Vacuum-UV Oxidation The H2O-VUV AOP

Unlike the H2O2-UV process the VUV oxidation of organic substrates in water (H2O-VUV) is initiated by the photochemical homolysis of water producing a series of reactive species (cf Fig.s 5-9 and 7-3, and Equations 5-18 to 5-20). In many cases water itself is the prominent absorber of VUV radiation at 172 nm (cf Ex- 

550 cm (cf Chapter 3-9). Thus, the penetration depth of 172 nm radiation into water is very low (cf Example 3-9) and total absorbance (AJ7 2) of radiation occurs within an aqueous layer with a thickness of less than 0.1 mm. 

Example 7-1 The (decadic) absorption coefficient of absolute methanol a(CH30H) at X of 172 nm is about 4000 cm (Weeks et al, 1963). Calculate the portion of 172 nm radiation that is absorbed by methanol in an aqueous solution containing 0.11 mol of methanol (with [CH30H]pure = 24.56 mol M=32.04 gmoh, p=0.787 kg then = aJ, oj3/[CH30H]pure= 163 L moh cm ) refer to Example 3-9. 

In the H2O-VUV AOP no additional auxiliary oxidants must be used to produce sufficient amounts of OH radicals. The technical development of incoherent exci-mer VUV and UV sources of electromagnetic radiation (see Chapter 4.3) led to a renaissance of research related to water photolysis. Hence, the experimental conditions and results of several recent investigations that deal with the applications of VUV and UV incoherent excimer lamps in the field of AOP research (mainly in aqueous media) are briefly summarized in Tab. 7-2. 

Substrate Excimer light source Pe//W Irradiated volume V/L [cJ IrngL- Analytical method Rrferences 

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