电化学剥离法制备超亲水石墨表面和水分散石墨胶体。

Superhydrophilic graphite surfaces and water-dispersible graphite colloids by electrochemical exfoliation.

机构信息

Department of Chemical and Materials Engineering, National Central University, Jhongli, 320 Taiwan.

出版信息

J Chem Phys. 2013 Aug 14;139(6):064703. doi: 10.1063/1.4817680.

Abstract

Superhydrophilic graphite surfaces and water-dispersible graphite colloids are obtained by electrochemical exfoliation with hydrophobic graphite electrodes. Such counterintuitive characteristics are caused by partial oxidation and investigated by examining both graphite electrodes and exfoliated particles after electrolysis. The extent of surface oxidation can be explored through contact angle measurement, scanning electron microscope, electrical sheet resistance, x-ray photoelectron spectroscopy, zeta-potential analyzer, thermogravimetric analysis, UV-visible, and Raman spectroscopy. The degree of wettability of the graphite anode can be altered by the electrolytic current and time. The water contact angle declines generally with increasing the electrolytic current or time. After a sufficient time, the graphite anode becomes superhydrophilic and its hydrophobicity can be recovered by peeling with adhesive tape. This consequence reveals that the anodic graphite is oxidized by oxygen bubbles but the oxidation just occurs at the outer layers of the graphite sheet. Moreover, the characteristics of oxidation revealed by UV peak shift, peak ratio between D and G bands, and negative zeta-potential indicate the presence of graphite oxide on the outer shell of the exfoliated colloids. However, thermogravimetric analysis for the extent of decomposition of oxygen functional groups verifies that the amount of oxygen groups is significantly less than that of graphite oxide prepared via Hummer method. The structure of this partially oxidized graphite may consist of a graphite core covered with an oxidized shell. The properties of the exfoliated colloids are also influenced by pH of the electrolytic solution. As pH is increased, the extent of oxidation descends and the thickness of oxidized shell decreases. Those results reveal that the degree of oxidation of exfoliated nanoparticles can be manipulated simply by controlling pH.

摘要

通过使用疏水电极进行电化学剥落，可以得到超亲水石墨表面和可分散在水中的石墨胶体。这种有违直觉的特性是由部分氧化引起的，并通过检查电解后的石墨电极和剥落颗粒来进行研究。通过接触角测量、扫描电子显微镜、电阻、X 射线光电子能谱、Zeta 电位分析仪、热重分析、UV-可见分光光度计和拉曼光谱，可以探索表面氧化的程度。通过改变电流和时间，可以改变石墨阳极的润湿性。随着电流或时间的增加，水接触角通常会降低。经过足够的时间，石墨阳极变得超亲水，其疏水性可以通过用胶带剥离来恢复。这一结果表明，阳极石墨是被氧气气泡氧化的，但氧化仅发生在石墨片的外层。此外，通过 UV 峰位移、D 和 G 带峰比值以及负 Zeta 电位揭示的氧化特性表明，在剥落胶体的外壳上存在氧化石墨。然而，热重分析用于分解氧官能团的程度证实，氧基团的数量明显少于通过 Hummer 法制备的氧化石墨的数量。这种部分氧化石墨的结构可能由石墨核和氧化壳组成。剥离胶体的性能也受到电解液 pH 值的影响。随着 pH 值的增加，氧化程度下降，氧化壳的厚度减小。这些结果表明，通过控制 pH 值，可以简单地控制剥落纳米颗粒的氧化程度。