Maarg Manthan · Topic 15.3

Nanomaterials: Carbon Nanotubes, Graphene, Quantum Dots

Science & Technology › Materials Science, Nanotechnology and Robotics · Topic 15.3

Nanomaterials are materials with structure at the nanoscale. Carbon gives several important forms. Fullerenes are hollow cages such as C60, found in 1985. Carbon nanotubes are rolled sheets of graphite forming cylinders that are about a nanometre wide and are very strong and good conductors; Sumio Iijima reported them in 1991. Graphene is a single layer of carbon atoms in a honeycomb pattern, isolated in 2004 by Andre Geim and Konstantin Novoselov, who received the Nobel Prize in Physics in 2010. Quantum dots are tiny semiconductor crystals of a few nanometres whose colour depends on size; the 2023 Nobel Prize in Chemistry went to Moungi Bawendi, Louis Brus and Alexei Ekimov for them. These materials are used in electronics, displays, sensors, energy storage and medicine.

5 min read · UPSC Prelims · Science & Technology · Materials Science, Nanotechnology and Robotics

At a Glance

Fullerene 1985, C60
Carbon nanotube 1991, Iijima
Graphene 2004, Geim and Novoselov
Quantum dot Nobel 2023
Graphene hybrid Strong, conducting, 2D
Exam link UPSC Prelims, Science & Technology: Materials Science, Nanotechnology and Robotics

Where Does It Fit?

This topic follows the account of nanoscience. It looks at the most asked nanomaterials, which prepare for the next topic on how these are applied in medicine, energy and agriculture. Previous topic: Nanoscience and Nanotechnology: Origin and Basic Concepts. Next topic: Applications of Nanotechnology: Nanomedicine, Textiles, Sustainable Energy, Agriculture, Semiconductors.

What Are the Main Carbon Nanomaterials?

Material	Features
Fullerene	Hollow cage of carbon atoms, with C60 shaped like a football, called buckminsterfullerene. Discovered in 1985 by Kroto, Curl and Smalley (Nobel Prize in Chemistry, 1996)
Carbon nanotube	A rolled sheet of graphene forming a tube. Single walled or multi walled. Very high tensile strength, excellent electrical and thermal conductivity. Reported by Sumio Iijima in 1991
Graphene	A one atom thick sheet of carbon in a hexagonal lattice. Strong, light, transparent and a very good conductor. Isolated by peeling graphite with sticky tape in 2004 at Manchester
Graphene oxide	Oxidised graphene, easy to disperse in water and used in membranes and composites
Allotropes of carbon	Diamond, graphite, fullerene, nanotubes and graphene are different forms of the same element
Carbon dots	Tiny fluorescent carbon particles used in imaging and sensing
Hybridisation	Graphene and nanotubes have sp2 bonded carbon

What Are Quantum Dots and Where Are These Materials Used?

Quantum dots: semiconductor nanocrystals of about 2 to 10 nm, such as cadmium selenide, where electrons are confined in all three dimensions
Size and colour: smaller dots emit blue light and larger dots emit red light, so colour is tuned by size
Nobel Prize 2023: Moungi Bawendi, Louis Brus and Alexei Ekimov, for discovery and synthesis of quantum dots
Displays: QLED televisions use quantum dots for pure and bright colours
Medicine: labelling cells and tumours for imaging, and drug delivery
Solar cells: quantum dot solar cells aim for higher efficiency
Electronics: graphene and nanotubes for transistors, flexible screens and conductive inks
Composites: nanotubes in sports goods, aircraft parts and body armour

What Else Should You Remember?

Strength of nanotubes: many times stronger than steel by weight, though real materials are weaker than the ideal figure
Graphene conductivity: electrons move very fast in graphene, which behaves like a zero gap semiconductor
Graphene Nobel Prize: 2010, Physics
Batteries: graphene and nanotubes can improve electrodes of lithium-ion batteries and supercapacitors
Water filtration: membranes with graphene oxide or nanotubes can filter salts and microbes
Sensors: very sensitive gas and biosensors using nanotubes and graphene
Cost and scale: large scale, defect free production is still hard and expensive
Toxicity concern: some nanotubes may act like fine fibres in the lungs, as in Adverse Health and Environmental Impacts of Nanotechnology
Other 2D materials: molybdenum disulphide, boron nitride and MXenes are other sheet like materials
Metal nanoparticles: silver for germ killing, gold for diagnostic tests and titanium dioxide for sunscreens and paints
Nanoclay: used in packaging to improve barrier properties
Aerogels: ultra light porous materials used for insulation
Indian work: Indian laboratories and start-ups work on graphene, and a graphene innovation centre was set up in Kerala in cooperation with industry
Metamaterials: engineered structures with unusual optical properties, such as bending light backwards
Uses in defence: light armour and sensors benefit from nanomaterials
Link: the basic ideas are in Nanoscience and Nanotechnology: Origin and Basic Concepts
Memory aid: C60 is a cage, CNT is a tube, graphene is a sheet and a quantum dot is a point
Production methods: graphene is made by exfoliation, chemical vapour deposition and chemical routes, while nanotubes are made by arc discharge, laser ablation and chemical vapour deposition
Magic angle graphene: two sheets twisted at a small angle can become superconducting, a 2018 discovery that links with Superconductivity
Cadmium concern: many quantum dots contain cadmium, a toxic metal, so safer indium or carbon based dots are being developed
Buckyball medicine: fullerenes are studied as antioxidants and drug carriers

