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Crystalline phases and optical properties of titanium dioxide films deposited on glass substrates by microwave method

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Abstract

Anatase films were deposited on glass substrates by 180, 300, 450 and 500 W microwave for 1.5 min. Upon calcination the 450 and 500 W films at 450 °C for 1 h, additional rutile phase was detected by X-ray diffraction (XRD). Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses revealed morphologies of the films which were composed of a number of nanoparticles orientated in different directions with the lowest roughness for the film synthesized by 450 W microwave combined with the high temperature calcination. Band gaps of the films without calcination determined by UV–visible spectroscopy were 3.30–3.35 eV and were considerably decreased to 2.92–3.20 eV by the high temperature calcination.

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... No noticeable change in the crystal phase has been observed in TiO 2 -component by the influence of the CeO 2 -component in the NC. Promnopas et al. [69] calcined TiO 2 films at 450°C and reported having detected an insignificant amount of rutile phase crystals in addition to the predominant anatase crystalline phase [69]. In this work, however, pure TiO 2 shows anatase crystalline phase only, and no transition to rutile phase is detected in CeO 2 /TiO 2 NCs (both formed by calcination at 500°C). ...
... No noticeable change in the crystal phase has been observed in TiO 2 -component by the influence of the CeO 2 -component in the NC. Promnopas et al. [69] calcined TiO 2 films at 450°C and reported having detected an insignificant amount of rutile phase crystals in addition to the predominant anatase crystalline phase [69]. In this work, however, pure TiO 2 shows anatase crystalline phase only, and no transition to rutile phase is detected in CeO 2 /TiO 2 NCs (both formed by calcination at 500°C). ...
... No noticeable change in the crystal phase has been observed in TiO 2 -component by the influence of the CeO 2 -component in the NC. Promnopas et al. [69] calcined TiO 2 films at 450°C and reported having detected an insignificant amount of rutile phase crystals in addition to the predominant anatase crystalline phase [69]. In this work, however, pure TiO 2 shows anatase crystalline phase only, and no transition to rutile phase is detected in CeO 2 /TiO 2 NCs (both formed by calcination at 500°C). ...
... No noticeable change in the crystal phase has been observed in TiO 2 -component by the influence of the CeO 2 -component in the NC. Promnopas et al. [69] calcined TiO 2 films at 450°C and reported having detected an insignificant amount of rutile phase crystals in addition to the predominant anatase crystalline phase [69]. In this work, however, pure TiO 2 shows anatase crystalline phase only, and no transition to rutile phase is detected in CeO 2 /TiO 2 NCs (both formed by calcination at 500°C). ...
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... TiO 2 has three common crystalline phases, rutile, anatase, and brookite ( Figure 1A). 27,29 At ambient pressure and temperature, rutile (space group P4 2 /mnm) is the only thermodynamically stable phase of TiO 2 , with a melting point of 1843°C ( Figure 1B,C). Other crystalline polymorphs, including the commonly encountered anatase (space group I4 1 /amd) and brookite (space group Pbca), are either metastable or stabilized under high pressure. ...
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Brookite is the least studied TiO2, and its photocatalytic activity higher or lower than that of anatase still remains unclear. In this work, three different model reactions have been used for the activity assessment. Phase-pure brookite and anatase were homemade at different temperatures (Ts = 200-500 degrees C), as confirmed by X-ray diffraction and Raman spectroscopy. For phenol oxidation in aerated aqueous solution, brookite showed an apparent activity higher and lower than that of anatase at low and high T-s, respectively. For chromate reduction in aerated aqueous suspension, the apparent activity of brookite was always lower than that of anatase. However, with the same amount of Cr(VI) or Ag(I) adsorbed on the oxide in water for Cr(VI) reduction or for phenol degradation under ND the intrinsic activities of brookite and anatase not only became similar at given Ts but also increased with the increase of Ts. Moreover, for O-2 reduction to H2O2 in the presence of excess phenol, the BET surface area normalized activity of brookite was always higher than that of anatase, the trend of which was similar to that observed from phenol degradation in aerated aqueous solution. It is proposed that brookite has a stronger affinity to O-2 in water than anatase. Then, the observed difference between brookite and anatase in the apparent photocatalytic activity for phenol degradation is ascribed to the combined effect of T-s, surface area, and sorption capacity toward the dissolved O-2 in water.
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Transparent thin film of TiO2 is deposited on glass substrate by e-beam evaporation method with the pressure, deposition rate, and substrate temperature of 3.0 x 10-6m.bar, 3 nm/s and 100 0C respectively. The film is annealed at 500 0C for about 1 hour. The structural property of the films has been studied using GIXRD. The optical property of the film has been studied using UV-Visible and Photoluminescence spectroscopy (PL). Photoluminescence spectra shows intense and sharp peak at 440 nm. The dielectric property of the film is studied by measuring capacitance at different frequencies at room temperature. It is observed that the capacitance decreases with increase in frequency but at high frequency, the capacitance becomes constant. GIXRD data indicates the crystalline property of the film.
