The intrinsic electrical conductivity of graphene is one of the key factors affecting the electrical conductance of its assemblies, such as papers, films, powders, and composites. Here, the local electrical conductivity of the individual graphene flakes was investigated using conductive atomic force microscopy (C-AFM). An isolated graphene flake connected to a pre-fabricated electrode was scanned using an electrically biased tip, which generated a current map over the flake area. The current change as a function of the distance between the tip and the electrode was analyzed analytically to estimate the contact resistance as well as the local conductivity of the flake. This method was applied to characterize graphene materials obtained using two representative large-scale synthesis methods. Monolayer graphene flakes synthesized by chemical vapor deposition on copper exhibited an electrical conductivity of 1.46 ± 0.82 × 10⁶ S/m. Reduced graphene oxide (rGO) flakes obtained by thermal annealing of graphene oxide at 300 and 600 °C exhibited electrical conductivities of 2.3 ± 1.0 and 14.6 ± 5.5 S/m, respectively, showing the effect of thermal reduction on the electrical conductivity of rGO flakes. This study demonstrates an alternative method to characterizing the intrinsic electrical conductivity of graphene-based materials, which affords a clear understanding of the local properties of individual graphene flakes.

Water is one of the most important resources for human survival and development. Efficient wastewater treatment techniques such as coagulation, filtration, ozonation, and reverse osmosis have been studied to remove toxic materials from water. Implementation of adsorption columns has been proven to be an efficient wastewater treatment method, particularly for the removal of organic contaminants. In this study, we present the preparation of an eco-friendly graphene oxide–chitosan (GC) composite hydrogel column (GCCHC) and its application as a broad-spectrum adsorbent for wastewater treatment. The GCCHC shows a high removal capacity towards different contaminants including both cationic dyes [methylene blue (MB) and rhodamine B (RhB)] and anionic dyes [methylene orange (MO) and congo red (CR)]. Moreover, the samples can be regenerated and recycled without loss of contaminant removal capacity over successive adsorption and washing cycles.

Graphene powders obtained via the reduction of graphene oxide flakes have been widely used in various applications as they can be synthesized in large quantities with outstanding properties. The electrical conductivity of graphene powders is critical for their uses in fabricating high-performance devices or materials. Here, we investigated the bulk electrical conductivity of reduced graphene oxide (rGO) powders depending on the applied pressure and additional thermal annealing. The electrical conductivity of the rGO powders was correlated with the change in the carbon-to-oxygen ratio via additional thermal reduction. Furthermore, the effect of the morphology of the rGO powders was studied through electromechanical measurements. This study provides a reliable method for the electromechanical characterization of rGO powders and a better understanding of the electrical conductivity of graphene-based materials.

Over the past few years, many researchers have been excited with the advent of two-dimensional (2D) materials such as graphene and molybdenum disulfide (MoS ₂ ) because of their intriguing physical and chemical properties. Furthermore, they have great potential in various applications including nanoelectronics, flexible or stretchable devices, energy conversion or storage devices, sensors, nanocomposites, and others. In addition to their electrical, mechanical, optical, and thermal properties, interfacial properties of 2D materials such as adhesion energy have recently attracted attention from researchers since interfacial interactions of 2D materials with others are of great importance in obtaining mechanical integrity of nanomanufacturing processes and related devices. In this respect, this paper reviews the adhesion properties of 2D materials. Measurement methods and characteristics of adhesion behaviors were summarized and discussed mainly for graphene and MoS ₂ .