Anatase Titania Films Research Articles

Flexible Antibacterial Respiratory Monitoring Sensor Based on Controllable Au-Modified Surface of Highly {001} Preferred Anatase Titanium Dioxide Thin Film.

Respiratory signals are critical clinical diagnostic criteria for respiratory diseases and health conditions, and respiratory sensors play a crucial role in achieving the desired respiratory monitoring effect. High sensitivity to a single factor can improve the reliability of respiratory monitoring, and maintaining the hygiene of the sensors is also important for daily health monitoring. Herein, we propose a flexible Au-modified anatase titanium dioxide resistive respiratory sensor, which can be mechanically compliantly attached to curved surfaces for respiratory monitoring in different modalities (i.e., respiratory intensity, frequency, and rate). The uniform and preferentially oriented anatase titanium dioxide films gained by the polymer-assisted deposition technique can be fabricated on flexible substrates through a liquid-assisted transferring process. The Au modification can enhance surface plasmon resonance to facilitate the photocatalytic activity of titanium dioxide, and the optimized distribution of Au on the surface of titanium dioxide film made the sensor have an excellent antibacterial effect. The uniquely designed encapsulation can effectively control the contact between the surface of titanium dioxide films and electrodes, allowing the flexible sensor to exhibit fast response time (0.71 s) and recovery time (1.06 s) to respiratory as well as insensitivity or low sensitivity to other factors (i.e., gas composition, humidity, temperature, stress, and strain). This work provided an effective strategy for flexible wearable respiratory sensors and has great potential in daily respiratory monitoring for health management and pandemic control.

First principles study of the electronic and optical properties of high‐valence transition metal‐doped anatase titanium dioxide

AbstractThe formation energies and electronic and optical properties of anatase titanium dioxide doped with high‐valence transition metals (niobium, tantalum, tungsten, and molybdenum) were studied through first‐principles calculations based on density functional theory. The results showed that the doped titanium dioxide systems exhibited a typical n‐type metallic characteristic and high transmittance within the visible light spectrum. The high‐valence transition metal‐doped anatase titanium dioxide films should be formed under oxygen‐rich conditions and the niobium‐doped anatase titanium dioxide film is easier to synthesize and more stable than the other three films. Moreover, the band gaps of the doped titanium dioxide systems decrease due to the hybridization of transition metal d, tantalum 3d and oxygen 2p states. Niobium‐ and tantalum‐doped titanium dioxide have lower effective mass and higher electron mobility than tungsten‐ and molybdenum‐doped titanium dioxide, hence are more suitable for transparent conductive oxide materials.

Pulsed-laser deposition and photocatalytic activity of pure rutile and anatase TiO2 films: Impact of single-phased target and deposition conditions

Titanium dioxide is a technologically interesting material in many applicative fields that, however, exhibits critical aspects in terms of phase purity and synthesis/growth conditions.The presented work deals with the deposition, in vacuum, of single-phase rutile and anatase titania films by excimer laser ablation (λ = 248 nm) of anatase and rutile targets. Post-deposition thermal treatment at 450 °C in air was applied to drive the crystalline evolution of the as-deposited films, limit oxygen desorption and avoid changes in the polymorph phase.Unlike the typical use of oxygen as a background gas and Ti target in pulsed laser deposition of TiO2, our setting vacuum background atmosphere not only allows to relate the final phase of the film directly to the target phase but also to rule out phase transitions and mixed-phase, by the interplay between post-growth temperature and limited oxygen desorption. Herein, we study and discuss how the ablation process impacts on and determines film composition and morphology. The discussed influence of the target phase on the optical, morphological and photocatalysis properties of the titania films points out good performances of our samples and the importance to tune deposition to obtain the titania polymorph phase more suitable for specific applications.

