外文翻译简易合成易回收的分层核壳Fe3O4

1、w 外文文献原稿和译文原 稿Facile synthesis of hierarchical coreshell Fe3O4MgAlLDHAu as magnetically recyclable catalysts for catalytic oxidation of alcoholsA novel coreshell structural Fe3O4MgAlLDHAu nanocatalyst was simply synthesized via supporting Au nanoparticles on the MgAlLDH surface of Fe3O4MgAlLDH nanos

2、pheres. The catalyst exhibited excellent activity for the oxidation of 1-phenylethanol, and can be effectively recovered by using an external magnetic field.The selective oxidation of alcohols to the corresponding carbonyl compounds is a greatly important transformation in synthesis chemistry. Recen

3、tly, it has been disclosed that hydrotalcite (layered double hydroxides: LDH)-supported Cu, Ag and Au nanoparticles as environmentally benign catalysts could catalyse the oxidation of alcohol with good efficiency. In particular, the Au nanoparticles supported on hydrotalcite exhibit high activity fo

4、r the oxidation of alcohols under atmospheric O2 without additives. It has been extensively demonstrated that the activity of the nanometre-sized catalysts will benefit from decreasing the particle size. However, as the size of the support is decreased, separation using physical methods, such as fil

5、tration or centrifugation, becomes a difficult and time-consuming procedure. A possible solution could be the development of catalysts with magnetic properties, allowing easy separation of the catalyst by simply applying an external magnetic field. From the green chemistry point of view, development

6、 of highly active, selective and recyclable catalysts has become critical. Therefore, magnetically separable nanocatalysts have received increasing attention in recent years because the minimization in the consumption of auxiliary substances, energy and time used in achieving separations can result

7、in significant economical and environmental benefits.Magnetic composites with a coreshell structure allow the integration of multiple functionalities into a single nanoparticle system, and offer unique advantages for applications, particularly in biomedicine and catalysis. However it is somewhat of

8、a challenge to directly immobilize hierarchical units onto the magnetic cores. In our previous work, the Fe3O4 submicro-spheres were first coated with a thin carbon layer, then coated with MgAlLDH to obtain an anticancer agent-containing Fe3O4DFURLDH as drug targeting delivery vector. Li et al. prep

9、ared Fe3O4MgAlLDH through a layer-by-layer assembly of delaminated LDH nanosheets as a magnetic matrix for loading W7O24 as a catalyst. These coreshell structural nanocomposites possess the magnetization of magnetic materials and multiple functionalities of the LDH materials. Nevertheless, these rep

10、orted synthesis routes need multi-step and sophisticated procedures. Herein, we design a facile synthesis strategy for the fabrication of a novel Fe3O4MgAlLDHAu nanocatalyst, consisting of Au particles supported on oriented grown MgAlLDH crystals over the Fe3O4 nanospheres, which combines the excell

11、ent catalytic properties of Au nanoparticles with the superparamagnetism of the magnetite nanoparticles. To the best of our knowledge, this is the first instance of direct immobilization of vertically oriented MgAlLDH platelet-like nanocrystals onto the Fe3O4 core particles by a simple coprecipitati

12、on method and the fabrication of hierarchical magnetic metal-supported nanocatalysts via further supporting metal nanoparticles.As illustrated in Scheme 1, the synthesis strategy of Fe3O4MgAlLDHAu involves two key aspects. Nearly monodispersed magnetite particles were pre-synthesized using a surfact

13、ant-free solvothermal method. First, the Fe3O4 suspension was adjusted to a pH of ca. 10, and thus the obtained fully negatively charged Fe3O4 spheres were easily coated with a layer of oriented grown carbonateMgAlLDH via electrostatic attraction followed by interface nucleation and crystal growth u

14、nder dropwise addition of salts and alkaline solutions. Second, Au nanoparticles were effectively supported on thus-formed support Fe3O4MgAlLDH by a depositionprecipitation method (see details in ESI).Fig. 1 depicts the SEM/TEM images of the samples at various stages of the fabrication of the Fe3O4M

15、gAlLDHAu nanocatalyst. The Fe3O4 nanospheres (Fig. 1a) show a smooth surface and a mean diameter of 450 nm with a narrow size distribution (Fig. S1, ESI). After direct coating with carbonateMgAlLDH (Fig. 1b), a honeycomb like morphology with many voids in the size range of 100200 nm is clearly obser

