Environmentally relevant impacts of nano-TiO2 on abiotic degradation of bisphenol A under sunlight irradiation

Abstract Understanding the effects of nano-TiO 2 particles on the environmental behaviors of organic pollutants in natural aquatic environments is of paramount importance considering that large amount of nano-TiO 2 is being released in the environment. In this study, the effect of nano-TiO 2 on the degradation of bisphenol A (BPA) in water was investigated under simulated solar light irradiation. The results indicated that nano-TiO 2 at environmentally relevant concentration (1 mg/L) could significantly facilitate the abiotic degradation of BPA (also at low concentration) under mild solar light irradiation, with the pseudo first-order rate constant ( k obs ) for BPA degradation raised by 1–2 orders of magnitude. As reflected by the inhibition experiments, hydroxyl radicals ( OHs) and superoxide radical species were the predominant active species responsible for BPA degradation. The reaction was affected by water pH, and the degradation rate was higher at acidic or alkaline conditions than that at neutral condition. Humic acid (HA) also affected the reaction rate, depending on its concentration. At lower concentration (the mass ratio of HA/nano-TiO 2 was 0.1:1), HA improved the dispersion and stability of nano-TiO 2 in aquatic environment. As a result, the yield of OHs by nano-TiO 2 under sunlight irradiation increased and BPA degradation was facilitated. When the HA concentration increased, a coating of HA formed on the surface of nano-TiO 2 . Although nano-TiO 2 became more stable, the light absorption by nano-TiO 2 was significantly reduced due to the strong light absorption of the HA coated on the surface. As a consequence, the yield of OH decreased and BPA degradation was depressed. The results imply that nano-TiO 2 at low concentration may distinctly mediate BPA degradation, and can contribute to the natural attenuation of some organic pollutants in aquatic environment with low level of HA. However, this process would be significantly reduced in the presence of high level of HA.