摘要
UiO-66-NH_2是以Zr4+为金属,以2-氨基对苯二甲酸为配体制备得到的金属有机骨架材料,它是目前报道中具有较高热稳定性和化学稳定性的材料之一。本文以Fe_3O_4为核,以UiO-66-NH_2为壳,采用层层自组装方法制备了核-壳结构的磁性金属有机骨架材料Fe_3O_4@UiO-66-NH_2。利用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)和氮气吸附等对其进行了表征,并考察了该磁性材料在克脑文盖尔(Knoevenagel)缩合反应中的催化性能。结果表明,该磁性材料Fe_3O_4@UiO-66-NH_2为核-壳结构,壳层厚度约为100 nm,氨基含量为1.70 mmol·g-1。该磁性复合材料具有Fe_3O_4和UiO-66-NH_2的双重功能,既可以磁性分离,又具有UiO-66-NH_2的孔结构和催化性能。由于壳层材料中Lewis酸性位(Zr4+)和碱性基团(-NH_2)的协同催化能力及其壳层的纳米尺寸效应,该磁性材料在Knoevenagel缩合反应中表现出和UiO-66-NH_2纳米粒子相当的催化活性。而且,通过磁性分离实现催化剂的多次循环使用后,其结构没有明显变化。
Magnetic metal organic frameworks exhibit both magnetic characteristics and catalytic properties.However, their applications as heterogeneous catalysts are still very limited. Herein, a novel kind of core-shell structured Fe3O4@UiO-66-NH2 has been successfully fabricated by a layer-by-layer self assembly method which could be used as an active basic catalyst for Knoevenagel condensation. In a typical synthesis, Fe3O4 nanoparticals were synthesized by a solvothermal method and then surface modified with mercaptoacetic acid（MAA）. Dis-persing the MAA-modified Fe3O4 microspheres alternately in DMF solutions of Zr Cl4（10 mmol·L^-1） and 2-aminobenzenetricarboxylic acid DMF solution（10 mmol·L-1） at 120 ℃ for 2 h, Fe3O4@UiO-66-NH2core-shell structured microspheres were successfully prepared as expected. Its core-shell structure was confirmed by XRD and TEM techniques, composition by SEM-EDS and the amine functionality proven by IR spectroscopy. The shell thickness is about 100 nm and its weight content is about 60%. Correspondingly, the amino content was calculat-ed to be 1.7 mmol·g^-1. The core-shell Fe3O4@UiO-66-NH2 is an ideal recyclable catalyst for Knoevenagel condensation that derive from a combination of a superparamagnetic core for efficient magnetic separation and a thin porous MOF shell for high catalytic activity. The remarkable activities for Knoevenagel condensation reactions are thanks to the cooperative action of amino groups and Lewis acid Zr4＋ions in UiO-66-NH2. Obvious solvents effect on the activity and stability was observed, and DMF was selected as good medium for recyclability for a sacrificial balance between activity and recyclability. The catalyst could be easily separated from the reaction mixture and reused without significant change in the catalytic activity after four reaction cycles. Furthermore, its structure and morphology was not changed after the reaction in DMF, confirmed by the XRD, SEM and TEM techniques.Therefore, such kind of MOF-based core-shell magnetic catalysts is expected to be used in large scale industrial applications, where separation and recycling are critically required to reduce the cost as well as waste production.Moreover, the catalyst preparation procedure is fairly simple and the catalysts contain no toxic materials, thus this catalyst is green and cheap.
出处
《无机化学学报》
SCIE
CAS
CSCD
北大核心
2016年第4期609-616,共8页
Chinese Journal of Inorganic Chemistry
基金
国家自然科学基金(No.21203017)
国家重点实验室开放基金(No.N-11-03)
辽宁省高等学校优秀人才支持计划
中央高校基本研究业务费专项资金(No.DC201502020304)资助项目
