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 TiO 2 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/TiO 2 NTs with high efficiency was accordingly obtained. In this coupling, ZnO NRs could grow to flowerlike clusters directly grafted on the tops of TiO 2 NTs, acting just like a large number of lead wires, outstretched from the trunk TiO 2 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 on the Eg. With an appropriate graft amount, ZnO NRs/TiO 2 NTs exhibited broader optical absorption range and higher photocatalytic activity than pure TiO 2 NTs or ZnO NRs did. Under the illumination of 365 nm UV light, the photoelectric conversion efficiency was enhanced from 7.0% of pure TiO 2 NTs to 23.6% of ZnO NRs/TiO 2 NTs. In the photoelectrocatalytic oxidation application, ZnO NRs/TiO 2 NTs exhibited higher removal ability for bisphenol A (BPA). The kinetic constant was 21.4 × 10 −5 s −1, almost 2.3 times faster than that on pure TiO 2 NTs. Also, the stability of ZnO NRs was promoted on TiO 2 NTs with a stable BPA cyclic removal percentage because the receipted holes on ZnO NRs could prevent ZnO from photocorrosion efficiently.