Nanocatalysis on Tailored Shape Supports: Au and Pd Nanoparticles Supported on MgO Nanocubes and ZnO Nanobelts.

Active Au and Pd nano-particles supported on MgO nano-cubes, ZnO nano-belts, and transition metal-contg. MgO nano-belts were synthesized by combining evapn. and deposition-pptn. techniques. The high activity and stability of Au/CeO2 and Pd/CeO2 nano-particle catalysts deposited on MgO cubes were remarkable and imply a variety of efficient catalysts can be designed and tested using this approach. The significant increase in concns. of corner and edge sites in MgO nano-cubes make them well-defined supports to study the detailed mechanism of catalytic activity enhancement.

Vapor-phase synthesis of metallic and intermetallic nanoparticles and nanowires: magnetic and catalytic properties.

In this paper, we present several examples of the vapor-phase synthesis of intermetallic and alloy nanoparticles and nanowires, and investigate their magnetic and catalytic properties. In the first example, we report the vapor-phase synthesis of intermetallic aluminide nanoparticles. Specifically, FeAl and NiAl nanoparticles were synthesized via laser vaporization controlled condensation (LVCC) from their bulk powders. The NiAl nanoparticles were found to be paramagnetic at room temp., with a blocking temp. of approx. 15 K. The FeAl nanoparticles displayed room-temp. ferromagnetism. In the second example, we report the vapor-phase synthesis of cobalt oxide nanoparticle catalysts for low-temp. CO oxidn. The incorporation of Au and Pd nanoparticles into the cobalt oxide support leads to significantly improved catalytic activity and stability of the binary catalyst systems. Finally, we report the synthesis of nanowires of Ge, Mg, Pd, and Pt using the vapor-liq.-solid (VLS) method where the vapor-phase growth of the wire is catalyzed using a proper metal catalyst present in the liq. phase.

Nature of magnetism in Co- and Mn-doped ZnO prepared by sol-gel technique

Magnetic properties of sol-gel-prepd. bulk samples of Co0.05Zn0.95O and Mn0.05Zn0.95O are reported before and after annealing in 5%H2/95%Ar at 573 K for 6 h. The as-prepd. samples are paramagnetic with the magnetic susceptibility c following the Curie-Weiss law: c = c0 + C/(T-q). The magnitudes of C are consistent with the magnetic moments expected for the Co2+ and Mn2+ states. After hydrogenation, the magnetism of Mn/ZnO is unchanged but Co/ZnO acquires room-temp. ferromagnetism (RTFM) with a magnetic moment of 0.35mB/Co site and hysteresis loop with coercivity Hc .simeq. 600 Oe, remanence Mr .simeq. 0.45 emu/g, and satn. magnetization Ms .simeq. 1.2 emu/g. Electron magnetic-resonance spectroscopy at 9.28 GHz gives signals corresponding to the Co2+ and Mn2+ states for the paramagnetic states and a broad FM signal for the hydrogenated Co/ZnO. This difference under hydrogenation between Co/ZnO and Mn/ZnO suggests that n-type doping leads to stabilizing of RTFM in Co/ZnO but not in Mn/ZnO, the latter perhaps requiring p-type doping.

Vapor phase synthesis of supported Pd, Au, and unsupported bimetallic nanoparticle catalysts for CO oxidation

We report the vapor phase synthesis and characterization of supported Pd, Au and unsupported bimetallic nanoparticle catalysts for
CO oxidation. The approach utilized in the present work is based on the laser vaporization/controlled condensation technique which
uniquely combines the features of pulsed laser vaporization with the controlled condensation process from the vapor phase to synthesize
nanoparticle catalysts of controlled size and composition. The results indicate that supported Pd/CeO2, Au/CeO2, and unsupported
bimetallic CuPd, CuAu, and AuPd nanoparticle catalysts exhibit excellent activity for CO oxidation. The significance of the current
method lies mainly in its simplicity, flexibility and the control of the different factors that determine the activity of the nanoparticle
catalysts.
Full Story

Microwave Synthesis of Highly Aligned Ultra Narrow Semiconductor Rods and Wires

One dimensional nanostructures (rods, wires, tubes, ribbons) have recently attracted considerable attention. These nanostructures represent ideal systems for dimension dependent optical, electrical and mechanical properties, and are expected to play an important role as building blocks in devices and processes such as light-emitting diodes, solar cells, single electron transistors, lasers and biological labels.1,2 Many modern methods based on physical and chemical approaches have been developed for the synthesis of controlled size and shape of one dimensional nanostructures including, for example, vapor-liquid-solid and the solution-liquid-solid processes, solvothermal, template-assisted, kinetic growth control, self-assembly, and thermolysis of single-source precursor in ligating solvents.3 In addition to these methods, microwave irradiation (MWI) offers great advantges as the simplest and fastest procedure since selective dielectric heating, due to the difference in the solvent and reactant dielectric constants, can provide significant enhancement in reaction rates. Furthermore, MWI methods are unique in providing scaled-up processes without suffering thermal gradient effects, thus leading to a potentially industrially important advancement in the large-scale synthesis of nanomaterials. Although MWI methods have been demonstrated for the synthesis of a variety of high quality, nearly monodisperse semiconductor nanoparticles4, there are very few reports on the synthesis of one-dimensional semiconductors by MWI.3j-k,4 However, all the reported one-dimensional semiconductor nanostructures are wider than the Bohr radius, which limits the expected quantum confinement effects.
Full Story

A Room-Temperature and Microwave Synthesis of M-Doped ZnO (M = Co, Cr, Fe, Mn & Ni)

A room temperature and microwave method for the preparation M-Doped ZnO where M = Co, Cr, Fe, Mn & Ni is desribed. X-ray diffraction of the synthesized samples show a single phase ZnO structure without any indication of the dopant. Magnetic studies of the as prepared samples show it to be paramagnetic. However, hydrogenation of particular samples at 573 K for 6 hours resulted in transforming the samples to a room temperature ferromagnet.

Full Story