ABSTRACT
This chapter evaluates 69 different dyes, stains, and indicators at acidic, neutral, and alkaline pH values for the degradation of bromacil. In dye-sensitized photooxidations, either an oxygen transfer process or a hydrogen-abstraction reaction is involved. In the oxygen transfer process, the excitation of the dye to the singlet state is followed by intersystem crossing to the triplet state. Dye photosensitizers absorb energy in the visible spectral region, and transfer the energy either directly or indirectly to a substrate, which results in the photodecomposition of the substrate. The effects of pH value and different dyes on reaction rates were determined by testing 69 potential photosensitizing agents at pH values of 4, 7, and 10. The photosensitizing action of dyes results from the ability of dyes to act either as strong oxidizing or as strong reducing agents, in the presence of reducing or oxidizing substances, with subsequent regeneration.
