Correlation between types of defects/vacancies of Bi2S3 nanostructures and their transient photocurrent

Crystalline nanostructures possess defects/vacancies that affect their physical and chemical properties.In this regard,the electronic structure of materials can be effectively regulated through defect engineering;therefore,the correlation between defects/vacancies and the properties of a material has attracted extensive attention.Here,we report the synthesis of Bi2S3 microspheres by nanorod assemblies with exposed {211} facets,and the investigation of the types and concentrations of defects/vacancies by means of positron annihilation spectrometry.Our studies revealed that an increase in the calcined temperature,from 350 to 400 ℃,led the predominant defect/vacancy densities to change from isolated bismuth vacancies (VBi) to septuple Bi3+-sulfur vacancy associates (VBiBiBiSSSS).Furthermore,the concentration of septuple Bi3+-sulfur vacancy associates increased as the calcined temperature was increased from 400 to 450 ℃.The characterized transient photocurrent spectrum demonstrates that the photocurrent values closely correlate with the types and concentrations of the predominant defects/vacancies.Our theoretical computation,through first principles,showed that VBiBiBiSSSS strongly absorbs I2(sol),easily desorbs I-(sol),and enhances the electrocatalytic activity of the nanostructures.