氨基化磁性Fe3O4@Cu3(BTC)2材料的合成及其在Knoevenagel缩合中的催化性能

金属有机骨架材料具有大比表面积、高孔隙率、热稳定性好、规整且可调控的孔结构、易于功能化的骨架金属离子和有机配体等优点,是制备多相催化剂的重要材料之一.虽然减小金属有机骨架材料等多孔材料的粒径可以提高反应物的传质效率,从而提高其催化活性;但是,纳米尺寸催化剂的分离和回收困难.将磁性纳米粒子和金属有机骨架材料结合制备具有核-壳结构的磁性金属有机骨架材料是解决上述问题的有效方法.此类材料兼具磁性材料和金属有机骨架材料的双重优势,既可以磁性分离,又具有金属有机骨架材料的催化活性.而且,厚度可控的壳层材料表现出与纳米催化剂相当甚至更好的催化活性.我们采用逐层自组装方法制备了核-壳结构的磁性Fe3O4@Cu3(BTC)2复合材料,并对材料进行氨基化修饰,制备了基于金属有机骨架材料的磁性多相碱催化剂.采用粉末X射线衍射(XRD)、傅里叶变换红外光谱(FT-IR)、透射电镜(TEM)、扫描电镜(SEM)、氮气吸附等方法对材料的组成和结构进行了表征,并考察了材料在Knoevenagel缩合反应中的催化性能.首先采用粉末XRD表征材料的晶体结构.在复合材料Fe3O4@Cu3(BTC)2的XRD谱中,同时出现了Fe3O4和Cu3(BTC)2的特征衍射峰.采用氨基配体修饰后,材料的XRD谱没有明显变化,说明修饰后的材料保持了Fe3O4@Cu3(BTC)2的晶体结构.透射电镜结果表明,包裹25次得到的磁性复合材料Fe3O4@Cu3(BTC)2是以Fe3O4为核心,以Cu3(BTC)2为壳的核-壳结构,壳层厚度大约为200 nm.氨基修饰后,材料的透射电镜图相对修饰前无明显变化.扫描电镜结果表明,合成的Fe3O4为球形结构,粒径为100-600 nm.采用Cu3(BTC)2进行包裹后,在Fe3O4表面生长了由Cu3(BTC)2纳米颗粒组成的壳层.采用氨基配体修饰后,材料的形貌无明显改变.进一步采用氮气吸附表征材料的孔结构并测定材料的比表面积和孔体积.结果表明,由于大比表面的Cu3(BTC)2的引入,复合材料Fe3O4@Cu3(BTC)2的比表面积增大为462 m2/g,孔体积为0.38 cm3/g.氨基修饰后,材料的比表面积和孔体积都有较大程度的降低,说明配体分子占据了壳层材料Cu3(BTC)2中的纳米孔道.采用苯甲醛和氰基乙酸乙酯的Knoevenagel缩合反应作为模型,考察了材料的催化活性.研究发现,Fe3O4对此反应几乎没有活性,Fe3O4@Cu3(BTC)2给出了中等的催化活性.在材料上引入氨基后,由于氨基和Cu3(BTC)2上的Lewis酸性位点的协同效应,在很大程度了提高了材料的催化活性.溶剂效应实验结果表明,反应溶剂对材料的活性和选择性具有较大影响,极性或质子性溶剂有利于反应的进行.多相催化剂的循环稳定性是其重要评价指标之一.热过滤实验结果表明,滤液中无催化活性,反应中的催化活性来源于固体材料,此催化反应为多相催化.随后考察了材料的循环稳定性.虽然氨基化Fe3O4@Cu3(BTC)2材料在溶剂DMSO中表现出最高的催化活性,但XRD和电镜表征结果表明,材料在DMSO中结构遭到破坏,因此循环过程中催化剂的活性损失严重.然后考察了氨基化材料在乙醇中的循环稳定性,发现材料在乙醇中表现出较好的循环稳定性.通过简单磁性分离进行催化剂的分离和回收,催化剂循环使用3次而没有明显的活力损失.而且,XRD和电镜表征结果显示,催化剂的结构在反应过程中没有遭到明显破坏.     

Synthesis of 2,3-dihydroquinazolin-4(1H)-ones in the presence of Fe3O4@nano-cellulose–OPO3H as a bio-based magnetic nanocatalyst

In this research, we have used Fe₃O₄@nano-cellulose–OPO₃H as magnetic bio-based nanocatalyst for the synthesis of 2,3-dihydroquinazolin-4(1H)-ones via condensation of 2-aminobenzamide and different aldehydes. The major advantages of the present methodology are good yields, ecofriendly catalyst, and easy workup.     

A magnetic nanoparticle‐catalyzed regioselective ring opening of epoxides by aromatic amines

Sulfonic acid‐functionalized silica‐coated magnetic Fe₃O₄ nanoparticles were synthesized and applied as a green catalyst for an efficient and environmentally friendly ring opening of epoxides with aromatic amines in good to excellent yields with high chemoselectivity. Clean aminolysis of various aliphatic and aromatic epoxides in ethanol generates β‐hydroxyamines under mild reaction conditions. The synthesized acidic magnetic nanoparticles were recovered using a simple external magnet and successfully reused for five runs without any appreciable loss of catalytic activity. Copyright © 2016 John Wiley & Sons, Ltd.     

