Photocatalysts, titanium dioxide-based

SerponcN., Emeline A. V., Kuznetsov V. N. and Ryabchuk V. K. (2008), Second generation visible-light-active photocatalysts preparation, optical properties and consequences of dopants on the band gap energy of TiOi , in Environmentally Benign Catalysts—Applications of Titanium Dioxide-Based Photocatalysts, Anpo M. and Kamat P. V., eds.. Springer, New York, publication date October 2008. 

In 1977 Schrauzer and Guth published a seminal communication [1] in which the photocatalytic synthesis of ammonia from nitrogen and water was described. The process involved irradiation with UV-visible light in the presence of a titanium dioxide-based photocatalyst (Section II.A) and was described as the basis for a prototype solar cell for photochemical ammonia synthesis [2]. The photocatalytic process is represented by reaction 1. 

TiOa is one of the most commonly used photocatalysts. In Hong Kong, a study titled Ambient Air Treatment by Titanium Dioxide Based Photocatalyst was conducted in 2002 (116). The purpose of the study was to determine the durability of TiOa catalyst. Extensively used Ti02-coated paving blocks were tested for then-use in the photocatalytic oxidation of NOx. 

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). 

In considering photoactivity on metal oxide and metal chalcogenide semiconductor surfaces, we must be aware that multiple sites for adsorption are accessible. On titanium dioxide, for example, there exist acidic, basic, and surface defect sites for adsorption. Adsorption isotherms will differ at each site, so that selective activation on a particular material may indeed depend on photocatalyst preparation, since this may in turn Influence the relative fraction of each type of adsorption site. The number of basic sites can be determined by titration but the total number of acidic sites is difficult to establish because of competitive water adsorption. A rough ratio of acidic to basic binding sites on several commercially available titania samples has been shown by combined surface ir and chemical titration methods to be about 2.4, with a combined acid/base site concentration of about 0.5 mmol/g . 

Titanium dioxide (Ti02) has been attracting much attention for its important role in water photo-oxidation and photocatalyst, as well as a base material for dye-sensitized solar cells. A number of studies have been conducted on the mechanisms of interfacial photo-anodic reactions but the reported mechanisms still remain sketchy, and the detailed molecular mechanism has not yet been clarified. The main reason for confusion may arise from the possibility that the reaction mechanism depends on detailed chemical structures of the electrode surface. This implies that studies with well-defined surfaces are of key importance. 

This is a preliminary approach to the use of a new generation of solid-state sensors based on the capacity of the sensor element to catalyze the photodegradation of various kinds of organic compounds and to recognize their structure on the basis of the type of process catalyzed. The electron holes present in the Ti02 structure are able to promote the oxidative process of substances present in the environment, in particular the ones easily adsorbed on it. Titanium dioxide is a well-known photocatalyst [5-13]. Less famous are its characteristics as sensor material [14-18] of the ability of the organic molecules to be completely degraded, that is mineralized. 

Photocatalysts, based on titanium dioxide, were used for the purification of contaminated soil polluted by oil [442], Commercially produced slurry of titanium dioxide was modified with barium, potassium, and calcium. The experiments were performed under natural conditions in summer months (July and August) applying direct solar-light irradiation. The most active photocatalyst for soil purification was titanium dioxide modified with calcium. 

Semiconductor-based heterogeneous photocatalysts have been interested by a large number of scientists. Titanium dioxide (T1O2), whieh is inexpensive, nontoxic, resistant to photo-corrosion, and has high oxidative power, is the most widely used... 

A number of organic pollutants present in industrial and domestic wastewater resist biodegradation and they are poisonous even at low concentrations. A new method for removing toxicants from wastewater is based on the use of photocatalysis. It was found that titanium dioxide (Ti02) is the best photocatalyst for the detoxification of water because it is cheap, nontoxic and easy to use and handle. The energy gap in Ti02 is 3.2 eV and thus it can be activated at >400 nm. 

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