Mesoscopic Structures of Nanocrystals: Collective Magnetic Properties Due to the Alignment of Nanocrystals
摘要:
Maghemite nanocrystals, deposited by slow evaporation on HOPG (highly oriented pyrolytic graphite) substrate, form mesoscopic structures which strongly depend on the nanocrystal coating. When the coating consists of citrate ions and octanoic acid, tubelike structures are formed when the deposition process takes place under an applied magnetic field. Conversely, dense films are formed when the nanocrystals are coated with propanoic acid and dodecanoic acid. The magnetic behaviors markedly differ with the organization of nanocrystals and are attributed to the change in the anisotropy of the organized structures. Nanocrystals organized in tubes behave as nanowires.
Control of the Size of Cobalt Ferrite Magnetic Fluid
摘要:
Cobalt and iron(II) dodecyl sulfate, Co(DS)(2) and Fe(DS)(2), are used to make nanosize magnetic particles. The size of the particles is controlled by the surfactant concentration. The average size of the particles, determined by transmission electron microscopy and from simulation of Langevin curves, varies from 2 to 5 nm, with 30-35% polydispersity in the size distribution. The magnetic studies are performed on particles having 2, 3, and 5 nm diameter, respectively. These particles are characterized by a superparamagnetic behavior. The saturation magnetization decreases with the particle size and is explained in terms of an increase in the noncollinear structure at the interface. For 5 nm particles, a cubic magnetocrystalline anisotropy is observed. On decreasing the size of the particles, the surface anisotropy strongly increases.
The newly prepared bipyridine (S,S)‐2 was then tested as a chiral ligand in metal‐catalyzed enantioselectivereactions. Out of the studied reactions the most promising results were obtained in epoxide ring opening (82% yield, 98% ee) and Mukaiyama aldolreaction (>96% yield, 99/1 dr, 92% ee). In the case of Mukaiyama‐aldolreaction as well as in the Michael addition, novel ligand 2 proved its robustness
Cucurbit[7]uril modified iron oxide nanoparticles (CB[7]NPs) were loaded with palladium to form nano‐catalysts (Pd@CB[7]NPs) that, with microwave heating, catalysed Suzuki–Miyaura, Sonogashira, and Mizoroki–Heck cross‐coupling reactions. Reactions were run in environmentally benign 1:1 ethanol/water solvent under convenient aerobic conditions. In a preliminary screening, conversions and yields were
将Cucurbit [7]尿素修饰的氧化铁纳米颗粒(CB [7] NPs)与钯混合形成纳米催化剂(Pd @ CB [7] NPs),并通过微波加热催化Suzuki–Miyaura,Sonogashira和Mizoroki–颈交叉耦合反应。反应在方便的有氧条件下于环境友好的1:1乙醇/水溶剂中进行。在初步筛选中,转化率和产率始终很高,周转频率(TOF)为64至7360 h -1。可以用磁铁回收纳米催化剂,并重复使用几次(Suzuki–Miayura反应重复6次),而不会损失活性。
Magnetic nano-organocatalysts: impact of surface functionalization on catalytic activity
作者:E. Nehlig、L. Motte、E. Guénin
DOI:10.1039/c5ra20644h
日期:——
Nano-organocatalysts were synthesized using controlled click chemistry and studied in aldolization and Michael addition reactions. It was shown that small modifications of the nanosurface can have a drastic effect on the catalysis.
Control of the Size of Cobalt Ferrite Magnetic Fluid
作者:N. Moumen、M. P. Pileni
DOI:10.1021/jp9524136
日期:1996.1.1
Cobalt and iron(II) dodecyl sulfate, Co(DS)(2) and Fe(DS)(2), are used to make nanosize magnetic particles. The size of the particles is controlled by the surfactant concentration. The average size of the particles, determined by transmission electron microscopy and from simulation of Langevin curves, varies from 2 to 5 nm, with 30-35% polydispersity in the size distribution. The magnetic studies are performed on particles having 2, 3, and 5 nm diameter, respectively. These particles are characterized by a superparamagnetic behavior. The saturation magnetization decreases with the particle size and is explained in terms of an increase in the noncollinear structure at the interface. For 5 nm particles, a cubic magnetocrystalline anisotropy is observed. On decreasing the size of the particles, the surface anisotropy strongly increases.
SSG or SFM state in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si0009.gif" overflow="scroll"><mml:msub><mml:mrow><mml:mi>CoFe</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mrow><mml:mi mathvariant="normal">O</mml:mi></mml:mrow><mml:mrow><mml:mn>4</mml:mn></mml:mrow></mml:msub></mml:math> nano-agglomerates fabricated by micro-emulsion method
We report on magnetic properties of CoFe2O4 nano-agglomerates obtained by micro-emulsion technique under specific conditions. The samples form a unique morphology as observed by transmission electron microscopy and scanning electron microscopy investigations. Concerning magnetic properties, they exhibit a considerable coercivity of almost 1T at 2K, which continuously decreases up to the characteristic temperature, T-g = 350 K. The temperature dependence of the zero-field cooled (ZFC) and field cooled (FC) magnetization, respectively, is furcated at the T-g, and the temperature dependencies of the a.c. susceptibility exhibit a frequency-dependent maximum at similar to T-g. The observed behavior is discussed in terms of the super-spin-glass (SSG) and the super-ferromagnetic (SFM) regime considering the morphology of the nano-agglomerates. (C) 2010 Elsevier B.V. All rights reserved.