16、ved, and the LDH shell is composed of interlaced platelets of ca. 20 nm thickness. Interestingly, the MgAlLDH shell presents a marked preferred orientation with the c-axis parallel to, and the ab-face perpendicular to the surface of the magnetite cores, quite different from those of a previous repor

17、t. A similar phenomenon has only been observed for the reported LDH films and the growth of layered hydroxides on cation-exchanged polymer resin beads. The TEM image of two separate nanospheres (Fig. 1d) undoubtedly confirms the coreshell structure of the Fe3O4MgAlLDH with the Fe3O4 cores well-coate

18、d by a layer of LDH nanocrystals. In detail, the MgAlLDH crystal monolayers are formed as large thin nanosheet-like particles, showing a edge-curving lamella with a thickness of ca. 20 nm and a width of ca. 100 nm, growing from the magnetite core to the outer surface and perpendicular to the Fe3O4 s

19、urface. The outer honeycomb like microstructure of the obtained coreshell Fe3O4MgAlLDH nanospheres with a surface area of 43.3 m2 g_1 provides abundant accessible edge and junction sites of LDH crystals making it possible for this novel hierarchical composite to support metal nanoparticles. With suc

20、h a structural morphology, interlaced perpendicularly oriented MgAlLDH nanocrystals can facilitate the immobilization of nano-metal particles along with avoiding the possible aggregation.Scheme 1 The synthetic strategy of an Fe3O4MgAlLDHAu catalyst.Fig. 1 SEM (a, b and c), TEM (d and e) and HRTEM (f

21、) images and EDX spectrum (g) of Fe3O4 (a), Fe3O4MgAlLDH (b and d) and Fe3O4MgAlLDHAu (c, e, f and g).Fig. 2 XRD patterns of Fe3O4 (a), Fe3O4MgAlLDH (b) and Fe3O4MgAlLDHAu (c).The XRD results (Fig. 2) demonstrate that the Fe3O4MgAlLDH nanospheres are composed of an hcp MgAlLDH (JCPDS 89-5434) and fc

22、c Fe3O4 (JCPDS 19-0629). It can be clearly seen from Fig. 2b that the series (00l) reflections at low 2 angles are significantly reduced compared with those of single MgAlLDH (Fig. S2, ESI), while the (110) peak at high 2 angle is clearly distinguished with relatively less decrease, as revealed by g

23、reatly reduced I(003)/I(110) = 0.8 of Fe3O4MgAlLDH than that of MgAlLDH (3.9). This phenomenon is a good evidence for an extremely well-oriented assembly of MgAlLDH platelet-like crystals consistent with the c-axis of the crystals being parallel to the surface of an Fe3O4 core. The particle dimensio

24、n in the c-axis is calculated as 25 nm using the Scherrer equation (eqn S1, ESI) based on the (003) line width (Fig. 2b), in good agreement with the SEM/TEM results. The energy-dispersive X-ray (EDX) result (Fig. S3, ESI) of Fe3O4MgAlLDH reveals the existence of Mg, Al, Fe and O elements, and the Mg

25、/Al molar ratio of 2.7 close to the expected one (3.0), indicating the complete coprecipitation of metal cations for MgAlLDH coating on the surface of Fe3O4.The FTIR data (Fig. S4, ESI) further evidence the chemical compositions and structural characteristics of the composites. The as-prepared Fe3O4

26、MgAlLDH nanosphere shows a sharp absorption at ca. 1365 cm_1 being attributed to the 3 (asymmetric stretching) mode of CO32_ ions and a peak at 584 cm_1 to the FeO lattice mode of the magnetite phase, indicating the formation of a CO32LDH shell on the surface of the Fe3O4 core. Meanwhile, a strong b

27、road band around 3420 cm_1 can be identified as the hydroxyl stretching mode, arising from metal hydroxyl groups and hydrogen-bonded interlayer water molecules. Another absorption resulting from the hydroxyl deformation mode of water, (H2O), is recorded at ca. 1630 cm_1.Based on the successful synth

28、esis of honeycomb like coreshell nanospheres, Fe3O4MgAlLDH, our recent work further reveals that this facile synthesis approach can be extended to prepare various coreshell structured LDH-based hierarchical magnetic nanocomposites according to the tenability of the LDH layer compositions, such as Ni

