Graphene Oxide. Origin of Acidity, Its Instability in Water, and a New Dynamic Structural Model
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- 作者：Ayrat M. Dimiev ; Lawrence B. Alemany ; James M. Tour
- 刊名：ACS Nano
- 出版年：2013
- 出版时间：January 22, 2013
- 年：2013
- 卷：7
- 期：1
- 页码：576-588
- 全文大小：641K
- 年卷期：v.7,no.1(January 22, 2013)
- ISSN：1936-086X
文摘
The existing structural models of graphene oxide (GO) contradict each other and cannot adequately explain the acidity of its aqueous solutions. Inadequate understanding of chemical structure can lead to a misinterpretation of observed experimental phenomena. Understanding the chemistry and structure of GO should enable new functionalization protocols while explaining GO鈥檚 limitations due to its water instability. Here we propose an unconventional view of GO chemistry and develop the corresponding 鈥渄ynamic structural model鈥?(DSM). In contrast to previously proposed models, the DSM considers GO as a system, constantly changing its chemical structure due to interaction with water. Using potentiometric titration, 13C NMR, FTIR, UV鈥搗is, X-ray photoelectron microscopy, thermogravimetric analysis, and scanning electron microscopy we show that GO does not contain any significant quantity of preexisting acidic functional groups, but gradually generates them through interaction with water. The reaction with water results in C鈥揅 bond cleavage, formation of vinylogous carboxylic acids, and the generation of protons. An electrical double layer formed at the GO interface in aqueous solutions plays an important role in the observed GO chemistry. Prolonged exposure to water gradually degrades GO flakes converting them into humic acid-like structures. The proposed DSM provides an explanation for the acidity of GO aqueous solutions and accounts for most of the known spectroscopic and experimental data.