Fabrication of walnut-like BiVO<inf>4</inf>@Bi<inf>2</inf>S<inf>3</inf> heterojunction for efficient visible photocatalytic reduction of Cr(VI)

Abstract

As a typical visible-light-responsive photocatalyst, the photoreactivity of BiVO4 is not high enough for practical application due to its limited visible light harvesting ability and quick recombination rate of photo-generated electron-hole pairs. In the present study, surface modification of BiVO4 with Bi2S3, forming walnut-like core-shell structured BiVO4@Bi2S3, was achieved by a simple ion-exchange reaction between Na2S and BiVO4. The photoreactivity of the photocatalyst was evaluated by photoreduction of Cr(VI) in solution under visible light irradiation (λ ≥ 420 nm). The effect of weight ratio of Na2S·9H2O to BiVO4 on the structure and photocatalytic performance of BiVO4@ Bi2S3 hybridized photocatalyst was systematically studied. It was found that a layer of Bi2S3 was successfully covered on the surface of walnut-like BiVO4 microspheres after introduction of Na2S. The formed Bi2S3 shell not only widely extends the visible-light-responsive range, but also sharply retards the recombination of photo-generated electrons and holes of BiVO4 photocatalyst. With increase in the weight ratio of Na2S·9H2O to BiVO4, the photoreactivity of BiVO4 increases first and then decreases with an optimal wight ratio of 3.0 (S3 sample). The photocatalytic activity of S3 sample (BiVO4@Bi2S3) increases 57.2 times when compared with that of pristine BiVO4 sample after irradiation for 40 min. The enhanced photocatalytic activity of walnut-like BiVO4@Bi2S3 microsphere was attributed to the synergistic effect of enhanced visible light harvesting ability due to the sensitization of Bi2S3 and retarded recombination of carriers because of the formation of heterojunction between two semiconductors of BiVO4 and Bi2S3.