UV and visible light activated TiO2 photocatalysis of 6-hydroxymethyl uracil, a model compound for the potent cyanotoxin cylindrospermopsin

TiO2 photocatalyses of 6-hydroxymethyl uracil (6-HOMU) a model compound for the potent cyanotoxin, cylindrospermopsin (CYN), were carried out employing visible and UV irradiation using different non-metal doped TiO2 materials, nitrogen and fluorine-TiO2 (NF-TiO2), phosphorus and fluorine-TiO2 (PF-TiO2) and sulfur-TiO2 (S-TiO2). The model compound was readily degraded under UV TiO2 photocatalysis with pseudo-first-order rate constants (k) of 2.1, 1.0, and 0.44 h(-1) for NF-TiO2, PF-TiO2 and S-TiO2, respectively. Under visible light activated (VLA), NF-TiO2 was the most active photocatalyst, PF-TiO2 was marginally active and S-TiO2 inactive. VLA NF-TiO2 was effective and increased the k with increasing pH from 3 to 9. The presence of humic acid (HA), Fe3+ and Cu2+ can enhance the degradation. However, at 20 ppm HA significant inhibition was observed, likely due to shadowing of the catalyst, quenching of ROS or blocking active sites of TiO2. We probed the roles of different reactive oxygen species (ROS) using specific scavengers and the results indicate that O-2(center dot-) plays an important role in VLA TiO2 photocatalysis. Our results demonstrate that NF-TiO2 photocatalysis is effective under UV and visible irradiation and over a range of water qualities. VLA NF-TiO2 photocatalysis is an attractive alternative technology for the CYN contaminated water treatment. (C) 2013 Elsevier B.V. All rights reserved.