首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到10条相似文献,搜索用时 109 毫秒
1.
Titanium dioxide ultrafine particles (UFPs) are produced by pulsed laser ablation of titanium or titanium dioxide (anatase and rutile) rods in an atmosphere of He or O2/He mixture. The collected UFPs on cellulose membrane filters at the exit of the ablation chamber are analyzed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The TiO2 particles produced are composed of very small particles (diameter: 10–50nm) that are completely anatase, irrespective of the rod material, and relatively large particles (diameter: 100nm–1m) that are a mixture of anatase and rutile. The large particles consist of the direct strip-off fragments coming from the rod surface. The particles obtained from the laser ablation on TiO2 rods in an atmosphere of He contains gray particles that are supposed to be amorphous TiO2 (x < 2). In the presence of O2 in the ablation chamber, these oxygen defects in amorphous TiO2 are stabilized and anatase UFPs are formed. These results suggest that the crystal phase of the products can be controlled by adjusting the rod material and the gases used in the ablation process.  相似文献   

2.
The photocatalytic decomposition of diisopropylfluorophosphate (DFP) over nanostructured anatase and rutile TiO2 powder was investigated by FTIR and XPS. Upon irradiation with artificial solar light DFP decomposed on both polymorphs as evidenced by FTIR. For both crystalline structures acetone and subsequently coordinated formate and carbonate were observed on the surface during the photocatalytic reaction as the isopropyl groups dissociated from DFP. XPS revealed that small amounts of phosphates and inorganic fluoride (TiF) gradually built up on both TiO2 surfaces, while organic F was present only on the rutile phase. From repeated cycles of intermittent DFP adsorption and irradiation measurements, the decomposition rates and formation of residuals on the surface were deduced. It was found that the overall oxidation yield is higher on anatase than rutile. The oxidation rate decreases with increasing irradiation time, an effect that is more pronounced on rutile. We find that both the difference between the polymorphs and the initial decrease of the oxidation yield can largely be explained by variations in surface area rather than poisoning by POx or F species. In particular, we observe a dramatic decrease of the specific area of rutile as a function of photocatalytic oxidation cycle.  相似文献   

3.
C-cut and α-cut sapphire substrates are used to grow epitaxial titanium oxide films by pulsed-laser deposition at 700 °C under a controlled oxygen pressure in the 10−1-10−5 mbar range. The rutile phase is evidenced in films whatever the substrate and the oxygen pressure while the anatase phase is only observed on c-cut sapphire substrate and for oxygen pressure down to 10−3 mbar. No other titanium oxide phases (i.e. TiO, Ti2O3 or Magneli phases) are identified despite the oxygen-deficiency observed in films grown at low oxygen pressure. According to asymmetric X-ray diffraction measurements performed on films, the main axis growth and the in-plane epitaxial relationships between titanium oxide films and sapphire substrates are found to be depending on the orientation of the sapphire basal plane and on the oxygen pressure. The anatase crystallites are highly oriented with the following epitaxial relationship . The rutile phase is (2 0 0) oriented on c-cut sapphire substrate and displays two distinct in-plane relationships: . The use of α-cut sapphire substrate leads to the growth of rutile crystallites (2 0 0) or (1 0 1) oriented. In these cases, the in-plane orientations are , respectively. For the two substrates used, schematic views of atomic arrangement of the different interfaces are proposed.  相似文献   

4.
In order to improve the photocatalytic activity, N-doped titanium oxide (TiO2) films were obtained by thermal oxidation of TiN films, which were prepared on Ti substrates by ion beam assisted deposition (IBAD). The dominating rutile TiO2 phase was found in films after thermal oxidation. According to the results of X-ray photoelectron spectroscopy (XPS), the residual N atoms occupied O-atom sites in TiO2 lattice to form TiON bonds. UV-vis spectra revealed the N-doped TiO2 film had a red shift of absorption edge. The maximum red shift was assigned to the sample annealed at 750 °C, with an onset wavelength at 600 nm. The onset wavelength corresponded to the photon energy of 2.05 eV, which was nearly 1.0 eV below the band gap of pure rutile TiO2. The effect of nitrogen was responsible for the enhancement of photoactivity of N-doped TiO2 films in the range of visible light.  相似文献   

5.
A convenient method for the preparation of transparent, photocatalytic titania thin films is described. The films do not require annealing or thermal processing to develop photoactivity, thus can be applied to many thermally-sensitive substrates. Oxalic acid is used in place of the usual mineral acids to peptize the precipitated hydrous titania formed from the hydrolysis of titanium iso-propoxide. This leaves no inorganic residues in the film resulting in a higher quality film. The mineral phase and the photocatalytic activity produced are strongly influenced by the ratio of oxalic acid:titanium iso-propoxide employed. The peptization is carried out at 65 °C with vigorous stirring for 1 h in water containing 15% v/v ethanol, followed by a hydrothermal step at 95 °C. High oxalic acid:Ti molar ratios (0.5:1) result in rutile free sols, while lower ratios (0.25:1) result in anatase, rutile, brookite and TiO2(B) in varying proportions. The films were exposed to low level UV light to cure, and photodecompose the residual organic components in the film. The photodecomposition of residual oxalic acid in the cast films were monitored using infrared spectroscopy. Photo-activity of the UV-cured films was compared by monitoring the decoloration of methylene blue stains on the film, by UV–Vis spectroscopy. Transmission was greater than 99% across the visible light region (400–800 nm).  相似文献   

