A study of the kinetic solvent isotope effect on the destruction of microcystin-LR and geosmin using TiO2 photocatalysis

We have previously reported the effectiveness of TiO2 photocatalysis in the destruction of species generated by cyanobacteria, specifically geosmin and microcystin-LR. In this paper we report an investigation of factors which influence the rate of the toxin destruction at the catalyst surface. A primary kinetic solvent isotope effect of approximately 1.5 was observed when the destruction was performed in a heavy water solvent. This is in contrast to previous reports of a solvent isotope effect of approximately 3, however, these studies were undertaken with a different photocatalyst material. The solvent isotope effect therefore appears to be dependent on the photocatalyst material used. The results of the study support the theory that the photocatalytic decomposition occurs on the catalyst surface rather than in the bulk of the solution. Furthermore it appears that the rate determining step is not oxygen reduction as previously reported.

Figure optionsDownload as PowerPoint slideHighlights
► Solvent isotope study of photocatalytic degradation of two cyanobacterial species.
► Results indicate photocatalytic process occurs at catalyst surface rather than bulk of solution.
► Scale of isotope effect dependent on photocatalyst employed.
► Rate determining step appears to be substrate degradation and not oxygen reduction.