Photodegradation of 2,4-Dichlorophenoxy Acetic Acid on TiO2, ZnO and Fe2O3 by Sunlight

Abstract

The photocatalytic degradation of 2,4-dichlorophenoxy acetic acid (2,4-D) in aqueous solution containing a suspension of titanium dioxide (TiO₂), zinc oxide (ZnO) and ferric oxide (Fe₂O₃) was studied under sunlight or concentrated sunlight. As expected, in the presence of TiO₂ and ZnO irradiated by concentrated sunlight, the rate of photodegradation of 2,4-dichlorophenoxy acetic acid was seen to be faster than that irradiated by direct sunlight. Its degradation was not observed in the absence of catalyst and in the dark. TiO₂ and ZnO which possess more higher band gap energy than that of Fe₂O₃ are effective photosensitizer for the degradation of this pesticide under concentrated sunlight. The band gap energy of reddish brown Fe₂O₃ (2.2 eV) is lower than that of colourless TiO₂ (3.2 eV) and ZnO (3.2 eV). Fe₂O₃ absorbs more longer wavelength of the sunlight than others, but it is not successful as a catalyst under visible light. The results of all UV absorbtion spectroscopy and HPLC analysis regarding products illuminated showed that the complete degradations of 2,4-dichlorophenoxy acetic acid containing ZnO and TiO₂ were observed nearly 99 and 85 % only in 45 min under concentrated sunlight.