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.