Wang Zhao, Schmalbach Kevin M, Combs Rebecca L, Chen Youxing, Penn R Lee, Mara Nathan A, Stein Andreas
Department of Chemistry, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States.
Department of Chemical Engineering and Materials Science, University of Minnesota, 421 Washington Avenue SE, Minneapolis, Minnesota 55455, United States.
ACS Appl Mater Interfaces. 2020 Nov 4;12(44):49971-49981. doi: 10.1021/acsami.0c12877. Epub 2020 Oct 20.
Metal-organic framework (MOF) materials have shown promise in many applications, ranging from gas storage to absorption and catalysis. Because of the high porosity and low density of many MOFs, densification methods such as pelletization and extrusion are needed for practical use and for commercialization of MOF materials. Therefore, it is important to elucidate the mechanical properties of MOFs and to develop methods of further enhancing their mechanical strength. Here, we demonstrate the influence of phase purity and the presence of a pore-reinforcing component on elastic modulus and yield stress of NU-1000 MOFs through nanoindentation methods and finite element simulation. Three types of NU-1000 single crystals were compared: phase-pure NU-1000 prepared with biphenyl-4-carboxylic acid as a modulator (NU-1000-bip), NU-1000 prepared with benzoic acid as a modulator (NU-1000-ben), which results in an additional, denser impurity phase of NU-901, and NU-1000-bip whose mesopores were infiltrated with silica (SiO(OH)@NU-1000) by nanocasting methods. By maintaining phase purity and minimizing defects, the elastic modulus could be enhanced by nearly an order of magnitude: phase-pure NU-1000-bip crystals exhibited an elastic modulus of 21 GPa, whereas the value for NU-1000-ben crystals was only 3 GPa. The introduction of silica into the mesopores of NU-1000-bip did not strongly affect the measured elastic modulus (19 GPa) but significantly increased the load at failure from 2000 μN to 3000-4000 μN.
金属有机框架（MOF）材料在许多应用中都展现出了潜力，从气体存储到吸附和催化。由于许多MOF具有高孔隙率和低密度，因此在实际应用和MOF材料商业化过程中，需要采用造粒和挤压等致密化方法。因此，阐明MOF的力学性能并开发进一步提高其机械强度的方法非常重要。在这里，我们通过纳米压痕方法和有限元模拟，展示了相纯度和孔增强组分的存在对NU-1000 MOF弹性模量和屈服应力的影响。比较了三种类型的NU-1000单晶：以联苯-4-羧酸作为调节剂制备的纯相NU-1000（NU-1000-bip）、以苯甲酸作为调节剂制备的NU-1000（NU-1000-ben），后者会产生额外的、密度更高的NU-901杂质相，以及通过纳米铸造方法使介孔中渗入二氧化硅（SiO(OH)@NU-1000）的NU-1000-bip。通过保持相纯度并最小化缺陷，弹性模量可提高近一个数量级：纯相NU-1000-bip晶体的弹性模量为21 GPa，而NU-1000-ben晶体的值仅为3 GPa。将二氧化硅引入NU-1000-bip的介孔中对测得的弹性模量（19 GPa）影响不大，但显著提高了破坏载荷，从2000 μN增加到3000 - 4000 μN。
