This document discusses the chemistry of nanoscale materials including their synthesis, properties, and applications. Key points include:
- Nanoparticles exhibit unusual properties due to their small size such as changes in melting points, optical properties, and surface reactivity.
- Semiconductor nanoparticles known as quantum dots exhibit quantum confinement effects which alter their band gap.
- Common synthetic methods for nanoparticles include chemical reduction, sonochemistry, and electrochemical routes. Stabilization is needed to prevent aggregation.
- Dendrimers can template the synthesis of metal nanoclusters within their cores. Monitoring by UV-vis spectroscopy allows observation of cluster formation.
1. Chemistry of Nanoscale
Materials
Synthesis, Properties and Applications
Potential Impacts of Nanoscale Materials
Pharmacy Water purification
Therapeutic drugs Catalysts
Tagging DNA and DNA chips Sensors
Information Storage Nanostructured Electrodes
Chemical/Optical components Improved polymers
Environmental/Green Chemistry Smart magnetic fluids
Solar Cells Improved National Security
Environmental remediation
2. Definitions
Nanoparticle: A solid particle in the 1-1000 nm range that could be
noncrystalline, an aggregate of crystallites, or a single crystallite
Nanocrystal: A solid particle that is a single crystal in the nanometer
size range.
Quantum dot. A particle that exhibits properties of quantum
confinement.
Nanostructured/ Nanophase/ nanoscale material:
Any solid material that has a nanometer dimension;
Colloid: A stable liquid phase containing particles in the 1-1000
nm range. A colloidal particle is one such 1-1000 nm sized particle
Cluster: A collection of units (atoms or reactive molecules) of up
to about 50 units. Cluster compounds are such moieties
surrounded by a ligand shell that allows isolation of a molecular
species (stable, isolable, soluble)
3. Size Relationships of Chemistry, Nanoparticles,
and Condensed Matter Physics
Nanoscale Condensed
Atoms/Molecules Matter
Particles
1 125 70,000 6 x 106 ∞
Diameter 1-10 nm Diameter 100-∞ nm
Solid State
Quantum Chemistry ? Physics
In the nanoscale regime, neither quantum chemistry nor
classical laws of physics hold
4. Factors Affected by Size Reduction:
Bulk vs. Nano
Melting Points
Optical properties
Colors
Surface Reactivity
Magnetic properties
Conductivity
Specific heats
6. Matter has Unusual Properties on the nm Scale
If you take gold and
make particles about ruby-red
10 nm in diameter, it stained glass
looks wine-red or from gold
blue-gray, depending nanoparticles
on how close the
particles are together
7. Preparation of Au Nanoparticles by a
Chemical Route
Reducing agent
Capping agent
Au nanoparticles
Au3+ Salt
9. Gold Nanospheres with Increasing
Diameter Size
Bulk Au
4 nm 12 nm 25 nm 37 nm
• Optical properties of metal nanoparticles depend on their shape and size
• Particle functionalization can be done on the surface
• Visible optical changes occur
10. Origin of the Properties
Bulk Metal Nanoscale metal
Unoccupied Decreasing
states the size…
occupied
states
Separation between
Close lying bands the valence and
conduction bands
Unbound electrons have Electron motion becomes
motion that is not confined confined, and quantization sets in
Particle size < mean free path
of electrons
11. Band Structure in Metals
EF (Fermi Level)
EF depends on the density
Density ρ = N/V (where N = Number of electrons, V = volume)
Assuming all energy levels have the same number of electrons,
δ = EF / N
Since N ∝ V
Therefore, δ ∝ 1/V
V = L3 (where L = side length of the particle)
Hence,
δ ∝ EF/L3
As the side length of the particle decreases the energy level spacing increase
12. Gold Nanospheres with Increasing
Diameter Size
Bulk Au
4 nm 12 nm 25 nm 37 nm
• Optical properties of metal nanoparticles depend on their shape and size
• Particle functionalization can be done on the surface
• Visible optical changes occur
13. Surface Plasmon Absorption of Au Nanoparticles
Surface plasmon absorption in metal nanoparticles arises from the collective
oscillations of the free conduction band electrons that are induced by the
incident electromagnetic radiation.
