Preparation Process of Graphene Aqueous Dispersion

Overview: Graphene is a two-dimensional, honeycomb-structured carbon material with excellent properties. Its aqueous dispersion has high electron mobility, thermal conductivity, mechanical strength, and unique optical properties. Stable graphene dispersions can be used in various applications, including conductive agents, battery electrode materials, catalysts, supercapacitors, solar cells, semiconductor chips, conductive graphene films, computer memory, biomaterials, and transparent conductive coatings.

Detailed Preparation Steps

1. Materials Preparation
   • Graphite flakes
   • Absolute ethanol
   • Polyvinylpyrrolidone (PVP)
   • 1-Methyl-2-pyrrolidone (NMP)
2. Removal of Impurities from Graphite Flakes
   • Take 0.1 grams of commercially purchased graphite flakes and place them in a beaker.
   • Add a small amount of ethanol solution and sonicate or stir for 10 minutes to preliminarily clean the graphite flakes, removing lower-density impurities.
   • Allow the mixture to stand for 10 minutes, discard the ethanol, and retain the sediment at the bottom.
3. Solution Preparation
   • Add a small amount of PVP to the beaker to aid in better dispersion of graphite in the solution.
   • Finally, add 50 milliliters of NMP as a solvent.
4. Ultrasonic Treatment
   • Place the prepared mixture into an ultrasonic bath and sonicate for up to 5 days.
   • Ultrasonic vibrations help exfoliate the graphite layers, assisted by the strong solvation power of NMP, effectively separating graphite into small graphene nanosheets.
   • The low-pressure regions generated by ultrasonic waves can further break the graphene sheets into micron-sized pieces.
5. Centrifugation
   • After sonication, use a disposable pipette to collect the supernatant and place it into a 10 ml centrifuge tube.
   • Centrifuge at 3500 rpm to obtain the clear supernatant.
   • If a smaller amount of graphene aqueous dispersion is needed, further dilute the supernatant and continue ultrasonic treatment for several days, followed by centrifugation to obtain fewer layers or even single-layer graphene.

Characterization of Graphene

1. Droplet Deposition:
   • Drop the obtained solution onto a clean silicon wafer with an oxide layer.
   • Dry the droplet using a steam bath.
2. Microscopic Analysis:
   • Characterize the dried graphene using an optical microscope, scanning electron microscope (SEM), and Raman microscope.
   • Graphene nanosheets can appear as regular rectangular fragments under an optical microscope.
3. Raman Spectroscopy:
   • Use Raman spectroscopy to determine the number of layers. Graphene obtained via physical methods (e.g., exfoliation) typically shows minimal defects in Raman spectra compared to those produced by chemical vapor deposition (CVD).