Photodegradation of triphenylamino methane (magenta) by photosensitizer in oxygenated solutions.

Reactive oxygen species (ROS), namely superoxide anion (O2*-, singlet oxygen (1O2), are potentially important substances for the mineralization of toxic organic molecules. The utility of hematoporphyrindihydrochloride (HPDHC) as a photosensitizer to generate ROS and their subsequent role in the destruction of magenta (MaG) in aqueous media is the main concern. The light irradiation of oxygenated aqueous solution of HPDHC and 1.5 x 10(-5) mol dm(-3) MaG at pH 3 yielded micromolar levels of NO3(-) ions. A higher rate of photodegradation (1.02 mol dm(-3) min(-1)) at pH 3 was observed compared to that of at pH 6 (0.68 mol dm(-3) min(-1)). Experiments were carried out in the presence of 1,4-diazabicyclo[2.2.2]octane (DABCO) as singlet oxygen (1O2) quencher and bezoquinone (BQ) as superoxide anion (O2*-) quencher. Only BQ was able to stop photodegradation suggesting that the photooxidation of MaG is mainly caused by O2*-, which is generated by an electron transfer from the excited HPDHC to ground-state oxygen. The presence of iron(II) at pH 3.0, compared to that without iron(II), showed a higher rate of photodegradation due to the formation of extremely reactive hydroxyl radicals (HO*) upon dismutation of O2*- anion through H2O2 intermediate. The formation of O2*-, H2O2, and HO* is therefore evident, which may act as active sites for subsequent photodegradation of MaG.