Microwave Synthesis and Optical Properties of Uniform Nanorods and Nanoplates of Rare Earth Oxides.

We report on the rapid prodn., characterization, and spectral properties of uniform nanorods, nanowires, and nanoplates of rare earth oxides M2O3 (M = Pr, Nd, Sm, Eu, Gd, Tb, Dy). The method developed, based on microwave irradn. (MWI), allows the control of the size and shape of the rare earth oxide nanostructures by varying the MWI reaction time and the relative concns. of the org. surfactants. The uniformity of the rods and of the wires is demonstrated in their spontaneous assembly into highly ordered 2D supercrystals. The MWI method provides a unique opportunity for the large-scale synthesis of rare earth nanostructures without suffering thermal gradient effects.

Reversible paramagnetism to ferromagnetism in transition metal-doped TiO2 nanocrystals prepared by microwave irradiation.

TiO2 nanoparticles doped with 1%, 5%, and 10% M (M=Co, Fe, and Ni) were prepd. by microwave irradn. and characterized using x-ray diffraction, transmission electron microscopy, and magnetometry. The as-prepd. samples are found to be paramagnetic at room temp., with the magnetic susceptibility following the Curie-Weiss law in the investigated range of 2-300 K. However, transformation from paramagnetism to room-temp. ferromagnetism (RTFM) was obsd. by hydrogenating the samples at 400 °C. Reheating in air converted the samples back to paramagnetic while rehydrogenating the samples again induced ferromagnetism. It is argued that the reversible RTFM obsd. is due to interaction between the dopant metal ions and oxygen vacancies produced during hydrogenation. X-ray diffraction of the hydrogenated Co- and Fe-doped samples shows only a single TiO2 phase suggesting that the obsd. RTFM may be intrinsic, but for the Ni-doped samples the magnetism may arise from metallic Ni on the surfaces of the TiO2 nanoparticles.

Nanoparticles in astrochemistry: synthesis and characterization of meteorite dust nanoparticles.

Interstellar dust particles (IDPs) constitute most of the solid matter in the universe. Large quantities of IDPs are also present in the Solar System and fall on Earth. IDPs are also of interest as they can catalyze astrochem. reactions and prebiotic synthesis, and their org. contents are believed to have contributed to the origins of life. Their chem. compn. is similar to carbonaceous chondrite comets, asteroids and meteorites. The IDPs are microporous web-like aggregates of 10-100 nm phyllosilicate particles with morphologies similar to particles produced by the Laser Vaporization Controlled Condensation (LVCC) method. IDPs are available only as microscopic samples, and simulated IDPs are needed to study their chem. and catalytic effects. To produce such simulated IDPs, we formed nanoparticles from carbonaceous chondrite meteorites by LVCC processing. The compns., morphologies, particle size distribution, FTIR spectra, and catalytic properties of the meteorite-based nanoparticles were investigated and compared with the original meteorite materials and ref. minerals.

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.
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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.
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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.

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Sol–Gel Synthesis and Magnetic Studies of Titanium Dioxide Doped with 10% M (M=Fe, Mn and Ni)

TiO2 nanocrystals doped with 1%, 5% and 10% Co/TiO2 and 10% M (M=Fe, Mn and Ni) were prepared by the sol–gel technique and characterized using X-ray diffraction and SQUID. The as-prepared samples are found to be paramagnetic at room temperature, with the magnetic susceptibility following the Curie–Weiss law in the investigated range of 2–370 K. However, transformation from paramagnetism to room-temperature ferromagnetism (RTFM) for the 5% Co/TiO2 was observed by hydrogenating the sample at 573 K while the 1% sample remained paramagnetic. As the percentage of Co was increased from 5% to 10% the Curie temperature increased from 390 K to 470 K determined via extrapolation. Transformation from paramagnetism to room-temperature ferromagnetism (RTFM) was also observed by hydrogenation of 10% Fe/TiO2 at 573 K for 6 h. X-ray diffraction of the hydrogenated sample shows only single phase TiO2 structure suggesting that the observed RTFM may be intrinsic but
magnetic studies may suggest the possibility of Fe nanoparticles.
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Microwave Synthesis of Supported Au and Pd Nanoparticle Catalysts for CO Oxidation

