Morphology, structure and properties of Bi2S3 nanocrystals: role of mixed valence effects of cobalt

Transition metal ion-doped pnictogen-chalcogen binary V2VI3 compounds presents excellent photocatalytic activity due to the sp-d exchange interactions between host and magnetic ions. In this work for the first investigation, multi-valence states of cobalt-doped Bi2S3 nanocomposite catalysts were hydrothermally synthesized, their morphology, structure, chemical valence states, optical, magnetic, photoelectric and photocatalytic properties were characterized through varies techniques such as Scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Ultraviolet visible & photoluminescence spectra, Raman and FT-Infrared spectra, Vibration sample magnetometer, electron paramagnetic resonance spectra, and electrochemical impedance test. 15 nm-diameter well-dispersed nanorods were synthesized and the Co doping did not significantly increase the size of nanorods. The infrared and Raman spectra analysis indicate the Co entered the lattice and introduced strain and deformation on structure due to the difference of ionic radius and electronegativity of Co and Bi. X-ray photoelectron spectra display the co-existence of Co2+ and Co3+ inside Bi2S3 which give different contributions to optical bandgap, optical absorption and emission behaviors. Density functional theory modeling and calculation on the energy bandgap and electron excitation states were performed. The simulation is consistent with experimental results. All samples show typical ferromagnetism character with enhanced magnetization. The magnetic susceptibility versus temperature curves imply that Co-doped sample follow the Curie–Weiss law. The photocatalytic activity was greatly enhanced by the Co doping due to the active electron transition and charge transfers which were further verified by electron paramagnetic resonance spin trapping studies. The photoelectric performances were finally studied and the result explained the mechanism of photocatalytic improvement due to the increase of conductivity and photoelectric efficiency. BiCoS3 sample was proved to be effective photocatalyst for waste-water treatment.