Photoinduced Decomposition of Trihalomethanes in Aqueous Solution by UV Irradiation

Abstract

Ultraviolet irradiation with a low-pressure mercury lamp led to a decomposition of trihalomethanes, forming CO, CO2, HCl, and HBr in an aqueous solution at room temperature. In the presence of oxygen, CHCl3 decomposed to form CO2 and HCl. The light transmitted by a Vycor filter could not induce this reaction. In contrast to CHCl3, bromo-substituted trihalomethanes such as CHBrCl2, CHBr2Cl and CHBr3 decomposed even in the absence of oxygen. The decomposition rate of these compounds, which was independent of the presence of Vycor filter, was much larger than that of CHCl3 and the products were CO, HCl and HBr. On the basis of stoichiometry, the overall photochemical reactions were expressed by the following equations.