Elucidating the Formation of 2D Conjugated Metal Organic Frameworks via In-Situ Nanofluidic-Liquid-Cell Transmission Electron Microscopy

金属有机骨架（mof）是一类新兴的由含金属节点和有机配体构成的晶体多孔材料。mof的巨大化学和结构多样性为下一代应用量身定制的晶体工程开辟了令人兴奋的可能性。近年来，二维共轭mof （2D c- mof）以其在平面内π-离域和微弱的面外π-π叠加特性在二维材料大家庭中受到了广泛的关注。2D c- mof同时具有高导电性，丰富的活性位点和可调节的氧化还原态，使其成为未来电化学能量存储/转换应用的有希望的候选者。然而，尽管二维c- mof具有有趣的物理和化学性质，但它们的形成机制和结构-性能相关性仍然知之甚少。特别是，控制2D c- mof成核和生长的基本过程，以及反应参数与合成产物之间的关系，在很大程度上仍未被探索。在这里，我们的目标是通过原位液体细胞透射电子显微镜（LC-TEM）直接观察到分子/原子尺度的二维c-MOF形成。实现这一目标的主要挑战是：(1)LC内部的水分子辐射分解，导致高活性自由基，直接蚀刻反应产物和LC窗口；(2)传统LC设计包括大流体体积，可实现的分辨率明显低于仪器分辨率；(3)mof的极低电子弹性，特别是由于C-H键的存在。为了解决这些问题，我们将利用新设计的纳米流体LC进行高分辨率LC- tem。微制造的纳米通道可以很好地控制液体厚度到几纳米。微流体系统能够在成像过程中冲洗出放射性溶解产物，从而减少水放射性溶解的有害影响。作为一个额外的策略，将使用乏水来增加反应产物在液体环境中的寿命。除了液池设计外，mof的固有稳定性是本研究成功的另一个关键因素。在我们的初步研究中，我们发现无氢苯六硫醇（BHT） Cu MOF可以承受与无机材料相当的电子剂量。因此，为了大幅提高电子弹性，我们将合成无氢和卤化的2D c-MOFs，并将其用于LC-TEM研究。

Metal-organic frameworks (MOFs) represent an emerging class of crystalline porous materials constructed from metal containing nodes and organic ligands. The vast chemical and structural diversity of MOFs opens up exciting possibility of crystal engineering tailored for next generation applications. Recently, two-dimensional conjugated MOFs (2D c-MOFs), featuring in-plane π-delocalization and weak out-of-plane π-π stacking, have attract considerable attention in the grand family of 2D materials. 2D c-MOFs offers simultaneously high electrical conductivity, abundant active sites and tunable redox states, rendering them promising candidates for future applications in electrochemical energy storage/conversion. However, despite the intriguing physical and chemical properties of 2D c-MOFs, their formation mechanisms and structure-property correlations remain poorly understood. Particularly, the fundamental processes governing 2D c-MOFs nucleation and growth, and the relationship between reaction parameters and synthetic outcome, remain largely unexplored. Here, we aim at direct observation of 2D c-MOF formation via in-situ liquid-cell transmission electron microscopy (LC-TEM) down to molecular/atomic scale. The main challenges of reaching this goal are: (1) radiolysis of the water molecules within the LC, leading to highly reactive radicals, which directly etch the reaction products and LC windows, (2) the conventional LC design consists of large fluid volume, the achievable resolution is significantly inferior to the instrumental resolution, and (3) the extremely low electron resilience of MOFs, particularly due to the presence of C-H bonds. To address these issues, we will utilize a newly designed nanofluidic LC for high-resolution LC-TEM. The microfabricated nanochannels allow well-controlled liquid thickness down to a few nanometers. And the microfluid systems is able to flush out radiolytic products during imaging, thus reducing the detrimental effects of water radiolysis. As an additional strategy, deuterated water will be used to increase the lifetime of reaction products in the liquid environment. Apart from the liquid cell design, the intrinsic stability of MOFs presents another pivotal factor to the success of the proposed work. In our preliminary study, we found that a hydrogen-free benzenehexathiol (BHT) Cu MOF can withstand electron doses comparable to those of inorganic materials. Therefore, to substantially enhance the electron resilience, hydrogen-free and halogenated 2D c-MOFs will be synthesized and utilized for LC-TEM studies.