29、AlLDH and CuNiAlLDH (Fig. S3, ESI).Gold nanoparticles were further assembled on the honeycomb likeMgAlLDH platelet-like nanocrystals of Fe3O4MgAlLDH. Though the XRD pattern (Fig. 2c) fails to show the characteristics of Au nanoparticles, it can be clearly seen by the TEM of Fe3O4MgAlLDHAu (Fig. 1e)

30、that Au nanoparticles are evenly distributed on the edge and junction sites of the interlaced MgAlLDH nanocrystals with a mean diameter of 7.0 nm (Fig. S5, ESI), implying their promising catalytic activity. Meanwhile, the reduced packing density (large void) and the less sharp edge of LDH platelet-l

31、ike nanocrystals can be observed (Fig. 1c and e). To get more insight on structural information of Fe3O4MgAlLDHAu, the HRTEM image was obtained (Fig. 1f). It can be observed that both the Au and MgAlLDH nanophases exhibit clear crystallinity as evidenced by well-defined lattice fringes. The interpla

32、nar distances of 0.235 and 0.225 nm for two separate nanophases can be indexed to the (111) plane of cubic Au (JCPDS 89-3697) and the (015) facet of the hexagonal MgAlLDH phase (inset in Fig. 1f and Fig. S6 (ESI). The EDX data (Fig. 1g) indicate that the magnetic coreshell particle contains Au, Mg,

33、Al, Fe and O elements. The Au content is determined as 0.5 wt% upon ICP-AES analysis.Table 1 Recycling results on the oxidation of 1-phenylethanolThe VSM analysis (Fig. S7, ESI) shows the typical superparamagnetism of the samples. The lower saturation magnetization (Ms) of Fe3O4MgAlLDH (20.9 emu g_1

34、) than the Fe3O4 (83.8 emu g_1) is mainly due to the contribution of non-magnetic MgAlLDH coatings (68 wt%) to the total sample. Interestingly, Ms of Fe3O4MgAlLDHAu is greatly enhanced to 49.2 emu g_1, in line with its reduced MgAlLDH content (64 wt%). This phenomenon can be ascribed to the removal

35、of weakly linked MgAlLDH particles among the interlaced MgAlLDH nanocrystals during the Au loading process, which results in a less densely packed MgAlLDH shell as indicated by SEM. The strong magnetic sensitivity of Fe3O4MgAlLDHAu provides an easy and effective way to separate nanocatalysts from a

36、reaction system.The catalytic oxidation of 1-phenylethanol as a probe reaction over the present novel magnetic Fe3O4MgAlLDHAu (7.0 nm Au) nanocatalyst demonstrates high catalytic activity. The yield of acetophenone is 99%, with a turnover frequency (TOF) of 66 h_1, which is similar to that of the pr

37、eviously reported Au/MgAlLDH (TOF, 74 h_1) with a Au average size of 2.7 nm at 40 1C, implying that the catalytic activity of Fe3O4MgAlLDHAu can be further enhanced as the size of Au nanoparticles is decreased. Meanwhile, the high activity and selectivity of the Fe3O4MgAlLDHAu can be related to the

38、honeycomb like morphology of the support Fe3O4MgAlLDH being favourable to the high dispersion of Au nanoparticles and possible concerted catalysis of the basic support. Five reaction cycles have been tested for the Au nanocatalysts after easy magnetic separation by using a magnet (4500 G), and no de

39、activation of the catalyst has been observed (Table 1). Moreover, no Au, Mg and Al leached into the supernatant as confirmed by ICP (detection limit: 0.01 ppm) and almost the same morphology remained as evidenced by SEM of the reclaimed catalyst (Fig. S8, ESI).In conclusion, a novel hierarchical cor

40、eshell magnetic gold nanocatalyst Fe3O4MgAlLDHAu is first fabricated via a facile synthesis method. The direct coating of LDH plateletlike nanocrystals vertically oriented to the Fe3O4 surface leads to a honeycomb like coreshell Fe3O4MgAlLDH nanosphere. By a depositionprecipitation method, a gold-su

41、pported magnetic nanocatalyst Fe3O4MgAlLDHAu has been obtained, which not only presents high 1-phenylethanol oxidation activity, but can be conveniently separated by an external magnetic field as well. Moreover, a series of magnetic Fe3O4LDH nanospheres involving NiAlLDH and CuNiAlLDH can be fabrica

42、ted based on the LDH layer composition tunability and multi-functionality of the LDH materials, making it possible to take good advantage of these hierarchical coreshell materials in many important applications in catalysis, adsorption and sensors.This work is supported by the 973 Program (2011CBA00

