Tetrakis-2,3-[5,6-di-(2-pyridyl)-pyrazino]porphyrazine, and its Cu(II) complex as sensitizers in the TiO2-based photo-degradation of 4-nitrophenol

The tetrapyrrolic macrocycle tetrakis-2,3-[5,6-di-(2-pyridyl)-pyrazino]porphyrazine, [Py8TPyzPzH2], and its copper(II) derivative, [Py8TPyzPzCu] were used as sensitizers adsorbed on TiO2 (anatase) particles for the UV (300–400 nm) photo-degradation of 4-nitrophenol (4-NP) in water suspensions. A 3.5-fold increase of photocatalytic power over bare TiO2-anatase has been observed in the case of the Cu(II) complex and of more than a factor of two for the free base. Compared with previous data obtained with anatase samples impregnated with some structurally similar porphyrins and phthalocyanines derivatives, these results represent a significant improvement. On the contrary, upon impregnation with [Py8TPyzPzCu], both TiO2-rutile and TiO2-Degussa P25 did not show any improvement of their photocatalytic efficiency. Experimental evidences indicate that formation of singlet oxygen does not contribute to the beneficial effect of the macrocycles. Hydrogen peroxide was found not to participate to the 4-NP depletion. Some photo-bleaching of the adsorbed dye has also been observed.