We report the microwave synthesis and characterization of Au and Pd nanoparticle catalysts supported on CeO2, CuO, and ZnO nanoparticles for CO oxidation. The results indicate that supported Au/CeO2 catalysts exhibit excellent activity for low-temperature CO oxidation. The Pd/CeO2 catalyst shows a uniform dispersion of Pd nanoparticles with a narrow size distribution within the ceria support. A remarkable enhancement of the catalytic activity is observed and directly correlated with the change in the morphology of the supported catalyst and the efficient dispersion of the active metal on the support achieved by using capping agents during the microwave synthesis. 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.
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Nature of the reversible paramagnetism to ferromagnetism state in cobalt-doped titanium dioxide

We report that Co0.1Ti0.9O2 prepared by the sol-gel technique is a paramagnet following the Curie–Weiss law: x= x0+C/ (T+theta). However, hydrogenation at 673 K in H2/Ar 5% /95% gas converts a part of the paramagnetic sample to room temperature ferromagnet RTFM and reheating the sample at 573 K in air converts it back to a paramagnet completely. This reversible RTFM transition has been observed for additional cycles by alternately heating in air and H2 / Ar. It is argued that this RTFM is intrinsic and it is due to Co2+–Co2+ exchange interaction mediated by oxygen holes which are produced by hydrogenation but eliminated by oxidation.
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Controlled transformation of paramagnetism to room-temperature ferromagnetism in cobalt-doped titanium dioxide

Samples of Co0.1Ti0.9O22 anatase prepared by the sol–gel technique are found to be paramagnetic at room temperature, with the magnetic susceptibility following Curie–Weiss law in the investigated range of 2–370 K. However, transformation from paramagnetism to room-temperature ferromagnetism ~RTFM! is observed by hydrogenation of the sample at 573 K. The increase in the hydrogenation time from 1 to 6 h increases the remanance, and the Curie temperature 470 K is determined by extrapolation. X-ray photoelectron spectroscopy and transmission electron microscopy of the hydrogenated samples failed to detect Co nanoparticles, suggesting that the observed RTFM in the hydrogenated samples may be intrinsic.
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Surface Enhanced Raman Spectroscopy Using Silver Nanoparticles: The Effects of Particle Size and Halide Ions on Aggregation

A surface enhanced Raman spectroscopy (SERS) investigation of the aggregation of silver nanoparticles formed via LVCC with diameters in the range 5–50 nm were studied. It was found that with 647.1 nm excitation maximum enhancement is observed using particles with 11 nm diameters. Upon addition of sodium halides, enhancement is proportional to the polarizability of the anion. Maximum enhancement was observed when the concentration of the anion is approximately equal to the concentration of the adsorbate.
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Formation of Cobalt Nitrate Hydrate, Cobalt Oxide, and Cobalt Nanoparticles Using Laser Vaporization Controlled Condensation

Herein, we report for the first time the synthesis of cobalt nitrate hexahydrate, cobalt oxide, and cobalt particles formed from a high purity cobalt metal by a novel laser vaporization controlled condensation (LVCC) method under controlled pressures of N2 and O2. The metal vapor produced from a cobalt target in the presence of 50% N2 and 50% O2 results in the formation of cobalt nitrate. We also explored the possibilities of forming cobalt oxide and cobalt nanoparticles by altering the ratio of N2 and O2 present. For example, the synthesis of pure cobalt oxide (CoO) nanoparticles is of importance and challenging since a simple chemical route is complex. We believe that this work will be of significant importance since the present method is promising for the synthesis of metal mono oxides.
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Greetings

Welcome to the Blog dedicated to all things nano. As for myself, I am currently a post-doc at VCU researching nanoparticles as hydrogen storage materails and catalysts for CO oxidation.