Hierarchical Nanorods Research Articles

Directed growth of nanoarchitectured LiFePO 4 electrode by solvothermal synthesis and their cathode properties

We demonstrate a rapid and one-pot solvothermal synthesis of LiFePO 4 hierarchical nanorods and flowers like microstructures in a short reaction time (4–10 min) at temperature as low as 300–400 °C, without any high temperature post-annealing. The ethylene glycol was used as a solvent with hexane and oleic acid as co-solvent and surfactant, respectively. Addition of the co-solvent and/or surfactant played a key role in controlling the morphology and microstructures of the LiFePO 4 nanocrystals. The EG and oleic acid were acted as the size and morphology controlling agents and carbon source when annealed at 600 °C. Sample exhibited about 90% specific capacity at 0.5 °C and showed good cyclic performance. The high-resolution TEM image revealed that these nanorods were self-assembled to form flower like microstructure in presence of oleic acid during the synthesis.

Temperature induced hierarchical growth of ZnO microcrystal

Unique ZnO microcrystal composed of hierarchical nanorod arrays was successfully prepared by a surfactant-free process in aqueous solution under moderate temperature. The products were characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The as-prepared ZnO microstructures are of hexagonal phase and high purity. On the basis of SEM images and parallel experiments, a possible formation mechanism for this ZnO microcrystal with hierarchical nanorod arrays is proposed and the reaction temperatures are found to have great influence on inducing secondary nucleation and the hierarchical growth. In addition, the optical properties of the ZnO samples were also investigated by the photoluminescence (PL) spectrometer.

Ordered Co3O4 hierarchical nanorod arrays: tunable superhydrophilicity without UV irradiation and transition to superhydrophobicity

Ordered Co3O4 hierarchical nanorod arrays have been fabricated employing pulsed laser deposition (PLD) on polystyrene colloid spheres followed by an annealing process in air. The surface roughness and chemical composition were controlled successfully by adjusting the oxygen pressure during the PLD process and post-annealing temperature, respectively. The as-prepared Co3O4nanorod arrays had superior superhydrophilicity without UV irradiation, which was attributed to the improved roughness related to the hierarchical structures and the abundant OH−groups induced by the PLD and annealing processes. After chemical modification with fluorosilane, the superhydrophilicity was converted to hydrophobicity or superhydrophobicity with controlled water contact angles. Our results demonstrate the fabrication of a new stable superhydrophilic material without UV irradiation; well-controlled Co3O4 hierachical nanorod arrays may also find potential applications in the areas of field-emission, catalysis, and lithium-ion batteries.

Sunlight-assisted fabrication of a hierarchical ZnO nanorod array structure

A ZnO hierarchical structure built up of a well ordered nanorod array was obtained by a simple treatment of zincate ion aqueous solution and a zinc foil mixture with sunlight irradiation. The as-prepared ZnO nanorods are all single crystalline with a uniform [0001] preferential growth direction and have an average diameter of approximately 40 nm and a length of approximately 300 nm. It is believed that sunlight gave rise to the driving force for the preformed ZnO nanorod to self-assemble into plates, which served as the substrate for secondary heterogeneous nucleation, and subsequently the crystal growth resulted into formation of a ZnO nanorod array. The formation mechanism of the ZnO hierarchical nanorod array structure was discussed, based on controlled experiment results. Raman spectroscopy, cathodoluminescence and UV-Vis absorbance spectra of the as-prepared ZnO product have been performed.

Morphology evolution of hierarchical ZnO nanostructures modulated by supersaturation and growth temperature

Three kinds of ZnO hierarchical structures, nanocombs with tube- and needle-shaped teeth and hierarchical nanorod arrays, were successfully synthesized through the chemical vapor deposition method. Combining the experimental parameters, the microcosmic growing conditions (growth temperature and supersaturation) along the flux was discussed at length, and, based on the conclusions, three reasonable growth processes were proposed. The results and discussions were beneficial to further realize the relation between the growing behavior of the nanomaterial and microcosmic conditions, and the hierarchical nanostructures obtained were also expected to have potential applications as functional blocks in future nanodevices. Furthermore, the study of photoluminescence further indicated that the physical properties were strongly dependent on the crystal structure.