🔬 Unit 5 – Part A (2-Mark Q&A)

1. Write about the important categories of nanomaterials

Nanomaterials are categorized based on their dimensions:

• Zero-dimensional (0D): All three dimensions are at the nanoscale (e.g., nanoparticles, nanoclusters, quantum dots).
• One-dimensional (1D): Two dimensions are at the nanoscale, while one is larger (e.g., nanowires, nanorods, nanotubes).
• Two-dimensional (2D): One dimension is at the nanoscale, while two are larger (e.g., nanosheets, nanofilms, graphene).
• Three-dimensional (3D): Bulk materials that have a nanoscale structure or features (e.g., nanocomposites, nanoporous materials).

2. Give a brief description about the sol-gel principle

The sol-gel process is a wet-chemical method for synthesizing materials. It starts with a "sol" (a stable colloidal suspension of solid particles in a liquid) which is converted into a "gel" (a solid three-dimensional network) through hydrolysis and polycondensation reactions. This gel is then typically dried and heated (calcined) to produce the final solid material (e.g., ceramic, glass).

3. Define nanomaterials

Nanomaterials are materials possessing at least one external dimension in the size range of 1 to 100 nanometers (nm). Due to their small size and high surface-area-to-volume ratio, they exhibit unique physical, chemical, and biological properties compared to their larger, bulk counterparts.

4. What are nanoclusters?

Nanoclusters are zero-dimensional (0D) nanomaterials composed of an aggregate of atoms or molecules, typically containing from a few up to several hundred units. They represent an intermediate state of matter between individual atoms and bulk solids, and their properties are highly dependent on the exact number of atoms they contain.

5. Write any two applications of nanomaterials

Two major applications of nanomaterials are:

• Medicine: In targeted drug delivery systems to deliver medication directly to diseased cells (e.g., cancer) and as contrast agents for enhanced medical imaging (e.g., MRI).
• Electronics: To create smaller, faster, and more power-efficient components like transistors, and in the development of flexible displays and highly efficient solar cells.

6. What are carbon nano tubes? What are its type?

Carbon nanotubes (CNTs) are one-dimensional (1D) allotropes of carbon. They are cylindrical molecules made of rolled-up sheets of single-layer carbon atoms (graphene) and are known for their exceptional strength and electrical conductivity.

The main types are:

• Single-Walled Carbon Nanotubes (SWNTs): Consist of a single cylinder of graphene.
• Multi-Walled Carbon Nanotubes (MWNTs): Consist of multiple concentric cylinders of graphene nested within each other.

7. Differentiate SWNT and MWNT.

• Structure: SWNTs consist of a single graphitic cylinder, while MWNTs consist of multiple concentric graphitic cylinders.
• Synthesis: SWNTs are generally more difficult and expensive to synthesize in high purity compared to MWNTs.
• Properties: SWNTs have more clearly defined electronic properties (can be metallic or semiconducting). The properties of MWNTs are more complex, representing an average of the nested tubes.

8. Write any two applications of carbon nanotubes.

Two common applications of carbon nanotubes are:

• Composite Materials: Added to polymers to create materials that are exceptionally strong and lightweight, used in sports equipment (like bicycle frames, tennis rackets) and aerospace components.
• Battery Electrodes: Used in lithium-ion batteries to improve their charge capacity, lifespan, and charging speed due to their high conductivity and surface area.

9. Mention the difference between a nanorod and a nanowire.

Both nanorods and nanowires are one-dimensional (1D) nanomaterials. The main difference is their aspect ratio (length-to-width ratio):

• Nanorods: Have a small aspect ratio, typically between 1 and 20. They are shorter and more rigid.
• Nanowires: Have a very large aspect ratio, often greater than 20 (and sometimes over 1000). They are much longer and more flexible.

10. What is Laser ablation?

Laser ablation (or Pulsed Laser Ablation) is a "top-down" physical method for synthesizing nanomaterials. It involves focusing a high-power pulsed laser beam onto a solid target (often submerged in a liquid). The intense energy vaporizes (ablates) a small amount of the target, creating a plasma plume that rapidly cools and condenses into nanoparticles.

11. What are nanowires?

Nanowires are one-dimensional (1D) nanomaterials with a diameter on the nanoscale (1-100 nm) but an unconstrained length. This results in a very high length-to-diameter (aspect) ratio. They are highly studied for applications in electronics, sensors, and solar cells due to their unique properties.

12. Distinguish between nanoparticle and bulk material

• Size: Nanoparticles have at least one dimension in the 1-100 nm range. Bulk materials are macroscopic and have all dimensions much larger than 100 nm.
• Surface Area: Nanoparticles have a very high surface-area-to-volume ratio, whereas bulk materials have a low ratio.
• Properties: Nanoparticles exhibit size-dependent properties (e.g., gold nanoparticles are red, bulk gold is yellow) due to their high surface area and quantum confinement effects. Bulk properties are stable and independent of size.

13. Define Green Chemistry.

Green Chemistry (or sustainable chemistry) is a philosophy of chemical research and engineering that encourages the design of products and processes that minimize or eliminate the use and generation of hazardous substances. It aims to make chemistry safer for human health and the environment.

14. What is the role of Green Chemistry?

The role of Green Chemistry is to promote sustainability at the molecular level. It seeks to prevent pollution, reduce waste, conserve energy and resources, and design safer chemicals and processes, thereby minimizing the environmental impact of chemical activities.

15. Define Atom Economy.

Atom Economy is a key principle of Green Chemistry that measures the efficiency of a chemical reaction. It calculates the percentage of atoms from the reactants that are incorporated into the desired product, rather than being lost as waste (byproducts). A high atom economy (ideally 100%) signifies a more efficient and less wasteful process.

16. Write any one example of Green Solvent and Hazardous Solvent?

• Green Solvent: Water (H₂O) or Supercritical Carbon Dioxide (scCO₂). They are non-toxic, abundant, and environmentally benign.
• Hazardous Solvent: Benzene (C₆H₆) or Chloroform (CHCl₃). These are typically toxic, carcinogenic, and contribute to air pollution as volatile organic compounds (VOCs).