A yolk–shell Bi@void@SnO2 photocatalyst with enhanced tetracycline degradation

The yolk–shell Bi@void@SnO2 photocatalyst was synthesized via a step-by-step process. The composition, morphology, optical and photoelectrochemical properties as well as the surface chemical composition and states of the samples were characterized by X-ray diffraction, transmission electron microscopy, UV–Vis diffuse reflectance spectra, electrochemical impedance spectra and X-ray photoelectron spectrometer, respectively. The tetracycline has been used to evaluate the photocatalytic activities of the as-synthesized samples. Compared with the degradation efficiency of 16.33% for pure Bi and almost nothing for SnO2 under visible light irradiation, the as-developed Bi@void@SnO2 photocatalyst possesses 81.81% of degradation efficiency. Meanwhile, the light absorption of the as-developed yolk–shell composites is broadened from ultraviolet to visible light comparing to pure SnO2 due to the surface plasmon resonance effect of Bi spheres. Moreover, the superoxide radicals, especially in holes, play leading roles during the photocatalytic degradation process. In addition, the decomposition mechanism of the as-fabricated composites for tetracycline is analyzed in detail.