Enhanced piezocatalytic performance of ZnO nanosheet microspheres by enriching the surface oxygen vacancies

In this paper, ZnO nanosheet microspheres with a diameter of about 5 μm were obtained by a hydrothermal method and annealed in vacuum, hydrogen, and air. The photocatalytic, piezo-photocatalytic, and piezoelectric catalytic efficiency for degradation of different dyes (methyl orange, rhodamine blue (RhB), and AO7) by ZnO microspheres were studied. It is found that the free electrons originally bound by the oxygen vacancies could move toward the surface of ZnO nanosheet to participate in the degradation of RhB and AO7 by an alternating built-in piezoelectrical field. The higher oxygen vacancy concentration and the higher intensity and frequency of the dynamic piezoelectric field lead to higher piezoelectric catalytic efficiency of ZnO microspheres. The photocatalytic efficiency and piezoelectric catalytic efficiency of ZnO nanosheet microspheres can be improved by annealed in vacuum, which can greatly promote the application of ZnO porous catalyst through harvesting the ultrasonic energy.