Photolysis of bisphenol S in aqueous solutions and the effects of different surfactants

The photolysis of bisphenol S (BPS) in aqueous solutions was studied under a 20 W UV lamp (lambda = 254 nm). The proposed intermediates and possible photolysis pathways of BPS were analyzed, and the effect of three surfactants on this photolysis was determined. UV and liquid chromatography combined with ion-trap time-of-flight mass spectrometry analyses revealed that BPS photolysis mainly occurred in two steps, and the primary photodegradation intermediates or products were p-hydroxybenzenylsulfonic acid, p-hydroxyphenol, and sulfuric acid. The results showed that BPS photolysis fitted well to a first order kinetic equation. The surfactants did not directly participate in BPS photolysis and exerted different effects depending on the structure and concentration of surfactants. The anionic surfactant sodium dodecyl sulfate (SDS) exhibited a strong inhibiting effect on BPS photolysis that increased with increased SDS concentration. At 800 mg/L SDS, the half-life of BPS photolysis was prolonged from 91.2 to 150.7 min and the inhibiting ratio of SDS was 39.5 %. By contrast, the cationic surfactant cetyl trimethyl ammonium bromide (CTAB) showed a promoting effect on BPS photolysis that increased with increased CTAB concentration. At 120 mg/L CTAB, the half-life of BPS photolysis shortened from 91.2 to 63.0 min and the promoting ratio was 44.7 %. On the other hand, the nonionic surfactant polyoxyethylene lauryl ether (PLE) had a relatively weak inhibiting effect at < 120 mg/L PLE but a promoting effect at > 140 mg/L PLE. At 240 mg/L, the promoting ratio reached 7.9 %.