SYNTHESIS OF NANOPARTICLES

• WHAT ARE TWO METHODS TO SYNTEHSISE NANOMATERIALS

  top down and bottom up approach

  
• WHAT IS TOP-DOWN


  bulk materials are cut down/reduced to nano particle sizes e.g. ball milling
• WHAT IS BOTTOM UP


  synthesis of nanoparticle monomers from molecular species. these species are in excess leading to supersaturation conditions and therefore nucleation and then nanoparticle growth.
• 4 ADVANTAGES OF BOTTOM UP

  1. Homogenous composition

  2. Less defects

  3. Ordered structures

  4. Control over particle size/growth using surfactants and ligands
• WHAT IS GOLD COLLOIDAL SUSPENSION

  gold NPs are very small gold particles that are suspended in a liquid known as colloidal solution
• WHAT IS THE TURKEVICH METHOD

  earliest form of creating gold NP. it is a method that chemically reduces a gold salt HAuCl4 in water using a reducing agent called trisodium citrate to create gold NPs. 1.  Reduction – ions in gold salt reduced to gold atoms

  2. Stabilisation – trisodium citrate also acts as stabilising agent by surrounding the NPs to create an environment so other NPs repel each other. This prevents clumping

  3. Results – gold NPs
• WHAT IS THE FRENS METHOD

  modification of Turkevich method which adjusts concentrations of trisodium citrate to more uniform size distribution of particles and monodispersity
• WHAT MODEL CAN BE USED TO SHOW NUCLEATION AND CRYSTAL GROWTH OF NPs

  LaMer Model
• EXPLAIN LAMER MODEL


  1.  Formation of monomers leading to supersaturation

  2. Nucleation – once supersaturation and temperature conditions are satisfied (aggregates of NPs)

  3. Continuous crystal growth occurs as monomer concentrations decrease (growth by diffusion)

  • C_max is the maximum concentration of monomers when supersaturation is reached.
  • C_min is the minimum concentration needed to start forming nanoparticles.

  
• WHAT IS THE DIFFERENCE BETWEEN OSTWALD RIPENING AND DIGESTIVE RIPENING


  ostwald ripening - growth of larger molecules from smaller ones, increase size disparity and creates undesirable variability in sizes. digestive ripening - growth of particles from large to small, reduces size disparity and creates more uniform size distribution of particles
• DESCRIBE OSTWALD RIPENING


  it is the process where larger NPs grow at the expense of smaller Nps due to differences in solubility. small particles dissolve and material is redistributed onto larger particles. nucleation step occurs when monomer formation followed by the increase in monomer formation leading to supersaturation where cluster nucleation occurs. if the parameters are controlled burst nucleation can occur creating monodisperse particles (where nucleation is occurring simultaneously).
• NAME THE DISADVANTAGES OF DIGESTIVE RIPENING

  large particles grow at the expense of smaller ones so an unequal size of particles are created which is highly unliked. this will lead to the need of separation of particles therefore increasing production costs
• DESCRIBE DIGESTIVE RIPENING


  1. Formation of polydisperse NPs – synthesis using known methods/SMAD

  2. Modification of small + large NPs – adding ligands to attach to surface of large NP. These cause large NPs to shed atoms so smaller nanoparticles can gain them

  3. Formation of nearly monodisperse NPs – reflux solution with additional ligands to produce monodisperse NPs
• FACTORS THAT AFFECT DIGESTIVE RIPENING:


  1. Temperature – high temp – speed up reaction

  2. Duration – influence uniformity of size

  3. Ligand type

  4. Ligand concentration
• EXPLAIN HOW SMAD WORKS - solvated metal atom dispersion


  metals vapourised inside a vaccum. these atoms are co-deposited with a solvent vapour onto a very chilled surface (77 K and liquid nitrogen). the cooling of the reaction allows metal atoms to disperse as particles/clusters
• ADVANTAGES ON SMAD

  1.  No by products formed from metal salt reduction, pure metal colloids are formed

  2. Scalability for industrial applications

  3.  Can be refined using digestive ripening
• WHAT IS HYDRODYNAMIC RADIUS

  it is the measure of the particle/ion that moves through a solvent. it includes the particle size as well the layer of solvent molecules that has attached to it because of interaction with particles surface. the particle may appear bigger than usual because of this.
• 2 METHODS OF MEASURING HYDRODYNAMIC RADIUS


  1. DLS – measures particles diffusion

  2. TEM – provides image of just the particle, no solvent layer