Formation of Graphene Oxide Nanoscrolls in Organic Solvents: Toward Scalable Device Fabrication

In this work, formation of graphene oxide (GO) nanoscrolls in organic solvents was investigated upon dispersing GO nanosheets in organic solvents by sonication. It was found that, in some of the organic solvents, the single-layer GO sheets can effectively curl onto themselves to form the nanoscrolls that then sediment under gravity from the dispersion media. The sedimentation was monitored by UV-vis spectroscopy when the GO suspensions were left aside for different time periods after the sonication. The nanoscrolls were separated and characterized by transmission electron microscopy (TEM) and electron diffraction (ED). A typical solvent with such scroll-forming function is pyridine, where 82% of the GO sheets form the GO nanoscrolls and undergo the sedimentation. Scroll formation is also observed for N,N-dimethylformamide (DMF), methanol, ethanol, isopropyl alcohol, acetic acid, and isobutyric acid, but the yields vary with the solvents. The scrolls formed in pyridine suspension show the average length over 20 mu m, interlayer spacing of 0.6 nm, and average diameters of 186 and 192 nm for the two types of the GO samples used here. The scrolls formed in the other solvents show different average lengths and diameters governed by the properties of the solvents. The average lengths of the formed scrolls reflect the tendency of the GO sheets to curl into scrolls in the solvents, while the average number of the included sheets per scroll depends on the sedimentation rate in the suspensions. The scrolling behavior and mechanism are rationalized and elucidated by considering dipole moment, zeta potential, and Hansen solubility parameters of the solvents. Based on the above understanding, the GO scrolls with controllable lengths and diameters can be efficiently fabricated by selecting a suitable solvent, and are expected for applications in hydrogen storage, gas sensing devices, actuators, lubrication materials, and others.