The role of nitrogen plasma surface treatment and TiO2 seeding onto carbon fibers on the microwave-assisted growth of radially aligned TiO2 nanowires.

Radially aligned titanium dioxide (TiO 2) nanowires were synthetized on nitrogen plasma-treated carbon fibers (CF) using a two-step microwave-assisted solvothermal method. The TiO 2 synthesis consisted in seeding TiO 2 nuclei on CF followed by TiO 2 nanowire growth. To assess the role of the nitrogen plasma surface treatment and TiO 2 seeding, CF and CF-TiO 2 hybrids were analyzed by Raman spectroscopy, X-ray diffraction, scanning electron and atomic force microscopies, after each step of the TiO 2 synthesis. In addition, X-ray photoelectron spectroscopy was used to analyze the CF chemical composition upon the plasma treatment and TiO 2 seeding. Single fiber tensile tests were conducted on CF and CF-TiO 2 hybrids to track the mechanical changes induced by the surface treatment and TiO 2 synthesis. It was found that both, the nitrogen plasma surface treatment and TiO 2 nuclei seeding were essential to homogeneously synthesize radially aligned TiO 2 nanowires onto CF. No significant changes in the CF surface roughness after plasma treatment and TiO 2 seeding were found; however, upon TiO 2 nanowire growth, the surface roughness increased by about twelve times with respect to the pristine ones. The plasma surface treatment generates oxygen- and nitrogen-containing functional groups that promote TiO 2 nucleation onto CF. In addition, the CF internal heating due to microwave irradiation triggers a preferential nucleation of TiO 2 on the fibers rather than in the reaction medium. The tensile strength of CF remained without significative changes after the surface treatment and TiO 2 nanowire growth. The CF-TiO 2 hybrid materials developed in this work could be exploited in the development of multifunctional structural composites. [Display omitted] • Radially aligned TiO 2 nanowires were grown on plasma-treated carbon fibers. • A novel TiO 2 nanowire microwave-assisted synthesis is explored. • The role of the surface treatment and TiO 2 nuclei seeding is investigated. • The surface treatment and TiO 2 are crucial to radially grow TiO 2 on carbon fibers. • Oxygen and nitrogen species on the fibers promotes preferential TiO 2 nucleation. [ABSTRACT FROM AUTHOR]