Charge-tunable graphene dispersions in water made with amphoteric pyrene derivatives
Charge-tunable graphene dispersions in water made with amphoteric pyrene derivatives
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DOI：
10.1039/c9me00024k
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发表时间：
2019-06-01
影响因子：
3.6
通讯作者：
Casiraghi, Cinzia
中科院分区：
文献类型：
--
作者：
Shin, Yuyoung;Just-Baringo, Xavier;Casiraghi, Cinzia
石墨液相剥离(LPE)作为一种可大规模、低成本生产溶液处理石墨烯的方法显示出巨大的潜力，具有广泛的应用前景。由于石墨烯的疏水性质，需要一种稳定剂来剥离水中的石墨--尤其是已被证明在剥离石墨方面非常有效，通过产生带正电或负电的分散体，具体取决于所使用的官能团。在这项工作中，我们利用氨基酸基团(赖氨酸和牛磺酸)合成了两性芘衍生物，并将它们作为石墨烯LPE的剥离剂进行了测试。原子力显微镜显示薄片的平均尺寸在100到300 nm之间，而定性的拉曼分析表明，色散主要由单层和少数几层薄片组成，这一点也得到了透射电子显微镜的证实。最后，我们证明了石墨烯的表面电荷可以通过系统地改变pH水平来调节。虽然这两种稳定剂都能够剥离水中的石墨，但基于芘的赖氨酸可以产生更集中和稳定的石墨烯分散体，其表面电荷根据pH水平在正负之间变化。相反，在极端的pH条件下，用芘取代的牛磺酸得到的石墨烯分散体，观察到了分散物质的沉淀。这归因于牛磺酸中磺酸基团的低pK(A)值，即使在很低的pH下，牛磺酸仍然带负电荷。
Liquid-phase exfoliation (LPE) of graphite shows great potential as a mass scalable and low-cost method for production of solution-processed graphene, which can be used for a wide range of applications. Due to the hydrophobic nature of graphene, a stabilising agent is needed to exfoliate graphite in water - in particular, pyrene derivatives have been shown to be very effective in exfoliating graphite, by producing either positively or negatively charged dispersions, depending on the functional group used. In this work we have synthesised amphoteric pyrene derivatives, using amino acid-based functional groups (lysine and taurine), and tested them as exfoliating agents for LPE of graphene. Atomic force microscopy shows the flakes to have an average size between 100 and 300 nm, while qualitative Raman analysis shows the dispersion to be composed mainly of single and few-layer flakes, as also confirmed by transmission electron microscopy. Finally, we demonstrate that the surface charge of graphene can be adjusted by a systematic change of the pH level. Although both stabilisers demonstrated to be able to exfoliate graphite in water, pyrene-based lysine produces more concentrated and stable graphene dispersions, whose surface charge changes between positive and negative depending on the pH level. In contrast, sedimentation of the dispersed material was observed at extreme pH for graphene dispersions obtained with pyrene-substituted taurine. This is attributed to the low pK(a) value of the sulfonic group in taurine, which remains negatively charged even at very low pH.