核壳结构Fe3O4@UiO-66-NH2磁性纳米复合材料的合成及其催化Knoevenagel缩合反应性能

金属有机骨架(MOF)材料是由过渡金属离子与有机配体通过配位键连接构成的高度有序的超分子化合物.这类材料比表面积大,孔隙率高,热稳定性好,而且具有规整可调控的孔结构、易于功能化的骨架金属离子和有机配体,在多相催化领域具有潜在应用前景.将纳米尺寸的MOF材料等多孔材料作为催化剂,可以提高反应传质效率,从而提高催化反应活性,但纳米MOF催化剂的分离和回收困难.将磁性纳米粒子和MOF材料组装成核壳结构的磁性MOF材料,不仅可简化催化剂的分离回收,而且通过控制壳层材料的厚度可以实现催化剂的高活性和高选择性.我们曾将磁核Fe3O4纳米粒子交替放入含有一种MOF材料前体的DMF溶液中,采用层层组装法制备了磁性Fe3O4@UiO-66-NH2纳米复合材料.经过十步组装后的材料的透射电镜(TEM)结果证实为核壳结构.但未出现明显的UiO-66-NH2的X射线衍射(XRD)特征峰,说明壳层材料UiO-66-NH2的结晶度较低;同时由于其孔结构的破坏或堵塞,在反应中出现明显失活.本文进一步改进自组装方法制备了核壳结构的磁性Fe3O4@UiO-66-NH2纳米复合材料,用XRD、傅里叶变换红外光谱(FT-IR)、TEM、扫描电镜(SEM)和氮气吸附等方法对材料的组成和结构进行了表征,并考察了其在Knoevenagel缩合反应中的催化性能.结果表明,所制材料是以Fe3O4为核,以UiO-66-NH2为壳的核-壳结构材料.经三次组装后出现了一系列UiO-66-NH2的XRD特征峰,说明采用新方法制备的复合材料中壳层材料UiO-66-NH2结晶度高,晶体结构规整.N2吸附-脱附结果表明,材料具有较高的比表面积和孔容.该复合材料在Knoevenagel缩合反应中表现出与纳米UiO-66-NH2相当或更好的催化活性和选择性,而且因壳层材料的孔道限阈效应而对底物表现出尺寸选择性.由于材料结晶度和晶体结构规整度的提高,催化剂稳定性更好,通过简单磁性分离即可分离和回收催化剂,循环使用4次而未出现明显失活.相对于本课题组之前报道的Fe3O4@CuBTC-NH2,Fe3O4@IRMOF-3和Fe3O4@UiO-66-NH2材料,本文所制的Fe3O4@UiO-66-NH2是一类结构更加稳定的高效固体碱催化剂.     

Ni@Pd core–shell nanoparticles immobilized on yolk–shell Fe3O4@polyaniline composites as a highly efficient,magnetically separable and atom‐economical catalyst for reduction of nitrobenzenes

The preparation of Ni@Pd core–shell nanoparticles immobilized on yolk–shell Fe₃O₄@polyaniline composites is reported. Fe₃O₄ nanoclusters were first synthesized through the solvothermal method and then the SiO₂ shell was coated on the Fe₃O₄ surface via a sol–gel process. To prepare Fe₃O₄@SiO₂@polyaniline composites, polyvinylpyrrolidone was first grafted on to the surface of Fe₃O₄@SiO₂ composites and subsequently polymerization of aniline was carried out via an ultrasound‐assisted in situ surface polymerization method. Selective etching of the middle SiO₂ layer was then accomplished to obtain the yolk–shell Fe₃O₄@polyaniline composites. The approach uses polyaniline (PANI) conductive polymer as a template for the synthesis of Ni@Pd core–shell nanoparticles. The catalytic activity of the synthesized yolk–shell Fe₃O₄@PANI/Ni@Pd composite was investigated in the reduction of o‐nitroaniline to benzenediamine by NaBH₄, which exhibited conversion of 99% in 3 min with a very low content of the catalyst. Transmission electron microscopy, X‐ray photoelectron spectroscopy, TGA, X‐ray diffraction, UV–visible, scanning electron microscopy, X‐ray energy dispersion spectroscopy and FT‐IR were employed to characterize the synthesized nanocatalyst. Copyright © 2014 John Wiley & Sons, Ltd.     

