Degradation heterogeneous systems

A recent experiment compared for the first time pollutant degradation by chemotactic bacteria and nonchemotactic mutants [54]. The result suggested an important role of chemotaxis in the bioremediation of contaminated soils. In a heterogeneous system, in which naphthalene was supplied from a microcapillary, a 90% reduction in the initial amount of naphthalene took six hours with the chemotactic wild-type Pseudomonas putida PpG7, while a similar reduction with either a chemotaxis-negative or a nonmotile mutant strain took about five times longer. Only the systems inoculated with the chemotactic strain exhibited degradation rates in excess of the rate of naphthalene diffusion from the... 

In other words, photonic efficiency is a reaction rate normalised to the photon flow emitted by the light source. It describes how many molecules are transformed per photon incident on the system. Of course a more appropriate parameter to characterise the photochemical activity of heterogeneous systems is the more fundamental quantum yield (, eq. 5.88) of the photoreaction, which expresses (Serpone and Emeline, 2002) the ratio between the rate of molecules formed or degraded in the system, dNJdt (molecules s ), and the rate of photons absorbed by the system. 

Drug degradation in heterogeneous systems such as solids and semisolid states is affected by moisture. The effect of moisture and humidity on the degradation kinetics of various drug substances including ascorbic acid,416-417 thiamine salts,418-419 aspirin,420 vitamin A421 (Fig. 94), and ranitidine hydrochloride,422 to name a few examples, has been reported. 

M. A. Zoglio, H. V. Maulding, R. M. Haller, and S. Briggen, Pharmaceutical heterogeneous systems III. Inhibition of stearate lubricant induced degradation of aspirin by the use of certain organic acids, J. Pharm. Sci. 57, 1877-1880 (1968). 

Certain inorganic materials can be employed as photocatalysts for the synthesis or degradation of compounds in heterogeneous systems. Relevant devices contain, for example, films incorporating immobilized photocatalyst particles. Typically, titania, Ti02, is used for the treatment of water contaminated with chemical pollutants and/or bacteria [9]. The contaminants are oxidized by reactive species, i.e. hydroxyl and superoxide radicals, generated by reaction of electron/hole pairs with O2 and water adsorbed at the particle surface. Electron/hole pairs are formed when UV light (>, <400 nm) is absorbed by titania (see Scheme 14.5). 

The PLA/GA polymer system degrades through a mechanism of bulk heterogeneous degradation.The system can be subdivided into three classes of material, depending on the material s crystallisability (the notation PLAXGAT,... 

The above-mentioned typical temperature-dependent multiple mechanisms were found to occur in the thermal degradation of homogeneous PLLA-Ca. In heterogeneous systems, such as PLLA/metal oxide composites with two... 

The knowledge of conditions under which polymers degrade is essential to avoid and retard corrosion. Chemical properties of macromolecules are essentially those of small molecules only the reactivity is lower and the reaction conditions may be different. For example, polymer degradation caused by corrosive chemicals occurs in heterogeneous systems, since chemicals have to diffuse inside polymer matrices and the rate of diffusion of adverse chemicals depends on the chemical structure of polymers and on conditions such as temperature, humidity, etc. 

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