Synthesis of Bi₂S₃/BiVO₄ 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 (BiVO₄) and bismuth sulfide (Bi₂S₃) are about 2.40 eV and 1.30 eV, respectively. Although both BiVO₄ and Bi₂S₃ 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 (Bi₂S₃)/Bismuth vanadate (BiVO₄) 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 BiVO₄ was produced (sample 7.5); when the pH was 8.0 or 8.5, both Bi₂S₃ and BiVO₄ were produced (samples 8.0 and 8.5); and when the pH was 9.0, only Bi₂S₃ was produced (sample 9.0). In sample 8.0, Bi₂S₃ and BiVO₄ were closely integrated with each other, with Bi₂S₃ particles formed on the surface of concentric BiVO₄ 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 Bi₂S₃/BiVO₄ 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 Bi₂S₃/BiVO₄. The synthesis method proposed in this paper is expected to enable large-scale and practical use of Bi₂S₃/BiVO₄.

Ultrasonic irradiation-assisted synthesis of Bi2S3 nanoparticles in aqueous ionic liquid at ambient condition

In this work, an easy, fast and environmentally friendly method to obtain Bi₂S₃ nanostructures with sphere-like morphology is introduced. The promising material was successfully synthesized by a sonochemical route in 20% 1-ethyl-3-methylimidazolium ethyl sulfate [EMIM][EtSO₄] ionic liquid solution (IL). Morphological studies by electron microscopy (SEM and TEM) show that the use of IL in the synthesis of Bi₂S₃ favors the formation of nanocrystals non-agglomerated. Micro Raman and energy dispersive X-ray spectroscopy (EDXS) were used to determine the composition and purity of the synthesized material. X-ray powder diffraction (XRD) and selective area electron diffraction (SAED) revealed that ultrasonic radiation accelerated the crystallization of Bi₂S₃ into orthorhombic bismuthinite structure. The band gap calculated from the diffuse reflectance spectra (DRS) was found to be 1.5eV.