Graphene – Complete Revision Notes
NEET • JEE Main • JEE Advanced • GATE • CSIR-NET • IIT-JAM
1. What is Graphene?
- Single layer (monolayer) of sp²-hybridized carbon atoms
- Arranged in a honeycomb (hexagonal) lattice
- Basic building block of all graphitic materials (graphite, CNT, fullerene)
- Thinnest material ever (0.34 nm thick) yet strongest
- Discovered in 2004 by Geim & Novoselov → Nobel Prize 2010
2. Structure of Graphene
2D honeycomb lattice of sp² carbon atoms
- 2D hexagonal lattice
- C–C bond length: 0.142 nm
- Each carbon is sp² hybridized → 3σ + 1π bond
- Delocalized π-electrons above and below the plane → extraordinary conductivity
- Can be stacked to form graphite (van der Waals between layers)
JEE Advanced Favourite: Graphene is a zero-band-gap semiconductor (semi-metal) due to touching of valence and conduction bands at Dirac points.
3. Preparation Methods (Exam Hotspot)
| Method | Description | Quality & Use |
|---|---|---|
| Mechanical Exfoliation (Scotch Tape) | Repeated peeling of graphite using adhesive tape (2004 method) | Highest quality → research |
| Chemical Vapour Deposition (CVD) | CH4 + H2 on Cu/Ni foil at ~1000°C → large-area graphene | Industrial favourite → electronics |
| Reduction of Graphene Oxide (rGO) | Hummers method → GO → reduce with hydrazine/heat | Cheapest, bulk production (defective) |
| Epitaxial Growth on SiC | Thermal decomposition of SiC at >1200°C | High quality, wafer-scale |
| Liquid Phase Exfoliation | Sonication of graphite in solvents (NMP, DMF) | Scalable, few-layer graphene |
GATE/CSIR-NET Most Asked: CVD & Graphene Oxide reduction are commercially most viable.
4. Extraordinary Properties (Memorize This Table)
| Property | Value | Remark |
|---|---|---|
| Thickness | 0.34 nm (one atom) | Thinnest material |
| Strength | ~130 GPa | ~200× stronger than steel |
| Young’s Modulus | ~1 TPa | Stiffest known material |
| Thermal Conductivity | ~5000 W/m·K | Best heat conductor |
| Electrical Conductivity | ~10⁸ S/m | Better than copper |
| Electron Mobility | up to 2.5×10⁵ cm²/V·s | Highest at room temp |
| Optical Transparency | ~97.7% (single layer) | Almost transparent |
| Surface Area | 2630 m²/g | Highest theoretical |
| Band Gap | Zero (semi-metal) | But tunable in bilayer/ribbon |
5. Applications (High-Weightage in GATE & CSIR-NET)
- Next-generation transistors & flexible electronics
- Ultra-sensitive sensors (gas, biosensors)
- Transparent conductive electrodes (touchscreens, solar cells)
- Supercapacitors & lithium-ion batteries (fast charging)
- Water purification membranes (graphene oxide)
- Composite materials (stronger, lighter aircrafts)
- Thermal management (heat spreaders)
- Biomedical: drug delivery, cancer treatment
6. Derivatives & Related Materials (Frequently Asked)
| Material | Description |
|---|---|
| Graphene Oxide (GO) | Oxygen-functionalized → insulating, hydrophilic |
| Reduced Graphene Oxide (rGO) | Partially restored conductivity |
| Graphane | Fully hydrogenated graphene (insulator) |
| Fluorographene | Fully fluorinated → wide band gap |
| Bilayer Graphene | Tunable band gap with electric field |
High-Yield One-Liners for Last-Minute Revision
- Graphene = single layer of sp² carbon in honeycomb lattice
- Strongest, thinnest, best conductor of heat & electricity
- Zero band gap → Dirac fermions → extremely high electron mobility
- Almost transparent (absorbs only 2.3% light)
- CVD on copper → most scalable method
- Mechanical exfoliation → highest quality
- Graphene oxide → made by Hummers method
- Nobel Prize 2010 → Geim & Novoselov
- Phosphorene (black P) and graphene are both 2D materials, but graphene has zero band gap
Must Read Graphene MCQs asked in NEET, JEE Main, JEE Advanced, GATE, CSIR-NET, IIT-JAM
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