Photocatalytic degradation of trace-level of MicrocystinLR by nano-film of titanium dioxide

The occurrence of toxic water bloom of cyanobacte-ria algae, widely reported in eutrophic freshwater, hasbeen a serious pollution problem in recent years1]. Mi-crocystins (MCs), the most common cyanobacteriatoxin with a cyclic heptapeptide structure (Fig…

Photocatalytic degradation of trace-level of Microcystin-LR by nano-film of titanium dioxide

Microcystins, a group of hepatotoxin produced by cyanobacteria in eutrophic freshwater, have proven unreliable to be removed by conventional treatments. In this study, the photocatalytic degradation experiments of Microcystin-LR were conducted using nano-TiO₂ thin film, prepared by solgel and dip-coating method, with low UVA intensity irradiation. Analysis results from SPE (solid-phase extraction) combined with HPLC method showed that Microcystin-LR whose initial concentration (μg/L) around that occurs naturally was easily to be removed by photocatalytic system. The degradation efficiency of toxin was influenced by the pH conditions, initial concentration and UV intensity. The maximum initial rate of photocatalytic degradation occurred at pH 4 and over 95% of 20 μg/L Microcystin-LR was decomposed within 120 min under 400 μW/cm² UV illumination. The kinetic equations and parameters revealed that degradation reaction of trace level MC-LR, which was depicted by Langmuir-Hinshelwood kinetics model, was in accordance with pseudo first order kinetics process in appearance well. Under the condition of pH=6.7, irradiation intensity=400 μW/cm² and initial concentration=20 μg/L, the corresponding pseudo-first-order rate constant k and half-life were determined to be 0.0157 min⁻¹ and 44 min, respectively. During the range of 200–1000 μW/cm², the degradation rate increases with incident intensity to the 0.82 power and the corresponding apparent quantum yield (Φ _app) was found to be 5.19×10⁻⁸ g/J approximately.