The role of ruthenium photosensitizers in the degradation of phenazopyridine with TiO2 electrospun fibers

Abstract

Abstract There has been increased interest in titanium dioxide (TiO2) fibers as a photocatalyst for the degradation of persistent organic and biopharmaceutical toxins in the environment. The photocatalytic efficiency of TiO2 fibers is typically limited to UV irradiation due to its semiconductor bandgap. TiO2 fibers have been prepared and adsorbed the visible photosensitizer cis-dichlorobis(2,2′-bipyridyl-4,4′-dicarboxylic acid)ruthenium (II) (Ru(dcbpyH2)2Cl2) on the surface in order to absorb from 300 to 800 nm in the visible spectrum and drive photocatalysis. This dye fiber material has been applied to the degradation of 2,6-pyridinediamine,3-(phenylazo) monohydrochloride or phenazopyridine (PAP) as a model biopharmaceutical waste. The Ru(dcbpyH2)2Cl2–sensitized fibers degrade PAP under UV and visible irradiation following a first order reaction rate. The rate constants for PAP degradation in visible light when using bare TiO2 fibers and dye-sensitized TiO2 fibers were 0.014 ± 0.001 min−1 and 0.012 ± 0.001 min−1 respectively, showing little change. Under UV irradiation, the rate decreased from 0.032 ± 0.003 min−1 and 0.012 ± 0.002 min−1. These results suggest that the major pathway for the degradation of PAP may occur through the valence band.