Pathway Analysis Of Photocatalytic Of Microcystins

With the grave concern of pollution and eutrophication degree of fresh water, algal bloom has become more and more serious. The potent toxin microcystin is frequently released during cyanobacterial blooms in eutrophic waters and may impose a risk to human health and environment. The usual microcystins in China are MC-RR and MC-LR. This thesis discusses microcystins'optimized conditions of the extraction period and a fast analysis step is measured by using High Performance Liquid Chromatography; meanwhile, the degradations of MC-LR and MC-RR are studied under natural condition. Taking water sample during the eutrophication period in Taihu lake, it optimizes the conditions of chlorophyll, pH, irridation intensities, light wavelengths. It also focuses on the influence of different light sources through quantum yield. This thesis discusses the pathway and products of Microcystins of pigment concentrations to the photocatalytic degradation.After irritation with sunshine, the results show as follows: The results showed that chlorophyll was a key factor on photocatalytic degradation of MCs, and the degradation level was positively correlated with the concentration of Chlorophyll. With the occurrence of 0.1 mg·mL-1 chlorophyll, over 95% of MCs was degraded after 30 minutes'sunlight irradiation, while with the aid of 0.05 mg·mL-1 and 0.01 mg·mL-1 chlorophyll, only 65% and 56% of MCs was removed. The ultraviolet region (200～300 nm) of the sunlight plays a dominant role in photocatalytic degradation of MCs, and 240 nm was the optimal wavelength for optical excitation and photocatalytic degradation of MCs. The light intensity was also an important factor in MCs photocatalytic degradation, as a higher light intensity resulted in a higher removal ratio and removal rate of MCs.The oxidation kinetics of MC-LR and MC-RR was investigated in detail using chlorophyll according to the method of the law of isolated parameter. Experimental results indicated that the oxidation process was first order with respect to reactants in three actions of chlorophyll oxidation MC-LR, MC-RR. At pH 7.52 and 20℃, the rate constant k as follow, k2(MC-LR)0.0248 L/(mol·min)(R2 = 0.9792) , k2(MC-RR) 0.0185L/(mol·min)(R2=0.9731), respectively.It is discussed on the pathway and products of photocatalytic degradation of MCs using liquid chromatography - mass spectrometry. The results show that three pathways are concluded in the degradations, some products are found, which turn to CO2 and H2O in the end.