Graphene oxide (GO) was a specific branch of graphene research. It can be considered as a precursor for graphene synthesis by either thermal or chemical reduction processes. The schematic structure of graphite oxide (GO) was shown in Figure 16. 
It is indicated that GO sheet can be regarded as the combined structure of oxygen-containing functional groups, such as C–O, C=O, and −OH, supported on the surface of a single layer graphene sheet . 
The addition of oxygen-containing functional groups changed the structure and properties of GO sheet.
Compared with single-layer graphene, on the one hand, the presence of oxygen-containing functional groups indeed greatly increased defectiveness of GO sheet. 
This may lead to some loss in electrical conductivity, which possibly limits the direct application of GO in many areas.