Photodegradation methylene blue

Photolysis of nicotine (173) in the presence of oxygen and methylene blue with light wavelengths greater than 300 nm gave the pyrrolidone (174, 30%), nicotyrine (175, 23%) and TV-oxide (176, 7%). Under nitrogen, with eosin as photosensitizer, only nicotyrine (14%) was identified in the photodegraded mixture [112]. 

Photolytic. When a dilute aqueous solution (1-10 mg/L) of bromacil was exposed to sunlight for 4 months, the TV-dealkylated photoproduct, 5-bromo-6-methyluracil, formed in small quantities. This compound is less stable than bromacil and upon further irradiation, the de-brominated product, 6-methyluracil was formed (Moilanen and Crosby, 1974). Acher and Dunkelblum (1979) studied the dye-sensitized photolysis of aerated aqueous solutions of bromacil using sunlight as the irradiation source. After 1 h, a mixture of diastereoisomers of 3-5ec-butyl-5-acetyl-5-hydroxyhydantoin formed in an 83% yield. In a subsequent study, another minor intermediate was identified as a 5,5 -photoproduct of 3-5ec-butyl-6-methyluracil. In this study, the rate of photooxidation increased with pH. The most effective sensitizers were riboflavin (10 ppm) and methylene blue (2-5 ppm) (Acher and Saltzman, 1980). Direct photodegradation of bromacil is not significant (Acher and Dunkelblum, 1979 Ishihara, 1963). 

Color additives have been reported to also either enhance drug photodegradation or protect against it. Erythrosin, eosine, role bengal, methylene blue, azure A, and azure B accelerate the photodecomposition of pyridoxine hydrochloride and pyridoxamine HCl (26). Erythrosine was found to enhance the decomposition of phenylbutazone when irradiated with unfiltered light from a 300 W projector bulb, but was stable in the absence of the dye (27). Certain dyes such as methylene blue have been found to enhance the photostability of solutions of daunorubicin (87). 

Preliminary experiments on such a strategy of coupled separation and photodegradation were carried out on a simplified experimental device schematically represented in Figure 25.15a. It consists of two tanks separated by a 1.8 pm pore size alumina microfiltration symmetric membrane with grains coated with an anatase layer. The feed tank contained methylene blue (MB) and the reception tank was initially filled with pure water. Under continuous UV irradiation, MB is completely destroyed as it arrives in the reception tank (Figure 25.15b). The quantity of destroyed MB per surface area unit is equal to 1.0 X 10 mol.s. m . 

FIGURE 25.15 Preliminary experiments on coupling separation and photodegradation (a) experimental dialysis device (b) methylene blue concentration versus time in the reception tank. P70 and F67 are two types of anatase coatings. (From Bose, F., Ayral, A., and Guizard, C., in Proceedings of the ICIM8, J. Lin, Ed., Cincinnati, OFI, 2004.)... 

Photodegradation of methylene blue Soda-lime wafers Combined mercury-xenon arc lamp [19]... 

Photodegradation of methylene blue Microcharmel ceramic disk High-pressure mercury lamp [20]... 

Polydiacetylenes dissolved in common solvents such as tetrahydrofuran, CHCI3, CH2CI2, CCI4 are bleached very rapidly during UV irradiation due to chain scission [1561, 1824], The loss of effective conjugation causes a decrease of photoconductive properties. The photodegradation is accelerated in the presence of photoinitiators such as 2,2 -azobisisobutronitrile, benzo-phenone, anthraquinone and in the presence of dyes such as methylene blue and rhodamin 6G [1524, 2264],... 

The photocatalytic activities of TiOa particles with and without Pt nanoparticles were estimated based on the photodegradation reaction of methylene blue. A methylene blue aqueous solution (20 p,M, 20 mL), including TiOa particles with/without Pt nanoparticles (5 mg), was irradiated with UV light (300-350 nm, 10 p,W cm ) for 30 min, and the absorption spectra before and after UV irradiation were measured (Fig. 6.10). The photocatalytic activity of each sample was also estimated using Eq. (6.1). 

These results suggest that smaller Au nanoparticles lead to larger electronic-state changes, which in turn may exert a strong effect on the photocatalytic activities. Therefore, these were measured based on the photodegradation reaction of methylene blue. The experimental details are described in the Sects. 6.3.2 and 6.4.4. 

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