Papers by Keyword: Photoactivity

Abstract: Titanium dioxide (TiO₂) has been exploited extensively as it shows remarkable performance in photocatalytic applications. TiO₂ thin films can be deposited onto window glass which is workable for self-cleaning applications. In this article, we have studied the role of substrate temperature for spray pyrolysis (SP) of TiO₂ thin films for studying self-cleaning applications. For thin film deposition, TiO₂ sol is prepared by the sol-gel synthesis technique. The samples are deposited at room temperature and 250 °C, respectively. The samples are characterized via Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), and UV-Vis spectroscopy to determine the morphology, surface roughness, and optical properties of the thin films. SEM and AFM results show that samples deposited at 250 °C (pre-heated samples) have uniform size distribution, and defined grain boundaries, respectively. The results also show that the pre-heated sample is highly transparent in the visible region of the solar spectrum when analyzed by the steady-state UV-Vis spectrophotometer. The wettability of the prepared thin films is measured, and the results show that the pre-heated sample shows a hydrophilic character. The self-cleaning property of prepared thin films is evaluated by the photodegradation of Rhodamine B dye. It is observed that the pre-heated substrates show better photoactivity in presence of UV light irradiation. Hence, due to their hydrophilic nature and better photoactivity, these pre-heated thin films deposited by spray pyrolysis can be employed as efficient coatings for self-cleaning glass applications.

Abstract: The TiO₂-based photocatalysts have been synthesized by using sol-gel process and their photocatalytic activities were studied by the degradation of methylene blue (MB). It was shown that the calcination temperature has great influence on the crystalline phase transition of TiO₂. For all the samples (Ag-doped and undoped TiO₂ photocatalysts) calcined at 573K, only anatase phase was observed from XRD diffraction spectra and the intensity of peaks is weak. After the calcined at 773K, a mixture of anatase-rutile phase appeared. The contents of rutile phase were about 85% and77% for undoped and Ag-adopted TiO₂ photocatalysts.There were only rutile phases for all the TiO₂ photocatalysts calcined at 973K observed from XRD diffraction spectra. Magnetically stirring time of A solution before added B had no obvious effects on the polymorphs transition of TiO₂.

Abstract: The composite photocatalysts of Ni (OH)₂ modified Cd_1-xZn_xS (x=0, 0.2) nanorods were synthesized via a simple deposition-precipitation method using nanorods as support and Ni (NO₃)₂ as nickel hydroxide precursor. The structures, morphologies and optical properties of the catalysts were characterized by X-ray diffraction, scanning electron microscopy, high resolution transmission electron spectroscopy and UV-visible absorption spectroscopy. The photoactivities of the catalysts were examined toward hydrogen production by water splitting under simulated solar irradiation. Results show that the catalyst of Ni (OH)₂-Cd_0.8Zn_0.2S nanorods exhibits a significantly enhanced H₂-production activity in compared to the Ni (OH)₂-CdS nanorods. The reason for the different effects of Ni (OH)₂ modification on the photoactivities of the two catalysts was discussed, and the possible mechanism related to the photocatalytic process was proposed.

Abstract: Chromium doped rutile TiO₂ was synthesized by either co-precipitation or impregnation (surface-doping) and characterized by XRD and reflectance spectroscopy. Chromium addition did not change the TiO₂ structure nor did the structure of the co-precipitated products differ from that of the impregnated samples. However, chromium doping moved the absorption of both sets of products into the visible and significantly affected the TiO₂ photocatalytic activity for isopropanol (IPA) oxidation. At high chromium concentrations the photoactivity of the co-precipitated samples was reduced by a larger amount than that of the impregnated samples; this was attributed to a higher concentration of Cr³⁺ ions in the rutile lattice. Unexpectedly, increased photoactivity was measured for low Cr levels of surface-doped rutile. This may be caused by increased electron-trapping, at surface Cr⁶⁺ ions, and correspondingly reduced, electron-hole recombination.

