Synthesis and Processing of Nanomaterials
1. Nanomaterials vs Bulk Materials. Why does size matter?
The properties of nanomaterials vary greatly from the bulk materials due to two key
factors which are increased relative surface area and quantum effects. The elements
such as reactivity, intensity and electrical characteristics may alter or improve the
properties. For instance, gold nanoparticles have quite different properties from bulk
sized gold. Even though bulk sized gold is an inert metal, gold metal at a nanosize of 5
nm behaves as a catalyst in oxidizing carbon monoxide. In comparison to the bulk
material, large numbers of exposed atoms in gold nanoparticles allow them to function
as a catalyst. Thus, size affects the property.
2. Briefly describe the Chemical Vapour Deposition method of producing CNT.
The chemical vapor deposition (CVD) method is to cleave a carbon atom-containing gas
continuously flowing through the catalyst nanoparticle to generate carbon atoms and
then generate CNTs on the surface of the catalyst or the substrate. The synthesis
process is to let the catalyst decompose carbon source (usually hydrocarbon gas) at a
sufficiently high temperature in a tubular reactor. The figure below shows the schematic
diagram of the most common carbon nanotube production process by CVD.
(α) tip-growth mechanism and (β) root-growth mechanism
Two growth mechanisms:
1. Tip – growth
2. R
oot – growth
The reason for the two growth mechanisms is that the interaction between the catalyst
and the substrate is different.
3. What are CNT coated fibres and why are they important?
SEM images of several coated CNT fibers that: (A) illustrate the uniform nature of the polymer coating;
and (B) show the interface of the CNT fiber and its coating polymer.
CNT coated fiber is a CNT fiber coated with epoxy compatible coating with nano-dispersed
aqueous-based polymeric film formers and low viscous epoxy resin, respectively.
4. How are CNT coated fibres obtained?
Each CNT fiber piece of about 30 cm length was dipped in the aqueous coating
dispersion (for RIM R135 resin, the liquid stoichiometric resin/hardener mixture) with the
help of a pair of plastic tweezers and kept in the aqueous emulsion for 1 min. A heat
treatment of the fibers was done in an oven for 2 h at 130°C.
5. What are the variable process parameters for the production of CNT coated
Fibres?
6. What are the challenges in producing CNT coated fibres?
7. What is CNT yarn and how is it produced?
Carbon nanotube (CNT) yarn, consisting of 23 μm diameter CNT filaments. Recently,
Behabtu et al. [16], [17] described the fabrication of carbon nanotube (CNT) filaments
composed of tightly packed and well-aligned CNTs. In a novel development, tens to
hundreds of parallel CNT filaments form “CNT yarn”. The diagram above shows the
CNT yarn. CNT yarn can be used as capacitive electrodes that are long, flexible,
conductive and strong, for applications in energy and electrochemical water treatment.
A simple and continuous spinning method that combines twisting and shrinking
processes to produce carbon nanotube yarns. In this method, a yarn freshly spun from
a super-aligned carbon nanotube (SACNT) array is first twisted and then passes
through a volatile solvent for shrinking
Spinning setup and CNT yarns. (a) An illustration of the spinning setup: (1) a rotating
motor for twisting; (2) a long strip of SACNT array; (3) a twisted yarn; (4) immersing the
yarn in a glass vessel containing solvent; (5) a tube furnace for baking; (6) the final CNT
yarn after shrinking; (7) a rotating motor for yarn collection. (b) A long strip of SACNT
array after laser etching. The effective SACNT array for producing yarns is restricted
between the two etching lines and is about 5 mm in width in this figure. (c) Transmission
electron microscopy (TEM) image of CNT in SACNT arrays. (d) 40 m long CNT yarn
collected on a winder. The diameter of the yarn is about 10 μm.
8. How is graphene produced?
Graphene fabrication methods can be categorized into top-down and bottom-up
methods. Principal top-down methods include liquid-phase exfoliation and
micromechanical cleavage of graphite. An additional method involves the exfoliation of
initially oxidized graphite, leading to graphene oxide (GO), which is chemically and/or
thermally reduced to graphene, typically called reduced GO (rGO). The bottom-up
fabrication of graphene is usually performed by means of epitaxial growth on SiC or
chemical vapour deposition, typically on Cu using small molecules, such as methane,
as precursors.
1) Micromechanical exfoliation is a method of manufacturing graphene-based materials
that involves the use of adhesive tape to peel systematically ordered pyrolytic graphite.
It is a graphene processing technique, during which graphene is removed from graphite
crystals during this process. Peeling is the method used to manufacture graphene by
peeling it off the graphite.
2) One of the essential methodologies of deposition used for transition metals is CVD.
Nickel and copper are used for large-scale graphene processing in the CVD process.
Film deposits of metallic catalysts on the substrate during the CVD process. On the
deposited material on the substrate, chemical etching is done. After chemical etching, a
carbon containing mixture is moved to the reaction chamber.
9. What is the main difference between the CVD process of producing CNT
and graphene?
Catalyst, The catalyst is indispensable in the process of preparing CNTs by the
CVD method. It can reduce the decomposition temperature of the carbon source
and promote the nucleation of CNTs, which is the most important influencing
factor for the preparation of CNTs.
10. What is the advantage and disadvantage of producing graphene via the top
down approach?
The advantage of the top-down production approach is that it can use the existing
silicon infrastructure and methodologies for accurate placement and scalability of
features. According to the new cutting tool technology, the disadvantage of the
top-down strategy is the resolution constraint such as electron beam, ion-beam, etc.
(electron beam, ion-beam, etc.). (electron beam, ion-beam, etc.). Due to the type of
masking that is used with the cutting tool technology, the second and related
resolution-based limitation is the width resolution.
11. Give 5 examples of homologous forms of graphene.
1. Honeycomb
2.
12. What are graphite nanofibers or carbon nanofibres?
Carbon nanofibers (CNFs) are 1D cylindrical or conical nanostructures with diameters
ranging from less than a micron to millimeters in the range of few to hundreds of
nanometers and lengths.CNFs are conductive materials with a graphite-like electronic
structure. These nanofibers are also mesoporous and, up to 900 °C, have good air
thermal stability. It is simple and environmentally friendly to synthesize CNF, and the
process is cheaper than CNT. CNFs, on the other hand, have lower surface area, more
defects, and larger size in comparison with CNT.
13. What type of nanostructure could be obtained if GNF is used as the starting
material?
Herringbone GNF produces Graphene Oxide (GO) sheets while platelet GNF yields
GO quantum dots.
Herringbone GNF Platelet GNF
References
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strength of glass fibres with carbon nanotube–epoxy nanocomposite coating:
Effects of CNT morphology and dispersion state. Composites. Part A, Applied
Science and Manufacturing, 41(4), 539–548.
https://doi.org/10.1016/j.compositesa.2009.12.011
2. Mäder, E., Liu, J., Hiller, J., Lu, W., & Chou, T.-W. (2015). Coating of Carbon
Nanotube Fibers: Variation of Tensile Properties, Failure Behavior, and
Adhesion Strength. Frontiers in Materials , 2.
https://doi.org/10.3389/fmats.2015.00053
3. Rudrapati, R. (2019). Graphene: Fabrication Methods, Properties, and Applications
in Modern Industries. In Graphene Production and Application. Intechopen.
4. Hiremath, N., & Bhat, G. (2017). 4 - High-performance carbon nanofibers and
nanotubes. In G. Bhat (Ed.), Structure and Properties of High-Performance
Fibers (pp. 79–109). Woodhead Publishing.
https://doi.org/10.1016/B978-0-08-100550-7.00004-8
