Photocatalytic Degradation of Microcystin-LR and Off-Odor Compounds in Water under UV-A and Solar Light with a Nanostructured Photocatalyst Based on Reduced Graphene Oxide–TiO₂ Composite. Identification of Intermediate Products.

Microcystin-LR (MC-LR) is the most common and toxic variant of the group of microcystins (MCs) produced during the formation of harmful cyanobacterial blooms. Geosmin (GSM) and 2-methylisoborneol (MIB) may also be produced during cyanobacterial blooms and can taint water causing undesirable taste and odor. The photocatalytic degradation of MC-LR, GSM, and MIB in water under both UV-A and solar light in the presence of reduced graphene oxide–TiO 2 composite (GO–TiO 2 ) was studied. Two commercially available TiO 2 materials (Degussa P25 and Kronos) and a reference TiO 2 material prepared in the laboratory (ref-TiO 2 ) were used for comparison. Under UV-A irradiation, Degussa P25 was the most efficient photocatalyst for the degradation of all target analytes followed by GO–TiO 2, ref-TiO 2, and Kronos. Under solar light irradiation GO–TiO 2 presented similar photocatalytic activity to Degussa P25, followed by Kronos and ref-TiO 2 which were less efficient. Intermediate products formed during the photocatalytic process with GO–TiO 2 under solar light were identified and were found to be almost identical to those observed by Degussa P25/UV-A. Assessment of the residual toxicity of MC-LR during the course of treatment with GO–TiO 2 showed that toxicity is proportional only to the remaining MC-LR concentration. The photocatalytic performance of GO–TiO 2 was also evaluated under solar light illumination in real surface water samples, and GO–TiO 2 proved to be effective in the degradation of all target compounds.