B Tech 1st Sem Nano-Chemistry Notes and More (ASTU) 1

Nanochemistry

1. Introduction to Nanochemistry

Nanochemistry is the study of chemistry at the nanoscale, which is typically defined as the size range of 1 to 100 nanometers (nm). At this scale, materials exhibit unique properties that are different from their bulk counterparts. This is due to a number of factors, including the high surface-to-volume ratio of nanomaterials and their quantum confinement effects.

Size scale of nanomaterials

Nanomaterials

Nanomaterials can be classified into four main categories:

• Nanoparticles: These are zero-dimensional nanomaterials with all three dimensions in the nanoscale range.
• Nanotubes: These are one-dimensional nanomaterials with a hollow, tube-like structure.
• Nanowires: These are one-dimensional nanomaterials with a solid, wire-like structure.
• Nanofilms: These are two-dimensional nanomaterials with a thickness in the nanoscale range.

Properties of Nanomaterials

Nanomaterials exhibit a number of unique properties, including:

• High surface-to-volume ratio: This means that a large fraction of the atoms in a nanomaterial are located on the surface. This gives nanomaterials unique catalytic and adsorption properties.
• Quantum confinement effects: These are effects that occur when the size of a material is reduced to the nanoscale. Quantum confinement effects can lead to significant changes in the optical, electronic, and magnetic properties of nanomaterials.

Synthesis of Nanomaterials

There are a variety of methods for synthesizing nanomaterials. Some of the most common methods include:

• Top-down approach: This involves breaking down bulk materials into nanomaterials.
• Bottom-up approach: This involves building up nanomaterials from individual atoms or molecules.
• Self-assembly: This is a process in which nanomaterials spontaneously assemble themselves into larger structures.

Applications of Nanomaterials

Nanomaterials have a wide range of applications in a variety of fields, including:

• Electronics: Nanomaterials are used in a variety of electronic devices, such as transistors, sensors, and displays.
• Energy: Nanomaterials are used in solar cells, batteries, and fuel cells.
• Medicine: Nanomaterials are used in drug delivery, tissue engineering, and diagnostic devices.
• Environmental remediation: Nanomaterials are used to clean up pollution and improve water quality.

Challenges in Nanochemistry

One of the biggest challenges in nanochemistry is developing methods for synthesizing nanomaterials with controlled size, shape, and composition. Another challenge is understanding the unique properties of nanomaterials and how to design them for specific applications.

Conclusion

Nanochemistry is a rapidly growing field with a wide range of potential applications. The study of nanochemistry is essential for developing the next generation of materials and devices.

Examples of Nanomaterials

• Gold nanoparticles: These are used in drug delivery and biomedical imaging.
• Carbon nanotubes: These are used in electronics, composites, and sensors.
• Quantum dots: These are used in displays, solar cells, and biosensors.
• Graphene: This is a two-dimensional material with a wide range of potential applications in electronics, energy, and medicine.

Carbon nanotubes

Multifunctional applications of gold nanoparticles

Nanomaterials in everyday products

Future of Nanochemistry

Nanochemistry is a rapidly growing field with a wide range of potential applications. Some of the most promising areas of research in nanochemistry include:

• Development of new synthesis methods for nanomaterials with controlled size, shape, and composition.
• Understanding the unique properties of nanomaterials and how to design them for specific applications.
• Development of new nanomaterials-based devices for electronics, energy, medicine, and environmental remediation.

Nanochemistry is a field with great potential to revolutionize many aspects of our lives. By understanding and controlling the properties of nanomaterials, we can develop new technologies that can address some of the world's most pressing challenges.

2. Synthesis of Nanomaterials (Top-Down and Bottom-Up)

Top-Down Synthesis

Top-down synthesis methods can be further classified into two categories:

1. Lithography-based methods: These methods involve using a mask to pattern a bulk material. The patterned material is then etched or deposited to create nanostructures. Some examples of lithography-based methods include:

• Electron beam lithography (EBL): This method uses a focused beam of electrons to expose a resist material. The exposed resist is then developed and etched to create nanostructures. EBL is a very high-resolution method, but it is also very slow and expensive.
• Photolithography: This method uses ultraviolet (UV) light to expose a photoresist material. The exposed photoresist is then developed and etched to create nanostructures. Photolithography is less expensive and faster than EBL, but it has lower resolution.

2. Mechanical methods: These methods involve grinding or milling a bulk material into smaller particles. Some examples of mechanical methods include:

• Ball milling: This method involves placing a bulk material in a ball mill with a number of hard balls. The ball mill is then rotated, causing the balls to collide with the bulk material and grind it into smaller particles.

Ball milling

• High-energy milling: This method involves grinding a bulk material in a high-energy mill, such as a planetary ball mill or an attritor mill. High-energy mills can produce smaller particles than ball milling.

High-energy ball milling

Bottom-Up Synthesis

Bottom-up synthesis methods can also be further classified into two categories:

1. Wet chemical synthesis methods: These methods involve reacting precursors in a liquid solution to form nanomaterials. Some examples of wet chemical synthesis methods include:

• Chemical vapor deposition (CVD): This method involves depositing material from a gas phase onto a substrate. CVD can be used to produce a wide range of nanomaterials, including nanoparticles, nanowires, and nanotubes.

Chemical vapor deposition (CVD)

• Sol-gel synthesis: This method involves forming a gel from a solution of precursors. The gel is then dried and calcined to form nanomaterials. Sol-gel synthesis is a relatively simple method and can be used to produce a wide range of nanomaterials.

Sol-gel synthesis

• Hydrothermal synthesis: This method involves reacting precursors in a hot, pressurized aqueous solution. Hydrothermal synthesis can be used to produce nanomaterials with high crystallinity.

Hydrothermal synthesis reactor

2. Physical vapor deposition (PVD) methods: These methods involve depositing material from a solid phase onto a substrate. Some examples of PVD methods include:

• Sputtering: This method involves bombarding a target material with ions to eject atoms from the target. The ejected atoms are then deposited onto a substrate. Sputtering can be used to produce a wide range of nanomaterials, including thin films, nanoparticles, and nanowires.

Sputtering

• Thermal evaporation: This method involves heating a source material until it evaporates. The evaporated material is then deposited onto a substrate. Thermal evaporation can be used to produce a wide range of nanomaterials, including thin films and nanoparticles.

Thermal evaporation

Comparison of Top-Down and Bottom-Up Synthesis

The following table compares top-down and bottom-up synthesis methods in more detail:

Feature	Top-Down Synthesis	Bottom-Up Synthesis
Precision	High	Low
Control	Good	Difficult
Versatility	Low	High
Cost	High	Low
Time	High	Low
Suitable for	Mass production of nanomaterials with high precision	Production of nanomaterials with a wide range of sizes, shapes, and compositions

Conclusion

Both top-down and bottom-up synthesis methods have their own advantages and disadvantages. The best method for synthesizing a particular nanomaterial will depend on the specific requirements of the application.

In recent years, there has been a growing interest in developing hybrid synthesis methods that combine the advantages of top-down and bottom-up synthesis. For example, one promising approach is to use top-down methods to create templates that can then be used to synthesize nanomaterials using bottom-up methods. This approach could allow for the production of nanomaterials with high precision and control over their size, shape, and composition.

Fullerenes

Coming soon! (will be uploaded if there is any interest shown by students)