Why Does It Matter for the Exam?

Discoverers and years: Iijima 1991, Geim 2004
Prizes: 2010 Physics, 2023 Chemistry
Shapes: cage, tube, sheet, dot
Current affairs link: graphene products and QLED displays
Common errors: saying graphene is three layers thick or quantum dots are metals

As an analytical point, carbon nanomaterials have strong potential, but moving them from laboratory to industry needs cheap, consistent production and safety checks. India’s graphene work is at an early stage.

Why Is This Topic Important?

Forms Cage, tube, sheet
Prizes 2010 and 2023
Uses Electronics, medicine

What Came Next?

The next topic covers applications of nanotechnology. Next topic: Applications of Nanotechnology: Nanomedicine, Textiles, Sustainable Energy, Agriculture, Semiconductors.

Key People and Terms

Fullerene Carbon cage molecule
CNT Carbon nanotube
Graphene One atom thick carbon sheet
Quantum dot Semiconductor nanocrystal
Allotrope Different form of an element
MXene 2D carbide material

Exam Corner

Points to Remember

C60 found 1985; CNT 1991; graphene 2004.
Graphene Nobel: 2010.
Quantum dot Nobel: 2023.
Graphene is one atom thick.
Smaller dot gives bluer light.

Do Not Confuse With

CNT and graphene Rolled tube versus flat sheet
Graphene and graphite Single layer versus stacked layers
Quantum dot and nanoparticle Semiconductor with size dependent colour versus any nanosized particle

Memory Hook

Cage, tube, sheet, dot: C60, Iijima, Geim, Bawendi.

Mains Angle

Questions ask for names, years and uses. These points help.

Forms Carbon family
Properties Strong, conducting
Challenges Cost, safety

A Question You May Face

An original practice question, not a past paper question.

“Describe the properties and applications of carbon nanotubes, graphene and quantum dots.”

How to Answer

Forms Carbon allotropes.
Properties Strength, conductivity.
Uses Electronics, medicine.
Limits Cost, safety.

GS Relevance

Prelims: carbon forms, discovery years, properties, Nobel Prizes, uses. GS Paper 3: science and technology, materials.

Frequently Asked Questions

What is graphene?

Graphene is a single layer of carbon atoms arranged in a honeycomb lattice. It is extremely thin, strong, flexible, almost transparent and a very good conductor of heat and electricity. It was isolated in 2004 by Andre Geim and Konstantin Novoselov, who won the 2010 Nobel Prize in Physics.

What are carbon nanotubes?

Carbon nanotubes are cylinders made by rolling a sheet of graphene, with a diameter of about a nanometre and a length thousands of times larger. They are very strong and conduct electricity or heat well, and are used in composites, sensors, batteries and electronics. Sumio Iijima reported them in 1991.

What are quantum dots?

Quantum dots are tiny semiconductor crystals, a few nanometres wide, in which electrons are confined so that the colour of light they emit depends on their size. They are used in QLED displays, medical imaging and solar cells. The 2023 Nobel Prize in Chemistry honoured their discovery and development.

What is a fullerene?

A fullerene is a hollow molecule made only of carbon atoms in a closed cage shape. The best known, C60 or buckminsterfullerene, looks like a football with 60 carbon atoms. It was discovered in 1985 by Harold Kroto, Robert Curl and Richard Smalley, who received the 1996 Nobel Prize in Chemistry.

How are the carbon allotropes related?

Diamond, graphite, fullerenes, carbon nanotubes and graphene are all allotropes of carbon, differing in how the atoms are bonded. Graphite is made of stacked graphene sheets, a nanotube is a rolled graphene sheet and a fullerene is a graphene like sheet closed into a cage.

PYQ Practice — Statement Analysis

1 Graphene is a single layer of carbon atoms.

True

In a honeycomb lattice.

2 Carbon nanotubes were discovered by Andre Geim.

False

Iijima reported them in 1991.

3 The colour of a quantum dot depends on its size.