TOP-DOWN AND BOTTOM-UP APPROACH IN SYNTHESIS OF NANOPARTICLES.pptx

There are two approaches for the manufacturing of nanomaterials:

The “top-down” approach, which involves the breaking down of large pieces of material to generate the required nanostructures from them.

The “bottom-up” approach, which implies assembling single atoms and molecules into larger nanostructures.

Bottom-Up includes:-
Sol gel method
Template Assisted Synthesis
Chemical Precipitation
Microwave Assisted Synthesis
Self Assembly

Top-Down Includes:-
Mechanical Milling
High Pressure Torsion
Laser Ablation
Chemical Etching
Sputtering

1. T OP-DOWN AND BOTTOM-UP APPROACH IN SYNTHESIS OF NANOPARTICLES Presented By-Lubhanshi Raje Shisodia ROLL NUMBER-221240 MSc Biotechnology

2. Introduction ​ The synthesis of nanoparticles can be approached using either a top-down or bottom-up approach, each with its own advantages and limitations. These approaches are used in nanotechnology to create nanoparticles with specific properties and characteristics. ​

3. Top-Down Approach: In the top-down approach, larger bulk materials are broken down into smaller nanoparticles through various mechanical, chemical, or physical methods. This method is used for carving or sculpting a larger piece of material into a desired shape at the nanoscale.

4. Mechanical Milling: Mechanical milling is usually done using a planetary ball mill. A refractory or steel ball's energy transmission to a powder relies on the rotating (vibration) speed, size and quantity of balls, ball-to-powder mass ratio, duration and milling environment. The shear action of grinding produces nanoparticles. Mechanical milling is used to change the properties of silver powders, including disintegration of particle aggregates, particle shape, and particle surface characteristics.

5. Laser Ablation: Laser ablation or photoablation is the process of removing material from a solid surface by irradiating it with a laser beam. At low laser flux, the material is heated by the absorbed laser energy and evaporates or sublimates. At high laser flux, the material is typically converted to a plasma. 

6. High Pressure Torsion: In this the material sample is subjected to very high pressure typically in the gigapascals with the help of equipment such as hydraulic press machine along with high pressure then sample is subjected to torsion or shear this means the material is twisted or rotated along with pressure. Atoms arrange themselves into regular, repeating patterns to form a crystal lattice The grain size is a measure of how large or small these individual crystalline structures are within a given material

7. Chemical Etching: In this technique chemical is used for the synthesis of nanoparticles materials like metals and ceramics .In this technique basically the metal is first coated with masking material like wax – this material protect the areas that should not be etched, then the masked sample is submerged or exposed to the chemical which ultimately helps in breaking down the molecular bonds which helps in the synthesis of nanomaterials

8. Sputtering The sputtering process involves the removal of atoms or molecules from a solid target material and their deposition onto a substrate to form a thin film. The sputtering process takes place in a vacuum chamber to eliminate the interference of air or other gases. To initiate the sputtering process, a low-pressure inert gas (commonly argon) is introduced into the chamber. The gas is ionized and accelerated by an electric field, forming positively charged ions. These ions are then directed toward the target material. When the accelerated ions strike the target material, they transfer energy to the target atoms. This energy causes the atoms in the target to be dislodged from the target's surface. These dislodged atoms are ejected with sufficient energy to become vaporized. The vaporized target atoms travel through the vacuum chamber and are deposited onto the substrate, creating a thin film.

9. Bottom -Up Approach: A bottom-up approach to the synthesis of nanoparticles involves building or growing nanoparticles from individual atoms or molecules. This approach allows for precise control over the size, shape, and composition of nanoparticles and is commonly used in nanotechnology and materials science.

10. The sol–gel method This method is based on the transformation of a sol (a colloidal suspension of nanoparticles) into a gel-like network and the subsequent conversion of the gel into solid nanoparticles. It consist of the metal cations called precursors is added in the solvent to create a sol, then hydrolysis is done which helps in breaking down the precursors into hydroxides then the hydrolysed particles are condensed and form gel. Then the gel is carefully dried to remove solvent leaving behind the nanopowder

11. Template-Assisted Synthesis : In this technique templates or you can say moulds are used for the synthesis of nanoparticles, in these templates precursor material is filled . The precursor may be a metal salt or a chemical compound depending on the desired nanoparticle composition. It is a technique used to produce nanoparticles with controlled size, shape, and properties by using templates as scaffolds or molds for the nanoparticles to form around.

12. Chemical Precipitation : In this method, nanoparticles are formed by the precipitation of ions from a solution to create solid particles. A reagent, often a reducing agent or a precipitating agent, is added to the precursor solution. The reagent induces a chemical reaction, causing the metal ions to undergo a precipitation reaction and form solid nanoparticles. As the reaction proceeds, solid nanoparticles form and precipitate out of the solution. The nanoparticles are then separated from the solution through processes like centrifugation or filtration.

13. Microwave-Assisted Synthesis : : The reaction vessel containing the precursor solution is placed in the microwave cavity. When microwaves are applied, the molecules in the reaction mixture absorb energy and become highly energized. This localized and rapid heating initiates the nanoparticle synthesis. The tiny building blocks in the liquid come together to form the tiny particles. This is like building a tiny LEGO structure using the right pieces.

14. Self-Assembly : Self-assembly is a fascinating process where nanoparticles spontaneously arrange themselves into organized structures or patterns. This method is widely used in nanotechnology to create well-ordered and functional materials.Nanoparticles are put down in the liquid like water . Nanoparticles as we know have the property of magnet so they stick to each other like magnets

15. Reference https://pubs.rsc.org/en/content/articlelanding/2016/me/c6me00016a https://www.semanticscholar.org/paper/Synthesis-and-Characterization-of-ZnS-Nanoparticles-Hamed-Ahmed/57810d96935cccd2b01aa7509ddc257eba6bec02 https://pubs.rsc.org/en/content/articlehtml/2021/ma/d0ma00807a https://chat.openai.com/c/e91a929e-4bcb-492d-9247-75aec3fb463c