Ultraviolet light oxidation

The purple color of old bottles exposed to the sun for a long time is due to Mn04 ions. These are formed when ultraviolet light oxidizes manganese compounds in the glass. 

Ho, P. C. 1987. Evaluation of ultraviolet light/ oxidizing agent as a means for the degradation of toxic organic chemicals in aqueous solutions. Chem. Abstr. CA 109(2) 11146x. 

The luminescence properties of the composites, however, can be improved by photocorrosion. In photocorrosion, quanmm dots are illuminated with light above their band gap, typically near ultraviolet light. Oxidation processes are triggered by illumination (19.13) [44—47]. Since surface defects are photooxidized preferentially, photoactivation is a convenient technique to remove such defects and improve the photoluminescence quantum yield. 

When Iodide solutions of macro concentrations were exposed to ultraviolet light, oxidation processes took place and molecular Iodine vias liberated. Oxidation processes, however, could not be detected on Irradiation of carrier-free Iodide-131 solutions In quartz ampoules for 2.5 hours, employing the paper electrophoresis technique for analysis. 

Another factor in oxidative degradation is ultraviolet radiation, of which sunlight is a rich source. The oxidation of parylene appears to be enhanced by ultraviolet radiation. 02one may play a mechanistic role in the ambient temperature exposure of parylenes to ultraviolet radiation in the presence of oxygen. For the best physical endurance, exposure of the parylenes to ultraviolet light must be minimised. 

Scintillation detectors are substances which fluoresce when stmck by x-radiation. Scintillation can, therefore, serve to convert x-ray photons into visible or ultraviolet light. Scintillation materials include thaUium-activatedcrystals of sodium iodide, NaI(Tl), potassium iodide, KI(T1), or cesium iodide, CsI(Tl) crystals of stilbene (a, P-diphenylethylene) [588-59-0] and anthracene [120-12-7] bismuth germanium oxide [12233-56-6] ... 

The diacid components for the manufacture of poly(y -phenyleneisophthalamide) and poly(p-phenyleneterephthalamide) are produced by one of two processes. In the first, the diacid chlorides are produced by the oxidation of / -xylene [108-38-3] or -xylene [106-42-3] followed by the reaction of the diacids with phosgene [75-44-5]. In the second, process m- or -xylene reacts with chlorine initiated by ultraviolet light to form the m- or Nhexachloroxylene. This then reacts with the respective aromatic dicarboxyUc acid to form the diacid chloride. 

Ultraviolet radiation causes cleavage of the aryl ether linkage (23). DMPPO undergoes oxidation when exposed to ultraviolet light and oxygen by direct attack on the aromatic ring to produce a variety of ring-cleaved and quinoidal stmctures (24). 

Silver Fluoride. Silver fluoride, AgF, is prepared by treating a basic silver salt such as silver oxide or silver carbonate, with hydrogen fluoride. Silver fluoride can exist as the anhydrous salt, a dihydrate [72214-21-2] (<42° C), and a tetrahydrate [22424-42-6] (<18° C). The anhydrous salt is colorless, but the dihydrate and tetrahydrate are yellow. Ultraviolet light or electrolysis decomposes silver fluoride to silver subfluoride [1302-01 -8] Ag2p, and fluorine. 

EthylceUulose is subject to oxidative degradation in the presence of sun- or ultraviolet light, especially at elevated temperatures above the softening point. It must, therefore, be stabilised with antioxidants (44). EC is stable to concentrated alkah and brines but is sensitive to acids. 

Hydrogen peroxide can also be activated by ultraviolet radiation or o2one and ultraviolet radiation (178,188,189). One of the most active fields in waste treatment is ultraviolet-cataly2ed oxidation with hydrogen peroxide (190—194). The uv light activates the hydrogen peroxide converting it to hydroxyl radicals (195). 

A combination of ozone oxidation with simultaneous exposure to ultraviolet light seems to produce a self-renewing chain reaction that can significantly reduce the dose of ozone needed to accomphsh oxidation. 

Oxidants commonly used include ozone, permanganate, chlorine, chlorine dioxide, and ferrate, often in combination with catalysts. Standard-type mixed reactors are used with contact times of several minutes to an hour. Special reactors for use with ultraviolet light have been developed. 

Additives used include plasticisers such as diphenyl diethyl ether, ultraviolet light absorbers such as 5-chloro-2-hydroxybenzophenone (1-2% on the polymer) and stabilisers such as phenoxy propylene oxide. 

The commercial polymers are of comparatively low molecular weight (M = 25 000-60 000) and whilst being essentially linear may contain a few branches or cross-links arising out of thermal oxidation. Exposure to ultraviolet light causes a rapid increase in gel content, whilst heating in an oven at 125°C causes gelation only after an induction period of about 1000 hours. Eor outdoor applications it is necessary to incorporate carbon black. The polymers, however, exhibit very good hydrolytic stability. 

There are two ways in which chemicals can protect the skin from ultraviolet light they can either absorb the light or reflect the light. Zinc oxide and titanium dioxide reflect or scatter light of many frequencies, from infrared through ultraviolet. That is why these chemicals appear opaque white. 

Sulfur dioxide is a reducing bleach and can counter the effects of oxidizing bleaches, thus preserving color in fruits dried in the sun. The combination of fruit acids and ultraviolet light would otherwise react with the colorful compounds, making the fruit pale. 

First, oxidizing bleaches such as sodium hypochlorite break the molecules at the double bond. This results in either a shorter molecule that does not absorb visible light, or a molecule whose chromophore is either shorter or nonexistent. A shorter chro-mophore will absorb light of a shorter wavelength than visible light (such as ultraviolet light), and so does not appear colored. 

Vayalil PK, Mittal A, Kara Y, Elmets CA, Katiyar SK (2004) Green tea polyphenols prevent ultraviolet light-induced oxidative damage and matrix metal-loproteinases expression in mouse skin. J Invest Dermatol 122 1480-1487... 

Shindo, Y., Witt, E. and Packer, L. (1993). Anti-oxidant defence mechanisms in murine epidermis and dermis and their responses to ultraviolet light. J. Invest. Dermatol. 100, 260-265. 

Warren, J.B., Loi, R.K. and Coughlan, M.L. (1993). Involvement of nitric oxide synthase in the delayed vasodilator response to ultraviolet light irradiation of rat skin in vriv. Br. J. Pharmacol. 109, 802-806. 

Using the sensor technique for studying photolysis of adsorbed layers of cetene on metal oxides we observed tlie decay of adsorption layers under the influence of ultraviolet light. The reaction yields methylene radicals in the surface layer... 

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