Abstract: A low temperature solvothermal method was employed to synthesize nitrogen-fluorine doped TiO₂ materials (N/F -TiO₂) at various mole ratio of Ti:F; 10:1, 10:0.3 and 10:0.1, for photocatalytic applications. Doping fluorine and nitrogen in the TiO₂ structure extend the spectra response of the materials toward a visible region resulting in the high efficiency to oxidize methyl orange (MO) under UV-Vis irradiation. The microstructure and photocatalytic activity of the materials appeared to depend on titanium precursors, titanium isopropoxide (TTIP) or tetrabutyl orthotitanate (TBOT), and the concentration of dopant (NH4F). The highest MO decolorization efficiency under UV-Vis irradiation for 30 minutes is about 86 % by using N-F-TiO₂ (TTIP precursor) with Ti: F of 10: 3 as catalyst. The decolorization efficiencies of MO over N-F-TiO₂ materials (TTIP precursor) are twice higher than that of the undoped catalyst.

Abstract: The band structure and density of states (DOS) of Ti_1-xSn_xO₂ solid solutions with x=0, 1/8, 1/4, 1/2 and 1 were investigated by means of the first-principle calculations based on density functional theory. The result indicated that band gap and Fermi level of TiO₂-SnO₂ vary continuously from those of pure TiO₂ to those of Sn content increasing. In addition, the DOS moves towards low energy and the bang gap is broadened with growing value of x. The wide band gap and the low density of the states in the conduction band result in the enhancement of photoactivity in Ti_1-xSn_xO₂.

Abstract: Mesoporous anatase-TiO₂ nanoparticles mono-doped and co-doped with thulium and nitrogen were synthesized via a modified sol-hydrothermal method, and characterized by XRD, BET, XPS, FT-IR, DRS and PL techniques. The results showed that the Tm-doping inhibited both the transformation from anatase to rutile phase and the recombination of photogenerated electron-hole pairs, as well as increased the content of surface hydroxyl group, then improved the UV photoactivity of TiO2. The N-doping led to forming the N–Ti–O and N–O–Ti structures, which narrow the electronic band structure, then improved the photoactivity in the visible light region. However, the best visible light photoactivity for degradating methylene blue (MB) in aqueous solution was obtained in the N-doped sample instead of the co-doped sample, implying that no synergetic effect rises from Tm and N co-doping.

Abstract: Various ZnO nano and microstructures, such as nanorods, microflowers composed of nanorods, and microrods were hydrothermally self-assembled. The morphology of the formed ZnO nano and microstructures could be easily tuned by varying the experimental parameters of the NaOH concentration. The crystal structure of samples was investigated by XRD, and the diffraction peaks were indexed to hexagonal wurtzite structure. A possible growth mechanism was proposed on the basis of the morphology evolution of nano and microstructures observed by SEM. Furthermore, the photoluminescence and photocatalytic properties of ZnO nano and microstructures were investigated. The results show that the ZnO microrods and microflowers exhibited higher photodegradation efficiency than that of ZnO nanorods, which maybe due to the exposed polar faces of better crystalline rather than the size of ZnO.

Abstract: The N-doped TiO₂ films were prepared by cathode vacuum arc deposition with ion beam assisted. Influence of annealing temperature on the microstructure, optical property, photocatalytic activity and antibacterial activities of the N-doped TiO₂ films was studied. The experimental results indicate that annealing treatment significantly affects both microstructure and photoactivity. All the as deposited N-doped TiO₂ films retained an amorphous structure, the crystalline structure of N-doped TiO₂ films annealed in the range 400°C- 600°C were examined to be of anatase structure with a (101) preferential orientation，photocatalytic activity of the N-doped TiO₂ film annealed at 500°C was best under visible light, The N-doped TiO₂ films against E. coli and S. aureus had more than 99% antibacterial rate, and the antibacterial activity of the N-doped TiO₂ films stronger slightly with the increase of the annealing temperature.

Abstract: Aim to remove soluble humic acid (HA) in super-critical boiler make-up water, Y3+-doped ZnO/TiO2 composites were prepared using a solid-phase synthesis method, Their properties were characterized by x-ray diffraction, transmission electron microscopy, and UV-visible diffuse reflection spectroscopy (DRS); their visible light photoactivities were evaluated by the photodegradation of humic acid in an aqueous solution under sunlight irradiation.. The experiment results showed that Y3+-doped samples had a higher absorbance than pure TiO2, and a red shift appeared in the DRS spectrum; The Y3+-doped ZnO/TiO2 multiplex nanocomposite can expand the wavelength range for light absorption and increase the sunlight utilization efficiency. Samples with 3% Y3+ and 27% ZnO have the highest photoactivities.