14. Factors that Affect the Surface Plasmon
Absorbance of Metal Nanoparticles
Plasmon absorption of metal nanoparticles is
sensitive to the surrounding environment
1. Dielectric of the surrounding medium
2. Solvents (nature of the solvent)
15. Dielectric Constant and its Effect of the
Surface Plasmon Absorption Band
Position of the plasmon absorption band can be discussed
within the framework of the Drude model
λ2 = λp2 (ε∝ = 2εm)
Where λp is the bulk plasma wavelength, ε∝ is the high frequency dielectric
constants due to interband and core transitions, and εm is the medium dielectric
constant
The refractive index is directly related to its dielectric constant
n = (εm)1/2
16. Normalized surface plasmon absorption
band of Au nanoparticles in cyclohexane
and o-dichloromethane
J. Phys. Chem. B. 2002, 106, 7729
Inset shows the dependence of the square of the observed peak position of the surface plasmon
band as a function of twice the medium dielectric function. ( m was determined from the
expression, m = n2)
17. How Does SP Band of Alkanethiolate-Au
Clusters Vary with Refractive Index
The optical dielectric of the
ligand shell, and not that of the
solvent, dominates the Au cluster
dielectric environment
Langmuir 1998, 14, 17
Dodecanethiolate-stabilized Au cluster
18. Melting Points
Property is a consequence of the averaged coordination number
of the participating atoms
Typically, for bulk materials, surface atoms form a negligible
part of the total number of atoms
The smaller a particle becomes, the more the proportion of
surface atoms increases
Full shell clusters are constructed by successively packing layers
– or shells – of metal atoms around a single metal atom
The number of atoms per shell is
(Sum of atoms + 10n2 + 2)
where n = number of shell
19. The Relation Between the total number of atoms in
Full shell (‘Magic Number’) clusters and the
percentage of surface atoms
Full-shell Total Surface
Clusters Number of Atoms (%)
Atoms
1 Shell 13 92
2 Shells 55 76
3 Shells 147 63
4 Shells 309 52
5 Shells 561 45
7 Shells 1415 35
20. Relation Between the Size of Gold
Particles and Their Melting Point
1200
1000
Melting Point (oC)
800
600
400
200
0
0 1 2 3 4 5 6 7 8 9 10
Particle Radius (nm)
21. Other Important Properties of Metal
Nanoparticles
Gold nanoparticles have been shown to be
photoluminescent
Unique electrochemical properties
Gold nanoparticles have shown electron – acceptor
properties
Enhanced catalytic properties
22. Semiconductor Nanoparticles
Group 14 (old group IV) Si, Ge
III-V Materials: GaN, GaP, GaAs, InP, InAs
II-VI Materials: ZnO, ZnS, ZnSe, CdS, CdSe, CdTe
Quantum dots are
semiconductors particles
that has all three
dimensions confined to the
1-100 nm length scale
Colloidal CdSe quantum dots dispersed in hexane
23. Energy Diagrams Illustrating the
Situation for a Nanoparticle, in Between
a Molecule and a Bulk Semiconductor
NANOPARTICLE
MOLECULE
LUMO BULK SOLID
CB
Energy
∆E Eg
∆E
VB
HOMO
24. Quantum Confinement in
Semiconductor Nanoparticles
Eg (quantum dot) = Eg(bulk) + ( h2/8R2) (1/me + 1/mh) – 1.8e2/4πε 0εR
Eg = bandgap energy of a quantum dot or bulk solid
R = quantum dot radius
mc = effective mass of the electron in the solid
mh = effective mass of the hole in the solid
ε = dielectric constant of the solid
ε0 = permittivity of a vacuum
25. Room-Temperature Spectra of CdSe
Quantum Dots
(a) Absorption and
photoluminescence spectra
as a function of diameter
(b) Quantum yield of
photoluminescence as a
function of size. Squares
represents deep-trap
emission, and circles
represent band-edge
emission
Murray, C. B. Synthesis and characterization of II-VI quantum dots and their
assembly into 3D quantum ot superlattices. Ph.D Thesis, MIT, Cambridge , MA 1995
26. Inorganic Semiconductors
Trap states are caused by defects, such as vacancies, local
lattice mismatches, dangling bonds, or adsorbates at the
surface
27. Chemical Synthetic Routes for
Metal and Semiconductor
Nanoparticles and Structures
Additional Synthetic Approaches
• Sonochemical
• Electrochemical
• Photochemical
• Chemical Vapor Deposition
28. Aspects of Nanoparticle Growth in
Solution
Arrested precipitation
Precipitation under starving conditions: a large number
of nucleation centers are formed by vigorous mixing of
the reactant solutions.
