Materials Science Forum Vols. 486-487

Abstract: Rutile TiO2 nanoparticles have been synthesized by direct hydrolysis method using TiCl3, TiCl4 as starting materials, yielding two different morphologies. The hydrolysis of TiCl3 resulted in needlelike rutile titania with the specific surface area of 74.5m2/g, while round particles about 200~400 nm with small acicular at edge, with specific area as high as 175m2/g, were obtained using TiCl4 as starting materials. The precipitates from TiCl4 hydrolysis could be changed into anatase phase without filtering and separation by varying pH of the system. The phenomenon was explained from the viewpoint of structure. The photocatalysed properties of rutile powders were compared with those of anatase of the same specific surface area. Rutile powders with initial crystalline size of 7 nm were found to have higher photocatalysed activity in the phenol degradation reaction than that which anatase has. The high activity of the as prepared lab-made rutile was attributed to the abundance of hydroxy groups in powders, which was proved by TG data, making the degradation reaction have more active sites. The agglomeration form of the rutile powder makes it easy for separation and reuse.

Abstract: Dioxins are extremely toxic, and it is difficult to treat them with the conventional method. When irradiated by light, photocatalysts generate strong oxidative potential and decomposes almost all organic substances containing dioxins to water, carbon dioxide and others. Silica-gel has high adsorptive activity as well as large surface area, and it is transparent to ultraviolet light. Photocatalytic silica-gel was prepared by a dip coating method using TiO2 sol obtained by hydrolyzing titanium tetraisopropoxide on silica-gel bead (about 3mm in diameter) and heat-treated at 550°C. Since the surface area of the photocatalytic silica-gel is 300m2/g, the reaction area is large and allows the highly efficient decomposition of harmful organic substances, unpleasant odors and colored matters contained in waste water. The photocatalytic apparatus for decomposition of dioxins in emission gas from waste incinerators is composed of the catalyst layer consisting of 95dm3 photocatalytic silica-gel and 16 units of UV lamp. The photocatalytic apparatus was connected to the bypass line led from the outlet duct of cyclone, and the concentration of dioxins in the exhaust gas was measured. Decomposition test of dioxins in scrubber water was also performed using a photocatalytic apparatus with 150g photocatalytic silica-gel and 8 units of UV lamp. After 0.5dm3 of scrubber water containing dioxins was circulated in the photocatalytic apparatus for 1, 2 and 24 hour, each concentration of dioxins in the water was measured. As a result, the removal efficiency over 99% of dioxins in emission gas and scrubber water from waste incinerators has been obtained.

Abstract: Plasma spraying technique was used to deposit thin TiO2-based photocatalytic coatings on a foamed aluminum. Before spraying, the composites of nano-TiO2 powder (P25) and nano- ZnO/CeO2/SnO2 powders were agglomerated into microsized powders by a spray-drying process. XRD, SEM, TEM, XPS and the photocatalytic activity evaluation by the decomposition of benzene were applied to characterize the starting powders and the coatings, respectively. The results showed that all the three plasma sprayed TiO2-based coatings were the mixture phases of anatase and rutile. The XPS spectra results revealed that the oxygen element was composed of three kinds of chemical states, i.e., crystal lattice oxygen, hydroxyl oxygen and physical-adsorbed oxygen. The plasma sprayed 90%TiO2-10%CeO2 coating and 90%TiO2-10%SnO2 coating exhibited similar photocatalytic activity, which was higher than that of 90%TiO2-10%ZnO coating.

Abstract: Small quantities of lanthanum, yttrium and sulfur are doped in rutile n-TiO2 that was synthesized by an in-situ hydrothermal method. Their photocatalytic activities are characterized by the degradation of methylene blue (MB) under UV-Vis and visible light irradiation. The results show that lanthanum and yttrium ions are rich on the particle surface, which not only makes the surface energy decrease but also inhibits the recombination of photoexcited carriers, while S-doping produces states in the band gap of TiO2 that absorb visible light. Compared to the S-doping, La-doping, and Y-doping, respectively, the synergistic effects of (S, La)-codoping and (S, Y)-codoping result in a higher photocatalytic activity under visible light irradiation.

