Abstract
The large-scale preparation of stable graphene aqueous dispersion has been a challenge in the theoretical research and industrial applications of graphene. This study determined the suitable exfoliation agent for overcoming the van der Waals force between the layers of expanded graphite sheets using the liquid-phase exfoliation method on the basis of surface energy theory to prepare a single layer of graphene. To evenly and stably disperse graphene in pure water, the dispersants were selected based on Hansen solubility parameters, namely, hydrophilicity, heterocyclic structure and easy combinative features. The graphene exfoliation grade and the dispersion stability, number of layers and defect density in the dispersion were analysed under Tyndall phenomenon using volume sedimentation method, zeta potential analysis, scanning electron microscopy, Raman spectroscopy and atomic force microscopy characterization. Subsequently, the long-chain quaternary ammonium salt cationic surfactant octadecyltrimethylammonium chloride (0.3 wt.%) was electrolyzed in pure water to form ammonium ions, which promoted hydrogen bonding in the remaining oxygen-containing groups on the surface of the stripped graphene. Forming the electrostatic steric hindrance effect to achieve the stable dispersion of graphene in water can exfoliate a minimum of eight layers of graphene nanosheets; the average number of layers was less than 14. The 0.1 wt.% (sodium dodecylbenzene sulfonate: melamine = 1:1) mixed system forms π–π interaction and hydrogen bonding with graphene in pure water, which allow the stable dispersion of graphene for 22 days without sedimentation. The findings can be beneficial for the large-scale preparation of waterborne graphene in industrial applications.
Highlights
Graphene1 is a 2D nanomaterial composed of carbon atoms that are compactly formed through the hybridization of sp2 and has the thickness of one carbon atom (0.334 nm) [1,2]
To prevent the agglomeration behavior of graphene [21], an appropriate dispersant–solvent system was developed on the basis of the Hansen solubility parameters (HPSs) [22], that was, a dispersant that was hydrophilic, heterocyclic, and easy to combine with graphene was used to physically adsorb were combined on the surface of graphene to prevent the agglomeration of adjacent graphene nanoplatelets and make them stably dispersed in various types of liquid media
The Tyndall phenomenon is a common method for estimating the particle size of the solution in the liquid-phase phenomenon is a common method for estimating the particle size of the solution in the liquid-phase system after exfoliation
Summary
Graphene is a 2D nanomaterial composed of carbon atoms that are compactly formed through the hybridization of sp and has the thickness of one carbon atom (0.334 nm) [1,2]. The liquid-phase exfoliation method poses the highest potential for the large-scale preparation of graphene amongst the physical preparation methods [18]. Many researchers have applied liquid-phase exfoliation theory to study a surfactant-free graphene dispersion system. OH− was added to the surface of the graphene to increase its hydrophilicity and dispersion stability in aqueous media This dispersion theory did not include any surfactants and the entire experimental process was simple, low-cost and environmental-friendly. During the preparation of graphene dispersions, Mahdiyeh et al [31] discovered that the dispersion of the mixture of pure sodium dodecyl sulphate (SDS) and anionic surfactants in aqueous media was greater than that of pure hexadecyl trimethyl ammonium bromide (CTAB) and cationic mixtures.
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