外文翻譯簡(jiǎn)易合成易回收的分層核殼Fe3O4

1、w 外文文獻(xiàn)原稿和譯文原 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).譯 文簡(jiǎn)易合成易回收的分層核殼Fe3O4MgAlLDHAu磁性納米粒子催化劑催化氧化醇類物質(zhì)一種新的核殼結(jié)構(gòu)的Fe3O4MgAlLDHAu納米催化劑的制備只是通過Au離子負(fù)載在已合成的納米粒子Fe3O4MgAlLDH球體的MgAlLDH的表面上。這種催化劑表現(xiàn)出較好的氧化1-苯基乙醇的活性，而且其可以有效地利用外部磁場(chǎng)作用力進(jìn)行回收。在化學(xué)合成中，選擇性氧化醇類物質(zhì)是羰基化合物的一大重要轉(zhuǎn)變。最近研究表明，水滑石類化合物（層狀雙羥基復(fù)合金屬氧化物：LDH）負(fù)載銅，銀或金的納米粒子作為環(huán)保催化劑催化氧化醇類物質(zhì)具有較好的催化效果。特別是納米金負(fù)載在水滑石化合物上在純O2參與且無其他催化

44、劑的條件下氧化醇類物質(zhì)表現(xiàn)出較高的氧化性。通過降低納米微粒顆粒的大小能夠有助于改善納米級(jí)催化劑的活性已經(jīng)被廣泛證實(shí)。但是，隨著粒徑尺寸的減少，用物理方法分離比如過濾或者離心，這一過程將變的非常困難。一種行之有效的解決辦法就是研發(fā)出一種具有磁性的催化劑，一種很簡(jiǎn)單的分離方法只需用外部磁場(chǎng)的作用力就可以達(dá)到分離效果。從綠色化學(xué)的觀點(diǎn)來看，發(fā)展高活性、高選擇性、能再生利用的催化性已經(jīng)成為可能。因此，這些年磁性分離納米催化劑技術(shù)受到越來越廣泛的關(guān)注，因?yàn)檫@項(xiàng)技術(shù)不僅可以減少一些輔料，能源以及時(shí)間的消耗，而且可以在一些重要的經(jīng)濟(jì)和環(huán)境領(lǐng)域收到成效。有著核殼結(jié)構(gòu)的磁性復(fù)合材料允許多種功能的個(gè)體結(jié)合成一個(gè)單

45、一的納米顆粒系統(tǒng)，并具有獨(dú)特的應(yīng)用方面的優(yōu)勢(shì)，特別是在生物醫(yī)學(xué)和催化方面。然而，在某種程度上，將材料的直接組裝在磁核表面是一個(gè)重大的挑戰(zhàn)。在我們先前的工作中，在Fe3O4亞微米球體表面上首次涂覆一層很薄的碳層，之后又在其表面包覆了MgAlLDH制成了一種抗癌劑，而Fe3O4DFURLDH在這種抗癌劑中作為藥物目標(biāo)運(yùn)輸載體。李老師以及其團(tuán)隊(duì)人員用Fe3O4MgAlLDH通過逐層組裝分層的LDH納米片作為磁性矩陣負(fù)載在W7O24作為一種催化劑。這些具有核-殼結(jié)構(gòu)的納米復(fù)合材料同時(shí)具有磁性材料的磁化強(qiáng)度和LDH材料的多重功能。雖然如此，這些被報(bào)導(dǎo)的合成方法仍然具有多步及復(fù)雜的步驟。在這里，我們?yōu)樵摲N

46、新型納米級(jí)催化劑Fe3O4MgAlLDHAu的生產(chǎn)制備設(shè)計(jì)出了一種簡(jiǎn)便的合成方法，包含有在Fe3O4納米微球表面上定向生長(zhǎng)的MgAlLDH結(jié)晶體上負(fù)載納米金離子，這種納米微球兼?zhèn)浣鸺{米微粒的優(yōu)良催化特性以及磁鐵礦納米微粒的超順磁性。就我們所了解到的，這是第一個(gè)通過簡(jiǎn)單的共同沉淀方法，將MgAlLDH片晶狀的納米級(jí)結(jié)晶體，直接豎直地定向于Fe3O4核心分子上的例子。通過分層的具有磁性的金屬載體的納米級(jí)催化劑的生產(chǎn)制備更進(jìn)一步負(fù)載金屬納米粒子。由圖表1的圖解知，F(xiàn)e3O4MgAlLDHAu的合成方案包含兩個(gè)關(guān)鍵點(diǎn)。幾乎所有的單分散的磁鐵礦顆粒都通過無表面活性劑的疏溶劑的處理方法被前期合成。首先將F

47、e3O4懸浮納米粒子的pH值調(diào)整到10，因此獲得的完全帶負(fù)電荷的Fe3O4納米球粒子通過由界面成核作用帶來的靜電引力，很容易被附著上一層定向增長(zhǎng)的碳酸鹽MgAlLDH，隨后晶體通過不斷地滴加鹽類和堿性溶液不斷地生長(zhǎng)。其次，金納米粒子通過該種沉積-沉淀方法被有效地負(fù)載在如此組成的Fe3O4MgAlLDH的表面上（詳見ESI）。圖1 Fe3O4(a)、Fe3O4MgAlLDH(b和d)及Fe3O4MgAlLDHAu(c，e，f和g)的掃瞄式電子顯微鏡(a，b和c)、透射電鏡(d和e)、高分辨透射電子顯微鏡(f)圖像和X射線探測(cè)器光譜(g)。圖1描述了Fe3O4MgAlLDHAu納米催化劑在制備過程

