Controlled synthesis and chemical conversions of FeO nanoparticles
Controlled synthesis and chemical conversions of FeO nanoparticles
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DOI：
10.1002/anie.200701694
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发表时间：
2007-01-01
影响因子：
16.6
通讯作者：
Sun, Shouheng
中科院分区：
文献类型：
--
作者：
Hou, Yanglong;Xu, Zhichuan;Sun, Shouheng
MO 型过渡金属氧化物纳米粒子（其中 M 为 Mn、Co、Ni 或 Fe）最近引起了极大的兴趣，因为它们具有作为可充电固态电池的电极材料的潜力，[1] 作为燃料电池反应的有效催化剂，[2] 以及作为理解纳米磁性的纳米级磁性模型。 [3]方铁矿 (FeO) 是常见铁氧化物的一种形式，该族还包括赤铁矿 (a-Fe2O3)、磁赤铁矿 (g-Fe2O3) 和磁铁矿 (Fe3O4)。它具有岩盐结构，其中 Fe 和 O 形成非化学计量的 FexO (x= 0.83–0.96) 和有序分布的 Fe 空位。 [4]该结构化学性质不稳定，容易通过两步歧化过程分解成 a-Fe 和反尖晶石 Fe3O4，或氧化形成 Fe3O4、g-Fe2O3 和/或 a-Fe2O3。 [4]这种化学反应性使得 Fe3O 纳米颗粒难以制造，并且通过铁盐高温溶液相分解制备的纳米颗粒尚未得到充分表征。 [5]在此，我们报道了通过乙酰丙酮铁（III）（[Fe-(acac) 3]）与油酸（OA）和油胺（OAm）作为表面活性剂和溶剂的高温还原分解，轻松有机相合成单分散Fe3O纳米颗粒。通过控制加热条件将颗粒的尺寸从14纳米调整到100纳米，并且根据反应中使用的OA和OAm的体积比将颗粒的形状控制为球形或截角八面体。在氩气氛下热退火将这些 FeO 纳米颗粒转化为复合 Fe-Fe3O4 纳米颗粒，而 FeO 纳米颗粒的受控氧化导致 Fe3O4、g-Fe2O3 或 a-Fe2O3 纳米颗粒的形成。这些单分散 Fe3O 纳米颗粒在催化 [2c-f] 和气体传感器 [2g] 应用方面具有巨大潜力。顺磁性 Fe3O 纳米粒子的化学转化也可以被认为是合成各种磁性氧化铁或铁纳米粒子的替代方法，但更好的方法，其尺寸很难从以前的有机相合成中实现。[6]纳米粒子是通过在 2208C 和 3008C 的受控加热下从反应混合物（[Fe (acac) 3] 在 OA 和 OAm 的混合物中）生长的。在过量的OAm存在下，形成球形纳米粒子，而在等量的OA和OAm存在下，获得截短的八面体纳米粒子。通过简单地控制2208℃和3008℃的加热时间来调节两种纳米粒子的尺寸。例如，通过在 2208C 和 3008C 下用 OA (8 mL) 和 OAm (12 mL) 处理 [Fe (acac) 3] 30 分钟，合成 14 nm 球形纳米粒子。在 3008°C 下延长加热 1 小时，得到 22 nm 纳米粒子。将 [Fe (acac) 3]、OA (10 mL) 和 OAm (10 mL) 的反应混合物在 2208°C 和 3008°C 下分别加热 30 分钟，导致形成 32 nm 截头八面体纳米颗粒，同时将混合物在 2208°C 下加热 1 小时并在 3008°C 下加热 30 分钟，得到 53 nm 纳米颗粒，并在2208℃ 30 分钟，3008℃ 1 小时，得到 100 nm 截短八面体纳米颗粒。图 1 显示了代表性 Fe3O 纳米粒子的透射电子显微镜 (TEM) 图像。在图 1d 的扫描电子显微镜 (SEM) 图像中可以更好地看到颗粒的截断八面体形状。这些尺寸和形状控制的合成表明：1）使用 OA 和 OAm 作为溶剂和表面活性剂有利于 Fe3O 纳米颗粒的形成和稳定； 2) 过量 OAm 的存在有利于
Transition metal oxide nanoparticles of type MO, where M is Mn, Co, Ni, or Fe, have attracted tremendous interest recently because of their potential as electrode materials for rechargeable solid-state batteries,[1] as efficient catalysts for fuel-cell reactions,[2] and as nanoscale magnetic models for understanding nanomagnetism.[3] Wüstite (FeO) is one form of the common iron oxides, a group that also includes hematite (a-Fe2O3), maghemite (g-Fe2O3), and magnetite (Fe3O4). It has a rock-salt structure with Fe and O forming nonstoichiometric FexO (x= 0.83–0.96) and Fe vacancies in an ordered distribution.[4] The structure is not chemically stable and is prone to decomposition into a-Fe and inverse spinel Fe3O4 through a two-step disproportionation process or to oxidation to form Fe3O4, g-Fe2O3, and/or a-Fe2O3.[4] This chemical reactivity makes FeO nanoparticles difficult to make and those prepared from the high-temperature solution-phase decomposition of iron salt have not been fully characterized.