Synthesis and oxygen vacancy-related photocatalytic properties of ZnO nanotubes grown by thermal evaporation

ZnO nanotubes with breaches in the walls (Breached ZnO nanotubes) with diameters of 50–200 nm and lengths up to several micrometers have been produced in high yield on glass substrates by heating Zn powder at 600–700 °C at a total gas pressure of 20 Pa. We assume formation of ZnO nanotubes involves four steps: formation of Zn vapor; formation of ZnO nanoplates; transformation of ZnO nanoplates into ZnO nanoleaves; and transformation of ZnO nanoleaves into ZnO nanotubes. The optical properties of nanotubes were studied by use of photoluminescence spectroscopy; strong green emission related to oxygen vacancies was observed. Study of the degradation of methyl orange (MO) revealed that the photocatalytic activity of the nanotubes was high, because of their high surface-to-volume ratios and abundant oxygen vacancies near their surfaces. This type of high-surface-area ZnO nanotube has potential for environmental applications.