Clay minerals irradiation

Halmann and Aurian-Blajeni115 also examined C02 reduction by irradiation either with sunlight or a high-pressure Hg lamp of aqueous suspensions of various oxide semiconductors (i.e., Ti02, Fe203, W03, ZnO, and nontronite, an ion-containing clay mineral). 

Decabromodiphenyl ether (BDE-209) is a major industrial product from the polybrominated diphenyl ethers used as flame retardants derivatives of this product have been detected in the environment. After exposure to the land surface, these contaminants adsorb on soil materials and may reach the atmosphere as particulate matter these particulates are subsequently subject to photolytic reactions. In this context, Ahn et al. (2006) studied photolysis of BDE-209 adsorbed on clay minerals, metal oxides, and sediments, under sunhght and UV dark irradiation. Dark and light control treatments during UV and sunlight irradiation showed no disappearance of BDE-209 during the experiments. Data on half-lives and rate constants of BDE-209 adsorbed on subsurface minerals and sediments, as determined by Ahn et al. (2006) and extracted from the literature, are shown in Table 16.6. 

Fig. 16.19 GC-ECD chromatograms showing appearance of polybrominated diphenyl ether (PBDE) congeners, after sunlight irradiation of BDE-209 (retention time = 88.7 min) adsorbed on montmorillonite, at different times. Reprinted with permission from Ahn MY, Filley TR, Jafvert CT, Nies L, Hua I, Bezares-Cruz J (2006) Photodegradation of decabromodiphenyl ether adsorbed onto clay minerals, metal oxides, and sediment. Environ. Sci. Technol. 40 215-220. Copyright 2006. American Chemical Society...

The clay mineral or mixture was reacted with NaOH for about 20 minutes and then placed in a drying oven at 105 for 5 to 30 minutes to reduce the moisture content. The sample was then removed from the oven, filtered, water washed, and air dried. In a few experiments the caustic-treated clay mixture was filtered to remove excess moisture and then placed in the drying oven the sample was again filtered and water washed. These two sets of experiments evaluated the effect of the treatment steps prior to microwave irradiation. 

The clay mineral or mixture was reacted with the aqueous NaOH solution for about 20 minutes at room temperature and then was irradiated in a Microwave Drying/Digestion System (Model MDS-81, GEM Corporation, P. 0. Box 9, Indian Trail, N.C. 28079) at 500 watts (2.45 GHz) for 30 seconds to 3 minutes. The sample was then filtered, water washed, and air dried. 

The results of experiments in which binary and ternary mixtures of the three clay minerals were reacted with 30% NaOH and irradiated in the microwave oven are summarized in Tables IV and V, respectively. Reacting mixtures of these clay minerals did not result in the... 

The reactions between clay minerals, NaOH solutions, and micro-wave irradiation showed that the clay mineral structures began to break down, and the released Al and Si (and some K) combined with Na from the solution to form new minerals. The exact reaction path could not be determined from the present experiments. Since the new minerals formed had approximately the same Al Si ratio as the clay minerals, no excess Al (as AI2OJ or Al(OH)g) or quartz was expected, nor was any found in the XRD pattern. The following equations, arranged with increasing time, seem most reasonable to describe the reactions observed for kaolinite and illite ... 

It has been found that dihydropyrimidines are converted to the corresponding pyrimidines by irradiation with ultraviolet light in the presence of water vapor. The reaction is catalyzed by clay minerals, particularly montmorillo-nite, and an evaporating pond environment has been suggested as a reasonable prebiotic locale for such a reaction (Chittenden and Schwartz, 1976). If acetate salts are added to the system, thymine is formed in addition to uracil, presumably by addition of a methyl radical (Schwartz and Chittenden, 1977). An alternative route to thymine involves the addition of formaldehyde to uracil and subsequent reduction by formic acid (Choug-huley et al., 1977). (Formic and acetic acids are major products of the Miller experiment and are probably also abundantly formed from CH4—N2 mixtures.)... 

Aluminas, silicas, clays, zeolites or graphite can be selected as acidic, basic or neutral supports, depending on the type of reactions. Alumina alone can act as a base towards a acid compounds but if a strong base is necessary, KF on alumina can ionize carbon acids up to pKa = 35. On the other hand, montmorillonites (clays) such as K10 or KSF offer acidities very comparable to strong mineral acids (e.g., nitric and sulfuric acids, respectively). Reactions are simply performed by mixing reagents and a mineral support in the absence of any organic solvent followed by microwave irradiation [52]. 

The present mineral experiments were designed to look at the mineralogical changes that occur as clay components are subjected to each step in this process. The microwave irradiation step in our experiments, however, was not entirely comparable to that in the GE experiments because a smaller, 500-watt unit was used while the 2.0-kW unit was being constructed. Future experiments in our laboratory will monitor clay reactions at higher microwave power levels. 

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