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(vi). Binary Systems:
1. ZnO nanowires, CuO nanowires, and α-Fe2O3 nanotubes as well as their corresponding arrays have been successfully synthesized via a low cost, generalizable, and simplistic template method. Diameters of one-dimensional (1-D) metal oxide nanostructures (~60 – 260 nm), measuring microns in length, can be reliably and reproducibly controlled by the template pore channel dimensions. Associated vertically aligned arrays have been attached to the surfaces of a number of geometrically significant substrates, such as curved plastic and glass rod motifs. The methodology reported herein relies on the initial formation of an insoluble metal hydroxide precursor, resulting from the reaction of the corresponding metal solution and sodium hydroxide, and its subsequent transformation under mild conditions into the desired metal oxide nanostructures. Size- and shape-dependent optical, magnetic, and catalytic properties of as-prepared 1-D metal oxides were investigated and noted to be mainly comparable or better than the associated properties of the corresponding bulk oxides. Ref.: ACS Nano, v.2, 944 (2008).
2. VO2 nanorods have been initially generated as reactive nanoscale precursors to their subsequent conversion to large quantities of pure, highly crystalline V2O3 with no detectable impurities. Structural changes in VO2, associated with the metallic-to-insulating transition from the monoclinic form to the rutile form, have been investigated and confirmed using X-ray diffraction and synchrotron data, showing that the structural transition is reversible and occurs at around 63ºC. When this VO2 one-dimensional sample was subsequently heated to 800ºC in a reducing atmosphere, it was successfully transformed into V2O3 with effective retention of its nanorod morphology. We have also collected magnetic and transport data on these systems that are comparable to bulk behavior and consistent with trends observed in previous experiments. Ref.: PhysChemChemPhys, v.11, 3718 (2009) [invited].
3. We have characterized (a) discrete, individual motifs and (b) arrays of crystalline and pure semiconducting metal sulfide (CuS, PbS, and CdS) nanowires, synthesized via an inexpensive, generalizable, simplistic, and ambient modified template technique. We have demonstrated control over the diameters and lengths of our one-dimensional (1-D) nanostructures through corresponding variations in the template membrane’s pore size and thickness. We have not only successfully generated cubic-phase 1-D CdS nanowires but also produced, at slightly elevated temperatures, unusual CdS cactus-like, hierarchical nanostructures, consisting of tiny nano-needles projecting out from the outer surfaces of parent CdS nanotube motifs. Vibrational properties of all of these metal sulfide nanomaterials have been extensively studied. In addition, our results indicate that our as-prepared hexagonal-phase CdS cactus-like nanotubes evinced a higher photocatalytic degradation activity than that of both cubic CdS nanowires and their commercial bulk counterparts. Ref.: Chem. Mater., v.21, 4541 (2009).
4. Herein, we report the synthesis of one-dimensional chromium oxide nanostructures, utilizing a modified sol−gel technique combined with a constrained template environment. Using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM), we noted that individual nanowires were cylindrical in nature and appeared to be composed of smaller, crystalline, constituent nanoparticles, sintered and aggregated together so as to form a discrete, polycrystalline structure. Spectroscopic and diffraction investigations of our nanostructures confirmed their chemical composition with little if any impurities. Moreover, we further investigated the properties of our nanomaterials using both electrical and magnetic characterization. Interestingly, the magnetic properties of our nanostructures are strongly modified as compared with the bulk, due to the emergence of a net magnetic moment induced by uncompensated surface spins. Catalysis data showed that these nanostructures were active toward the thermal decomposition of KClO4. Ref.: Chem. Mater., v.23, 1000 (2011).
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