Photodegraduation Of Methyl Orange By LiFeO₄ And Oxalic Acid/Tartaric Acid

Azo dyes are typical environment pollutants which are severly toxic to humans. However, they have been widely used in textiles and leather products to meet the demand of industries.There are more than 2000 azo dyes with different structure in the word. Over 15% of the total world production of dyes is lost during the dyeing process and is released in the textile effluents as industrial wastewater into the environment. Owing to its complex structure, high chromaticity and poor biodegradability, traditional treatments for removal of dyes are not efficient. Therefore, the degradation of azo dyes for environmental treatment is receiving increasing attention. Photocatalytic degradation is considered to be a greener, favored, and cleaner technology for the removal of toxic organic pollutants from wastewater. In this paper, methyl orange was photodegradated by LiFeO4 and oxalic acid/ tartaric acid, and their reaction mechanism and impact factors were studied. The thesis includes two parts.In Part I:The possible reaction mechanism and influencing factors of the photodegradation of methyl orange (MO) by LiFePO4-tartaric acid system were studied through batch experiments in a pH range of 3.0 to 11.0 at 25℃. The results showed that the photodegradation of MO could be markedly accelerated when LiFePO4 and tartaric acid existed under ultraviolet light irradiation. The degradation rate of MO in LiFePO4-tartaric acid system was much higher than in the system of LiFePO4 or tartaric acid alone. Initial concentration of LiFePO4 and tartaric acid, pH, illumination strength, temperature played a important role in this process. When the initial concentration of MO was changed in the system of 250 mg·L-1 LiFePO4 and 5 mmol·L-1 tartaric acid solution under ultraviolet light irradiation, the degradation rate constants were almost the same value, which is a characteritics of zero-order kinetic.When the initial concentration of MO was 50 mg·L-1, 94% of MO was removed whthin 35 min.In Part II:The possible reaction mechanism and influencing factors of methyl orange photodegradation by LiFePO4 in the presence of oxalic acid were studied through batch experiments at pH 3.0-7.0 and 25℃. The results showed that the photodegradation of MO by LiFePO4 was significantly improved in the presence of oxalic acid than that in the system of LiFePO4 or oxalic acid alone under UV irradiation. The initial concentrations of LiFePO4 and oxalic acid, pH, illumination and temperature played an important role in the MO photodegradation process. The reaction of photocatalytic degradation of methyl orange obeyed to zero-order kinetics, and the degradation rate constant didn’t change with different initial concentrations of MO in the system of 20 mg·L-1 LiFePO4 and 2 mmol·L-1 oxalic acid solution under ultraviolet light irradiation. The degradation rate reached 96% within 14 min when the initial concentration of MO was 50 mg·L-1, which meant that MO was almost completely removed.