Recent technological advances have sought to exploit two-dimensional nanomaterials such as the nanosheets of transition-metal dichalcogenides, porous carbon and black phosphorus owing to auspicious nature as precursors for the synthesis of 2D carbon materials for energy storage. Specifically, porous carbon nanosheets have received much attention as they possess excellent energy storage capabilities therefore making them suitable candidates for applications such as in supercapacitors and lithium ion batteries. Synthesis of carbon nanosheets involves two common techniques: the hard template and the self-template methods. However, the thicknesses of the carbon nanosheets prepared by these two methods are usually above 20 nanometers and cannot be well controlled. As a consequence, they resultant nanosheets exhibit poor rate performance as electrode material. Recently, metal–organic framework (MOF) derived carbon materials have received much attention for energy storage owing to their controllable morphologies and pore structures and have potential to be utilized as precursors for the synthesis of ultrathin carbon nanosheets. Unfortunately, the synthesis of ultrathin carbon nanosheets from ultrathin MOF nanosheets has not been reported, mainly due to the high costs and low yields of the synthetic methods for ultrathin MOF nanosheets.
To this note, a team of researchers led by Professor Suqin Liu and Professor Zhen He from the College of Chemistry and Chemical Engineering at Central South University in China developed a facile and low-cost bottom-up synthesis technique of ultrathin zinc (II)- benzimidazole-acetate MOF nanosheets and their derived N-doped porous ultrathin carbon nanosheets for energy storage. They utilized the carbonization of the as-synthesized ultrathin-zinc (II)-benzimidazole-acetate nanosheets to obtain ultrathin carbon nanosheets of the desired thickness. Their work is currently published in the research journal, Journal of Material Chemistry A.
The research method employed commenced with the synthesis of zinc (II)-benzimidazole based MOFs. Next, the researchers prepared carbon nanocubes, layered carbon nanocubes and ultrathin carbon nanosheet materials from the synthesized zinc (II)-benzimidazole based MOFs. They then proceeded to undertake physicochemical characterizations of the prepared materials by investigating their morphologies and compositions. Lastly, electrochemical measurements were undertaken.
The authors observed that the ultrathin carbon nanosheets exhibited admissible capacitance at a high current density which was recorded as the best among the reported MOF-derived carbon materials for supercapacitor electrodes. Additionally, they noted that the ultrathin-carbon nanosheets also exhibited a high reversible capacity, greater than 500 mA h g-1 at 10 A g-1 and retained 100% coulombic efficiency after 1000 cycles at 2 A g-1 as an anode material for lithium-ion batteries.
Their study presented successful development of a low-cost approach for the synthesis of the ultrathin-zinc (II)-benzimidazole-acetate nanosheets, the N-doped ultrathin carbon nanosheets with a high specific surface area, suitable porous structure, and high conductivity through the carbonization of the as-synthesized ultrathin-zinc (II)-benzimidazole-acetate nanosheets. Altogether, the work has provided a new strategy for the high-yield and low-cost synthesis of ultrathin MOF nanosheets as well as 2D carbon materials and their metal or metal oxide composites for various applications.
Kuangmin Zhao, Suqin Liu, Guanying Ye, Qingmeng Gan, Zhi Zhou and Zhen He. High-yield bottom-up synthesis of 2D metal– organic frameworks and their derived ultrathin carbon nanosheets for energy storage. Journal of Material Chemistry A, 2018, volume 6, Page 2166Go To Journal of Material Chemistry A