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.