Preparation Process of Graphene Powder

Overview: Graphene powder is a unique material known for its conductivity and transparency. Typically, transparency in materials requires a bandgap, but graphene powder combines both properties, which makes it attractive for flexible electronic devices such as touchscreens. This review evaluates methods based on different requirements, including the purity, size, and quantity of graphene powder, as well as the complexity and reproducibility of the methods.

Preparation Methods: There are two primary methods to prepare graphene powder:

1. Exfoliation from Graphite Crystals:
   • Mechanical Exfoliation (Scotch Tape Method):
     • Graphene is exfoliated from graphite using adhesive tape. Multiple layers of graphene remain on the tape, which is then repeatedly peeled to produce thinner graphene sheets. These sheets are transferred to a substrate by dissolving the adhesive.
     • Advantages: Produces high-quality graphene with minimal defects.
     • Disadvantages: Low yield, labor-intensive, and difficult to scale up.
2. Liquid-phase Exfoliation:
   • Graphene Production in Liquid Phase:
     • Graphite is dispersed in organic solvents with surface energy similar to graphite. Energy barriers are overcome using ultrasonication or voltage application for several hours. The resulting solution is centrifuged to separate thick flakes, yielding high-quality graphene sheets.
     • Advantages: Higher yield compared to mechanical exfoliation.
     • Disadvantages: Still produces small-scale graphene with limited control over size and thickness.
3. Chemical Reduction of Graphite Oxide:
   • Oxidation and Reduction Method:
     • Graphite is oxidized to graphite oxide using chemical methods, which is then reduced using thermal or chemical treatments to produce graphene.
     • Advantages: Potential for larger-scale production.
     • Disadvantages: Lower quality compared to mechanically exfoliated graphene due to residual oxygen groups and structural defects.

Detailed Steps for Each Method:

1. Mechanical Exfoliation (Scotch Tape Method):
   • Step 1: Place a graphite crystal on adhesive tape and peel off the tape to leave multiple layers of graphene on it.
   • Step 2: Repeatedly peel the tape to thin down the graphene layers.
   • Step 3: Transfer the graphene sheets to a substrate, such as SiO2/Si, by dissolving the adhesive.
2. Liquid-phase Exfoliation:
   • Step 1: Disperse graphite in an organic solvent (e.g., NMP) that matches its surface energy.
   • Step 2: Apply ultrasonication or electrical voltage to exfoliate graphene from graphite.
   • Step 3: Centrifuge the solution to separate thicker flakes from thinner graphene sheets.
3. Chemical Reduction of Graphite Oxide:
   • Step 1: Oxidize graphite to graphite oxide using strong oxidizing agents.
   • Step 2: Disperse graphite oxide in water and sonicate to exfoliate into individual graphene oxide sheets.
   • Step 3: Reduce graphene oxide using thermal or chemical treatments to remove oxygen groups and restore conductivity.

Conclusion: Each method for preparing graphene powder has its own set of advantages and disadvantages. Mechanical exfoliation produces high-quality graphene but is not scalable, while liquid-phase exfoliation and chemical reduction methods offer higher yields but with varying degrees of quality and complexity. Understanding these methods allows for selecting the appropriate technique based on specific application requirements and production capacities.