48、中不同階段的掃瞄電鏡/透射電鏡的樣本圖片。Fe3O4納米球（圖1a）顯示出一個(gè)表面光滑、平均直徑在450納米粒度的較小間隙尺寸的分布狀態(tài)（圖S1, ESI）。在直接附著有碳酸鹽MgAlLDH以后(圖1b)，蜂窩狀的形態(tài)大小范圍在100200納米的空間能夠被清晰地觀察到，LDH殼體由厚度大約為20納米的交錯(cuò)的小片狀體組成。有趣的是,MgAlLDH殼體顯現(xiàn)出顯著的擇優(yōu)取向，與c軸并行，ab界面垂直于磁鐵礦核心的表面，與先前的報(bào)導(dǎo)截然不同。也有類似的現(xiàn)象只是在報(bào)導(dǎo)的LDH影像及聚合物樹脂小球陽離子交換中的多層氫氧化物的增長(zhǎng)中被觀察到。兩個(gè)獨(dú)立的納米球微粒的透射電子顯微鏡攝影圖片(圖1d) 無容置疑的

49、證實(shí)了Fe3O4核心被完全附著一層LDH納米晶體的Fe3O4MgAlLDHAu的核-殼結(jié)構(gòu)。具體的講，MgAlLDH結(jié)晶體單分子層形成為大片的薄狀的納米片狀顆粒，顯現(xiàn)出厚度大約為20納米，寬度大約為100納米的邊緣開裂的薄片狀片晶，由磁鐵礦核心增長(zhǎng)至其外表面并垂直于Fe3O4的表面。獲得的擁有表面積為43.3 m2 g，提供了足夠的可接近的殼進(jìn)入的邊緣和結(jié)合點(diǎn)的LDH結(jié)晶體的核-殼結(jié)構(gòu)的Fe3O4MgAlLDH納米球微粒的表面蜂窩狀的微結(jié)構(gòu)能夠使該種新型分層復(fù)合物負(fù)載金屬的納米球微粒。擁有該種結(jié)構(gòu)形態(tài)，交錯(cuò)垂直地定向于MgAlLDH納米結(jié)晶體上，能夠促進(jìn)納米級(jí)金屬顆粒的定向負(fù)載，而避免可能的聚

50、集。Coprecipitation 共同沉淀，DP method 聚合方法圖表1 Fe3O4MgAlLDHAu催化物的合成方法。圖2 Fe3O4(a)，F(xiàn)e3O4MgAlLDH(b)和Fe3O4MgAlLDHAu(c)的X射線衍射模式圖。X射線衍射結(jié)果(圖2)表明，F(xiàn)e3O4MgAlLDH納米微粒由六方最緊密堆積的MgAlLDH(粉末衍射標(biāo)準(zhǔn)聯(lián)合委員會(huì)89-5434) 和面心立方晶格的Fe3O4(粉末衍射標(biāo)準(zhǔn)聯(lián)合委員會(huì)19-0629)組成。在圖2b中能夠清楚的看到，系列(00l)反射光在低2角的狀況下，與那些單個(gè)的MgAlLDH(圖S2,ESI)相比較，有較明顯的減小。在高2角極大值的情況下，

51、能夠較清楚地分辨出較小的減少量，同時(shí)揭示了Fe3O4MgAlLDH的I(003)/I(110) =0.8比MgAlLDH(3.9)有較大的減少。該種現(xiàn)象證明了MgAlLDH片晶狀結(jié)晶體的極其較好的定向集成，結(jié)晶體的c軸與Fe3O4核心的表面相平行。在c軸的顆粒的尺寸大小，基于(003)線寬(圖2b)的謝樂公式(公式S1,ESI)，計(jì)算出理論值在25納米,與掃描電子顯微鏡/透射電子顯微鏡的結(jié)果有較好的吻合。Fe3O4MgAlLDH的能散X射線（能量彌散X射線探測(cè)器）的結(jié)果(圖S3,ESI)揭示出了鎂、鋁、鐵和氧元素的存在，并且接近于預(yù)期值(3.0)的Mg/Al摩爾比2.7，意味著MgAlLDH附

52、著于Fe3O4表面上的金屬陽離子完全共同沉淀。傅里葉轉(zhuǎn)換紅外分光光度計(jì)數(shù)據(jù)(圖S4,ESI)更進(jìn)一步證實(shí)了合成物的化學(xué)成分及結(jié)構(gòu)特征。所制備的Fe3O4MgAlLDH納米微粒大約在1365cm處表現(xiàn)出極大的吸附作用，被歸因于碳酸根離子的3(非對(duì)稱性的拉伸)模式以及磁鐵礦相的FeO晶格模式的峰值為584cm，表明在Fe3O4核心的表面上COLDH殼體的形成。同時(shí),在羥基伸縮模式下,從羥基金屬聚合物和氫鍵層間水分子中產(chǎn)生，一個(gè)大約在3420cm的強(qiáng)大光譜寬帶能夠被識(shí)別出來。另外一種由羥基變換成水的模式中產(chǎn)生的吸附作用，(H2O),記錄大約為1630cm。基于蜂窩狀的核-殼型分層狀的納米微粒的成功合成，F(xiàn)e3O4MgAlLDH，我們近期的研究更進(jìn)一步地表明這種簡(jiǎn)便的合成方法能夠被擴(kuò)展到LDH為基礎(chǔ)的物質(zhì)，根據(jù)磁性納米復(fù)合材料LDH層成分的可調(diào)性，調(diào)整不同的LDH基的核-殼結(jié)構(gòu)，從而得到不同分層的具有磁性的納米合成物，例如NiAlLDH以及CuN