Revisiting the two-dimensional structure and reduction process of graphene oxide with in-plane X-ray diffraction

The unique characteristics and low cost of graphene oxide (GO) make it a promising nanocarbon material for many practical applications. However, despite intensive studies with advanced spectroscopic and microscopic methods as well as theoretical calculation, the two-dimensional structure of GO remains controversial due to the structural complexity, inhomogeneity, and instability. Here, we employed a synchrotron in-plane X-ray diffraction (XRD) technique to elucidate its true 2D structure. An overall feature of the in-plane XRD profiles of GOs obtained by Hummers' and Brodie's methods revealed that the graphene-like hexagonal lattice was preserved without amorphization after severe chemical oxidation. The 10 reflection peak was analyzed to probe the intraplane lattice expansion, shrinkage, and microstrain that depend on the oxidation and reduction conditions due to the interconnected oxygen functional groups and carbon defects in a single crystalline domain. Based on the correlation between the global and local structures and the chemical composition, we established a three-step reduction process of GO consisting of deoxygenation, diffusionless lattice modification, and diffusional lattice modification. The updated 2D structural model and the generalized reduction process will facilitate the design and interpretation of GO-related materials.