Effects of Ag and Pt on photocatalytic degradation of endocrine disrupting chemicals in water

The effects of silver and platinum metals on the photocatalytic degradation of endocrine disrupting chemicals (EDCs) in water over TiO2 (Degussa P25) were investigated. The natural oestrogens 17β-oestradiol and oestriol were studied as well as the synthetic oestrogen 17α-ethynyloestradiol and the xenoestrogens bisphenol A, resorcinol and 2,4-dichlorophenol. Ag/TiO2 and Pt/TiO2 catalysts were prepared by photodeposition. Photocatalytic reactions were carried out in an immobilised TiO2 system and a TiO2 slurry system. It was found that the addition of silver or platinum had no effect on the photocatalytic degradation or mineralisation of all the endocrine disrupting chemicals at concentrations found in water. This was attributed to the high concentration of holes and hydroxyl radicals in the system compared to the low amount of organic matters to be degraded. It is therefore not viable to add expensive metals to photocatalytic systems for the removal of low concentrations of organic pollutants in water. At high concentration of EDC, a significant increase in the reaction rate was observed for bisphenol A and resorcinol over Pt/TiO2. However, there was a decrease in reaction rate for bisphenol A over Ag/TiO2 and no significant effect with resorcinol, indicating that the reactions are metal specific, substrate specific and may depend on the substrates molecular structure. The catalytic properties as well as the photocatalytic properties of the catalyst should also be considered. It was concluded that there is no universal explanation to explain the effects of metals on photocatalysis of organics in water and that there are many factors which should be considered.