Hydrogen peroxide production photocatalytic

FIGURE 7. Results of addition of 200 iL of 30% hydrogen peroxide solution to a steady-state photocatalytic reaction. Observed flow of products in mLymin of CH3OH (-----—-), O2... 

Catechol and hydroquinone by-products were also detected in the photocatalytic destruction of nitrophenols [117]. Ninety-nine percent destruction of 4-nitrophenol was achieved within 3 h, although for complete mineralisation up to 9 h irradiation was necessary. The presence of oxygen not only affected the level of mineralisation of the nitrophenol but also the extent of denitration, believed to be the major initial step of the photocatalytic process. Hydrogen peroxide was reported to significantly improve the rate of photocatalytic process increasing the destruction rate by up to 3 fold. Addition of Cu ions, however, had a detrimental effect [118]. 

As shown in the photocatalytic cycle, the continuous production of hydroxyl radicals as well as the presence of hydrogen peroxide leads to the oxidation of the organic pollutants and also of the generated by-products. This phenomenon permits, in many cases, the total mineralisation of the solution [89]. 

---