What are the two general approaches for the synthesis of nano Materials? Describe.
Top-down and bottom-up
Which properties need to be controlled during the synthesis of nanomaterials?
Size, size distribution, composition, morphology, texture, agglomeration.
What are the disadvantages of milling as a method for the synthesis of nanoparticles?
- contamination (mechanical device, environment); poor control (defect in mothermaterial will also be in nano material, texture, morphology); costs lots of energy
What are the advantages of bottom-up synthesis?
- more homogeneous, less defects, control, novel synthetic materials. - disadvantages: high costs and tedious processes (hampering producting of large amounts)
Why does high-energy ball milling needs to be performed in the presence of a liquid medium?
- size reduction to the nano scale will increase electrostatic and molecular interactions. The liquid medium disperses the particles as much as possible.
Mention 3 methods for the synthesis of inorganic NPs.
milling; pyrolysis; sol-gel
Describe the principle of pyrolysis in the formation of NPs
- vaporization; cooling; NPs
Describe the sol-gel method for the synthesis of nano particles.
1) Starting material in a solution (eg, metal alkoxides), either dissolved or a colloid particles. 2) material undergoes hydrolysis and/or polycondensation. (sol becomes gel) 3) removal of the solution (liquid phase) by drying. 4) thermal treatment (calcination) for further enhancement of mechanical properties.
What type of nano particles can be synthesised by the sol-gel method?
powder, monoliths (single crystal Wiki), coatings and fibers
Bowman et al. designed a NP to increase the efficacy of a HIV drug. Describe the NP.
AuNP, with a Au nucleus, then a protective layer and then a functionalised layer. The functionalised layer contained the drug.
Why are AuNPs an interesting type of NPs?
- optical, electronic properties, high stability, biological compatibility, controllable morphology and size distribution, and easy surface functionalisation
Describe the general principles of the synthesis of gold NPs.
Overall: reduction of AU(3+) to Au(0) in an appropriate solvent which includes a stabilising agent (eg thiols) to prevent aggregation. 2a) after synthesis, removal of stabilising agent by ligand exchange reactions. 2b) link ligands to the stabilising agent (eg amino acid coupled to COOH in ligand)
How large are the pores in mesoporous materials?
Mention some interesting properties of mesoporous silica.
narrowly defined pore size, large surface area, well-defined particle size.
Describe the principle of synthesising mesoporous nanomaterials.
1) solvent + surfactant. 2) mix with silica precursor. 3) in mixture something happens or not? 4) evaporation: self assembly of particles containing Si material and surfactant 5) further heating (calcination) evaporates the surfactant leaving a solid Si containing material with pores where the surfactant was.
Mention examples of organic nano materials.
Give the 5 allotropes of carbon.
fullerene (0d), nanotube (1d), graphene (2d), graphite (3d), diamant (3d).
How is graphite produced?
heating of amorphous carbon. during different temperature ranges filler components and impurities are removed. At 3000 degrees celcius graphite of optimal thermal and electrical conductivity is formed.
Describe the experiments by Kroto, Curl and Smalley with graphite.
1) piece of graphite 2) laser beam 3) intergration cup 4) MS results in MS were carbon clusters (especially C60) called fullerenes.
C60 is also called a bucky ball. In what way does this fullerene resemble a normal football?
20 hexogonal and 12 pentagonal faces.
Describe some properties of C60.
C-C = 1.44 Å each C: Sp2 hybridisation vd Waals diameter: 1.1 nm density: 1.65 gr/cm3 extremely stable in respect of T and p reactive surface: addition of species while maintaining spherical form behaves like a electron-deficient alkene (not superaromatic) hollow: can contain small molecules only allotrope of C that can be dissolved in common solvents at room T solutions of C60 have a deep purple colour
Mention methods for the synthesis of fullerenes. Describe each of them.
1) electric arc method (graphite electrodes under He atm), 2) combustion (carbohydrates), 3) lightening discharges in atmosphere, 4) laser ablation (graphite in inert gas-filled quartz tube, heated to 1200 degrees, laser etc) 5) total synthesis from Cl-benzene-Br
Describe 2 methods for the purification of fullerenes.
1) sublimation over a quartz wall with a temperature gradient. 2) solvent extraction followed by chromotography
For all materials: describe their properties and how to functionalise the surface
How can you functionalise the surface of C60?
chemistry on fullerenes: 1) hydrated fullerene (C60(H2O)24) 2) hydrogenation 3) halogenation 4) hydroxylation (C60(OH)26) - more water soluble
Mention some uses of fullerenes.
1) superconductors, lubricant, absorption of light, MRI, X-ray, radioimaging 2) drug delivery 3) scavenger of free radicals 4) activity of C60 itself (HIV, cancer)
What does X@Cn mean?
X is encaged atom in fullerene n is the number of carbon atoms in the fullerene
Give an example of how a fullerene has been used in imaging.
GdC60 with watersoluable surface; MRI contrast agent. Better than Gd alone because it delays excretion. Gd = gadolinium
How are fullerenes called with an atom inside?
There are many variations of nanotubes. What types exist and how do they differ?
single and multiple-walled rolling angle and radius determines their properties.