Visible-light photocatalytic degradation of bisphenol A on NaBiO3 nanosheets in a wide pH range: A synergistic effect between photocatalytic oxidation and chemical oxidation

An efficient method was developed for degrading endocrine disrupting bisphenol A (BPA) by simultaneously using the chemical oxidizing ability and visible-light photocatalytic activity of NaBiO3. It was found that in the presence of NaBiO3 (0.5 g L-1) under visible light illumination, the degradation removal of BPA (0.1 mmol L-1) and the removal of total organic carbon within 60 min were increased from 34% to 99.8% and from 12% to 86%, respectively, with decreasing initial reaction pH (pH(0)) from 9.0 to 5.5. NaBiO3 was reduced to Bi3+ self doped NaBiO3 at pH(0) values ranging from 4.2 to 8.0 or Bi(V)/Bi(III) composites at lower pH(0) values, being accompanied with generation of singlet oxygen. In general, a lower pH(0) value resulted in stronger generation of singlet oxygen, and the in-situ generated Bi3+ self doped NaBiO3 or Bi(V)/Bi(III) composites showed higher photocatalytic activity than their precursor NaBiO3. As major oxidizing species, photo-generated holes and chemically-induced singlet oxygen showed synergistic effects for the degradation and mineralization of BPA in the tested system. The generated singlet oxygen promoted the initial transformation, subsequent benzene ring cleavage and final mineralization of BPA by generating more hydroxylation and quinone intermediates, which were easily degraded through subsequent photo-generated hole oxidation. (C) 2016 Elsevier B.V. All rights reserved.