基于磁性金属有机骨架材料的多功能催化剂Fe_3O_4@IRMOF-3/Pd的制备及催化性能

采用逐层自组装方法制备了磁性Fe_3O_4@IRMOF-3复合材料,通过浸渍法将Pd纳米粒子负载到Fe3O4@IRMOF-3上,得到多功能催化剂Fe3O4@IRMOF-3/Pd.用粉末X射线衍射(XRD)、傅里叶变换红外光谱(FTIR)、透射电子显微镜(TEM)、扫描电子显微镜(SEM)及原子吸收(AAS)等方法对材料的组成和结构进行了表征,并考察了催化剂在Knoevenagel缩合反应、Suzuki偶联反应和烯烃催化加氢反应中的催化性能.结果表明,磁性Fe3O4@IRMOF-3/Pd催化剂在Knoevenagel缩合反应和Suzuki偶联反应中均表现出较好的催化活性和一定的循环稳定性.在烯烃的催化加氢反应中,催化剂可以高效催化多种烯烃的加氢反应,并表现出对底物的尺寸选择性.在苯乙烯的催化加氢反应中,催化剂循环使用9次,转化率依然大于99%,并且催化剂结构没有明显变化.     

Synthesis,characterization and application of sulfonic acid supported on ferrite–silica superparamagnetic nanoparticles

In this study, the synthesis of sulfonic acid supported on ferrite–silica superparamagnetic nanoparticles (Fe₃O₄@SiO₂@SO₃H) as a nanocatalyst with large density of acidic groups is suggested. This nanocatalyst was prepared in three steps: preparation of colloidal iron oxide magnetic nanoparticles (Fe₃O₄ MNPs), coating of silica on Fe₃O₄ MNPs (Fe₃O₄@SiO₂) and incorporation of sulfonic acid as a functional group on the surface of Fe₃O₄@SiO₂ nanoparticles (Fe₃O₄@SiO₂@SO₃H). The properties of the prepared magnetic nanoparticles were characterized using transmission electron microscopy, infrared spectroscopy, vibrating sample magnetometry, X‐ray diffraction and thermogravimetric analysis. Finally, the applicability of the synthesized magnetic nanoparticles was tested as a heterogeneous solid acid nanocatalyst for one‐pot synthesis of diindolyloxindole derivatives in aqueous medium. Oxindole derivatives were produced by the coupling of indole and isatin compounds with good to high yields (60–98%). Copyright © 2016 John Wiley & Sons, Ltd.     

Design,preparation, and characterization of Fe3O4 nanoparticles encapsulating β-cyclodextrin-bearing guanidine as a highly efficient and reusable heterogeneous base catalyst for synthesis of 3,4-dihydropyrano[3,2-c]chromenes

Chromene substructure is an important structural motif present in a variety of medicines, natural products, and materials showing biological activities. Here, a simple and convenient procedure for the synthesis of 3,4-dihydropyrano[3,2-c]chromene derivatives is described. For this purpose, Fe₃O₄ nanoparticles supported on β-cyclodextrin-guanidine were successfully prepared and used as catalyst. The structure of this catalyst was assigned by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, thermal gravimetric analysis, and vibrating sample magnetometer techniques. The prepared nanocomposites were used as a highly active, heterogeneous, and reusable nanocatalyst for the one-pot, three-component reaction of 4-hydroxycoumarin, aromatic aldehydes, and ethyl cyanoacetate. This method has advantages such as mild conditions, high yields, easy workup and simple purification of products, little catalyst loading, cost efficiency, and reusability of the catalyst.     

Palladium immobilized on amidoxime‐functionalized magnetic Fe3O4 nanoparticles: a highly stable and efficient magnetically recoverable nanocatalyst for sonogashira coupling reaction

We describe the synthesis of a novel Fe₃O₄/amidoxime (AO)/Pd nanocatalyst by grafting of AO groups on Fe₃O₄ nanoparticles and subsequent deposition of Pd nanoparticles. Prior to grafting of AO, the 2‐cyanoethyl‐functionalized Fe₃O₄ nanoparticles prepared through combining 2‐cyanoethyltriethoxysilane and Fe₃O₄ were treated with hydroxylamine. The AO‐grafted Fe₃O₄ nanoparticles were then used as a platform for the deposition of Pd nanoparticles. The catalyst was characterized using Fourier transform infrared spectroscopy, X‐ray diffraction, scanning and transmission electron microscopies, vibrating sample magnetometry, wavelength‐ and energy‐dispersive X‐ray spectroscopies and inductively coupled plasma analysis. Fe₃O₄/AO/Pd is novel phosphine‐free recyclable heterogeneous catalyst for Sonogashira reactions. Interestingly, the novel catalyst could be recovered in a facile manner from the reaction mixture by applying an external magnet device and recycled seven times without any significant loss in activity. Copyright © 2015 John Wiley & Sons, Ltd.     

Fe3O4纳米催化剂的制备及其F-T合成性能研究

基于溶剂热合成体系,制备了不同形貌的Fe₃O₄微球和纳米片催化剂,考察了水热合成条件对Fe₃O₄晶粒形貌的影响,并研究了Fe₃O₄纳米催化剂的费托合成(F-T)性能。结果表明,成核和晶体生长速率是控制Fe₃O₄晶体形貌的关键。与传统的沉淀铁催化剂相比,Fe₃O₄纳米催化剂更容易还原和向活性相转变,因此,具有更高的F-T反应活性、低碳烯烃选择性及C₅₊选择性;Fe₃O₄微球催化剂比纳米片催化剂更易维晶粒的稳定,具有更高的反应活性和稳定性。