Chapter 3 Nanomaterials Fabrication

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Part II Principles and Methods
Chapter 3 Nanomaterials Fabrication
The ability to fabricate nanomaterials (often in
the form of nanoparticles) with strictly
controlled size, shape and crystalline structure,
has inspired the application of nanochemistry to
numerous fields, including catalysis, optics and
electronics.
The synthesis of nanoparticles with control over
size, shape, and size distribution has been a
major part of colloid chemistry ???? for decades.
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Under these conditions, solid matter such as
metal oxides, chalcogenides??????? , metals, or
carbon can be obtained at the nanometric scale.
An ultra-dispersed system ????? with a high
surface energy can be only kinetically ???
stabilized ??. Ultrafine powders ??? cannot be
synthesized by methods involving energies that
exceed a threshold ??, but rather through methods
of soft chemistry???? that maintain the forming
particles in a metastable state (stable excited
state). Additives ??? and/or synthesis
conditions that reduce the surface energy are
needed to form nanoparticles stabilized against
sintering???? , recrystallization???,
aggregation??.
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Synthesis methods for nanoparticles are typically
grouped into two categories
The first involves division of a massive solid
into smaller portions. This top-down approach
may involve milling or attrition??
(mecanosynthesis), chemical methods for breaking
specific bonds (e.g. hydrogen bonds) that hold
together larger repeating elements of the bulk
solid, and volatilization ?? of a solid by laser
ablation, solar furnace, or some other method,
followed by condensation of the volatilized
components. The second category of
nanoparticles fabrication methods involves
condensation of atoms or molecules entities in a
gas phase or in solution. This is the bottom-up
approach in which the chemistry of metal
complexes in solution holds an important place.
This approach is far more popular in the
synthesis of nanoparticles, and many methods have
been developed to obtain oxides, chalcogenides,
and metals.
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The liquid-phase colloidal synthetic approach is
an especially powerful tool for convenient and
reproducible shape-controlled synthesis of
nanocrystals. Fabrication of metal oxide
nanoparticles From molecular species to
nanopaticles Begin with individual ions or
molecular complexes of metals.
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metal oxides complex
metal oxide nanomaterials
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Metal oxides ?????
One common approach is to build from the
bottom-up method, beginning with individual
ions or molecular complexes ??? of
metals. Hydroxylation?? of metal cations in
aqueous solution and condensation?? Inorganic
polymerization ??????????????
Hydrolysis ?? equilibrium ?? M(H2O)nz h H2O
? M(OH)h(H2O)n-h(z-h) h H3O

nanoparticle Neutralization ?? with a base
? M(H2O)nz h OH- ? M(OH)h(H2O)n-h(z-h)
h H2O
nanoparticle
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The electric charge of the nanoparticle will
be Positive complex (polycation) if h lt z and
is soluble Negative complex (polyanion) if h gt
z and is soluble Neutral complex if h z and
is a solid as precipitate ??? ?
nanoparticle precursor ??
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Condensation ???? of aquohydroxo complexes
proceed by elimination ?? of water and formation
of hydroxo bridges ?(olation) P. 33
d d- d H2O - M - OH HO - M - OH2
? H2O - M - O - M - OH2 H2O More similar
reactions will make the nanoparticle grow in
size!
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• P. 35 The precipitation of a nanoparticle
  involves four kinetic ??? steps
• Formation of the zero-charge precursor
  M(OH)h(H2O)n-h0 which is able to condense and
  form a solid phase.
• Creation of nuclei, through condensation of
  zero-charge precursors.
• Growth of the nuclei through addition of matter,
  until the primary ?? particle stage is reached.
• Aging ?? of the reaction allows the system toward
  or reach stability ??, usually associated with
  the modifications ?? of some physical or chemical
  characteristics of the particles.