Effects of water-to-methanol ratio on the structural, optical and photocatalytic properties of titanium dioxide thin films prepared by mist chemical vapor deposition

The mist chemical vapor deposition method was used to synthesize pure anatase phase titanium dioxide thin films on glass substrates. The effects of water-to-methanol ratio on the structural, optical and photocatalytic properties of titanium dioxide thin films were investigated. Titanium dioxide films deposited by mist chemical vapor deposition were always anatase phase independent of the various water-to-methanol ratios investigated. From the GIXRD results, it was found that with the decrease of the water-to-methanol ratio, the growth of {001} facets was enhanced. The uniformity of the synthesized titanium dioxide thin films was characterized by field emission scanning electron microscopy and atomic force microscope. The highest surface roughness and surface area was obtained with a water-to-methanol of 0 %, corresponding to undiluted 100 % methanol. The transmittance of all anatase titanium dioxide films was higher than 70 % in the visible region. By decreasing the water-to-methanol ratio, the photocatalytic efficiency of the anatase titanium dioxide films exhibited an increasing trend. Due to the highest ratio of {001} facets and maximized surface area, the titanium dioxide films deposited with a water-to-methanol of 0 % have the optimum photocatalytic efficiency, with a high potential for photocatalyst applications.

TiO2 films by sol‐gel spin‐coating deposition with microbial antiadhesion properties

Intensive use of antibiotics induced adaptations in bacteria, which developed antibiotic resistance. This is becoming a serious health problem, particularly in the hospital, food industry, or public transport. It is also important to produce surfaces that not only are bactericidal but also prevent adhesion and the consequent biofilm formation, which can make the bacteria resistant to conventional disinfection methods. In this work, a simple and inexpensive method to obtain surfaces TiO2 film coated has been realized to prevent attachment and bacterial proliferation on surfaces. The synthesis and deposition procedure has been finalized to the realization of a uniform coating, whose physical, morphological, and structural features are suitable to inhibit the proliferation of the bacteria and in particular the adhesion of the biofilm. The suitability of the obtained coating has been attested by RBS, X‐ray diffraction (XRD), SEM, UV‐vis, and Raman techniques. The obtained coatings were homogeneous anatase titania films with an excellent adherence to the substrate and a transmittivity higher than 80% in the visible region. The results show that the TiO2 films considerably reduce microbial contamination on the surface (~98% reduction) feature that makes this coating suitable for antibacterial applications.

Pulsed DC magnetron sputtering deposition of crystalline photocatalytic titania coatings at elevated process pressures

The use of elevated process pressures is described in the magnetron sputter deposition of titanium dioxide photocatalytic coatings to enable the direct low-temperature formation of the most photoactive titania crystal phase; anatase. Most other works on this subject deal with relatively low ‘conventional’ pressures (0.1–0.5Pa). However, the present work describes pulsed DC reactive magnetron sputtering deposition of titanium dioxide thin films at process pressures in the range 2–5Pa in a purpose-built sputtering rig. The influence of the other deposition conditions, such as pulse frequency and duty cycle, is also discussed. Additionally, a series of N-doped titania coatings was produced by using air as the reactive gas. The morphological and compositional properties of the coatings were studied using energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Wettability of the films was studied through measurement of water contact angles under UV light irradiation. Photocatalytic properties of the samples were assessed through the degradation of two model pollutants, methylene blue and stearic acid, under UV light irradiation. The results showed that elevated process pressures (4Pa and above) allow the direct deposition of anatase titania films, without additional heat treatment, while amorphous titania tends to form at lower process pressures.

Dielectric Measurements on Sol\u2013Gel Derived Titania Films

Alternating current (AC) impedance measurements were performed on 37 nm thick nanostructured sol–gel derived anatase titania films on ultrasonically cleaned (100) p-silicon substrates at temperatures T ranging from 100 K to 300 K over a frequency range between 20 Hz and 1 MHz. The frequency-dependent behavior of the AC conductivity σac(f, T) obeys the universal power law, and the values of the effective hopping barrier and hopping distance were found to be 0.79 eV and 6.7 × 10−11 m from an analysis due to the correlated barrier-hopping model. The dielectric relaxation was identified as a thermally activated non-Debye process involving an activation energy of 41.5 meV.

Deposition of photocatalytic anatase titanium dioxide films by atmospheric dielectric barrier discharge

