The properties of metal oxide nanocrystals can be tuned by incorporating mixtures of matrix metal elements, adding metal ion dopants, or constructing core/shell structures. However, high-temperature conditions required to synthesize these nanocrystals make it difficult to achieve the desired compositions, doping levels, and structural control. We present a lower temperature synthesis of ligand-stabilized metal oxide nanocrystals that produces crystalline, monodisperse nanocrystals at temperatures well below the thermal decomposition point of the precursors. Slow injection (0.2 mL/min) of an oleic acid solution of the metal oleate complex into an oleyl alcohol solvent at 230 °C results in a rapid esterification reaction and the production of metal oxide nanocrystals. The approach produces high yields of crystalline, monodisperse metal oxide nanoparticles containing manganese, iron, cobalt, zinc, and indium within 20 min. Synthesis of tin-doped indium oxide (ITO) can be accomplished with good control of the tin doping levels. Finally, the method makes it possible to perform epitaxial growth of shells onto nanocrystal cores to produce core/shell nanocrystals.
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A highly enantioselective 1,2-aza-FriedelCrafts reaction of N-tert-butyldimethylsilylindole with N-tert-butoxycarbonyl aromatic imines is demonstrated using a BINOL-derived monophosphoric acid catalyst. The present approach provides efficient access to 3-indolylmethaneamines with aryl substituents in excellent enantioselectivities (up to 98 % ee). An inversion in the sense of enantioselection was found between monophosphoric acid catalysts bearing different substituents introduced at the 3,3'-position of binaphthyl backbone. We also calculated the three-dimensional structure of the monophosphoric acid catalysts to speculate on the inversion of the stereochemical outcome.
A modified alcohol reduction process by controlling the complexation and reduction of metallic ions was developed to obtain compositionally and structurally controlled Ni-Pt nanoparticles (NPs) with sizes less than 20 nm in a high yield. The characterization of NPs synthesized under different experimental conditions suggested that the reduction of Pt and subsequent formation of cubic-shaped Ni-Pt NPs were strongly dependent on the formation of Pt-oleylamine (OAm) complexes. Thus, prior to the synthesis of Ni-Pt NPs, the formation and reduction process of Pt complexes in the solution-state were investigated by in situ UV-Visible and X-ray spectroscopies. The complexation of Pt ions along with their reduction prior to the formation of Pt metal and their influence on the size and the elemental distribution of Pt within the Ni-Pt NPs were revealed. Then, the above findings were actively utilized to design and to obtain Pt(core)-Ni(shell), Ni-Pt alloy, and Ni(core)-Pt(shell) nanostructures by regulating the OAm concentration in the system. The specific distribution of Pt on the Ni-Pt surface was confirmed by decolorization of methylene blue. Furthermore, Ni-Pt NPs with a Pt concentration of 10 at.% exhibited a mass activity four times larger than that of commercial Pt during the oxygen reduction reaction (ORR).
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