6.
To study the relationship between the phase structures of TiO2 and the photoinduced hydroxyl radicals (OH), TiO2 nanocrystallines were synthesized by a hydrolysis-precipitate method using tetrabutylorthotitanate (TBOT) as precursor, and then calcined at 450, 600, 700, 800 and 900 °C for 2 h, respectively. The calcined samples were characterized by X-ray diffraction and N2 sorption. The formation rate of OH on the surface of UV-illuminated TiO2 was detected by the photoluminescence (PL) technique using terephthalic acid as a probe molecule. The results show that with increasing calcined temperatures, the amorphous (Am) TiO2 precursor begins to turn into anatase (A) at 450 °C and rutile (R) phase appears at 600 °C, which is completely turned into the rutile phase at 900 °C. The BET specific surface areas of the catalyst decrease as the calcined temperatures increase. TiO2 sample calcined at 600 °C, with a mixed phase of anatase and rutile, shows the highestOH formation rate, and the order of the OH formation rate is as follows: A+R>A>R>Am. Phase structures of TiO2 play a more important role than specific surface areas in the OH formation rate. Two phase structure of anatase and rutile with a proper ratio is beneficial to the OH formation due to decrease of the combination rate of photo-generated electrons and holes. Our experimental result implies that the mixed phase of anatase and rutile can markedly enhance the photocatalytic activity of TiO2.  相似文献   

7.
We report on the photoinduced anisotropy in the holographic recording in spiropyran doped polymers as a result of the photoizomerization of spiropyran into merocyanine. Photoizomerization is achieved with UV polarized light ( = 355 nm) from the third harmonic of Q-switched Nd:YAG laser. After UV illumination a strong and broad polarization-dependent absorption peak centered 600 nm appears. Absorption holograms were recorded with low power He–Ne lasers with 2.2% output diffraction efficiency for polarization parallel to the polarization of the UV laser. The extremely long lifetime of the merocyanine states (12 days in the dark) and their high resolution makes this material promising as an optical memory element.  相似文献   

8.
The results on the optical characteristics of the glow–discharge plasma in an He/H2O mixture are presented. It has been established that it is a source of UV radiation in the region 306–315 nm (max = 309.6 nm). Radiation lines of the atoms of hydrogen (H 486.1 nm and H 656.3 nm) and helium (491.1, 501.1, 587.6, and 667.8 nm) were recorded in the visible region of the spectrum; they can be used as diagnostic lines in measuring the parameters of this plasma (n e, T e) by the method of emission spectroscopy. The intensity of the UV bands and of the spectral lines HI and HeI have been optimized depending on the partial pressure of helium and the discharge current. The results obtained are of interest for the development of an ecologically pure source of UV radiation on the basis of chemiluminescence of water vapors in a longitudinal glow discharge.  相似文献   

9.
Titania from nanoclusters to nanowires and nanoforks   总被引:1,自引:0,他引:1  
A novel method - inverse microemulsion has been developed not only for synthesizing low cost TiO2 nanoclusters but also for the first time preparing titania nanowires and nanoforks with rutile structure of single crystal. With two microemulsion systems, spherical TiO2 nanoclusters of 5 nm in average diameter are produced. These nanoclusters are amorphous and turned into anatase at an annealing temperature lower than 750 °C, and changed into rutile when annealed at higher temperature. When three microemulsions with TiCl4, ammonia and NaCl as aqueous phase, are used, the precursor powder containing Ti(OH)4/NaCl with molar ratio of 1000 are annealed at 750 °C and then TiO2 rutile nanowires with 22 nm in thickness and 4 m in length are formed. At the same time two kinds of nanoforks with defined boundary structures are constructed: one is a bent wire composed of two straight whiskers related by twinning on a (101) plane with the angle of 114° between the two legs, and the other by twinning on a (301) planes with the angle of 55° between the legs. Screw dislocations and a periodic structure are found in (301) twin boundary, while edge dislocations are observed in (101) twin boundaries.The experiments demonstrate that the titania rutile nanowires are formed through solid state phase transformation and sodium chloride play an important role in the process.  相似文献   

10.
A dye-sensitized solar cell (DSC) is a solar cell that uses an anatase film as a photovoltaic device. Since the anatase film and dye play the roles of electron carrier and electron generator, respectively, in the DSC, porous anatase films are desirable. In this paper, in order to develop a low-cost fabrication process for the photovoltaic device of the DSC, photocatalytic titanium oxide film deposition was carried out by atmospheric thermal plasma CVD. Ar gas, which served as the working gas for the plasma jet and substrate, and a 20 $times$ 40 $times$ 3 mm transparent acrylic resin plate were used. Titanium tetra iso butoxide was used as feedstock. Consequently, by cooling the substrate, an anatase-dominant film could be deposited at 773 K in deposition temperature without meltdown of the substrate on the condition of 100 mm in deposition distance, even in the case of acrylic resin substrate use. By wettability and methylene-blue decoloration tests, it was confirmed that the film showed hydrophilic and decolored methylene blue perfectly by 8-h UV irradiation. Furthermore, the DSC in which the titanium oxide film deposited by this technique was included as a photovoltaic device generated a photoelectromotive force of 25 mV. From these results, these thermal plasma processes were found to have high potential for DSC fabrication.   相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号