Homoepitaxial Size Control and Large-Scale Synthesis of Highly Monodisperse Amine-Protected Palladium Nanoparticles
Homoepitaxial Size Control and Large-Scale Synthesis of Highly Monodisperse Amine-Protected Palladium Nanoparticles
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DOI：
10.1002/smll.201001685
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发表时间：
2011-02-18
期刊：
影响因子：
13.3
通讯作者：
Teranishi, Toshiharu
中科院分区：
文献类型：
--
作者：
Sato, Ryota;Kanehara, Masayuki;Teranishi, Toshiharu
据报道，配体。以Pd前驱体为原料，在简单温和的条件下，采用化学还原法制备单分散Pd纳米粒子。由此得到的Pd纳米粒子由于其高度的单分散性而自组装成六重对称的超晶格结构。通过原位同质外延生长，Pd纳米粒子的尺寸可以精确地控制在2~5 nm之间。在大规模合成中，这种方法在不改变尺寸或分散性的情况下提供了几乎0.5克Pd纳米颗粒的高产量(>；90%)。胺保护的Pd纳米粒子有可能成为形成异质结构的结构单元，如Pd/γ-Fe2 O3异质结构纳米粒子。在50℃的空气中，将1.5 mmol的四丁基硼氢化铵(TBAB，1.5 mm ol)溶解在氯仿(2 M L)中，注入到乙酸钯(0.5 m ol)、油胺(OAM，10 m ol)和油酸(OAc，10 m ol)的混合物中，合成了Pd纳米颗粒。透射电子显微镜图像(图1a，b)表明，它们的平均直径为3 nm，尺寸分布窄(标准偏差σ=6.7%)。纯化后的纳米颗粒易在氯仿、四氢呋喃、甲苯、正己烷等非极性溶剂中重新分散。高分辨电子显微镜(HRTEM)分析(图1c)表明，Pd纳米粒子具有许多晶界，并且是多晶的。从粉末X射线衍射图(图1D)可以看出，Pd纳米粒子为面心立方(FCC)Pd。图1D中Pd纳米粒子的衍射角(例如2θ(111)=39.740)与块体Pd(例如2θ(111)=40.115)相比向更低的角度移动。这表明Pd-Pd纳米粒子形成后，Pd-Pd原子间距增大，这与以前的报道一致。[10A]在Pd-Pd粉末样品中，(200)和(220)衍射峰与(111)衍射峰的强度比分别为0.10和0.04，远低于传统粉末样品的强度比(0.42和0.25)。这表明合成的Pd纳米粒子在{111}面上分布丰富。用图1D中(111)峰的半高全宽(FWHM(111)=5.0)和Scherrer方程计算了1.7 nm处的平均晶体尺寸。这比用透射电子显微镜测得的Pd纳米粒子的平均粒径3.0 nm要小，这表明Pd纳米粒子是多晶的，这与HRTEM观察到的结果一致。OAM和OAc均可作为Pd纳米粒子的保护性配体，并用1H-核磁共振对其进行了表征。首先，对烯烃氢化学位移进行了监测，因为核磁共振很难检测到。
ligands is reported. The monodisperse Pd NPs were synthesized by chemical reduction of Pd precursors under simple and mild conditions. The resulting Pd NPs self-assembled into six-fold symmetrical superlattice structures due to their high monodispersity. The size of the Pd NPs could be precisely controlled from 2 to 5 nm by in-situ homoepitaxial growth. In a large-scale synthesis this method provided a high yield (> 90%) of almost 0.5 g of Pd NPs without changing the size or dispersity. The amine-protected Pd NPs have potential as structural units for the formation of heterostructures, such as Pd/γ-Fe 2O 3 heterostructured NPs. The Pd NPs were synthesized by injection of tetrabutylammonium borohydride (TBAB, 1.5 mmol) dissolved in chloroform (2 mL) into a mixture of palladium (II) acetate (0.5 mmol), oleylamine (OAm, 10 mmol), and oleic acid (OAc, 10 mmol) at 50 C under air. Transmission electron microscopy (TEM) images of the Pd NPs (Figure 1a, b) showed that they have a mean diameter of 3.0 nm and a narrow size distribution (standard deviation σ= 6.7%). The purified NPs were readily redispersed in chloroform, tetrahydrofuran, toluene, n-hexane, and other nonpolar solvents. High-resolution TEM (HRTEM) analysis (Figure 1c) revealed the Pd NPs had many grain boundaries and were polycrystalline. From their powder X-ray diffraction (PXRD) pattern (Figure 1d) the Pd NPs were identified as face-centered cubic (fcc) Pd. The diffraction angles of the Pd NPs in Figure 1d (eg 2 θ (111)= 39.740) were shifted toward lower angles as compared with bulk Pd (eg 2 θ (111)= 40.115, JCPDS 00–005-0681). This indicates that the Pd–Pd interatomic distance increased after formation of the Pd NPs, which is consistent with a previous report.[10a] The intensity ratios of the (200) and (220) diffraction peaks to the (111) peak in the PXRD pattern were 0.10 and 0.04, respectively, much lower than those for a conventional powder sample (0.42 and 0.25, respectively). This suggests that the synthesized Pd NPs are rich in {111} planes. The mean crystalline size was calculated at 1.7 nm using the full width at half maximum (FWHM) of the (111) peak in Figure 1d (FWHM (111)= 5.0) and the Scherrer equation. This is smaller than the mean particle size of 3.0 nm estimated from TEM, which indicates that the Pd NPs are polycrystalline in accordance with the HRTEM observation. Both OAm and OAc could act as protective ligands for the Pd NPs synthesized by this method, and the ligands protecting the Pd NPs were investigated by 1H-NMR. At first, the alkene hydrogen chemical shifts were monitored for this, because it is quite difficult to detect the NMR