Syntheses, characterization and properties of novel nanostructures consisting of Ni/titanate and Ni/titania

Ni/titanate one-dimensional nanostructures and Ni/titania nanocrystal composites were produced by a facile synthetic procedure using protonic titanate nanotubes as the precursor templates. The formation mechanisms for the nanostructures were proposed. The nickel ions first enter into the titanate matrix through three approaches, ion-exchanges reaction with the interlayered hydrogen ions, capillary forces from the microcavities, and electrostatic adsorptions due to the negatively charged outer surface of the titanate nanotubes. The following metallic nickel nucleation and growth may have occurred for these three kinds of the nickel ions reduced under hydrogen gas flow at elevated temperatures. The supports' titanate nanotubes may phase transform into the anatase titania nanocrystals and further into the mixture of anatase and rutile titania along with the increases of temperature. The Ni/titanate nanocomposites demonstrate paramagnetic behaviors and the Ni/titania nanocrystals display typical ferromagnetic behaviors. The Ni/titania sample reduced at 550 °C containing 14.5% rutile has higher photocatalytic activities than the sample reduced at 350 °C containing pure anatase, which is ascribed to a synergistic effect between anatase and rutile. The ferromagnetic characteristics of the Ni/titania products make them available as magnetically separable photocatalysts, which can be separated and recovered quickly by applying an external magnetic field.