Photodegradation efficiency

PAHs adsorbed on particles of carbon black were also photostabilized (Behymer and Hites, 1988). However, Barofsky and Baum (1976) demonstrated that BaP, anthracene, BaA, and pyrene deposited on carbon microneedle field desorption emitters and exposed to UV radiation were all photooxidized to carbonyl compounds. Similarly, PAHs can photodegrade efficiently in air when adsorbed to substrates of silica gel, alumina, or glass plates (e.g., see Lane and Katz, 1977 Kormacher et al., 1980 Behymer and Hites, 1985 Yokely et al., 1986). 

It was proposed that the temperature dependence of polymer 5 arises from the temperature dependence of the kA step. Specifically, it was suggested that the polymer segments to which the radicals are attached are conformationally stressed. There are two possible modes for the newly formed radicals to relax and become separated They can rotate or recoil away from each other (Scheme 9). These secondary motions of the polymer arise from the relaxation of unfavorable bond conformations that are formed during the polymer casting process. The increased thermal energy facilitates the rotation and recoil relaxation processes, which effectively increases the rate constant for diffusion of the radicals out of the cage, kA. This leads to decreased radical-radical recombination and consequently an increase in photodegradation efficiency. 

The pH value affects the UV photodegradation efficiency. From the same concentration of initial sugar solution, the absorbance obtained is greater for alkaline pH than for neutral or acidic pH. Thus, an isosbestic point is found in the pH series of the absorption spectra (Fig. 73). Alkaline conditions are needed for solutions containing low sugar concentrations. However, for solutions with high sugar concentrations, it is still better to use alkaline conditions because this reduces the analysis time. 

Irradiation time (h) % Decolourisation Final COD (mg /1) Photodegradation efficiency (%) ... 

A new hybrid Cu"porphyrin-ZnO system has been recently evaluated as a photocatalyst for the photodegradation of rhodamine B, both under UV-vis and visible light. The system displayed higher photodegradation efficiency than bare ZnO, maintaining the photocatalytic activity over several recycles. This makes Cu°porphyrin-ZnO a promising photocatalyst for future applications. ... 

Considering all of the mentioned findings regarding the synthesis of photocatalysts by coprecipitation of the ZnAl-LDH and impregnation of TiO onto thermally activated LDHs, it could be concluded that the developed synthesis method enables favorable interactions among active phases. This synthesis method demonstrates that proper thermal history - thermal activation of LDHs enables formation of stable photocatalytic systems with high photodegradation efficiency. 

Apparition of peroxi radicals is a rapid stage controlled by oxygen diffusion in the polymer bulk. Photodegradation efficiency during propagation is related to the rate of hydroperoxide decomposition and to their capacity of generating new free oxi- and peroxi- radicals, as given in relation (13) ... 

The photodegradation kinetics and mechanism of clacyfos (HW02) in the organic solvents were studied at 25 °C under the irradiation of ultraviolet light. Photochemical reaction of clacyfos in organic solvents such as n-hexane, methanol, xylene, and acetone under UV light could be well described by the first kinetic equation, and the photodegradation efficiency decreased with a order of n-hexane > methanol > xylene > acetone (Fig. 8.3). 

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