z907 from the top to the bottom of the porous titania surface as a function of dipping time. The DSCs based on the double dye-layer structure were able to harvest light in a wide range of wavelengths.