Session 9-2

Abstract

Chemical exfoliation has been widely used to obtain monolayers of various layered compounds, such as clay minerals, transition metal chalcogenides, and oxides.[1] To develop highly functional devices using these nanosheets, we need to further understand and control the 2D structures. Here, we present our recent studies focusing on the 2D structures, including graphene oxide (GO)[2] and RuO₂.[3]
The 2D structure of GO remains controversial due to its structural complexity, heterogeneity and instability. Therefore, we have used synchrotron in-plane X-ray diffraction (XRD) to reveal the true 2D structure of GO. The general feature of the in-plane XRD profiles of GOs obtained by the Hummers and Brodie methods is that the graphene-like hexagonal lattice is preserved without amorphization even after severe chemical oxidation. The analysis of the 10 reflection peaks allowed us to study the oxidation and reduction condition dependent expansion, contraction and microstrain of the in-plane lattice due to the interaction between oxygen functional groups and carbon defects in the single crystal domains. As a second topic, we will present the 2D phase engineering of 2D ruthenates. We found that the oblique phase in the nanosheet is metastable and continuously transitions to the rectangular phase upon heating. Based on these findings, we further developed a phase-controllable synthesis by Co doping. Co doping in ruthenate nanosheets unexpectedly suppressed the redox and catalytic activity under acidic conditions. In contrast, under alkaline conditions, the Co2+/3+ redox pair is activated, producing conductive nanosheets with high electrochemical capacitance.