Will low pressure mercury UV lamp produce a different degradation pathway (and intermediates) for the photolysis degradation of Methylene Blue as compared to high pressure mercury UV lamp?
I would say that the high pressure Hg lamp could result in different pathways as compared to the low pressure lamp.
The high pressure mercury UV lamp will generate more degradation pathways than the low pressure lamp.
Has there been any articles published on these effects? If so, pls share. Thankyou
Omotayo, are you saying that degradation with the low pressure lamp will reach mineralization earlier than high pressure lamp due to the low pressure lamp having less degradation pathways than the high pressure lamp for the same target pollutant?
The answers could be a bit more detailed. I think the answers consider primary photolysis and are based on that medium pressure lamps produce photons in a broad spectrum of wavelengths and therefore it is likely to transfer many different energy doses compares to the discrete spectra from a low pressure lamp (192, 254, 365 nm).
If methylene blue was able to absorb light at a wavelength that the low pressure lamp doesn't emit and this absorption could lead to a different photodegradation product than the low pressure lamp could produce from reactions at the few wavelengths it produces we could expect to see more different degradation products from photodegradation with a medium pressure lamp.
After a few photolysis reactions the degradation products will likely not contain any chromophores so direct photolysis will cease. If the lamps are made with super pure quartz there will be secondary photolysis there low wavelength photons photolyse water to produce hydroxyl radicals that can degrade the products further until mineralisation. There is no difference between hydroxyl radicals produced by low or medium pressure UV lamps.
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