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

摘要

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-TiO_2 thin film, prepared by solgel and dip-coating method, with low UVA intensity irradiation. Analysis resules from SPE(solid-phase extraction) combined with HPLC method showed that Microcystin-LR whose initial concentration (pg/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 percent of 20 pg/L Microcystin-LR was decomposed within 120 min under 400 mu W/CM~2 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 mu W/cm ~2 and initial concentration=20 mu g/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 mu W/cm~2, the degradation rate increases with incident intensity to the 0.82 power and the corresponding apparent quantum yield (psi_(app)) was found to be 5.19 X 10~(-8) g/J approximately.