Fabrication, Characterization, and Photoelectrocatalytic Application of ZnO Nanorods Grafted on Vertically Aligned TiO2 Nanotubes

In this article, ZnO nanorods (NRs) were grafted on Ti-based vertically aligned TiO2 nanotubes (NTs) by a feasible seed-induced hydrothermal reaction. Through such a simple but interesting structure combination of the two semiconductors, a novel composite photocatalytic anode of ZnO NRs/TiO2 NTs with high efficiency was accordingly obtained. In this coupling, ZnO NRs could grow to flowerlike clusters directly grafted on the tops of TiO2 NTs, acting just like a large number of lead wires, outstretched from the trunk TiO2 NTs. Thus, the grafted ZnO NRs could serve conveniently as favorable hole channels and receptors for the efficient separation of photoelectrons and holes, which resulted in a slight shift of the band gap absorption edges and consequently changed the band gap energy (Eg). Moreover, the graft amount would further make a certain impact oil the Eg. With in appropriate graft amount, ZnO NRs/TiO2 NTs exhibited broader optical absorption range and higher photocatalytic activity than pure TiO2 NTs or ZnO NRs did. Under the illumination of 365 nm UV light, the photoelectric conversion efficiency was enhanced from 7.0% of pure TiO2 NTs to 23.6% of ZnO NRs/TiO2 NTs. In the photoelectrocatalytic oxidation application, ZnO NRs/TiO2 NTs exhibited higher removal ability for bisphenol A (BPA). The kinetic constant was 21.4 x 10(-5) s(-1), almost 2.3 times faster than that on pure TiO2 NTs. Also, the stability of ZnO NRs was promoted on TiO2 NTs with a stable BPA cyclic removal percentage because the receipted holes on ZnO NRs Could prevent ZnO from photocorrosion efficiently.