Department of Chemistry and Pharmacy and Institute of Advanced Materials and Processes, University Erlangen-Nürnberg, Henkestrasse 42, 91054 Erlangen, Germany.
Chemistry. 2013 Jul 15;19(29):9490-6. doi: 10.1002/chem.201300387. Epub 2013 Jun 18.
The structure of graphene oxide (GO) is of crucial importance for its chemical functionalization. However, the sulfur content present in GO prepared by Hummers' method has only been addressed by a few authors so far. It has been reported that hydrolysis of sulfur species takes place and that stable sulfonic groups are present in graphite oxide. In this manuscript, in contrast to earlier reports, sulfate species are identified that are covalently bound to GO and still present after extensive aqueous work-up. Additionally, we exclude the possibility that sulfonic groups are present in GO as major species after aqueous work up. Our results are based on bulk characterization of graphene oxide by thermogravimetry and subsequent analysis of the decomposition products using mass spectroscopy and infrared spectroscopy. Up to now, the combustion temperature between 200 and 300 °C remained almost unaddressed. In a temperature dependant experiment we reveal two main decomposition steps that differ in temperature and that are closely related to the sulfur species in GO. While the decomposition, between 200 and 300 °C, is related to the degradation of organosulfate, the other one, between 700 and 800 °C, is assigned to the pyrolysis of inorganic sulfate. Furthermore, organosulfate is to some extent responsible for the reactivity of GO. Therefore, the structural model of GO was extended by adding organosulfate in addition to epoxy and hydroxyl groups, which are predominantly covalently bound above and below the carbon skeleton. Furthermore, the identification of organosulfate groups beneath epoxy groups makes new molecular architectures feasible and can be used to explain the properties of GO in various applications.
氧化石墨烯（GO）的结构对于其化学功能化至关重要。然而，到目前为止，只有少数作者研究了Hummers 法制备的 GO 中存在的硫含量。据报道，硫物种发生水解，并且在石墨氧化物中存在稳定的磺酸基团。在本文中，与早期的报告相反，鉴定出与 GO 共价结合并且在广泛的水相后处理后仍然存在的硫酸盐物种。此外，我们排除了磺酸基团在水相后处理后作为 GO 中的主要物种存在的可能性。我们的结果基于热重法对氧化石墨烯的整体表征，以及随后使用质谱和红外光谱对分解产物的分析。到目前为止，200 至 300°C 之间的燃烧温度几乎没有得到解决。在依赖温度的实验中，我们揭示了两个主要的分解步骤，它们在温度上有所不同，并且与 GO 中的硫物种密切相关。在 200 至 300°C 之间的分解与有机硫酸盐的降解有关，而另一个在 700 至 800°C 之间的分解与无机硫酸盐的热解有关。此外，有机硫酸盐在某种程度上与 GO 的反应性有关。因此，除了主要通过共价键结合在碳骨架上方和下方的环氧和羟基基团之外，GO 的结构模型还添加了有机硫酸盐基团。此外，在环氧基团下方鉴定出有机硫酸盐基团使得新的分子架构成为可能，并可用于解释 GO 在各种应用中的性质。
