Controllable extracellular biosynthesis of bismuth sulfide nanostructure by sulfate-reducing bacteria in water-oil two-phase system

Due to strong hydrolysis of Bi³⁺ as precursor in aqueous media, there are no reports on biosynthesis of bismuth sulfide (Bi₂S₃) nanomaterials. In this work, the water-oil two-phase system was used to biosynthesize the Bi₂S₃ nanomaterials based on the coupling reaction of biological reduction and chemical precipitation process for the first time. The results showed that the water-oil two-phase system successfully eliminated hydrolysis of the Bi³⁺ and controllably and extracellularly fabricated the Bi₂S₃ crystal with high purity. The nanorods with diameter of about 100 nm and length of about 1.0 μm were attained under high dose of lactic acid and SO₄^2-; while low dose obtained the nanobundles consisted of nanoneedles with tip diameter of 10-20 nm and length of about 5.0-10.0 μm. The Bi₂S₃ nanorods as photocatalyst almost completely degraded methylene blue from solution within 12 h; whereas the Bi₂S₃ nanobundles removed about 87% of the dye. The amount of the Bi₂S₃ nanorods decreased by 48% due to photocorrosion, whereas 52% with the nanobundles. The Bi₂S₃ nanorods had relatively higher photocatalysis activity and slightly stronger photocorrosion resistance than the Bi₂S₃ nanobundles.