Oxygen vacancy induced superior visible-light-driven photo-catalytic performance in the BiOCl homojunction

The photocatalytic performance of semiconductors can be enhanced by expanding the spectral response range and accelerating the photo-induced charge separation. Introduction of oxygen vacancies and construction of homo-junctions in BiOCl were adopted to widen the absorption spectra and reduce the photogenerated electron-hole pair recombination, further enhancing its photocatalytic activity. Black BiOCl with oxygen vacancies and a homo-junction was fabricated using a simple one-pot hydrothermal method. Meanwhile, white BiOCl nanosheets and nanorods with crystal growth in different orientations were simultaneously synthesized to compare with the black BiOCl homo-junction, which exposed the same crystal facets as those of black BiOCl. High resolution transmission electron microscopy (HRTEM) was performed to confirm the formation of the crystal-facet homo-junction, while the existence of oxygen vacancies in black BiOCl was proved by X-ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR) spectroscopy. The spectral absorption range and the photo-generated electron-hole pair separation ability of catalysts were characterized by UV-vis diffuse reflectance absorption spectroscopy (UV-vis DRS), transient photocurrent density and electrochemical impedance spectroscopy (EIS). The photo-catalytic activities of the black BiOCl homo-junctions were evaluated through degradation of RhB and disinfection performance towards E. coli and S. aureus , and they can degrade 99.9% of RhB solution and disinfect 97% of bacteria under simulated sunlight irradiation. Further, the possible photo-catalytic mechanism and the improvement of photo-catalytic performance could be ascribed to the introduction of oxygen vacancies and the construction of homo-junctions, which was also confirmed by theoretical computation. The black BiOCl homojunction with oxygen vacancies has a wide absorption range and results in effective separation of photo-generated electron-hole pairs, which contribute to its superior visible-light-driven photo-catalytic degradation and disinfection ability.