ZnO Nanotubes Grown at Low Temperature Using Ga as Catalysts and Their Enhanced Photocatalytic Activities

We report the synthesis of ZnO nanotubes grown via the Ga-catalyzed vapor transport method at low temperature and their photocatalytic activity. The low melting point of Ga (29 °C) resulted in the growth of ZnO nanotubes at a low temperature of 80 °C, enabling us to use Kapton film or ITO glass as substrates. Structure analysis shows that the nanotube is single crystal and has a hollow structure with a wall thickness of ∼2 nm, is several tens of micrometers long, and has a diameter of 60-300 nm. Photocatalytic activity of ZnO nanotubes was determined by measuring the photoinduced degradation of rhodamine B (RB) and an azobenzene-containing polymer poly{1-4[4-(3-carboxy-4-hydroxyphenyl-azo)benzenesulfonamido]-1,2ethanediyl sodium salt} (PAZO) solution, respectively. The measurement reveals that the photodecomposition reactions of both RB and PAZO follow the first-order rate law with the rate constant of 0.018 and 0.004 s-1, respectively. The photocatalytic activity of ZnO nanotubes was shown to be much enhanced compared with ZnO thin films and ZnO nanowires. Therefore, this work demonstrates a novel and simple way to synthesize ZnO nanotubes on flexible substrates, which can potentially serve as excellent photocatalysts for the degradation of organic pollutants in water.