Intercalator-assisted plasma-liquid technology: an efficient exfoliation method for few-layer two-dimensional materials
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Published online 5 August 2020 | https://doi.org/10.1007/s40843-020-1416-0
Intercalator-assisted plasma-liquid technology: an efficient exfoliation method for few-layer twodimensional materials Hao Huang
1,2†
, Ming Gao
1,2†
1,2,3
, Jiahong Wang
3
1,2*
, Paul K. Chu , Yifan Huang
Few-layer two-dimensional (2D) materials have attracted enormous interest since 2004 when graphene was successfully exfoliated from graphite by mechanical exfoliation [1]. In recent years, the burgeoning 2D family with unique and novel properties have found new applications in a myriad of fields including electronics, optoelectronics, catalysis, energy, and biomedicine [2–4]. However, in order to be commercially viable, a mass fabrication technique to synthesize few-layer 2D materials with high quality is critical. The typical large-scale fabrication strategy for few-layer 2D materials is liquid exfoliation from the bulk counterparts with a layered structure [5]. Although the exfoliation by chemical oxidation can produce graphene oxide from graphite on a large scale [6], functional groups are generally introduced and defects are produced [7]. Ultrasonic/shear liquid exfoliation applies to most 2D materials but requires a long processing time (generally several hours) and often obtains small and thick sheets. Modified physical exfoliation methods such as ultrasonic-ball milling and intermediate-assisted grinding exfoliation improve the yield and quality of the exfoliated materials; however, a further purification is needed [8,9]. Recently, methods based on electrochemical technology (ET) have been proposed [10–18]. Generally, intercalator-assisted electrochemical technique (IA-ET) with intercalators such as quaternary + ammonium salts or Li complexes enables the intercalation of ions/molecules into the interlayer, leading to the expansion of the bulk layered materials, thus facilitating subsequent exfoliation into few-layer sheets [11,13,15].
and Xue-Feng Yu
1,2*
However, IA-ET exfoliation often damages the structure and alters the properties of the materials due to the residual intercalators [16]. Considering the complexity and variety of 2D materials, it is highly desired to develop a new exfoliation method for mass production of different types of few-layer 2D materials. Plasma processing is a common method in surface modification, surface etching, and thin film deposition due to the production of abundant active species [19–23]. The plasma-liquid technology (PLT) has been adopted for nanomaterials synthesis and doping because it can effectively transfer the active species to the liquid through the plasma-liquid interface for the chemical reactions [20,24,25]. Compared with ET, PLT can produce more active species and trigger various charge transfer reactions such as quick decomposition and polymerization of organic molecules. Furthermore, PLT only requires a simple and economical atmospheric-pressure plasma system operated under ambient conditions. Our previous work has demonstrated that PLT enables scalable production of ph
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