Hydrogen peroxide photodecomposition

Moza, P.N., Fytianos, K., Samanidou, V., and Korte, F. Photodecomposition of chlorophenols in aqueous medium in presence of hydrogen peroxide, Bull. Environ. Contam. Toxicol, 41(5) 678-682, 1988. 

The advanced oxidation process with ozone and UV-radiation is initiated by the photolysis of ozone. The photodecomposition of ozone leads to hydrogen peroxide (Peyton, 1988). Ultraviolet lamps must have a maximum radiation output at 254 nm for an efficient ozone photolysis. 

Photoreduction of ferric ion. Lunck and co-workers observed the enhanced rate of photo-oxidation of salicyclic acid by hydrogen peroxide in the presence of Fe(III) as well as the increased rate of photodecomposition of hydrogen peroxide in the presence of transition metal ions.23 The ferrous ion reacts with hydrogen peroxide, generating a second hydroxyl radical and ferric ion, and the cycle continues. 

Stringer and Attrep compared hydrogen peroxide-sulphuric acid digestion and U.V. photodecomposition methods for the decomposition in water samples of triphenylarsine oxide, disodium methane-arsonate and DMAA to inorganic arsenic prior to reduction to arsine and determination by atomic absorption spectroscopy or by the AgDDC spec-trophotometric method . 

All these results concur to exclude the involvement of hydrogen peroxide as a coproduct of the photo-oxidation of water and intermediate of other photo-oxidation reactions at Ti02. The high rates of its photodecomposition at open circuit and photooxidation under anodic bias render unlikely the build-up of any significant concentration of H2O2 at the surface of irradiated titanium dioxide or in the nearby solution. 

Schrauzer et al. have also investigated the photoreduction of nitrate and nitrite over iron-doped Ti02 under argon and reported that nitrite was reduced to N2, but no reduction of nitrate was observed [59], The photodecomposition of ammonia over iron-doped titania which had been pretreated with hydrogen peroxide was also carried out, and was reported to yield a mixture of nitrate and nitrite [59]. Few details were found for the experiments described in this paragraph. 

Transition metals accelerate the photodecomposition of hydrogen peroxide (photo-Fenton reactions cf. section 5.6). 

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