Semiconductor Mediated Photocatalytic Degradation of Plastics and Recalcitrant Organic Pollutants in Water: Effect of Additives and Fate of Insitu Formed H2O2

摘要

Contamination of water by chemical and bacterial pollutants as well as 'white pollution' caused by carelessly discarded waste plastics are major environmental problems. In the current study, the possibility of using semiconductor photocatalysis for the removal of last traces of organic water pollutants of different types is investigated. Semiconductors ZnO and TiO2 were characterized by standard techniques and evaluated as photocatalysts. The pollutants tested include low density polyethylene plastics (PEP), phenol, catechol and organophosphorous pesticides such as phosphamidon, monocrotophos and dichlorvos. Hydrogen peroxide (H2O2) and peroxydisulphate (PDS) enhance the TiO2 catalysed photomineralization rate. More than 10% of PEP could be irreversibly degraded in presence of UV-TiO2-PDS in 300 hr time. The degradation is pH dependent in all cases though no thumb rule can be applied. H2O2 formed insitu during the degradation undergoes parallel decomposition resulting in stabilization or oscillation in its concentration depending on the equilibration or domination of the formation/decomposition process. Anions naturally present in water such as NO3-, Cl- and CO32- inhibit the degradation while SO42- enhances the same. However, this effect depends on a number of factors and no generalized conclusions are possible. The results and the probable mechanism for the degradation of the pollutants are discussed.