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Figure 3.2 The four kinetic steps of the
formation of nanoparticles
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Control of particle size, crystalline structure
????, and morphology ????. There are different
techniques to form the complex of zero charge and
to obtain a solid. The most common method
consists of adjusting the pH of the reaction.
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Figure 3.4 Nanoparticle size variation against pH
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P. 45 Hydrolysis ?? of metallo-organic
compounds ??????? Metal alkoxides ???????? are
precursors of hybrid ??? organic-inorganic
materials and involved in sol-gel chemistry
??-???? of oxide nanomaterials? M(OR)z zH2O ?
M(OH)z zROH ? MOz/2 z/2 H2O zROH metal
alkoxide metal
oxide, nanoparticle
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Figure 3.7 TEM (transmission electron microscope
????) micrographs ????? of nanoparticles
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Figure 3.9 SEM (scanning electron micrograph
?????) of nanoparticles
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P. 49 Non-hydrolytic ??? routes to oxide
nanoparticles In nonaqueous media ???? in the
absence of surfactant ?????, one method is the
use of metal halide ????? complexes and
alcohols. M X ROH ? M OH
RX metal halide alcohol metal hydroxide
complex complex
M OH M X ? M O - M HX

nanoparticle
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P. 54 From minerals ?? to materials The
formation of nanoparticles from inorganic metal
(top-down approach) . One common example is the
formation of aluminum oxide nanoparticle (Al O
Al) from the hydrolysis of aluminum compounds.
Figure 3.15
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Semiconductor Nanoparticles ??????? (Quantum
dots??? and quantum rods??? ) The synthesis of
semiconductors as nanoscale particles yields
materials with properties of absorbance and
fluorescence that differ considerably from those
of the larger, bulk-scale material. These
materials are of great interest in applications
ranging from medical imaging and sensing.
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Traditional semiconductors Semiconductor is a
material that has an electrical conductivity due
to electron flow (as opposed to ionic
conductivity) which is intermediate in magnitude
between that of a conductor and an insulator. The
conductivity increases with temperature and in
the presence of impurities. Semiconductor
materials are the foundation of modern
electronics, including radio, computers,
telephones, and many other devices. In
semiconductors, current is often schematized as
being carried either by the flow of electrons or
by the flow of positively charged holes.
semiconductors commercially. The common
semiconductor materials include silicon?,
germanium?, gallium arsenide???, and silicon
carbide???.
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Two fundamental factors, both related to the size
of the individual nanocrystal, are responsible
for these unique properties The first is the
large surface to volume ratio (the number of
surface atoms to those in the interior
increases). The second factor is the actual size
of the particle (increase of band gap
energy). The most studied nonoxide
semiconductors are caddmium chalcogenides (CdE,
with Esulfide, selenide and telluride).
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• 3 types of metallic nanoparticles
• 1. Precious metal ??? nanoparticles, e.g. silver
  and gold, to produce yellow to red colored
  nanoparticles
• Copper and ruthenium ? nanoparticles used as
  catalysts???
• Cobalt, iron and nickel ???? become magnetic
  nanoparticles can be used for information
  storage, and microwave composite materials

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Synthesis of metallic nanoparticles by reduction
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MZ reducing agent ? M0 Ox metal salt
zero valent metal
The reduction reaction involves the formation of
monosized nanoparticles that is achieved by a
combination of a low concentration of solute an a
protective layer (polymer, surfactant or
functional groups).
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P.77 Carbon Based Nanomaterials The different
allotrope????? of carbon, graphite, diamond and
C60 (buckyball), which was discovered in 1985 by
Curl, Kroto and Smalley who were awarded the
Nobel Price in Chemistry in 1996.
Fullerenes??? C60, C70, C74, C76, C78, etc. has
to follow two principles Eulers theorem and the
isolated pentagon rule (IPR)
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Carbon fullerenes are large, closed caged carbon
structures in a spherical shape. Fullerenes,
discovered in 1985, are stable in gas form and
exhibit many interesting properties that have not
been found in other compounds before. It is a
representation of a C60 Fullerene molecule. A
fullerene is a spherical structure composed of
both pentagonal ??? and hexagonal ??? carbon
rings. Fullerenes are considered zero dimensional
quantum structures which exhibit interesting
quantum properties. Once fullerenes were proven
to exist, research for other fullerene like
structures led to the discovery of Carbon
nanotubes in 1991.
A fullerene Molecule diagram
TEM
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• Carbon nanotubes
• Multiwalled nanotubes (MWNTs)
• Single-walled nanotubes (SWNTs)

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Nanotubes are the 1 dimensional wire form of a
fullerene the diameter is typically 1 to 5
nanometers (nm), while the length can be in the
range of microns. Single Walled Nanotubes (SWNT)
can be considered as a flat graphene sheet
cylindrically rolled into a tube. The tubes
consist of two regions the sidewall of the tube,
and the end region of the tube.