Photocatalysts, titanium dioxide

THERMO- AND PHOTO-LUMINESCENCE FROM A PHOTOCATALYST TITANIUM DIOXIDE (TiOi)... 

Thermo- and Photo-luminescence from Photocatalyst Titanium Dioxide... 

Taking into account its possible appHcations such as gas sensors, dielectric ceramics, and photocatalysts, titanium dioxide (Ti02) has been extensively studied, and it has been shown that titanium oxide as anatase phase can be synthesized at room temperature without use of any previous or further thermal or hydrothermal treatment, performing hydrolysis and polycondensation processes in saturated metal chloride solutions. 

For the intentional destruction of these herbicide residues, the ideal agent would be inexpensive, rapid acting, dissipative or controllable, non-polluting, and 2idded directly to the rice field or the adjacent drains. From a survey of a variety of reagents, the semiconductor photocatalysts titanium dioxide and zinc oxide emerged as attractive candidates. 

Heterogeneous Photocatalysis. Heterogeneous photocatalysis is a technology based on the irradiation of a semiconductor (SC) photocatalyst, for example, titanium dioxide [13463-67-7] Ti02, zinc oxide [1314-13-2] ZnO, or cadmium sulfide [1306-23-6] CdS. Semiconductor materials have electrical conductivity properties between those of metals and insulators, and have narrow energy gaps (band gap) between the filled valence band and the conduction band (see Electronic materials Semiconductors). 

Tioxide process. This process is similar to that used to produce fumed silicas. Ultra-low particle size titanium dioxide (15-35 nm) is obtained for use as photocatalyst or UV absorber (for instance in sun protective creams). 

Fig.3 shows an effect of titanium dioxide loading on the decomposition of ethylene over a 20mesh wire-net photocatalyst. The decomposition rate increased in proportion to the amount of titanium dioxide loaded The specific initial rate (ro=(-dc/dt)t=o) was (1.8 0.2)x 10 ppm s g-catalysf. ... 

The photocatalytic activity of 20mesh wire-net photocatalyst was observed to be nearly equal to that of 350mesh one under the same amount of titanium dioxide loading (1.88 g). 

Ward MD, White JR, Bard AJ (1983) Electrochemical investigation of the energetics of particulate titanium dioxide photocatalysts. The methyl viologen-acetate system. J Am Chem Soc 105 27-31... 

Ranjit KT, Willner I, Bossmann SH, Braun AM (2001) Lanthanide oxide doped titanium dioxide photocatalysts Novel photocatalysts for the enhanced degradation of p-chlorophe-noxyacetic acid. Environ Sci Technol 35 1544—1549... 

Uzunova-Bujnova M, Todorovska R, Dimitrov D, Todorovsky D (2008) Lanthanide-doped titanium dioxide layers as photocatalysts. Appl Surfac Sci 254 7296-7302... 

Awazu, K., Fujimaki, M., Rockstuhl, C., Tominaga, J., Murakami, H., Ohki, Y., Yoshida, N., and Watanabe, T. (2008) A plasmonic photocatalyst consisting of silver nanoparticles embedded in titanium dioxide. Journal of the American Chemical Society, 130 (5), 1676-1680. 

Nanomaterials can also be tuned for specific purposes through doping. Specifically, the effect of the presence of manganese oxides on photocatalysis involving primarily titanium dioxide will be considered in this section. Titanium dioxide is a well-known photocatalyst and will be considered separately. K-OMS-2, which has a cryptomelane structure, is illustrated in Figure 8.4. Not all the literature discussed in this section, however, involves OMS tunnel structure materials. For example, amorphous manganese oxide (AMO) is also discussed as a photocatalyst. Manganite (MnOOH) is also included in battery applications. 

Han, F., Kambala, V.S.R., Srinivasan, M., Rajarathnam, D. and Naidu, R. (2009) Tailored titanium dioxide photocatalysts for the degradation of organic dyes in wastewater treatment a review. Applied Catalysis A General, 359, 25-40. 

To be used as photocatalysts, especially in the so-called clean technologies, active materials must fulfill the following requirements (1) very low toxicity, (2) resistance to photo-corrosion, (3) high availability, (4) high catalytic efficiency, and (5) low cost. From all the materials cited above, titanium dioxide and its derivatives seem to offer the best answer to these requirements, being by far the most commonly utilized photocatalysts. To be used in gas-phase photocatalysis, in addition to the above requirements, two other conditions are still necessary, that is, a very small pressure drop and an easy recovery. 

Titanium dioxide is a well-known powerful photocatalyst for decomposing a wide range of substances, including inorganic compounds [276-279], organic compounds including 2-propanol and methylene blue [280-292], and microorganisms such as bacteria and plankton [293-296] and decomposition of NOx in ambient air [297],... 

Frank SN, Bard AJ. 1977. Heterogeneous photocatalyst oxidation of cyanide ion in aqueous solutions at titanium dioxide powder. J Amer Chem Soc 99(l) 303-304. 

Ranjit, K.T., Cohen, H., Willner, I., Bossmann, S., Braun, A. 1999. Lanthanide oxide-doped titanium dioxide effective photocatalysts for the degradation of organic pollutants. J Mater Sci 34 5273-5280. 

Photolytic. Pelizzetti et al. (1990) studied the aqueous photocatalytic degradation of prometon and other s-triazines (ppb level) using simulated sunlight (7, >340 nm) and titanium dioxide as a photocatalyst. Prometon rapidly degraded forming cyanuric acid, nitrates, the intermediate tentatively identified as 2,4-diamino-6-hydroxy-7V,A -bis(l-methylethyl)-s-triazine, and other intermediate compounds similar to those found for atrazine. Mineralization of cyanuric acid to carbon dioxide was not observed. 

Interestingly, titanium dioxide can also act as a photocatalyst [87]. In some investigations into these phenomena a moisture-mediated redox reaction has been postulated. 

A variation of this process, using an aqueous-phase treatment of TiO2 with 3 hydrochloric acid solution, was used by d Hennezel and Ollis for prechlorination of a titanium dioxide photocatalyst [68] ... 

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