43、508).译 文简易合成易回收的分层核壳Fe3O4MgAlLDHAu磁性纳米粒子催化剂催化氧化醇类物质一种新的核壳结构的Fe3O4MgAlLDHAu纳米催化剂的制备只是通过Au离子负载在已合成的纳米粒子Fe3O4MgAlLDH球体的MgAlLDH的表面上。这种催化剂表现出较好的氧化1-苯基乙醇的活性，而且其可以有效地利用外部磁场作用力进行回收。在化学合成中，选择性氧化醇类物质是羰基化合物的一大重要转变。最近研究表明，水滑石类化合物（层状双羟基复合金属氧化物：LDH）负载铜，银或金的纳米粒子作为环保催化剂催化氧化醇类物质具有较好的催化效果。特别是纳米金负载在水滑石化合物上在纯O2参与且无其他催化

44、剂的条件下氧化醇类物质表现出较高的氧化性。通过降低纳米微粒颗粒的大小能够有助于改善纳米级催化剂的活性已经被广泛证实。但是，随着粒径尺寸的减少，用物理方法分离比如过滤或者离心，这一过程将变的非常困难。一种行之有效的解决办法就是研发出一种具有磁性的催化剂，一种很简单的分离方法只需用外部磁场的作用力就可以达到分离效果。从绿色化学的观点来看，发展高活性、高选择性、能再生利用的催化性已经成为可能。因此，这些年磁性分离纳米催化剂技术受到越来越广泛的关注，因为这项技术不仅可以减少一些辅料，能源以及时间的消耗，而且可以在一些重要的经济和环境领域收到成效。有着核壳结构的磁性复合材料允许多种功能的个体结合成一个单

45、一的纳米颗粒系统，并具有独特的应用方面的优势，特别是在生物医学和催化方面。然而，在某种程度上，将材料的直接组装在磁核表面是一个重大的挑战。在我们先前的工作中，在Fe3O4亚微米球体表面上首次涂覆一层很薄的碳层，之后又在其表面包覆了MgAlLDH制成了一种抗癌剂，而Fe3O4DFURLDH在这种抗癌剂中作为药物目标运输载体。李老师以及其团队人员用Fe3O4MgAlLDH通过逐层组装分层的LDH纳米片作为磁性矩阵负载在W7O24作为一种催化剂。这些具有核-壳结构的纳米复合材料同时具有磁性材料的磁化强度和LDH材料的多重功能。虽然如此，这些被报导的合成方法仍然具有多步及复杂的步骤。在这里，我们为该种

46、新型纳米级催化剂Fe3O4MgAlLDHAu的生产制备设计出了一种简便的合成方法，包含有在Fe3O4纳米微球表面上定向生长的MgAlLDH结晶体上负载纳米金离子，这种纳米微球兼备金纳米微粒的优良催化特性以及磁铁矿纳米微粒的超顺磁性。就我们所了解到的，这是第一个通过简单的共同沉淀方法，将MgAlLDH片晶状的纳米级结晶体，直接竖直地定向于Fe3O4核心分子上的例子。通过分层的具有磁性的金属载体的纳米级催化剂的生产制备更进一步负载金属纳米粒子。由图表1的图解知，Fe3O4MgAlLDHAu的合成方案包含两个关键点。几乎所有的单分散的磁铁矿颗粒都通过无表面活性剂的疏溶剂的处理方法被前期合成。首先将F

47、e3O4悬浮纳米粒子的pH值调整到10，因此获得的完全带负电荷的Fe3O4纳米球粒子通过由界面成核作用带来的静电引力，很容易被附着上一层定向增长的碳酸盐MgAlLDH，随后晶体通过不断地滴加盐类和碱性溶液不断地生长。其次，金纳米粒子通过该种沉积-沉淀方法被有效地负载在如此组成的Fe3O4MgAlLDH的表面上（详见ESI）。图1 Fe3O4(a)、Fe3O4MgAlLDH(b和d)及Fe3O4MgAlLDHAu(c，e，f和g)的扫瞄式电子显微镜(a，b和c)、透射电镜(d和e)、高分辨透射电子显微镜(f)图像和X射线探测器光谱(g)。图1描述了Fe3O4MgAlLDHAu纳米催化剂在制备过程

