The effective site-selective interaction between the π-bonds in the aromatic rings of the polyaniline and the graphitic structure of multiwall carbon nanotubes would strongly facilitate the charge-transfer reaction between the two components. We adopted multiwall carbon nanotubes (MWNTs) with minimal defects as templates and facilely fabricated carbon nanotube−polyaniline nanocomposites with uniform core−shell structures by ultrasonic assisted in situ polymerization. By varying the ratio of aniline monomers and carbon nanotubes, the thickness of polyaniline layers can be effectively controlled. The results indicated that the presence of carbon nanotubes with minimized defects induced the formation of a more planar conformation of polyaniline even when a high weight percent of aniline was loaded. As a result, macroscopically, great improvements in the electrical and electrochemical properties of the resulting nanocomposites were observed.

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The morphological modulation and phase conversion of a-and b-Ni(OH) 2 complex architectures with varying subunits from nanopetals, nanocolumns, nanocones, and nanoflakes were investigated using a facile coordination homogeneous precipitation method in the Ni(NO 3 ) 2 + urea system. Slow growth and nucleation rates due to relatively low reaction temperatures and molar ratios of CO(NH 2 ) 2 to Ni(NO 3 ) 2 induced the formation of uniform flower-like a-Ni(OH) 2 architectures. Such flower-like architectures originated from subordinate nanopetals that grow perpendicular to the primordial nanopetal surface and are driven by minimum surface free energy effects. At relatively high reaction temperatures, flower-like a-Ni(OH) 2 can transform into b-Ni(OH) 2 microspheres assembled from nanocolumns, nanocones, and even nanoflakes by varying the reaction time. These processes could be related to the synergetic effect of the anisotropic growth and continuous increase in mass transportation along the [001] direction. Flower-like a-Ni(OH) 2 exhibited better electrochemical activity for glucose oxidation compared with b-Ni(OH) 2 microspheres consisting of nanocones because of its special flower-like morphology with high specific surface areas, well-ordered pores, and layered structures intercalated by water and anions. The approach in this study can be used to fabricate other metal hydroxide nanostructures. Flower-like Ni(OH) 2 nanoarchitectures have potential applications in rechargeable batteries, photonic catalysis, and non-enzymatic sensors for glucose.

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A facile template-free and one-pot thermal decomposition approach was used for the mass preparation of submicrometer-sized NiO octahedra. Ni octahedra with tailored crystallization and texture characteristics are easily achieved through H 2 -annealing of NiO octahedra at various temperatures. The good morphology retention of Ni octahedra is due to the principle of minimum surface free energy as well as the similar crystallographic system to that of NiO. Studies on static magnetic and microwave electromagnetic properties reveal the relationships among the reactivity, shape, and resultant properties of the nanomaterials. Because of their high BET specific surface area and favorable crystal size, porous Ni octahedra produced at 300 C exhibit excellent matching and absorbing properties with a minimum R L value of À37.93 dB at 12.80 GHz and 11.60 GHz bandwidth (below À20 dB). Thus the Ni octahedra described here are believed to have a wide range of applications, including catalysis, electromagnetic shielding, and absorption.

Flower-like Co superstructures composed of leaf-like flakes were synthesized via a facile hydrothermal approach independent of surfactants or complex precursors. The evolution of the morphology and crystal phase was closely related to the variation of the electrode potentials, in which NaOH and hydrazine hydrate played crucial roles. The microwave electromagnetic and absorbing properties of the flower-like Co/wax composites varied strongly with the mass ratios (l) of Co powder to wax. At the low l of Co powder to wax, flower-like Co superstructures functioned as the random distributed patches in wax matrix and, therefore composites exhibited frequency selective surface (FSS) behaviors. Owing to high conductance and eddy current losses, however, composites with high l showed excellent microwave absorption performances, with a minimum reflection loss (R L ) of À40.25 dB observed at 6.08 GHz, corresponding to a matching thickness of 2.5 mm. In particular, the absorption bandwidth (R L # À20 dB) was 13.28 GHz. The current work provides insights into the absorption mechanism of flower-like complex absorption materials.

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