If concentration growth is kept small, nuclei growth is
stopped due to lack of material.
Particles had to be protected from Oswald Ripening by stabilizers
Oswald Ripening
The growth mechanism where small particles dissolve,
and are consumed by larger particles. As a result the
average nanoparticle size increases with time and the
particle concentration decreases. As particles increase
in size, solubility decreases.
29. Synthetic Approaches for Metal and
Semiconductor Nanoparticles
via Chemical Routes
1. Metal Compound
• Positively charge metal salt, or
• Metal centers of complexes
2. Solvents (depends on the nature of the salt)
• Water
• Polar organic solvents
• Non-polar organic solvents
3. Reducing agent (determined by the nature of the metal compound)
• Gaseous hydrogen
• Hydridic compounds
• Reducing organics, e.g. alcohols
Many others
30. Stabilization of Nanoclusters Against
Aggregation
1. Electrostatic stabilization
Adsorption of ions to the + - - - - - + - - - +
-- - + -
surface. Creates an electrical - δ+ δ+ δ+ - δ+ δ δ+ --
-- --
double layer which results in a - δ+ δ+ - + δ+ δ+ -
+ - - --- - --
- - -+
Coulombic repulsion force + -
between individual particles
2. Steric Stabilization
Surrounding the metal center
by layers of material that are
sterically bulky,
Examples: polymers,
surfactants, etc
31. Synthetic Approaches for Metal and
Semiconductor Nanoparticles
via Chemical Routes
4. Stabilizers
Role of stabilizers:
Stabilizing agents/ligands/capping agents/passivating agents
• prevent uncontrollable growth of particles
• prevent particle aggregation
• control growth rate
• controls particle size
• Allows particle solubility in various solvents
35. Synthesis of Metal Nanoparticles in
Organic Media
Biphasic reduction procedure
Add phase
transfer reagent Extract
e.g. tetraoctyl
ammonium
Aqueous bromide
(TOAB)
solution of
metal salt Add
Reducing
agent
36. TEM Image of Au Nanoparticles Prepared
in the Presence of a Surfactant (CTAB)
CTAB = cetyltrimethylammonium bromide
J. Phys. Chem. B. 2001, 105, 4065
37. Nucleation and Growth
Homogeneous nucleation occurs via a stepwise sequence of
bimolecular additions until a nucleus of critical size is obtained.
a. Nucleation from supersaturated solution
nS Sn
b. Diffusion-Controlled Growth
Sn + S Sn+1
LaMer et al. J. Am. Chem. Soc. 1950, 72, 4847
Highly monodisperse nanoparticles are formed if the processes
of nucleation and growth can be successfully separated
• Nucleation process must be fast
• Growth process must be slow
38. Nucleation
Nucleus Radius is calculated as follows:
∆G = 4πσ(r2 – [2r3 / 3r*])
Where r = nucleus radius
r* = critical nucleus radius
σ = surface tension
∆G(nucleus) = n(∆G formation, bulk – ∆G formation, free atom) + σA
Where A = particle surface area
40. Dendrimer-Templated Nanocluster Synthesis
Pioneered in 1998, by
Donald A. Tomalia (Michigan Molecular Institute
Richard M. Crooks (TAMU)
Hydrazine
PAMAM + CuAc2 1 x 10-4 mol
1 x 10-6 mol Cu Nanoclsuters
1 x 10-5 mol
Formation of Cu nanoclusters
can be monitored by UV-vis
spectrophotometry
Reaction is pH dependent:
Presumably H+ ions compete
with Cu2+ ions for the tertiary
amine sites
J. Am. Chem. Soc. 1998, 120, 4877
J. Am. Chem. Soc 1998, 120, 7355
41. Reverse Micelles
Water-in-oil droplets
[H2O]
Water pool w =
[surfactant]
Particle size is controlled by the size of the water
droplets in which synthesis takes place
Consider that: V = volume , R = radius,
R = 3V/A A = surface area
3Vaq[H2O] σ = head polar group area
