Reduced formation of undesirable by-products from photocatalytic degradation of trichloroethylene

Photocatalytic degradation of trichloroethylene (TCE) was investigated using a tubular photoreactor packed with TiO2 powders prepared by sol-gel techniques. Powders of the following metals: Cr, Fe, Ni, Cu and Pt, or Ca(OH)2 were uniformly mixed with the TiO2 powders and then their effect on the formation of COCl2, CHCl3, and CHCl2COCl as by-products was examined. Concentrations of COCl2 and CHCl3 were determined in a product gas stream by GC/MS while CHCl2COCl accumulated on the catalyst surface. When the catalysts were immersed in water after TCE photodegradation, the formation of Cl- and CHCl2COO− ions was confirmed by ion-chromatography. Of the chemicals tested, only Cu and Ca(OH)2 inhibited the formation of the chlorinated by-products. With increasing Cu and Ca(OH)2 content, TCE conversion decreased while the stoichiometric ratio ([CO2]formed/[TCE]degraded) increased. Concentrations of COCl2, CHCl3, and CHCl2COCl decreased with increasing Cu and Ca(OH)2 content. Especially, the formation of COCl2 was remarkably suppressed with Ca(OH)2.