[5] Herein we report a facile organic-phase synthesis of monodisperse FeO nanoparticles through high-temperature reductive decomposition of iron (III) acetylacetonate ([Fe-(acac) 3]) with oleic acid (OA) and oleylamine (OAm) both as surfactants and solvents. The sizes of the particles are tuned from 14 to 100 nm by controlling the heating conditions and the shapes of the particles are controlled to be either spherical or truncated octahedral depending on the volume ratio of OA and OAm used in the reaction. Thermal annealing under an argon atmosphere converted these FeO nanoparticles into composite FeÀFe3O4 nanoparticles, while controlled oxidation of the FeO nanoparticles resulted in the formation of Fe3O4, g-Fe2O3, or a-Fe2O3 nanoparticles. These monodisperse FeO nanoparticles have great potential for catalysis [2c–f] and gas-sensor [2g] applications. The chemical conversions of the paramagnetic FeO nanoparticles may also be considered as an alternative, yet better, approach to the synthesis of various magnetic iron oxide or iron nanoparticles with sizes that are difficult to achieve from previous organic-phase syntheses.[6]The nanoparticles were grown from the reaction mixture ([Fe (acac) 3] in a mixture of OA and OAm) by controlled heating at 2208C and 3008C. In the presence of an excess amount of OAm, spherical nanoparticles were formed, whereas in the presence of equivalent amounts of OA and OAm, truncated octahedral nanoparticles were obtained. The size of both kinds of nanoparticles was tuned by simply controlling the period of heating at 2208C and 3008C. For example, 14-nm spherical nanoparticles were synthesized by treating [Fe (acac) 3] with OA (8 mL) and OAm (12 mL) at 2208C and 3008C, each for 30min. Extended heating at 3008C for 1 h gave 22-nm nanoparticles. Heating of a reaction mixture of [Fe (acac) 3], OA (10 mL), and OAm (10 mL) at 2208C and 3008C, each for 30 min, led to the formation of 32-nm truncated octahedral nanoparticles, while heating of the mixture at 2208C for 1 h and at 3008C for 30 min gave 53-nm nanoparticles and heating at 2208C for 30 min and at 3008C for 1 h yielded 100-nm truncated octahedral nanoparticles. Figure 1 shows transmission electron microscopy (TEM) images of representative FeO nanoparticles. The truncated octahedral shape of the particles can be better seen in the scanning electron microscopy (SEM) image of Figure 1d. These size-and shape-controlled syntheses suggest that 1) the use of OA and OAm both as solvents and surfactants facilitates the formation and stabilization of FeO nanoparticles; 2) the presence of an excess of OAm facilitates