Influence of Halide Ions on the Oxidation of Aqueous Ammonia under UV Irradiation

The influence of UV irradiation on the oxidation of ammonia (NH3) in the presence of individual halide ions (bromide (Br-), chloride (Cl-) and iodide (I-)) was investigated and revealed that the ions have the potential to accelerate ammonia photo-oxidation. The process was found to be dependent on solution pH, the type of halide ion and the concentrations of halide ion and aqueous ammonia. Protons are released during the reaction while the halide ion concentrations remain unchanged. Nitrite (NO2-) and nitrate (NO3-) are produced as final stable nitrogen species, with the yield being dependent on the initial pH of the irradiated solution. NH3 oxidation occurred with Br- and Cl- at all pH levels, but in the presence of I- it proceeded only at basic pH. Sulfur hexafluoride (SF6) was used as an electron (e-) scavenger to demonstrate that ammonia oxidation generates e- in solutions containing halide ions. The process was confirmed with the formation of fluoride (F-) and sulfate (SO42-) ions.