In this study, TiO2 films are easily deposited in a single-step process from titanium tetraisopropoxide (TTIP) using a dielectric barrier discharge (DBD) device under atmospheric pressure at room temperature. The surface morphology of the as-deposited TiO2 films is observed by scanning electron microscopy (SEM). The as-deposited TiO2 films exhibit nanometer-sized particles with a lot of agglomerates. The cross section images indicate that the deposition rate of TiO2 films can reach about 70nm·min−1, which is much faster than that of conventional low pressure chemical vapor deposition (CVD) (typically <4nm·min−1). In order to confirm the structure composition and optical properties of the films, glancing incidence X-ray diffraction (GIXRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR) are employed. The as-deposited TiO2 films are partly crystalline which show a good photocatalytic activity in the degradation of methylene blue under UV irradiation. After annealing at 673K, the TiO2 films are in the anatase phase and composed by homogeneous nanoparticles. The photocatalytic degradation rate of methylene blue of the TiO2 films after annealing (~0.6h−1) is almost 4 times higher than that of the as-deposited TiO2 films (~0.16h−1). The photocatalytic degradation rate of the TiO2 film after annealing is the same as the one of the commercial anatase TiO2 spin coated film when the error bar is taken into account. The TiO2 films show excellent photocatalytic stability during 3 recycling photocatalytic measurements.

Anatase TiO2 nanotube arrays and titania films on titanium mesh for photocatalytic NOX removal and water cleaning

An anodization method was developed for the preparation of highly photoactive titania nanotube arrays (TiNTs) on commercially available titanium mesh. The prepared material was characterized from the point of view of its structure and possible photocatalytic applications and was compared with titania films deposited on the Ti-mesh by liquid deposition (TiO2-LD) and sol-gel methods (TiO2-SG). The photoactivity was determined in gas phase using NOX decomposition according to the ISO standard no. 22 197-1 (2007) as well as in liquid phase by decolorization of organic dyes e.g. methylene blue (MB) and rhodamine B (RhB). The investigated anatase nanotube arrays on Ti mesh showed the highest photoactivity in both gaseous and liquid phases and are promising for applications in photocatalytic reactors for environmental purification.

Effect of Solvent, Dye-Loading Time, and Dye Choice on the Performance of Dye-Sensitized Solar Cells

Anatase titania films with a thickness of up to 20 μm and deposited over a fluorine-doped tin-oxide substrate are impregnated with ruthenium dyes N-719 and N-749 using Dip and supercritical-fluid methods for the purpose of fabricating dye-sensitized solar cell devices. The dyes are dissolved in different solvent mixtures, including supercritical carbon dioxide, as well as combinations of more traditional solvents including mixtures of acetonitrile, and t-butanol. Analytical studies included thin-film analyzing and scanning electron microscopy to measure titania film thickness and porosity, UV-Vis spectroscopy to quantify dye concentration, and current-voltage device characterizations to assess energy conversion efficiency, as well as open-circuit voltage decay measurements and quantum efficiency to examine electron collection efficiency. A significant result is that using the dye N-749 in a solvent that includes supercritical carbon dioxide leads to energy conversion efficiencies that are higher for devices with a thick 20 μm semiconductor film than for the case of devices with thinner films, including the 10 μm film thickness that is traditionally considered an upper threshold. The supercritical-fluid method for the N-719 dye also enabled shorter impregnation duration than more conventional classical Dip Methods.

Axis‐Oriented, Continuous Anatase Titania Films with Exposed Reactive {100} Facets

Homogeneous TiO2 single crystals with high exposure of {100} reactive facets were constructed as a seed monolayer on transparent conductive substrates with the desired orientation of reactive facets. A secondary growth process was subsequently carried out on the monolayer seed film to form an axis-oriented continuous reactive film. Performing secondary growth with different precursors led to optimized conditions for high-performance photoelectrochemical activity of anatase TiO2 films. Experimental techniques such as UV/Vis absorption spectroscopy, X-ray diffraction, high-resolution SEM, and photoelectrochemistry were used to characterize the structural, optical, and photoelectrochemical properties of the as-synthesized films. As a photoanode in a photoelectrochemical cell, the axis-oriented reactive film shows a maximum photocurrent density of 0.3 mA cm(-2), as opposed to 0.075 mA cm(-2) for non-axis-oriented (randomly oriented) TiO2 film.

