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Development of Hybrid Nanostructures for Photocatalysis and Fuel Cell Applications

Final Report Summary - HYBRID NANOMATERIALS (Development of Hybrid Nanostructures for Photocatalysis and Fuel Cell Applications)

The synthesis of metal oxide nanostructures is attracting the attention of many reseracher due to their unique properties. The main advantage of the metal oxide materials is their stability in aqueous solutions. In this report we describe the sythesis of various metal oxide nanostructures at different shapes and sizes and study their electrical, optical and catalytic properties. Furthermore, we also report the synthesis of metal oxide-metal hybrid nanostructure grown in organic solvent. The growth of the metal nanoparticles on ZnO nanopyramids is shown.
Metal-oxide materials and their hybrid nanostructures
A facile one-step approach for the synthesis and assembly of copper and copper-oxide nanocrystals
A simple one-step approach for the formation of close packed films of copper and copper oxide nanoparticles is described. Thermal decomposition of copper cupferrate, a single-source precursor, on silicon produces a well-controlled, assembled film of Cu nanocrystals. Upon oxidation, Cu2O is formed with retention of the assembly. Similarly, the thermal decomposition of manganese cupferrate results in the formation of porous MnO nanowires. Various solvents were used to examine their influence on the composition and assembly of the nanoparticles. This approach enables an easy and reproducible process for the synthesis and assembly of metal oxide nanostructures.
Paper: Diab, M.; Moshofsky, B.; Jen-La Plante, I.; Mokari, T. J. Mater. Chem., 21, 11626, 2011.
Formation of iron oxide, cobalt oxide and tin oxide via thermal decomposition of single source precursors:
Synthesis of various types of metal-oxide and metal-sulfide nanostructures via thermal decomposition of single-source molecular precursors was demonstrated. By varying the reaction conditions such as solvent, precursor concentration, temperature and time, we were able to control the shape of Fe3O4 (rectangles and belt-like structures), CoO nanofibers and SnO2 nanowires. Two sulfides are also presented - CdS filling of a vertically aligned ZnO nanowire array – creating a hybrid structure, and SnS wires. The formation of various phases of iron-oxide and cobalt-oxide is also shown.
Paper: Diab, M.; Volokh, M.; Moshofsky, B.; Jen-La Plante, I.; Flomin, K.; Chockler, E.; Mokari, T. Israel Journal of Chemistry, 52, 1081, 2012.
Formation of ultrathin tugsten oxide nanowires:
Tungsten oxide ultrathin nanowires have potential applications in electrochromic devices, dye sensitized solar cells and gas sensors and as photocatalysts. Herein, we report a synthesis for solution phase ultrathin nanowires with independent control over the length and diameter. W(CO)6 is used as the tungsten source, and the solvents octadecanol and octadecene are used. Morphological control is obtained by varying the ratios between these three components as well as reaction conditions such as time and temperature. Such precise synthetic tuning will enable future investigations on the role of the aspect ratio and diameter for the above-mentioned applications. We can infer from experimental data a plausible nucleation pathway that involves the formation of tungsten alkoxide clusters. Raman spectroscopy, X-ray photoelectron spectroscopy, electron microscopy, and X-ray and electron diffraction are used to characterize the nanowires, and the results indicate the phase to be a crystallographic sheer structure, such as W20O58.

Paper: Moshofsky, B.; Mokari, T. Chem. Mater., 25, 1384, 2013.
Electrochromic Properties of Ultrathin Nanowires of Tungsten Oxide
Electrochromic devices have benefited from the use of nanocrystalline films of particles to improve upon coloration and bleaching times while simultaneously enabling the use of solution based film making processes. In this work, electrochromic properties of ultrathin nanowires of substoichiometric tungsten oxide deposited on ITO via electrophoretic deposition are studied. These films show large coloration changes with very rapid coloration and bleaching times of 4.1 and 2.9 seconds respectively for an optical density change of 0.58 using H+ as the charge-balancing ion. These fast switching times are due to the combination of fast diffusion of ions into the narrow diameter wires and density control of the film through the deposition process. We also show good film stability over 300 colour–bleach cycles. This development not only advances the potential of WOx films in display applications, but can also improve their performance in smart windows.
Paper: Moshofsky, B.; Mokari, T. J. Mater. Chem. C., 2 , 3556, 2014.
Formation of metal-semiconductor Interface.
Metal-ZnO hybrid nanostructures:
Hybrid nanostructures of metal (Cu, Au, Ag)–ZnO nanopyramids were synthesized. These hybrid nanostructures possess two distinctmorphologies where the metal can be selectively attached to either the base or the tip of the ZnO pyramids. This is the first time that suchmorphologies are reported for Cu–ZnO and Ag–ZnO hybrid nanostructures.
Paper: Flomin, K.; Jen-La Plante, I.; Moshofsky, B.; Diab, M.; Mokari, T. Nanoscale, 6, 1335, 2014.