Rw = Vaq = volume of water
σ[s]
42. Parameters Affecting Particle Growth/
Shape/ Structure
• Type of capping agent/stabilizers
• Concentration of the reactants
• pH value of the solution
• Duration of heat treatment
44. Sonochemical Approaches for
Nanoscale Particle Synthesis
Step 1:
• Bubble expands when surrounding medium experiences –ve
pressure
• Bubble collapses when surrounding medium experiences +ve
pressure
• Bubble collapse leads to extreme temperatures (5,000 – 50, 000
K), and pressure (100 atm) within the bubble
Step 2:
Solvent or solute molecules present within the bubbles are
decomposed under these extreme conditions and generate highly
reactive radicals
45. Formation of Highly Reactive Radicals
Depending on the liquid medium, sonication leads to the
generation of oxidizing and reducing radicals
In aqueous solution
H2O • H + •OH
M+ + H • M + H+
In solutes like alcohols, sonication leads to secondary radicals
RHOH + H (OH• )
• ROH• + H2(H2O)
ROH • + M+ M + RO + H+
46. Examples of Metal Nanoparticles
Prepared by Sonication
Ag nanoparticles prepared in aqueous solution at 1 MHz
H2O • • H + OH
Ag+ + H • Ag + H+
J. Phys. Chem. 1987, 91, 6687
Au nanoparticles prepared by sonication
ROH •
AuCl4- Au + Products
Langmuir 2002, 18, 7831-7836
47. Synthesis of CdS Nanoparticles
General:
Anionic or
Cd(II) salt + Lewis basic + Sulfide 1-10 nm
polymers source CdS
Sodium
Cd(NO3)2.4H2O + polyphosphate + Na2S CdS
2 x 10-4 M 2 x 10-4 M 2 x 10-4 M
Chem. Mater. 1999, 11, 3595
48. Synthesis of CdSe Nanoparticles
General: High
Phosphine oxide
Cd(CH3)2 + Se reagent + temperature
surfactant CdSe
HAD-TOPO-TOP
Cd(CH3)2 + (C8H17)3PSe CdSe
HAD-TOP-TOP = hexadecylamine-trioctylphosphine oxide-trioctylphosphine
J. Am. Chem. Soc. 1993, 115, 8706
49. Synthesis of ZnSe Nanoparticles
Zn(CH3CH2)2 + (C8H17)3PSe Zn/Se TOP
Solution
Zn/Se TOP + Hexadecylamine 270 C
o
ZnSe
Solution
J. Phys. Chem. B. 1998, 102, 3655
TOPO binds too strongly to Zn
TOP binds too weakly
Amines, however have intermediate strength
50. Synthesis of III-V Semiconductor
Nanoparticles
Synthesis of III-V semiconductor nanoparticles is quite complex
Requires high temperature
370 – 400 oC
GaCl3 + tris-(trimethylsilyl)phosphine + TOPO-TOP GaP
GaP particles prepared in this manner lacked monodispersity
GaCl3 + As(SiMe3)3 ~ 700 oC GaAs
Chem. Mater. 1989, 1, 4
J. Am. Chem. Soc. 1990, 112, 9438
51. Synthesis of InP and InCl3
260 oC, TOP InP nanocrystals
InCl3 + [(CH3)3Si]3P
Synthesis of InAs via Dehalosilylation
Me3SiCl Me3SiCl Me3SiCl
evolved evolved evolved
InCl3 + (Me3Si)3As InAs
3 days, rt 70-75 C
o
150 C
o
4 days 4 days
Chem. Mater. 1989, 1, 4
52. Factors Affecting the Nature of the
Nanoparticle
• Particle size and shape
• Surface properties
• Particle-solvent interactions
• Particle-particle interactions
53. Common Methods for Nanoparticle
Characterization
Surface state
Particle Surface Surface Surface
Size Area composition structure;
Topography
Surface
Complexes
Electron Microscopy
X-ray diffraction LEED
Magnetic Measurements AES, SEM
XPS, TEM
SIMS, EXAFS
EPMA,
EXAFS
IR, UV-Vis, ESR, NMR, Raman
54. UV-Visible Spectroscopy
• Particularly effective in characterizing semiconductor and
metal particles
• Useful for metal nanoparticle characterization whose surface
plasmon absorbance lies in the visible range, e.g. Cu, Au, Ag
• Can be used to determine particle size:
(For semiconductor nanoparticles: as the radius decreases, the
band gap increases and λmax shifts to lower energy.
