Self-assembly of ZnO nanoparticles to electrostatic coordination sites of functionalized carbon nanotubes

We report the hierarchical self-assembly of ZnO nanoparticles on single-walled carbon nanotubes (SWCNT-ZnO) and multi-walled carbon nanotubes (MWCNT-ZnO) by utilizing an electrostatic coordination approach. The affinity for Zn atoms to the oxygen of the C = O in the carboxyl groups is utilized to decorate oxidized single-walled and multi-walled carbon nanotubes with ZnO nanoparticles. The CNT-ZnO structures are indicative of the carboxyl group distribution along the carbon nanotubes (CNTs). By this technique we have achieved complex design architecture such as T- and Y-junctions that would be useful for device applications. The ZnO conjugation is a reversible process; that is, the ZnO nanoparticles can be washed off from the CNTs by dissolving in NaOH or H₂SO₄. The conjugation leaves the suspension with carbon nanotubes of smaller lengths compared to the average lengths of the material that we started with. Scanning and transmission electron microscopy along with energy dispersive spectroscopy (EDS) were used to characterize the conjugation.