Photocatalytic degradation of microcystin-LR using TiO2 nanotubes under irradiation with UV and natural sunlight

In order to investigate the catalytic performance of anodic TiO₂ nanotubes and their practical application in the treatment of refractory microcystins (MCs) in natural-water samples, TiO₂ nanotubes of diameter of 50–80 nm were fabricated by anodization in C₂H₂O₄·2H₂O containing NH₄F. Under irradiation with natural sunlight, MC-LR was totally degraded after 1 d using the anodic TiO₂ nanotubes. In contrast, the removal efficiency without TiO₂ nanotubes was as low as 47.7% within 20 d. In addition, a mixture of anatase and rutile TiO₂ gave higher photocatalytic activity than the single phase did. The pH also influenced the adsorption capacity of the TiO₂ nanotubes. The order of MC-LR degradation efficiencies at different pH values was 3.5 > 8.0 > 10.0. After five repeated experiments on the degradation of MC-LR for 7 h, the degradation efficiency was still stable.