Image: (a) Schematic diagram of decomposition of macro-compression force Fc and Fc? Into smaller microscopic forces fi and fi? The layer material is loaded by the force intermediate. (b) The peeling mechanism of layered materials. fi and fi? Transfer to sliding friction ffi and ffi? Due to the rotation of the bottom container, under the relative sliding of the intermediate body and the layered material. (c) Atomic force microscope image of a two-dimensional thin section. (d) Several bottom photos of two-dimensional molybdenum disulfide flakes in aqueous solution. see more 

A large number of two-dimensional materials, including graphene, hexagonal boron nitride (h-BN), transition metal dichalcogenides (TMDCs) (such as MoS2 and WSe2), metal oxides (MxOy), black phosphorene (bP), etc., Provides a wide range of performance and many potential applications.

To realize its commercial use, the prerequisite is large-scale production. Bottom-up strategies such as chemical vapor deposition (CVD) and chemical synthesis have been widely explored, but so far only a small number of 2D materials have been produced. Another important strategy for obtaining 2D materials is the top-down path, by stripping the bulk material into a single-layer or few-layer 2D material, such as ball milling, liquid phase stripping, and so on. It seems that top-down strategies are most likely to be, however, when scaled up, they only apply to specific materials. So far, only graphene and graphene oxide can be prepared at the ton level, while for other two-dimensional materials, they are still in a laboratory state due to low yields. Therefore, it is necessary to develop an efficient and low-cost two-dimensional material preparation method to develop from the laboratory to our daily lives.

The failure of the solid lubricant is caused by the sliding between the layers of the bulk material, and the result of the sliding is that the bulk material will peel off into fewer layers. Based on this understanding, in a new research article published in the National Science Review in Beijing, the low-dimensional materials and device laboratory led by Professor Cheng Huiming and Professor Liu Bilu of Tsinghua University proposed an exfoliating technology named Intermediate grinding and exfoliation (iMAGE). The key to this peeling technology is to use intermediate materials to increase the friction coefficient of the mixture and effectively apply sliding friction to the layered materials, thereby significantly improving the peeling efficiency.

Taking into account the situation of 2D h-BN, the yield and energy consumption can reach 0.3 g h-1 and 3.01×106 J g-1, respectively, which are one to two orders of magnitude better than the previous results. The average thickness of the resulting exfoliated 2D h-BN flakes was 4 nm, and the average lateral size was 1.2 μm. In addition, this iMAGE method has been extended to exfoliate a series of layered materials with different characteristics, including graphite, Bi2Te3, bP, MoS2, TiOx, h-BN and mica, covering two-dimensional metals, semiconductors and insulators with different band gaps.

It is worth mentioning that, in cooperation with Luoyang Shenyu Molybdenum Industry Co., Ltd., the natural mineral molybdenite concentrate, which is cheap and rich in earth resources, was used as an example for the industrial-scale stripping production of two-dimensional molybdenum disulfide flakes.

"This is the first time that a two-dimensional material other than graphene has been produced with a yield exceeding 50% and a productivity exceeding 0.1g h-1. It is expected that the annual production capacity of 2D h-BN will reach our iMAGE technology exceeding 10 tons." Professor Liu Bilu, one of the main authors of the study, said: "Our iMAGE technology overcomes a major challenge of two-dimensional materials, namely their mass production, and is expected to accelerate their commercialization in a wide range of applications in electronics, energy, etc. "

Chi Zhang, Junyang Tan, Yikun Pan, Xingke Cai, Xiaolong Zou, Hui-Ming Cheng* and Bilu Liu* mass-produce two-dimensional materials Natl Sci Rev 2019 through intermediate auxiliary grinding and exfoliation; doi: 10.1093/nsr/nwz156 https: //doi.org/10.1093/nsr/nwz156

"National Science Review" is China's first comprehensive academic journal published in English, which aims to connect China's rapidly growing group of scientists with the frontiers of global science and technology. The magazine also aims to draw the world's attention to the progress of scientific research in China.

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Cheng Huiming hmcheng@sz.tsinghua.edu.cn

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Copyright © 2021 American Association for the Advancement of Science (AAAS)