A mixed-solvent strategy for efficient exfoliation of inorganic graphene analogues.
A mixed-solvent strategy for efficient exfoliation of inorganic graphene analogues.
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DOI：
10.1002/anie.201105364
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发表时间：
2011-11
影响因子：
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通讯作者：
Kai-Ge Zhou;Nan-nan Mao;Hang-Xing Wang;Yong Peng;Hao‐Li Zhang
中科院分区：
文献类型：
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作者：
Kai-Ge Zhou;Nan-nan Mao;Hang-Xing Wang;Yong Peng;Hao‐Li Zhang
层状二维（2D）纳米材料，如石墨烯，是一种概念上的新材料，为低维物理提供了新的途径。除了公知的石墨烯之外，无机石墨烯类似物（IGA）如层状过渡金属二硫属化物（例如，MoS 2和WS 2）[5-7]和氮化硼（BN）在过去几年中引起了迅速增加的关注。这些IGA有望表现出独特的性能，并在晶体管，储能，热导体和拓扑绝缘体等应用中具有巨大的潜力。此外，像MoS 2和WS 2这样的IGA具有固有的带隙和高迁移率，甚至可以在某些领域与石墨烯竞争。然而，IGA的研究已经大大阻碍了这些二维纳米材料的制备和组装的实际困难。只有少数几种方法来获得几层IGA已被报道。首先使用机械剥离从其本体材料获得层状IGA。其他正在探索的方法包括化学合成和液体剥离。科尔曼等人最近报道了一种无表面活性剂的液体剥离方法，该方法可以制备分散在各种有机溶剂中的IGA的少层纳米片。热力学分析表明，由于IGA的高表面能，最好的溶剂可能具有高沸点。使用非挥发性溶剂使得难以将IGA加工成器件，这是由于难以去除溶剂以及在缓慢溶剂蒸发期间发生聚集。迄今为止，层状MoS 2和WS 2在挥发性溶剂中的液体剥离已经取得了非常有限的成功。在这里，我们展示了一个通用的和scaleable mixedsolvent策略的液体剥离的IGA，包括WS 2，二硫化钼，BN，在挥发性溶剂。通过选择具有适当组成的溶剂，可以在低沸点溶剂混合物中获得高度稳定的伊加悬浮液，然后可以容易地用于进一步的应用。汉森溶解度参数（HSP）理论可以部分预测纳米材料在液体中的分散，HSP是一种用于解释溶解行为的半经验关联式。三个HSP参数用于描述溶剂或材料的特性：dD、dP和dH，分别是分散性、极性和氢键溶解度参数。溶出过程是溶剂和溶质的HSP参数之间的适应过程。HSP距离Ra用于评估适应水平[等式2]。①]。
Layered two-dimensional (2D) nanomaterials such as graphene are a conceptually new class of materials that offers new access to low-dimensional physics. Besides wellknown graphene, inorganic graphene analogues (IGAs) such as layered transition metal dichalcogenides (e.g., MoS2 and WS2) [5–7] and boron nitride (BN) have been attracting rapidly increasing attention in the past few years. These IGAs were expected to exhibit unique properties and have great potential in applications like transistors, energy storage, thermal conductors, and topological insulators. Moreover, IGAs like MoS2 and WS2 have intrinsic band gap and high mobility, and may even compete with graphene in certain fields. However, investigations on IGAs have been significantly hindered by the practical difficulties in the preparation and assembly of these 2D nanomaterials. Only a few approaches to obtain few-layered IGAs have been reported. Mechanical exfoliation was first used to obtain layered IGAs from their bulk materials. Other approaches that are being explored include chemical synthesis and liquid exfoliation. Coleman et al. recently reported a surfactant-free liquid-exfoliation method which can produce few-layered nanosheets of IGAs dispersed in various organic solvents. Thermodynamic analysis suggested that, because of the high surface energy of IGAs, the best solvents are likely to have high boiling points. Using nonvolatile solvents makes it difficult to process IGAs into devices, due to the difficulties in the removal of solvent and the occurrence of aggregation during the slow solvent evaporation. To date, liquid exfoliation of layered MoS2 and WS2 in volatile solvent has met with very limited success. Herein we demonstrate a versatile and scaleable mixedsolvent strategy for liquid exfoliation of IGAs, including WS2, MoS2, and BN, in volatile solvents. By choosing solvents with appropriate composition, highly stable IGA suspensions can be obtained in low-boiling solvent mixtures, which can then be easily used in further applications. The dispersion of nanomaterials in liquids can be partially predicted by the theory of Hansen solubility parameters (HSP), which is a semi-empirical correlation developed to explain dissolution behavior. Three HSP parameters are used to describe the character of a solvent or material: dD, dP, and dH, which are the dispersive, polar, and hydrogen-bonding solubility parameters, respectively. The dissolution process is one of adaptation between the HSP parameters of solvents and solutes. The HSP distance Ra is used to evaluate the level of adaptation [Eq. (1)].