Preparation of flower-like ZnO photocatalyst with oxygen vacancy to enhance the photocatalytic degradation of methyl orange

Porous ZnO nanosheets show great potential in photocatalysis applications for their excellent properties. "Defect engineering" has now been considered as an effective strategy to improve their photocatalytic activity. In this paper, flower-like ZnO photocatalysts assembled with porous nanosheets were prepared by the hydrothermal method and calcination treatment in different atmosphere. The effect of calcination atmosphere on the oxygen vacancies and photocatalytic performance of ZnO were investigated comprehensively. The results show that ZnO photocatalysts calcined in air (Air-ZnO), Ar (Ar-ZnO) and N2 (N2-ZnO) atmosphere show a porous structure with different content of oxygen vacancies. Compared with Air-ZnO, Ar-ZnO and N2-ZnO exhibit larger specific surface area and higher visible light absorption. Meanwhile, more oxygen vacancies are introduced into Ar-ZnO, which reduce its bandgap to 3.03 eV and improve the separation and transfer efficiencies of photogenerated carriers. Therefore, the photodegration efficiency of methyl orange (MO) by Ar-ZnO is enhanced to 94.5 % within 30 min under ultraviolet irradiation, and its degradation rate constant Kap (∼0.09763 min−1) is 3.2 times greater than that of Air-ZnO (∼0.03089 min−1). Meanwhile, the Kap (∼0.02072 min−1) of Ar-ZnO is 6.3 times higher than that of Air-ZnO (∼0.0033 min−1) under visible light irradiation.