How is single graphene dispersed evenly in water?

Generally, graphene and water are not well mixed. When graphene is in water, "dangling bonds" appear (the hydrogen atoms of water molecules point to the surface of graphene), and water molecules near graphene cannot form more than three. Hydrogen bonds, while pure water has an average of 3.6 hydrogen bonds per water molecule. Therefore, graphene and non-polar hydrocarbons can destroy hydrogen bonds in water to cause hydrophobic interactions, resulting in difficulty in dissolving graphene in water. In addition, graphene promotes the nucleation of nanobubbles dissolved in water on the surface of graphene, which also exacerbates the agglomeration and precipitation of graphene. The graphite intercalation compound can be stripped into a single layer of graphene in an aprotic solvent to produce a thermodynamically stable negative graphene solution. Negatively charged graphene is a strong reducing agent, while organic solvents are sensitive to air and moisture. Recently, George et al. (DOI: 10.1038/NCHEM.2669) achieved uniform distribution of single-layer graphene sheets in water-removing water. This graphene aqueous solution is stable in air and does not require the addition of a surfactant.

Dissolving graphite potassium in tetrahydrofuran THF in an inert atmosphere to form a single layer of negatively charged graphene polyion, and then oxidizing the negatively charged graphene ions into graphene by exposure to air in THF, and then rapidly transferring to degassed water, The process of exposure to air forms peroxide cations and neutral graphene. Under normal experimental conditions, the adsorption of gases dissolved in water on the graphene surface results in long-range attraction between dispersed individuals, thereby promoting agglomeration. On the contrary, if the water is degassed, the water ions have been adsorbed on the surface of the graphene. This adsorption causes the dispersed graphene layer to have a certain charge, and the electrostatic repulsion can stabilize the dispersion state of the graphene sheet. In general, in degassed water, re-aggregation of graphene in degassed water is drastically slowed down due to the low attraction of the diffusion between the graphene sheets and the electrostatic repulsion stability. Due to the oxidation and water decomposition of negatively charged graphene, OH-- ions spontaneously adsorb on the surface of graphene, and graphene is charged in water. When two graphenes meet, they cause repulsion. Therefore, graphene can be effectively dispersed in water at a concentration of 0.16 g/L, and can be stably stored for several months.

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