Heterogeneous Photodegradation Of Acid Orange 7 In The Presence Of Schwertmannite And Small Molecular Organic Acids

Azo dyes have been the most used dyes at present and mainly used in textile, leather and food industries. There are about 2000 kinds of azo dyes with different structures in the word. Over 15% of the total world production output of dyes has been discharged into the environment during the dyeing process as industrial wastewater. Due to its complex structure, high chroma and poor biodegradability, azo dyes are difficult to degrade by simple traditional physical or chemical methods. Photocatalytic oxidation has the advantages of high efficiency, fast and safe to destroy many of the structural stability and bio-refractory organic pollutants,which has received great attention. This paper mainly study the factors and reaction mechanism of schwertmannite photocatalytic degradation of acid orange 7 in the presence of small molecular organic acids concluding citric acid and oxalic acid.This paper is divided into two parts.Part Ⅰ:Schwertmannite was synthesized through oxidation of FeS04 by Acidithtobacillus ferrooxidans strains (i.e.A.ferrooxidans LX5), and the synthesis products was identified as pure schwertmannite by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy and Surface area and porosimetry analyzer.It is proved that the product is Schwertmannite.Part Ⅱ:Under different conditions of pH, concentration of organic acids, the amount of schwertmannite, temperature and light intensity and so on, to study photocatalytic degradation of schwertmannite in the presence of organic acids including citric acid and oxalic acid. By the variable-control method, we can obtain from the experiment that as for the photodegradation reaction system, it exists an optimum reaction conditions. As for the citric acid, the optimum condition was 25℃, the UV intensity to be 300W, pH=5.0, of initial concentration of citric acid to be 10 mmol/L, and the amount of schwertmannite to be 0.50 g/L.As for the citric acid, it influence the reaction greatly if the value of pH is too high. So we add buffer to maintain the value of pH of the system to be 5.0.The other optimum condition was 25℃, the UV intensity to be 300W, initial concentration of citric acid to be 10 mmol/L, and the amount of schwertmannite to be 0.50 g/L. The results showed that in the presence of schwertmannite or small molecular organic acids (citric, oxalic) co-exist, the degradation rate of acid orange 7 was extremely raised under UV irradiation. This paper preliminary discussed the reaction mechanism of schwertmannite in the presence of small molecular organic acids concluding citric acid and oxalic acid.