Semiconductors titanium dioxide

Keywords metal nanoparticles, nanomaterials, photoelectrochemistry, photocatalysis, electrocatalysis, semiconductor, titanium dioxide. 

The prototype of a heterogeneous photocatalytic reaction is based on the irradiation of particles of the semiconductor titanium dioxide (Ti02) in the presence of... 

Several researchers focused on Ti02 nanoparticles and its application as a photocatalyst in water treatment. Nanoparticles that are activated by light, such as the large band-gap semiconductors titanium dioxide and... 

The basic photophysical properties of a dye molecule are maintained upon immobilisation on a semiconductor surface, but the interaction with the semiconductor may open new reactive routes and/or change the rate of particular photochemical processes. An example of the importance of these routes is the fact that some polypyridyl complexes, intrinsically photolabile in solution, become photostable when bound to the semiconductor titanium dioxide, and actually constitute the class of dyes that has enabled some of the most efficient cells constructed to date [4, 5]. 

Fujihira, M., Satoh, Y., and Osa, T, Photoelectrochemistry at semiconductor titanium dioxide/ insulating hydrocarbon liquid interface,/. Electroanal. Chem., 126, 277, 1981. 

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). 

Titanium Sesc uioxide. Ti202 has the comndum stmcture. At room temperature it behaves as a semiconductor having a small (0.2 eV) band gap. At higher temperatures, however, it becomes metallic. This is associated with marked change in the mean Ti—Ti distance. As with TiO, titanium sesquioxide, Ti202, may be made by heating a stoichiometric mixture of titanium metal and titanium dioxide powders at 1600°C under vacuum in an aluminum or molybdenum capsule. 

The most common oxidation state of titanium is +4, in which the atom has lost both its 4s-electrons and its two 3d-electrons. Its most important compound is tita-nium(IV) oxide, Ti02, which is almost universally known as titanium dioxide. This oxide is a brilliantly white (when finely powdered), nontoxic, stable solid used as the white pigment in paints and paper. It acts as a semiconductor in the presence of light, and so it is used to convert solar radiation into electrical energy in solar cells. 

Somasundaram S, Chenthamarakshan CR, Tacconi NR, Ming Y, Rajeshwar K (2004) Photoassisted deposition of chalcogenide semiconductors on the titanium dioxide surface Mechanistic and other aspects. Chem Mater 16 3846-3852... 

All of these uses are based on the behavior of titanium dioxide as a semiconductor. Photons having energies greater than v 3.2 eV (wavelengths shorter than 400 nm) produce electron/hole separation and initiate the photoreactions. Electron spin resonance (esr) studies have demonstrated electron capture by adsorbed oxygen to produce the superoxide radical ion (Scheme 1) (11). Superoxide and the positive hole are key factors in photoreactions involving titanium dioxide reported here are the results of attempts to alter the course of these photoreactions by use of metal ions and to understand better the mechanisms of these photoreactions. 

Polycrystalline GaN UV detectors have been realized with 15% quantum efficiency [4], This is about 1 /4 of the quantum efficiency obtained by crystalline devices. Available at a fixed price, however, their increased detection range may well compensate their lack in sensitivity. Furthermore, new semiconductor materials with a matching band gap appear as promising candidates for UV detection if the presumption of the crystallinity is given up. Titanium dioxide, zinc sulfide and zinc oxide have to be mentioned. The opto-electronic properties and also low-cost production processes for these compound semiconductors have already been investigated to some extent for solar cell applications [5]. 

In the near future, UV photodiodes made from polycrystalline wide band-gap semiconductors may fill the gap in the market. Although they have a lower sensitivity (photocurrent per area) they promise to have a better merit-rating in terms of photocurrent per sensor costs. The other major drawback of polycrystalline photodiodes, the risetime of micro- to milliseconds, is not relevant for household applications. Fuji Xerox Laboratories in Japan are developing visible-blind UV photodiodes made from polycrystalline GaN [12], while twlux AG in Berlin, Germany is developing visible-blind UV photodiodes made from polycrystalline titanium dioxide [13]. A prototype is shown in Fig. 5.45. 

Fujishima and Honda reported the splitting of water by the use of a semiconductor electrode of titanium dioxide (rutile) connected through an electrical load to a platinum black counter-electrode. Irradiation of the Ti02 electrode with near-UV light caused electrons to flow from it to the platinum counter-electrode via the external circuit. 

Since the discovery of photoelectrochemical splitting of water on titanium dioxide (TiOj) electrodes (Fujishima and Honda, 1972), semiconductor-based photocatalysis has received much attention. Although TiO is superior to other semiconductors for many practical uses, two types of defects limit its photoeatalytic activity. Firstly, TiO has a high band-gap (E =3.2 eV), and it can be excited only by UV light (k < 387 nm), which is about 4-5% of the overall solar spectmm. Thus, this restricts the use of sunlight or visible light (Kormann et al., 1988). Secondly, the... 

The antenna effect as it is found in natural photosynthetic systems is an attractive tool for increasing light absorption of solar cells. Some of the work done on dye sensitization of polycrystalline titanium dioxide shows aspects of antenna behavior [76,83-87]. Most of the problems in the systems where an electron is injected into the semiconductor arise in the regeneration process of... 

The Matrix TiOa photocatalytic treatment system is a technology that destroys dissolved organic contaminants in water in a continuous-flow process at ambient temperature. The technology uses ultraviolet (UV) light and a titanium dioxide (TiOa) semiconductor catalyst to break hydroxide ions (OH ) and water (H2O) into hydroxyl radicals (OH ). The radicals oxidize the organic contaminants to form carbon dioxide, water, and halide ions (if the contaminant was halogenated). 

Ti02. - Semiconductor photocatalysis based on titanium dioxide (Ti02)... 

Design and Development of New Titanium Dioxide Semiconductor Photocatalysts... 

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