A facile liquid foam based synthesis of nickel nanoparticles and their subsequent conversion to NicoreAgshell particles: structural characterization and investigation of magnetic properties
A facile liquid foam based synthesis of nickel nanoparticles and their subsequent conversion to NicoreAgshell particles: structural characterization and investigation of magnetic properties
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DOI：
10.1039/b405335b
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发表时间：
2004-01-01
影响因子：
--
通讯作者：
Sastry, M
中科院分区：
文献类型：
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作者：
Bala, T;Bhame, SD;Sastry, M
报道了一种在稳定的水性泡沫中合成镍纳米颗粒的简便方法。Ni纳米颗粒的尺寸约为12 - 15 nm，并且当使用油酸作为封端剂时，作为水性悬浮液或粉末是稳定的。考虑到银纳米涂层提供的额外稳定性和增强的操纵能力，这些Ni纳米颗粒随后用银壳涂覆。这是通过一个简单的transmethalide反应，其中纳米粒子表面镍原子作为本地化还原剂的银离子在溶液中。当通过表面反应形成银壳时，发生Ni核的平均尺寸的减小。在核-壳结构形成之后，Ni-核具有10 - 20 nm的平均直径，而Ag-壳具有2 - 4 nm的厚度。用振动样品磁强计对油酸包覆的镍和镍-银壳纳米粒子的磁特性进行了研究。初生的油酸包覆的Ni纳米颗粒显示出20 K的低超顺磁性阻断温度TB。场依赖的磁性行为以上和以下T-B显示对应于超顺磁性的标准功能，如预期的非常小的Ni微晶再次表明，每个12纳米的颗粒是多晶的。在NicoreAgshell系统中的磁贡献仅来自Ni核，并且可以预测的是，由于Ni核的较小尺寸，该系统的阻断温度低于12 K。
A facile route for the synthesis of nickel nanoparticles in stable aqueous foams is reported. The Ni nanoparticles were roughly 12 - 15 nm in size and were stable as aqueous suspensions or powders when oleic acid was used as a capping agent. These Ni nanoparticles were subsequently coated with a silver shell in view of the extra stability and the enhanced manipulative ability afforded by the silver nanocoating. This was accomplished by a simple transmetallation reaction wherein the nanoparticle surface nickel atoms act as localized reducing agents for the silver ions in solution. As the silver shell is formed through the surface reaction a reduction in the average size of the Ni-core occurs. After the core - shell structure formation, the Ni-core has an average diameter of 10 - 20 nm while the Ag-shell has a thickness of 2 - 4 nm. The pristine oleic acid coated Ni and NicoreAgshell nanoparticles were probed for their magnetic characteristics by a vibrating sample magnetometer. The nascent, oleic acid coated Ni nanoparticles display a low superparamagnetic blocking temperature, TB, of 20 K. The field dependent magnetic behaviour above and below T-B displays the standard features corresponding to superparamagnetism, as expected for very small Ni crystallites suggesting again that each 12 nm particle is polycrystalline. The magnetic contribution in the NicoreAgshell system comes from only the Ni core and predictably, the blocking temperature of this system is below 12 K due to the smaller size of the Ni core.