Understanding the pH-Dependent Behavior of Graphene Oxide Aqueous Solutions: A Comparative Experimental and Molecular Dynamics Simulation Study
Understanding the pH-Dependent Behavior of Graphene Oxide Aqueous Solutions: A Comparative Experimental and Molecular Dynamics Simulation Study
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DOI：
10.1021/la203607w
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发表时间：
2012-01-10
期刊：
影响因子：
3.9
通讯作者：
Blankschtein, Daniel
中科院分区：
文献类型：
--
作者：
Shih, Chih-Jen;Lin, Shangchao;Blankschtein, Daniel
理解氧化石墨烯（GO）水溶液的pH依赖性行为对于生产用于电子、光学和生物应用的组装GO或还原GO膜是重要的。我们进行了比较实验和分子动力学（MD）模拟研究，以揭示GO在不同pH值下聚集和表面活性背后的机制。在低pH下，羧基被质子化，使得GO片变得不那么亲水并形成聚集体。MD模拟进一步表明，聚集体表现出GO-水-GO三明治状结构，因此在水中稳定而不是沉淀。然而，在高pH下，去质子化的羧基是非常亲水的，使得单个GO片优选像常规盐一样溶解在本体水中。发现在低pH下形成的GO聚集体是表面活性的，并且不表现出表面活性剂胶束的特征。我们的研究结果表明，GO在pH 1和14的水溶液中不像传统的表面活性剂那样表现。本文提出的对GO溶液行为的分子水平理解可以促进和改进用于在溶液相中合成和分选大的、均匀的GO分散体的实验技术。
Understanding the pH-dependent behavior of graphene oxide (GO) aqueous solutions is important to the production of assembled GO or reduced GO films for electronic, optical, and biological applications. We have carried out a comparative experimental and molecular dynamics (MD) simulation study to uncover the mechanisms behind the aggregation and the surface activity of GO at different pH values. At low pH, the carboxyl groups are protonated such that the GO sheets become less hydrophilic and form aggregates. MD simulations further suggest that the aggregates exhibit a GO-water-GO sandwich like structure and as a result are stable in water instead of precipitating. However, at high pH, the deprotonated carboxyl groups are very hydrophilic such that individual GO sheets prefer to dissolve in bulk water like a regular salt. The GO aggregates formed at low pH are found to be surface-active and do not exhibit characteristic features of surfactant micelles. Our findings suggest that GO does not behave like conventional surfactants in pH 1 and 14 aqueous solutions. The molecular-level understanding of the solution behavior of GO presented here can facilitate and improve the experimental techniques used to synthesize and sort large, uniform GO dispersions in a solution phase.