UV Photodegradation of Inorganic Chloramines

The ultraviolet (UV) photolysis of monochloramine (NH2Cl), dichloramine (NHCl2), and trichloramine (NCl3) in aqueous solution was investigated at wavelengths of 222, 254, and 282 nm. All three chloramines can be degraded by UV irradiation, and the quantum yields for these processes are wavelength-dependent. Stable photoproducts include nitrite, nitrate, nitrous oxide, and ammonium. Solution pH was observed to have little effect on the rate of photodecay; however, the product distribution showed strong pH dependence. Nitrate formation was favored at low pH, while nitrite formation was favored at high pH. The effects of pH on formation of N2O and NH4+ were less clear. On the basis of the results, a mechanism of photodecay of monochloramine is proposed.