Department of Materials, University of Oxford , Parks Road, Oxford OX1 3PH, United Kingdom.
ACS Nano. 2016 Aug 23;10(8):7515-22. doi: 10.1021/acsnano.6b02391. Epub 2016 Jul 19.
Graphene oxide (GO) and reduced GO (rGO) are the only variants of graphene that can be manufactured at the kilogram scale, and yet the widely accepted model for their structure has largely relied on indirect evidence. Notably, existing high-resolution transmission electron microscopy (HRTEM) studies of graphene oxide report long-range order of sp(2) lattice with isolated defect clusters. Here, we present HRTEM evidence of a different structural form of GO, where nanocrystalline regions of sp(2) lattice are surrounded by regions of disorder. The presence of contaminants that adsorb to the surface of the material at room temperature normally prevents direct observation of the intrinsic atomic structure of this defective GO. To overcome this, we use an in situ heating holder within an aberration-corrected TEM (AC-TEM) to study the atomic structure of this nanocrystalline graphene oxide from room temperature to 700 °C. As the temperature increases to above 500 °C, the adsorbates detach from the GO and the underlying atomic structure is imaged to be small 2-4 nm crystalline domains within a polycrystalline GO film. By combining spectroscopic evidence with the AC-TEM data, we support the dynamic interpretation of the structural evolution of graphene oxide.
氧化石墨烯（GO）和还原氧化石墨烯（rGO）是唯一可以在公斤级规模制造的石墨烯变体，但它们的结构被广泛接受的模型在很大程度上依赖于间接证据。值得注意的是，现有的氧化石墨烯高分辨率透射电子显微镜（HRTEM）研究报告了具有孤立缺陷簇的 sp(2)晶格的长程有序。在这里，我们提出了 GO 的不同结构形式的 HRTEM 证据，其中 sp(2)晶格的纳米晶区域被无序区域包围。在室温下吸附在材料表面的污染物的存在通常会阻止对这种有缺陷的 GO 的固有原子结构的直接观察。为了克服这一点，我们使用具有校正像差的透射电子显微镜（AC-TEM）中的原位加热支架，从室温到 700°C 研究这种纳米晶氧化石墨烯的原子结构。当温度升高到 500°C 以上时，吸附剂从 GO 上脱离，并且可以成像到在多晶 GO 薄膜内的小的 2-4nm 晶畴。通过将光谱证据与 AC-TEM 数据相结合，我们支持了氧化石墨烯结构演化的动态解释。