Article
At present, composite photocatalysts containing MoS2 as a co-catalyst and a subjective semiconductor material are usually obtained via various complex reduction methods using NH4MoS4 or Na2MoO4 as a precursor. In this work, a simple method was proposed to synthesize MoS2-TiO2 composite photocatalysts via mechanochemistry using MoS2 as a direct precursor. 4.0% MoS2-TiO2 after ball-milling at 300 rpm for 2 h possessed the maximum photocatalytic activity for H2 evolution. The rate of H2 evolution was up to 150.7 μmol h(-1), which was 48.6 times higher than that of pure TiO2. The MoS2-TiO2 composite possesses stable photocatalytic performance for H2 evolution. Photoelectrochemical measurements confirmed the electronic interaction between TiO2 and MoS2. The photo-generated electrons on the conduction band of TiO2 could easily transfer to the MoS2 co-catalyst, which promoted efficient charge separation and improved the photocatalytic performance.
Article
Titanium dioxide (TiO2) thin films were synthesized on glass substrates by spray pyrolysis. The effect of solution flow rate on the physical properties of the films was investigated by use of x-ray diffraction (XRD), scanning electron microscopy, atomic force microscopy (AFM), and spectrophotometry techniques. XRD analysis revealed the tetragonal anatase phase of TiO2 with highly preferred (101) orientation. AFM images showed that grain size on top of TiO2 thin films depended on solution flow rate. An indirect band gap energy of 3.46 eV was determined by means of transmission and reflection measurements. The envelope method, based on the optical transmission spectrum, was used to determine film thickness and optical constants, for example real and imaginary parts of the dielectric constant, refractive index, and extinction coefficient. Ultraviolet and visible photoluminescence emission peaks were observed at room temperature. These peaks were attributed to the intrinsic emission and to the surface defect states, respectively.
Article
Using TiCl4, Ti(SO4)2 and TBOT as different Ti precursor, titania (TiO2) photocatalysts with high specific surface area were prepared by rapid microwave hydrothermal method. The as-prepared catalysts were characterized by TEM, XRD, DRS and N2 adsorption. The dependence of degradation efficiency of MB on the surface area, crystal structure and band gap of the obtained TiO2 particles were investigated. Results showed that compared with the TiO2 derived from TiCl4 and Ti(SO4)2 precursor, the TiO2 from TBOT exhibited best photocatalytic performance due to its higher surface area, capability of homogenous dispersion and its characteristic of anatanse structure.
Article
10-time lithium rate improvement and 4-time photocatalytic performance enhancement have been achieved with TiO2 nanocrystals when coated with a thin layer of amorphous carbon. The enhanced performances can be attributed to lower lithium ion diffusion and electronic conduction resistance across the carbon layer into the TiO2 electrode material and better surface adsorption of the dye molecules and ions. Thus, the current study may provide us an alternative approach in improving the performances of TiO2 nanocrystals in both lithium ion battery and photocatalysis applications.
Article
Titanium dioxide (TiO2) films are deposited on quartz substrates by atmospheric pressure (AP)CVD, and then annealed under simulated air (80% nitrogen, 20% oxygen) at temperatures from 600 to 900 °C to investigate the change in microstructure and the effect on the photocatalytic activity on the simulated pollutant stearic acid. The as-deposited TiO2 film is mainly composed of pure anatase phase while the rutile phase is detected only after annealing the film at 900 °C for 1 h. The photocatalytic activity of the annealed films on stearic acid under UV irradiation is found to deteriorate after the films are annealed at temperatures above 700 °C. This decrease in photocatalytic performance is observed to be the result of two possible mechanisms induced by the annealing temperature. The first mechanism is the increase in defect concentration (O− and Ti vacancies) in the annealed TiO2 films for annealing temperatures below 800 °C, and the second mechanism is the formation of large rutile grains at a higher temperature, 900 °C.
Article
The mechanism of phase transformation in nanocrystalline TiO2 powders at ambient temperature during high energy ball milling and the role of brookite phase in anatase-to-rutile phase transformation were investigated by the use of Rietveld analysis of X-ray diffraction patterns and Raman spectroscopy methods. The milling process was performed on a fully anatase phase nanocrystalline TiO2 powder via a high energy planetary ball mill with different ball-to-powder weight ratios followed by annealing of the as-milled samples. Some transformation from anatase-to-brookite was observed in all as-milled powders by high resolution transmission electron microscopy. It was proposed that brookite occurs at the {112} twin surfaces of anatase phase and therefore promotes anatase-to-rutile phase transformation. Based on the XRD and Raman results, it was proposed that brookite appears as an essential intermediate phase in mechanically induced anatase-to-rutile phase transformation which facilitates the phase transformation at ambient temperatures and also at higher temperatures during the post-annealing step.