Abstract: The photocatalytic activity of samples of the new ceramic semiconductor, Na2ZrTi5O13 sol-gel, was studied using two different reactions, the decomposition (oxidation) of methylene blue and reduction-oxidation of Pb (II) from aqueous solutions at room temperature. We synthesised Na2Ti5ZrO13, which is isostructural to the family of compounds with general formula AnMTimO13, (A = Li, Na, K; M = Zr). These materials present a zig zag arrangement forming rectangular tunnels in their structure. The synthesis of this compound was achieved by sol-gel technique using metalic alcoxides at two different pH, 3 and 9. The fresh gels were heat treated at 200°C, 400°C, 600°C and 800°C. The reaction products were characterized by X-ray diffraction (XRD), thermal analysis (DTA, TGA) and infrared spectroscopy (FTIR). The band gap energy (Eg) of each sample prepared was calculated from the UV-Vis absorption spectra. . The values of Eg obtained ranged from 3.5 to 3.2 eV. The best activity found for the methylene blue degradation was performed by the Na2ZrTi5O13 sol-gel pH 9, treated at 800oC (99%). We assumed that the photocatalytic activity is favored when the structure was already formed. Lead photocatalysed reactions using Na2ZrTi5O13 sol-gel pH 9, treated at 600 oC showed a higher eficiency (98%) than that obtained by TiO2 (degussa) (85%).

Abstract: The photocatalysed degradation of various selected pesticide derivatives, namely N,NDimethyl- a-phenyl benzene acetamide (Diphenamid) [1], 1,2-diethyl phthalate (DEP) [2], 5-bromo- 3-sec.butyl-6-methyl uracil (Bromacil) [3], 3-tert-butyl-5-chloro-6-methyluracil (Terbacil), 2,4,5- tribromoimidazole (TBI) [4], Methoxychlor, Chlorothalonil and Disulfoton [5] as well as that of two selected priority organic pollutants, namely benzidine and 1,2-diphenyhydrazine (DPH) [6], has been investigated in aqueous suspensions of titanium dioxide (TiO2) under a variety of conditions. The degradation was studied by monitoring the change in substrate concentration employing UV spectroscopic analysis or HPLC technique and the decrease in total organic carbon (TOC) content, respectively, as a function of irradiation time. The degradation kinetics was studied under different conditions such as reaction pH, substrate and photocatalyst concentration, type of photocatalysts and the presence of alternative additives such as H2O2, KBrO3 and (NH4)2S2O8 besides molecular oxygen. The degradation rates and the photonic efficiencies were found to be strongly influenced by the above parameters. A toxicity test was performed for irradiated samples of few selected systems measuring the luminescence of bacteria Vibrio fischeri after 30 minutes of incubation.

Abstract: 5, 10, and 30 nm thickness of transparent TiO2 thin films were fabricated using sol-gel process, and the influence of film thickness on the photocatalytic property was investigated. The increase in film thickness was found to enhance the photocatalytic property of the films. Photocatalytic properties of each film were estimated by decomposition of stearic acid. The amount of decomposed stearic acid increased with film thickness (5 - 30 nm). For the case of 30 nm thickness film, the stearic acid was decomposed perfectly in twelve minutes. UV-vis spectra and photocurrents of each film clearly showed that the photoactivities of TiO2 films were related to the amount of absorbed UV light and band gap shift.

Abstract: A novel TiO2−ZnFe2O4 coating was prepared by plasma spraying. The effects of spraying parameters and the composition of powders on the microstructure and surface morphology of plasma sprayed coatings are studied. The photocatalytic efficiency of the as-sprayed coatings was evaluated through the photo mineralization of methylene blue. It was found that TiO2 coatings can decompose methylene blue under the illumination of ultraviolet rays, and the degrading efficiency is improved with an increase in the content of FeTiO3 in the coatings. However, the presence of a large amount of ZnFe2O4 compound will substantially lower the photocatalytic efficiency of the TiO2−ZnFe2O4 coatings for the unfavorable photo-excited electron-hole transfer process.

Abstract: Nanostructured titania coatings were prepared by atmospheric plasma spraying using commercial nano-powder. The effects of plasma forming gas H2 on microstructure and anatase content of coatings were examined by X-ray diffraction and field emission scanning electron microscopy. Photocatalytic properties of coatings were evaluated through a photo degradation of methylene blue in water solution under ultraviolet illumination. The results obtained indicated that the TiO2 coating was a mixture of anatase and rutile. The anatase content of coatings increased with increase in the flow rate of plasma forming gas H2. The content of anatase was as high as 60% in the as-sprayed coatings under optimal spray parameters. The photocatalystic property was improved by the content of anatase in coatings. It was found that all fabricated TiO2 coatings exhibited photocatalytic activity for the methylene blue test regardless of spraying parameters.