2. Synthesis Flashcards
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?
2-50 nm
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.
xx
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
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?
endohedral fullerene
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.
Three different kinds of single-walled carbon nanotubes can be formed. Which?
Armchair (n,0); zig-zag (n,n); chiral
What is the distance between layers in a multi-layer carbon nanotube?
3.4 Å; similar to the distance between the graphene layers in graphite.
Describe different methods for the synthesis of carbon nanotubes.
ordinary flames. electric arc laser ablation chemical vapor deposition
Describe the principles of chemical vapor deposition.
1) prepare catalyst Ni, Co, Fe 2) methane, CO, acethylene gas
What is the growth mechanism proposed in CVD?
atom C dissolves in the metal droplet, diffuses to and deposits it at the growth substrate.
How do you control the yield of carbon nanotubes during synthesis with laser ablation?
1) the cooling rate if the medium where the active, secondary (?) catalyst particles are formed. 2) the residence time 3) the temperature (1000-2000 K range) 4) the catalyst used
What do you synthesise with the HiPco process and how does it work in principle?
It is an industrial scale chemical vapour deposition (CVD) process for the production of carbon nanotubes. Gas phase CO and catalytic amounts of Fe(CO)5 are pumped through a heated reactor.
Describe the principles of the solar energy reactor in the production of carbon nanotubes.
mirrors, focuspoint, evaporation of graphite and catalyst, vapours dragged by neutral gas, and then condensate on cold walls of thermal screen.
What is the most efficient way of separating nanotubes of a certain kind?
density-gradient ultracentrifugation.
How do you purify carbon nanotubes?
1 - oxidation with air of H2O2: oxidizes impurities, oxidizes structurally defect nanotubes and clears the surface of the metal catalyst. 2 - acid treatment: removal of metal catalyst (HNO3, HCl) 3 - annealing: high T (impurities pyrolyse and metal melts) 4 - microfiltration 5 - functionalisation (more soluble) 6 - chromatochraphy 7 - density-gradient ultrcentrifugation
Give examples of functionalisation of single-wall nanotubes.
fluorination, arylation, hydrogenation, cycloaddition.
Describe the characteristics of multi-wall carbon nanotubes.
- strong and stiff under tensile stress, weak under compression. - thermal conductors along the tube and thermal insulators laterally to the tube axis. - thermally stable up to 2800 celcius in vacuum and up to 750 celcius in air. - low friction properties between the walls: atomically perfect linear or rotational bearing (rotational motor).
Mention some applications of carbon nanotubes.
Use has mostly been limited to bulk nanotubes (unorganized fragments of nanotubes). Bulk nanotube materials may never achieve a tensile strength similar to that of individual tubes, but may yield strengths sufficient for many applications. Bulk carbon nanotubes have already been used as composite fibers in polymers to improve the mechanical, thermal and electrical properties of the bulk product. Current applications: Sport equipment (rackets, skies, bikes) Tips for atomic force microscope probes Tissue engineering, carbon nanotubes can act as scaffolding for bone growth
What is graphene?
allotrope form of carbon. sheet of sp2 hybridized C atoms. C-C: 1,42Å aromatic conduction of electricity as efficiently as coper conduction of heat: the best there is transparent dense (the smallest atom cannot pass) light strong
Give descriptions of several methods for the synthesis of graphene.
- graphite, tape, dissolve in aceton, sediment on a silicon wafer, microscope - same as above but dry deposition - liquid phase exfoliation of graphite, solvent with surface tension, sonication - heat SiC (siliconcarbide) to T over 1100 celcius under low pressure. Gives epitaxial graphene. - chemical vapor deposition - bottom-up total synthesis (only small sheets)
What are possible applications of graphene in life science?
tissue engineering and drug delivery
What is a dendrimer?
tree-like polmers, branching out from a central core and subdividing into further branching units. subclass of dendritic polmers (hyperbranched, dendrigraft, dendronised)
What are the special properties of a dendrimer?
dense sruface, hollow core diameter smaller than 15 nm but high Mw.
Why is it difficult to purify dendrimers, synthesized by a divergent method?
if reaction steps not to completion - some shorter branches. However, this does not result in large differences in size.
Mention 2 methods for the synthesis of dendrimers.
divergent (difficult to purify from those with shorter branches) and convergent (smaller due to steric hindrance) syntheses
What are PAMAM dendrimers and how are they synthesised?
poly(amido amine) synthesised in generations NH3 - methylacrylate (G0) - diamine (G1) , alternating methylacrylate - diamine etc Early generations: flexible Late generations: solid particles with dense surface
Mention applications of dendrimers in biology/medicine.
targeted drug delivery targeted radiosensitiser delivery macromolecular carriers surface engineering biomimetic materials
Which factors influence the pore size, pore volume and morphology of mesoporous silica nanoparticles?
- Source of silica
- type of surfactant
- pH
- composition reaction mixture
- Temperature
- time
- calcination conditions
