Rapid microwave synthesis of I-doped Bi4O5Br2 with significantly enhanced visible-light photocatalysis for degradation of multiple parabens

Parabens, a class of preservatives widely used in cosmetic and pharmaceutical products, are currently considered as potential emerging contaminants in the environment. Photocatalytic degradations of different parabens (methyl-, ethyl-, propyl-, and butylparaben) and their mixture were performed for the first time under visible-light irradiation using I-doped Bi4O5Br2 photocatalysts, synthesized by a facile, fast, and energy-saving microwave route. Compared with pure Bi4O5Br2, I-doped samples exhibited enhanced photocatalytic activities in the degradation of the parabens. I-0.7-Bi4O5Br2 achieved the best performance, showing approximately 9.5, 10.4, 15.7, 24.2, and 27 times higher activities than those of Bi4O5Br2 in the degradation of methylparaben, ethylparaben, propylparaben, butylparaben, and a mixture of parabens, respectively. The structures of the as-synthesized photocatalysts were carefully characterized, and the primary reactive oxygen species (ROS) in the photocatalytic process were identified. Photogenerated holes and superoxide radicals were found to be the key reactive species. Through doping with iodine, the valence-band potentials of the Bi4O5Br2 photocatalysts were reduced, leading to decreases in their band-gap energies, while the separation efficiencies of the photogenerated carriers were significantly enhanced. Thus, I-doped Bi4O5Br2 could absorb more visible-light and yield more superoxide radicals, resulting in excellent visible-light photodegradations of the parabens. In addition, the as-prepared I-0.7-Bi4O5Br2 catalyst maintained a strong stability of photocatalytic performance, indicating its potential for practical applications. (C) 2017 Elsevier B.V. All rights reserved.