Controllable biosynthesis and characterization of α-ZnS and β-ZnS quantum dots: Comparing their optical properties

The controllable biosynthesis of α-ZnS and β-ZnS quantum dots by Clostridiaceae sp. using different concentration of hydroxypropyl starch as dispersant are demonstrated. The structure and properties are characterized by XRD, TEM, HRTEM, UV-Vis and fluorescence spectra, and so on. The results indicate that the α-ZnS quantum dots with wurtzite structure and diameter of 8±2 nm were attained under low dose of hydroxypropyl starch, while high dose obtained the β-ZnS quantum dots with sphalerite structure and diameter of 4±1 nm. The UV-Vis absorption of β-ZnS quantum dots have an evident red shift compared with α-ZnS quantum dots, and the as-biosynthesized β-ZnS quantum dots have a stronger fluorescence activity than α-ZnS quantum dots. This work displays a simple biosynthetic method to control the crystal structure and particle size of metal sulfide nanoparticles under mild conditions.