Effects of Hydrothermal Crystallization on the Morphologies and Photocatalytic Activity of TiO&lt;sub&gt;2&lt;/sub&gt; Nanotubes

Anatase titania (TiO2) films with highly photocatalytic activity were prepared by hydrothermal treatment of amorphous TiO2 nanotubes (NTs) via electrochemical anodization of titanium (Ti) in fluorine-containing electrolyte. The as-prepared TiO2 films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM). The photocatalytic activity of the as-prepared TiO2 films was evaluated by the photocatalytic degradation of methyl orange (MO) aqueous under UV-light irradiation. The effects of hydrothermal temperature and time on the morphologies, microstructure and photocatalytic activity of TiO2 films were investigated and discussed. It was found that TiO2 NTs were converted to nanoparticles after hydrothermal treatment. The mechanism of deformation of TiO2 NTs was discussed. Hydrothermal treatment enhances the phase transformation of TiO2 films from amorphous to anatase and crystallization of anatase. An optimal hydrothermal condition (150 oC for 8 h) was determined. The anatase TiO2 films prepared under optimal hydrothermal conditions posses larger surface area and higher relative anatase crystallinity and its photocatalytic activity is higher than that of anatase TiO2 films prepared under other hydrothermal conditions.

Effect of the Preparation Procedure on the Morphology of Thin TiO2 Films and Their Device Performance in Small-Molecule Bilayer Hybrid Solar Cells

Flat titanium dioxide films, to be used as the acceptor layer in bilayer hybrid solar cell devices, were prepared by spray-pyrolysis and by spin-casting. Both preparation methods resulted in anatase titania films with similar optical and electronic properties but considerably different film morphologies. Spray pyrolysis resulted in dense TiO₂ films grown onto and affected by the surface roughness of the underlying conducting glass substrates. The spin-casting preparation procedure resulted in nanoporous titania films. Hybrid solar cell devices with varying layer thickness of the small-molecule semiconducting dye TDCV-TPA were investigated. Devices built with spray-pyrolyzed titania substrates yielded conversion efficiencies up to 0.47%. Spin-cast titania substrates exhibited short circuits for thin dye layer thickness. For thicker dye layers the performance of these devices was up to 0.6% due to the higher interfacial area for charge separation of these nanoporous TiO₂ substrates.

UV to NIR photon conversion in Nd-doped rutile and anatase titanium dioxide films for silicon solar cell application

Undoped and Nd-doped titanium dioxide anatase and rutile films have been grown by pulsed-laser deposition at 700°C under 0.1mbar O2. By selecting adequate substrates, TiO2 films doped with 1, 2 or 5at.% Nd were grown and constituted with polycrystalline rutile, highly oriented (200) rutile film, or oriented (004) anatase. An UV to NIR photon conversion is evidenced in the films. Indeed, intense and well-resolved emission lines from Nd3+ have been observed upon excitation above the TiO2 bandgap at room temperature. The sensitised emission of Nd3+ is found to be much efficient in rutile than in anatase structure. Low temperature photoluminescence measurements lead to fine resolved peaks corresponding to the Nd3+ 4f transitions with different spectral characteristic according to the host matrix used. Photoluminescence dependence temperature evidences that the light emission from Nd3+ in anatase-based films is probably influenced by the presence of self-trapped excitons or by orbital interaction. Mechanisms of sensitisation host to Nd3+ are proposed for both matrixes. Finally, the Nd dopant concentration and the microstructure of TiO2 rutile films are found to affect the photoluminescence emission intensity. Rutile film (200) oriented is the most adapted host matrix to sensitise 1at.% Nd3+ ions for an emission around 1064nm making such Nd-doped layers interesting for photon conversion by down shifting process.

Sol–Gel Processing of Bi2Ti2O7 and Bi2Ti4O11 Films with Photocatalytic Activity

A new sol–gel synthesis based on chloride compounds as precursors has been used to prepare bismuth titanate (BT) films. The films have been deposited by dip‐coating and fired at different temperatures in air; they remain amorphous up to 500°C, and crystallize into the pyrochloric cubic phase Bi2Ti2O7 between 600° and 700°C while at higher temperatures of firing the stable Bi2Ti4O11 monoclinic phase is formed. The films have been characterized by X‐ray diffraction analysis at gracing incidence, X‐ray photoelectron spectroscopy, ellipsometric spectroscopy, UV–visible absorption, and atomic force microscopy. The photocatalytic properties of the films have been evaluated by exposing a methyl orange solution containing the BT films to UV light. The test has shown that the Bi2Ti2O7 films have a higher activity in comparison with reference anatase titania films.

