Enhancing visible light photocatalytic activity by transformation of Co3+/Co2+ and formation of oxygen vacancies over rationally Co doped ZnO microspheres

Abstract

As a typical semiconductor, ZnO is considered as a favorable photocatalyst due to its excellent photoelectrochemical properties. However, low response of visible light and the recombination of photoinduced carriers limits its application in photocatalysis. Herein, a novel, robust and recyclable heterogeneous photocatalyst based on flower-like Co doped ZnO microspheres was presented without changing the hierarchical morphology. The crystal structure, light absorption, and electrochemical performance were systematically investigated, and the response of Co doped ZnO to visible light significantly enhanced with the gap band reduced from 3.20 eV to 2.54 eV. Due to the transformation of Co2+ to Co3+, more oxygen vacancies were produced, with more photoinduced electrons transferring to Co3+ which would greatly inhibit the recombination of photoinduced electrons and holes and improve photocatalytic activity. 2-Mercaptobenzothiazole (MBT) which is considered as a long half-life intermediate of antibiotic medicine is chosen as a target. As a result, the 7% Co-ZnO photocatalyst exhibited excellent photocatalytic activity for the degradation of MBT with the rate constant of 0.1498 min−1 and removing ratio of 97.3% in 50 min. The formation of excess oxygen vacancies and the conversion between Co2+ to Co3+ were further identified by XPS analysis. This work provides new sights for doping transition metal with different chemical valence in semiconductors for producing oxygen vacancy and improving the photocatalytic efficiency.