Division of Chemistry and Materials, Faculty of Textile Science and Technology, Shinshu University , Ueda 386-8567, Japan.
Department of Applied Chemistry, Faculty of Engineering, Nagasaki University , Nagasaki 852-8521, Japan.
Langmuir. 2017 Dec 26;33(51):14565-14570. doi: 10.1021/acs.langmuir.7b03328. Epub 2017 Dec 11.
Fabrication of nanographene shows a promising route for production of designed porous carbons, which is indispensable for highly efficient molecular separation and energy storage applications. This process requires a better understanding of the mechanical properties of nanographene in their aggregated structure. We studied the structural and mechanical properties of nanographene monoliths compressed at 43 MPa over different times from 3 to 25 h. While in monoliths compressed over shorter time adsorption isotherms of Ar at 87 K or N at 77 K exhibited a prominent hysteresis due to presence of predominant mesopores, compression for long time induces a low pressure hysteresis. On the other hand, compression for 25 h increases the microporosity evaluated by Ar adsorption, not by N adsorption, indicating that 25 h compression rearranges the nanographene stacking structure to produce ultramicropores that can be accessible only for Ar. TEM, X-ray diffraction, and Raman spectroscopic studies indicated that the compression for 25 h unfolds double-bent-like structures, relaxing the unstable nanographene stacked structure formed on the initial compression without nanographene sheets collapse. This behavior stems from the highly elastic nature of the nanographenes.
纳米石墨烯的制造为设计多孔碳的生产展示了一条有前途的途径，这对于高效的分子分离和储能应用是不可或缺的。这个过程需要更好地了解纳米石墨烯在其聚集结构中的机械性能。我们研究了在 43 MPa 下压缩不同时间（3 至 25 小时）的纳米石墨烯单体的结构和机械性能。虽然在较短时间内压缩的单体中，由于存在主要的中孔，Ar 在 87 K 或 N 在 77 K 的吸附等温线表现出明显的滞后现象，但长时间压缩会导致低压滞后。另一方面，25 小时的压缩增加了通过 Ar 吸附评估的微孔度，而不是通过 N 吸附，这表明 25 小时的压缩重新排列了纳米石墨烯的堆积结构，产生了仅对 Ar 可及的超微孔。TEM、X 射线衍射和拉曼光谱研究表明，25 小时的压缩展开了类似于双弯曲的结构，在初始压缩中形成的不稳定的纳米石墨烯堆积结构没有坍塌的情况下，缓解了其不稳定性。这种行为源于纳米石墨烯的高弹性性质。
