The photolysis of hydrogen peroxide

When hydrogen peroxide is formed in the photo-oxidative degradation of polymers it is also necessary to take into account the secondary reactions due to its photolysis. 

The quantum yield for the decomposition of aqueous solutions of hydrogen peroxide at X = 2537 A is j = 0.94, while in the presence of allyl alcohol the yield is 0 = 0.54 [299, 644]. The main reaction is 

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The stoichiometric yield of OH0 is the greatest from the photolysis of hydrogen peroxide. But - as already mentioned - the photolysis of ozone yields more OH0 than that from hydrogen peroxide because of the higher molar extinction coefficient of ozone compared to hydrogen peroxide (see Table 2-3). 

Baxendale, J.H. and Wilson, J.A., The photolysis of hydrogen peroxide at high light intensity, Trans. Faraday Soc., 53, 344-356, 1957. 

Nitrate photolysis is a relevant source of hydroxyl in natural waters. A study carried out on the Greifensee Lake water indicates that nitrate photolysis is a much more important source of hydroxyl when compared with the photolysis of hydrogen peroxide or the Fenton reaction [12]. Nitrate photochemistry can thus lead to a steady-state hydroxyl concentration around 5 x 10 16 M [8]. 

Other peroxygen species can also be photolytically cleaved to yield the hydroxyl radical and another radical centre. For example, homolysis of peroxymonosulfate (HOOSO3) generates OH and SO4-. The concentration of the generated hydroxyl radical can be controlled by variation of the wavelength and the intensity used. The photolysis of hydrogen peroxide in the presence of alcohol produces EPR (electron paramagnetic resonance) spectra which indi-... 

Secondary radicals may be formed by reaction between primary radicals and solvent. Thus hydroxyl radicals are produced by the photolysis of hydrogen peroxide in an isopropanol glass . At 110° K a seven-line spectrum, with intensities of 1 6 15 20 15 6 1, was observed. Such a structure is to be expected from an unpaired electron which interacts equally with six protons, and since it is known that there is no interaction with the proton of the -OH group in alcohol radicals, the spectrum suggests that the radical is (CH3)2COH. 

The rate coefficients for the gas-phase reaction of OH radicals with dimethyl sulphide were determined using a relative rate method. The kinetic experiments were performed at a total pressure of 1000 mbar diluent gas (N2, synthetic air, or N2/O2 mixtmes), at three different O2 partial pressure ( 0 mbar, 205 mbar, and 500 mbar) and six different temperatures (250 K, 260 K, 270 K, 280 K, 290 K, and 299 K). The photolysis of hydrogen peroxide (H2O2) was used as the OH radical source ... 

The hydroxy radical, which can be formed either by the photolysis of hydrogen peroxide and per-acid, by Reaction 5, or by non-terminating... 

Hydroxyl radicals can also be produced by the photolysis of hydrogen peroxide, however, this process is not efficient since the absorption of H2O2 > 300 nm is very small. Thus nitrate photolysis would appear to be the major source of hydroxyl radicals in surface waters. 

Matsuura, T. and K. Omura. 1966. The hydroxylation of phenols by the photolysis of hydrogen peroxide in aqueous media. J. Chem. Soc. Chem. Commun. 127-128. 

Hydrogen peroxides are key intermediate products in the degradation of plastics molecules. The photolysis of hydrogen peroxide groups leads to primary or secon-... 

The classic photoreaction within photo-oxidative degradation is the photolysis of hydrogen peroxides. Also known in organic photochemistry are photo-induced reactions such as Norrish type I and Norrish type II reactions that result in cleavage of the carbon structure and thus to a loss in molecular weight, Figure 5.12 [381. 

Strong evidence in favor of mechanism B was obtained when it was discovered that singlet oxygen produced chemically by the reaction of hydrogen peroxide and sodium hydrochlorite or from gaseous oxygen excited by an electrodeless discharge yields the same products as the direct photolysis/85-8 ... 

Hambly, D.M. Gross, M.L. Laser flash photolysis of hydrogen peroxide to oxidize protein solvent-accessible residues on the microsecond timescale. J. Am. Soc. Mass Spectrom. 

The absence of hydrogen peroxide in photolysis in static systems and the low-quantum yield of water decomposition may be explained by vari-... 

Stefan, M.I., Hoy, A.R., and Bolton, J.R., Kinetics and mechanism of the degradation and mineralization of acetone in dilute aqueous solution sensitized by the UV photolysis of hydrogen peroxide, Environ. Sci. Technol., 30, 2382-2390, 1996. 

Reactions of ozone can be initiated by HO or HOO or by photolysis of hydrogen peroxide. Ozone can also be decomposed through the following reaction pathways ... 

It was previously noted that no evidence for direct photolysis for PFOS or PFOA has been observed experimentally. In aqueous solutions alone and in the presence of hydrogen peroxide (H2O2), iron oxide (Fe203) or humic material, PFOS has been observed to undergo some indirect photolysis [28] whereas PFOA did not undergo indirect photolysis [29]. Using an iron oxide photo-initiator matrix model, the indirect photolytic half-life for PFOS was estimated to be > 3.7 years at 25 °C. The half-life of PFOA was estimated to be > 349 d. 

Fluorophores are another type of trace moiety that is lost through photolysis (Pullin and Cabaniss, 1997 Langford and Bruccoleri, 2000). The decrease in fluorescence by photolysis is confirmed by the observation that the fluorescence intensity per mg DOC is a good indicator of the production of hydrogen peroxide from DOM photolysis in a wide range of freshwaters (Scully and Lean, 1994). As discussed above, the relative fluorescence intensity of the fulvic acid fraction is fairly simple to measure. Furthermore, measurement of FI and/or 813C may allow for differentiation between a decrease in fluorescence intensity per mg C due to mixing with fulvic acid from microbial material and a decrease due to photolysis. 

Photolysis irradiated by UV at 290 nm in the presence of hydrogen peroxide and titanium dioxide, respectively, in aqueous solution resulted in 29% and 84% transformation in 2.5 h (Moza et al. 1994). 

Another possible mechanism of photolysis is through the formation of secondary photooxidants that can be formed from one of the photosensitizer routes shown above. For example, a possible mechanism with humic substances as photosensitizers [90] could involve the formation of hydrogen peroxide and, subsequently, hydroxyl radicals ... 

Photolysis of hydrogen peroxide was first studied by Baxendale and Wilson [99]. They reported that the decomposition of 1 mol of hydrogen peroxide needed one Einstein of incident 254 nm UV radiation ... 

Lipczynska-Kochany E. Degradation of nitrobenzene and nitrophenols in homogeneous aqueous solution. Direct photolysis versus photolysis in the presence of hydrogen peroxide and the Fenton reagent. Water Pollut Res J Can 1992 27 97-122. 

Figure 3. Effect of MWCNT on a) amount of hydroxyl radicals generated by photolysis of hydrogen peroxide, measured by ESR/spin trapping technique b) amount of superoxide radicals generated by a xantine/xantine oxidase system, measured by UV spectroscopy. Light gray bars no NT, dark gray bars in the presence of NT.31...

Fenton type reactions are particularly important in atmospheric waters [10], which are acidic. An additional source of hydroxyl radical that is significant only when using UV light of wavelength shorter than about 300 nm (i.e. in the case of water treatment using UV lamps, but not for sunlight) is represented by photolysis of hydrogen peroxide ... 

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