Article
We report here that a facile sol–gel dip-coating technique can be used to fabricate a SiO2/TiO2 bilayer film with self-cleaning and antireflection properties. The bottom SiO2 layer acts as an antireflection coating due to its lower refractive index; the top TiO2 layer acts as a self-cleaning coating generated from its photocatalysis and photo-induced superhydrophilicity. The maximal transmittance of SiO2/TiO2 bilayer film at normally incident light can be reached 96.7%, independent of the high refractive index and coverage of TiO2 nanoparticles. However, the photocatalytic activity of the bilayer film shows a close dependence on coverage of TiO2 nanoparticles. After illuminated by ultraviolet light, the SiO2/TiO2 bilayer films are superhydrophilic with water contact angle less than 2°, which favors greatly the self-cleaning function of the films.
Article
We report, the structural and optical properties of nanocrystalline anatase TiO2 thin films grown on glass substrate by dc magnetron sputtering at room temperature. The influence of sputtering power and pressure over crystallinity and surface morphology of the films were investigated. It was observed that increase in sputtering power activates the TiO2 film growth from relative lower surface free energy to higher surface free energy. XRD pattern revealed the change in preferred orientation from (101) to (004) with increase in sputtering power, which is accounted for different surface energy associated with different planes. Microstructure of the films also changes from cauliflower type to columnar type structures with increase in sputtering power. FESEM images of films grown at low pressure and low sputtering power showed typical cauliflower like structure. The optical measurement revealed the systematic variation of the optical constants with deposition parameters. The films are highly transparent with transmission higher than 90% with sharp ultraviolet cut off. The transmittance of these films was found to be influenced by the surface roughness and film thickness. The optical band gap was found to decrease with increase in the sputtering power and pressure. The refractive index of the films was found to vary in the range of 2.50–2.24 with increase in sputtering pressure or sputtering power, resulting in the possibility of producing TiO2 films for device applications with different refractive index, by changing the deposition parameters.
Article
Cubic ZnTe nanocrystals were produced from 1:1 and 1.8:1 molar ratios of Zn:Te by a 900 W microwave plasma. The phase was detected using X-ray diffraction (XRD), which are in accordance with those of the simulations, and selected area electron diffraction (SAED). Raman spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that the products were nanocrystals with different orientations, including three longitudinal optical (LO) vibrations at 205, 410 and 620 cm− 1 and a transverse optical (TO) vibration at 166 cm− 1. Their green emissions were detected at 562 nm (2.21 eV) using luminescence spectrophotometry.
Article
Hierarchically structured TiO(2) (HS-TiO(2)) was prepared on a flexible ITO-PEN (polyethylene naphthalate) substrate via electrospray deposition using a commercially available TiO(2) nanocrystalline powder in order to fabricate flexible DSSCs under low-temperature (<150 °C) conditions. The cell efficiency increased when using flexible ITO-PEN substrates post-treated by either a mechanical compression treatment or a chemical sintering treatment using titanium n-tetrabutoxide (TTB). The mechanical compression treatment reduced the surface area and porosity of the HS-TiO(2); however, this treatment improved the interparticle connectivity and physical adhesion between the HS-TiO(2) and ITO-PEN substrate, which increased the photocurrent density of the as-pressed HS-TiO(2) cells. The electron diffusion coefficients of the as-pressed HS-TiO(2) improved upon compression treatment, whereas the recombination lifetimes remained unchanged. An additional chemical sintering post-treatment involving TTB was tested for its effects on DSSC efficiency. The freshly coated TiO(2) submitted to TTB hydrolysis in water at 100 °C yielded an anatase phase. TTB treatment of the HS-TiO(2) cell after compression treatment yielded faster electron diffusion, providing an efficiency of 5.57% under 100 mW cm(-2), AM 1.5 global illumination.
Article
A preparation technique of TiO2 screen-printing pastes from commercially-available powders has been disclosed in order to fabricate the nanocrystalline layers without cracking and peeling-off over 17 µm thickness for the photoactive electrodes of the dye-sensitised solar cells. A conversion efficiency of 8·7% was obtained by using a single-layer of a semi-transparent-TiO2 film. A conversion efficiency of 9·2% was obtained by using double-layers composed of transparent and light-scattering TiO2 films for a photon-trapping system. Copyright © 2007 John Wiley & Sons, Ltd.
Article
The quality of human life depends to a large degree on the availability of energy. This is threatened unless renewable energy resources can be developed in the near future. Chemistry is expected to make important contributions to identify environmentally friendly solutions of the energy problem. One attractive strategy discussed in this Forum Article is the development of solar cells that are based on the sensitization of mesoscopic oxide films by dyes or quantum dots. These systems have already reached conversion efficiencies exceeding 11%. The underlying fundamental processes of light harvesting by the sensitizer, heterogeneous electron transfer from the electronically excited chromophore into the conduction band of the semiconductor oxide, and percolative migration of the injected electrons through the mesoporous film to the collector electrode will be described below in detail. A number of research topics will also be discussed, and the examples for the first outdoor application of such solar cells will be provided.
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