电子束敏感材料的原子尺度结构研究

分子筛和金属有机骨架(MOF)材料以其独特的孔道和骨架结构在催化、 储能、 干燥及净化和吸附分离等领域有着广泛应用, 对其结构的原子尺度表征对于深入理解其构效关系具有重要意义. 但其大孔道结构和有机骨架使得它们对电子束辐照极为敏感, 在常规透射电镜成像模式下结构会很快被破坏变为非晶, 从而无法获得孔道和骨架的原子排列信息. 最近发展起来的基于积分差分相位衬度扫描透射电子显微(iDPC-STEM)技术在电子敏感材料和轻元素组分成像方面展现出明显优势, 使得对多孔骨架材料及烃池物种的表征成为了可能. 本文综述了本课题组近期利用该技术对分子筛和MOF材料原子尺度结构方面的研究. 将iDPC-STEM技术应用到ZSM-5分子筛催化剂中, 实现了对该分子筛的原子级骨架结构的成像分析. 在MOF体系中, 利用该技术观察到MIL-101骨架内部有机连接体与金属节点的配位方式, 在此基础上解析了MIL-101结构中有机配体的连接和金属节点的苯环结构, 并观察了MOF的原子级表面、 界面和缺陷等局域结构特征. 最后对iDPC-STEM技术在原子尺度成像方面的应用潜力进行了总结与展望.

Atomic Scale Structure of Beam Sensitive Materials

Molecular sieves and metal organic framework(MOF)materials are widely used in the fields of catalysis,energy storage,drying,purification,and adsorption separation due to their unique pores and framework structures.The atomic scale characterization of their structures is significance for a deep understanding of their structure-activity relationships.However,their large pore structure and organic framework make them extremely sensitive to electron beam.The structure will be quickly destroyed and become amorphous in the conventional transmission electron microscope imaging mode,and the atomic arrangement information of the pores and framework cannot be obtained.The recently developed scanning transmission electron microscopy technology based on integrated differential phase contrast(iDPC-STEM)has shown obvious advantages in imaging of beam sensitive materials and light element components,making the characterization of porous framework materials and hydrocarbon pool species become possible.This article reviews our research group’s recent research on molecular sieve and MOF material atomic structure using this technology.The iDPC-STEM technology was applied to the ZSM-5 molecular sieve catalyst for methanol conversion to realize the imaging analysis of the atomic-level framework structure of the molecular sieve.In the MOF system,the coordination mode of the organic linker and the metal node in the MIL-101 framework was observed using this technology.On this basis,the benzene ring structure of the organic link and the metal node was analyzed,and the atomiclevel surface,interface and defects and other local structural features of the MOF were observed.Finally,the application potential of iDPC-STEM technology in atomic scale imaging is summarized and prospected.