REDOX PHOTODEGRADATION OF 2,4-DICHLOROPHENOXYACETIC ACID OVER TIO2

The photodegradation of 2,4-dichlorophenoxyacetic acid using titanium dioxide as photocatalyst was investigated. The yield of 2,4-D photodeg radation depends on the mass of the semiconductor, temperature and lig ht intensity, The highest conversion rates were obtained at pH=3.5, wh ich is close to the pK(a) of the acid and lower than the point of zero charge of TiO2. The experimental data fit a Langmuir-Hinshelwood kine tic model. The rate and equilibrium adsorption constants were obtained from those data at different temperatures. Some aromatic intermediate products of 2,4-D photodegradation were detected (2,4-dichlorophenol, hydrohydroquinone, chlorohidroquinone). An analysis of total organic carbon (TOC) showed that a complete mineralization of 2,4-D can be eas ily achieved. On the other hand, the results obtained in experiments u sing platinized TiO2 lead us to assume that both oxidation and reducti on steps should be taken into account if an explanation of the experim ental data is to be made.