Optical, surface charge state and photocatalysis study of ZnO with different exposure faces

A hydrothermal method was used to synthesize zinc oxide (ZnO) with different exposure faces. Only when the ratio of OH - / Zn2 + is 2/1, ZnO with different morphologies and exposure faces can be obtained by controlling the amount of the polyvinylpyrrolidone as a capping agent. Five samples with representative morphology and wurtzite crystal structure were selected from 28 different synthesis conditions. Their optical, surface charged, and photocatalytical properties are closely related to the exposed faces. The ultraviolet fluorescence emission is related to the nonpolar faces in the low index exposure face. All samples are n-type semiconductors and oxygen element is lacking compared to Zn. There is a great possibility that the oxygen vacancy is the oxygen defect that causes the visible fluorescence emission of the nanosheet. Samples are all positive-charged on the surface. The surface charge is not only related to the particle size but also directly affected by the polarity of exposed face and the missing atoms of the sample. The photocatalytic activity of ZnO with nanocolumn morphology is the best, due to high exposure ratio of the polar faces, maximum positive charge, and moderate particle size.