48、中不同阶段的扫瞄电镜/透射电镜的样本图片。Fe3O4纳米球（图1a）显示出一个表面光滑、平均直径在450纳米粒度的较小间隙尺寸的分布状态（图S1, ESI）。在直接附着有碳酸盐MgAlLDH以后(图1b)，蜂窝状的形态大小范围在100200纳米的空间能够被清晰地观察到，LDH壳体由厚度大约为20纳米的交错的小片状体组成。有趣的是,MgAlLDH壳体显现出显著的择优取向，与c轴并行，ab界面垂直于磁铁矿核心的表面，与先前的报导截然不同。也有类似的现象只是在报导的LDH影像及聚合物树脂小球阳离子交换中的多层氢氧化物的增长中被观察到。两个独立的纳米球微粒的透射电子显微镜摄影图片(图1d) 无容置疑的

49、证实了Fe3O4核心被完全附着一层LDH纳米晶体的Fe3O4MgAlLDHAu的核-壳结构。具体的讲，MgAlLDH结晶体单分子层形成为大片的薄状的纳米片状颗粒，显现出厚度大约为20纳米，宽度大约为100纳米的边缘开裂的薄片状片晶，由磁铁矿核心增长至其外表面并垂直于Fe3O4的表面。获得的拥有表面积为43.3 m2 g，提供了足够的可接近的壳进入的边缘和结合点的LDH结晶体的核-壳结构的Fe3O4MgAlLDH纳米球微粒的表面蜂窝状的微结构能够使该种新型分层复合物负载金属的纳米球微粒。拥有该种结构形态，交错垂直地定向于MgAlLDH纳米结晶体上，能够促进纳米级金属颗粒的定向负载，而避免可能的聚

50、集。Coprecipitation 共同沉淀，DP method 聚合方法图表1 Fe3O4MgAlLDHAu催化物的合成方法。图2 Fe3O4(a)，Fe3O4MgAlLDH(b)和Fe3O4MgAlLDHAu(c)的X射线衍射模式图。X射线衍射结果(图2)表明，Fe3O4MgAlLDH纳米微粒由六方最紧密堆积的MgAlLDH(粉末衍射标准联合委员会89-5434) 和面心立方晶格的Fe3O4(粉末衍射标准联合委员会19-0629)组成。在图2b中能够清楚的看到，系列(00l)反射光在低2角的状况下，与那些单个的MgAlLDH(图S2,ESI)相比较，有较明显的减小。在高2角极大值的情况下，

51、能够较清楚地分辨出较小的减少量，同时揭示了Fe3O4MgAlLDH的I(003)/I(110) =0.8比MgAlLDH(3.9)有较大的减少。该种现象证明了MgAlLDH片晶状结晶体的极其较好的定向集成，结晶体的c轴与Fe3O4核心的表面相平行。在c轴的颗粒的尺寸大小，基于(003)线宽(图2b)的谢乐公式(公式S1,ESI)，计算出理论值在25纳米,与扫描电子显微镜/透射电子显微镜的结果有较好的吻合。Fe3O4MgAlLDH的能散X射线（能量弥散X射线探测器）的结果(图S3,ESI)揭示出了镁、铝、铁和氧元素的存在，并且接近于预期值(3.0)的Mg/Al摩尔比2.7，意味着MgAlLDH附

52、着于Fe3O4表面上的金属阳离子完全共同沉淀。傅里叶转换红外分光光度计数据(图S4,ESI)更进一步证实了合成物的化学成分及结构特征。所制备的Fe3O4MgAlLDH纳米微粒大约在1365cm处表现出极大的吸附作用，被归因于碳酸根离子的3(非对称性的拉伸)模式以及磁铁矿相的FeO晶格模式的峰值为584cm，表明在Fe3O4核心的表面上COLDH壳体的形成。同时,在羟基伸缩模式下,从羟基金属聚合物和氢键层间水分子中产生，一个大约在3420cm的强大光谱宽带能够被识别出来。另外一种由羟基变换成水的模式中产生的吸附作用，(H2O),记录大约为1630cm。基于蜂窝状的核-壳型分层状的纳米微粒的成功合成，Fe3O4MgAlLDH，我们近期的研究更进一步地表明这种简便的合成方法能够被扩展到LDH为基础的物质，根据磁性纳米复合材料LDH层成分的可调性，调整不同的LDH基的核-壳结构，从而得到不同分层的具有磁性的纳米合成物，例如NiAlLDH以及CuN