Synthesis of Bi(2)S(3)/BiVO(4) Heterojunction with a One-Step Hydrothermal Method Based on pH Control and the Evaluation of Visible-Light Photocatalytic Performance

The band gaps of bismuth vanadate (BiVO(4)) and bismuth sulfide (Bi(2)S(3)) are about 2.40 eV and 1.30 eV, respectively. Although both BiVO(4) and Bi(2)S(3) are capable of strong visible light absorption, electron–hole recombination occurs easily. To solve this problem, we designed a one-step hydrothermal method for synthesizing a Bismuth sulfide (Bi(2)S(3))/Bismuth vanadate (BiVO(4)) heterojunction using polyvinylpyrrolidone K-30 (PVP) as a structure-directing agent, and 2-Amino-3-mercaptopropanoic acid (l-cysteine) as a sulfur source. The pH of the reaction solution was regulated to yield different products: when the pH was 7.5, only monoclinic BiVO(4) was produced (sample 7.5); when the pH was 8.0 or 8.5, both Bi(2)S(3) and BiVO(4) were produced (samples 8.0 and 8.5); and when the pH was 9.0, only Bi(2)S(3) was produced (sample 9.0). In sample 8.0, Bi(2)S(3) and BiVO(4) were closely integrated with each other, with Bi(2)S(3) particles formed on the surface of concentric BiVO(4) layers, but the two compounds grew separately in a pH solution of 8.5. Visible-light photocatalytic degradation experiments demonstrated that the degradation efficiency of the Bi(2)S(3)/BiVO(4) heterojunction was highest when prepared under a pH of 8.0. The initial rhodamine B in the solution (5 mg/L) was completely degraded within three hours. Recycling experiments verified the high stability of Bi(2)S(3)/BiVO(4). The synthesis method proposed in this paper is expected to enable large-scale and practical use of Bi(2)S(3)/BiVO(4).