Photocatalytic activity and electrochemical response of titania film with macro/mesoporous texture

Multifunctional anatase titania (TiO 2) films with macro/mesoporous texture have been prepared using a non-acidic polyethylene glycol-associated titanium alkoxide precursor sol, followed by 500 °C calcination. It was found that increasing polyethylene glycol 2000 loading in the sol not only increases the macroporous size in the films, but can also lead to an enhancement of mesopore volume (the number of mesopores). This is considered to have major contribution to increasing the final specific surface area due to inhibition of pore shrinkage or collapse at high calcination temperature (i.e., 500 °C). Good dissolution of polyethylene glycol 2000/acetonitrile solution in the isopropanol based sol can lead to the formation of the resulting TiO 2 films with uniform and macroporous surface morphology. The film at optimum polyethylene glycol loading (20 g/L polyethylene glycol 2000, 500 °C) exhibits good mechanical stability, enhanced photocatalytic activity in the degradation of 2,4-dichlorophenol in water and superior electrochemical response to catechol in the presence of ascorbic acid (a common interferent) by cyclic voltammetry. The unique textural structure, including enhanced specific surface area/pore volume and macroporous morphology with mesoporous anatase titania wall (average macrospore size in the range of 150–200 nm, mesoporous size of ~ 5 nm) are considered to be the main factor attributing to such a multifunction of the titania films.

Preparation and characterization of porous C-modified anatase titania films with visible light catalytic activity

Visible-light-activated C-modified anatase titania films have been synthesized from TiCl 4 and carbonic ink by using the sol–gel route. The synthesized photocatalysts were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and optical measurements. The modifying carbon not only produces homogeneous worm-like structure with uniform pores, but also extends the absorbance spectra of the as-prepared films into visible region. The results of visible-light-induced degradation of methyl orange (MO) show that the C-modified titania films exhibits much higher photocatalytic activities than that of pure titania film prepared at the same conditions.

Low-temperature deposition of the high-performance anatase-titania optical films via a modified sol–gel route

Anatase-titania films with high optical performances have been deposited via a modified sol–gel route. This involved several precisely controlled processes including a sufficient hydrolysis of titanium tetraisopropoxide (TTIP) with excessive water, a peptization at pH value of 1–2, a restrained condensation under the hydrothermal conditions at 373 K, and finally a spin-coating process at 293 K. A full characterization of the sols and films indicated that such a well-controlled hydrolysis and condensation of TTIP enabled the formation of high-quality precursor sols consisting of anatase-titania colloidal particles with the mean hydrodynamic diameter of about 17.2 nm, and then endowed the as-deposited films with nanocrystalline structure and the corresponding high refractive index of 1.92 (at 632.8 nm). Moreover, the prepared films exhibited large optical bandgap of 3.38 eV and high laser-induced damage threshold of 16.3 J/cm 2 (at 1064 nm, 3 ns pulse duration and R/1 testing mode), which must be closely related to their homogeneous and nearly defect-free network structures derived from the low-temperature sol–gel deposition route.

Nanocolumnar titania thin films uniquely incorporated with carbon for visible light photocatalysis

Carbon-doped or carbon-covered titania can enhance photocatalytic performance under visible light. Here we report the first instance of synergistic effect of the carbon incorporation in anatase titania (TiO2−xCx:C) films with both substitutional doping and surface covered characteristics, by reactively co-sputtering Ti metal and graphite targets. The nature of incorporated carbon is characterized by Raman spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscopy. The absorption edge of the carbon incorporated titania thin films shifted from ultraviolet to visible region and directly depended on the carbon content. The photocatalytic performance, e.g., photodegradation of methylene blue (MB), photo-reduction of silver-ions and super hydrophilicity, was greatly enhanced with increasing carbon content. The best photocatalytic activity is obtained in the TiO2−xCx:C film of the most carbon concentration about 9.3at.% with a degradation rate-constant of 0.108h−1 for MB under visible-light illumination.

Effects of post-deposition chemical treatment on the formation of mesoporous titania films

Mesoporous titania films have been synthesized by a modified sol–gel method in conjunction with amphiphilic triblock copolymers. The effects of ammonia vapor treatment on the formation of mesoporous structures were investigated. Mesoporous titania films with hexagonal structures were obtained by ammonia vapor treatment. Without ammonia vapor treatment, it was found that the mesoporous structures collapse due to crystallization. The framework of mesoporous titania was found to be amorphous. Mesoporous titania films prepared by ammonia vapor treatment showed thermal stability up to 500 °C. Mesoporous samples showed better photo-catalytic activity than anatase titania films under UV-light irradiation.