Effects of nitrite anions and ammonium cations on the photolysis of bisphenol S in nitrate solution

The effects of nitrate ions on the photolysis of bisphenol S (BPS) under UV irradiation were studied using reaction kinetics. Based on this research, we investigated how nitrite anions and ammonium cations codissolved with nitrate affected the UV photolysis of BPS. The BPS photolysis fitted well to a first-order kinetic equation, and the half-life of BPS photolysis varied with changes in pH value, shortening from 95.0 min at pH 2 to 42.3 min at pH 10. Nitrate added to the BPS solution inhibited the BPS photolysis, but the extent of the inhibitory effect was associated with the pH value of the aqueous solution. The inhibiting ratio remained within 19.2-27.6% in acidic and neutral solutions, while it stayed at about 3.6% in alkaline solutions. Nitrite anions exhibited a strong inhibitory effect on BPS photolysis, but the inhibitory effect of NO2- coexistent in a BPS-NO3- solution was weaker than that of separate NO2-, indicating that the inhibitory effect of mixed form of NO2- and NO3- were not simply additive; some offset might exist between them. Ammonium cations had no effect on BPS photolysis, but NH4+ codissolved in NO3- solution weakened the inhibition of NO3-, thus indirectly promoting BPS photolysis in NO3- solution. When 32 mg/L NH4+ was added to a BPS-NO3- solution, the coexistent NH4+ exhibited a promoting effect on BPS photolysis, and the promoting ratio reached 5.3% at 64 mg/L NH4+. The mechanisms of BPS photolysis under the presence of nitrate ions were also discussed