Study On Photocatalytic Degradation Process Of Azo Dye Congo Red In Water

The wastewater from printing and dyeing plant is one of the well known problem to deal with in the world. The traditional process for treatment of these effluents (such as active sludge biochemical process) has proved to be insufficient and even to be possible of producing potentially more hazardous aromatic amines under anaerobic conditions. The photocatalytic degradation of dyeing wastewaters is regarded as an ideal method with high efficiency and low cost. The use of heterogeneous photocatalytic oxidation (PCO) for wastewater treatment has been subject to a wide range of investigations during the past decade. But, because of the complexity of the dye molecule, there has been short of detailed comprehension in its photocatalytic degradation process. The key problem is difficult to detect the intermediates clearly. In this paper, the photocatalytic degradation of azo dye Congo red in water solution was investigated on UV irradiating TiO2 in the homemade reactor. The optimization conditions were determined and then the rate of decolorization, COD decrease, yield of CO2 and varies pH of aqueous solution during illumination were detected; The varies of the possible intermediates during degradation process were monitored with UV-VIS spectrum and HPLC. The possible mechanism of Congo red photocatalytic degradation is discussed combined with the data of MS. The results of experiences indicated that, (1) In addition to a prompt removal of the colors, TiO2/UV-based photocatalysis was able to deepen oxidize the dyes, with a complete mineralization of carbon into CO2. The reaction conditions have obvious effects on the rate of Congo red photocatalytic degradation. The high efficiency is achieved under the reaction conditions with 80 ml/min of O2,1.5 g/l of TiO2,16 W of light intensity and normal pH in solution. (2) The rate of decolorization in different concentration is different, but the fast decrease of COD is occurred after decolorization in common. Congo red was photocatalytically degradated by the two steps as follow: decolorization and mineralization, and mineralization occurred after decolorization. The yield of CO2 and varies pH of aqueous solution during degradation are also confirmed this conclusion. The solution was acidified along with the decolorization, some acid substances were accumulated during decolorization and then destructed during mineralization. (3) Through the study on the variation of UV-VIS spectrum and HPLC spectrometer, we find some intermediate products, and following the progress of the photodegradation, the intermediates are increasing firstly and then disappear gradually at last. It attests to the conclusion too. The possible photodegradation pathway of Congo red is described through the detection of intermediate with HPLC and MS.The innovation of this paper is as follow: The establishment of HPLC analytic method is a breakthrough in the study of photodegradation process; Overcoming the disadvantage of single analytic method—decolorization analysis in the study of photodegradation of dyes, The photodegradation process of azo dye is systematic research by multi-analytic method, and the general degradation process which is decolorization firstly and then mineralization is bring forward. This study deepen understand of the degradation mechanism, and has a well deserved its practical applications.