• Particle aggregation
• Information about the surface, e.g. presence of adsorbates
55. Infrared Spectroscopy
IR has been used as a surface probe for nanostructures
Example illustrated by Bardley:
Adsorbing CO onto the metal nanoparticle surface resulted in IR
depending on particle size
More face:
More edge:
bridged CO
linear CO is
is stable
stable 2.5 nm 4 nm 6 nm
As particle size increased, the ratio of terminal CO to bridging
CO decreased et al. Chem. Mater. 1992, 4, 1234
Bradley,
56. Nuclear Magnetic Resonance (NMR)
Two uses:
1. Probing the ligands that surround metal core
2. Probing the intra-core metallic atoms (difficult)
Probing the intra-core metallic atoms
Nuclear spin relaxation time, and nuclear resonance frequency,
are sensitive to any metallic property the particle may exhibit
Change in frequency (known as ‘Knight shift’) is a consequence
of the interaction of the metal nucleus with the conduction band
electrons
If particles are very small, in favorable cases, the Knight shift
allows resonances for surface and interior metal particles to be
identified
57. Microscopy
• TEM: High voltage beam passes through a very thin
sample. The sample areas that do not allow passage of
electrons allow image to be presented
• STM: Involves dragging a sharp needlelike probe across a
sample very close to the surface. The tunneling current
between the sample and probe tip can be monitored . As
probe approaches an elevated portion, the probe moves up
and over, and produces a surface map.
• AFM: The probe tip is essentially touching the surface,
and the surface can be mapped by the weak interaction
between the tip and the sample.
58. Transmission Electron Microscopy
• Provides direct visual information of size, shape, dispersity,
structure and morphology
• Routine magnifications > 40,000 to 0.2 nm
Drawbacks
• Samples are dried and examined under high vacuum conditions
• Therefore, no direct information is gained on how particles exist in
solution
• Only a finite number of particles can be examined and counted,
which may not be a representative of the sample as a whole
• Requires electron beam in which case, some nanoparticles may
undergo structural rearrangement, aggregation or decomposition.
59. Scanning Tunneling Microscopy (STM)
Makes possible the determination of the total diameter of the
nanoparticle, including the stabilizing ligand shell
Effective probe of the electronic properties of nanoparticles
Reetz et al. Science 1995, 267, 367-369
A combined STM/TEM study of Pd nanoparticles stabilized by
R4N+Br-.
Determined thickness of stabilizing ligand shell by subtracting
the STM determined diameter from the TEM determined
diameter
60. Shortcomings to STM
• Nanoparticles may not stick well to the substrate surface,
preventing good images from being obtained
• Geometry of the tip shape may lead to inaccurate
measurements or artifacts in the image
• Tunneling mechanism is not well understood
• Samples have to be dried
• Specific techniques applied to imaging are not mature, i.e.
standard literature protocols have not been established
61. Atomic Force Microscopy
• Technique is purely mechanical
– A cantilevered tip attached to a spring is dragged across
a sample
– Increase or decrease in tip height is measured yielding a
surface height profile as a function of distance
– Can be carried out on non-conducting samples
Shortcomings
• Can reliably determine particle height but not diameter
• Cannot distinguish between subtle shape differences, or
image particles that are not spatially close to each other
62. High Aspect Ratio Nanoparticles
• What is a high aspect ratio nanoparticle?
• Aspect ratio refers to the ratio of a particles length to its
width
Aspect ratio = length
width
• High aspect ratio nanoparticles have elongated structure
Examples: nanotubes, nanowires, nanorods
• Often have distinctive properties as opposed to the bulk
materials or even spherical particles
e.g. Chemical, electrical, magnetic, optical, etc.
63. Types of High Aspect Ratio Nanoparticles
Nanowires Aspect ratio
Synthetic Method
Ni, Au, Pt, Ag, Co, Cu, ZnO Templated electrodeposition Up to 250
TiO2, ZnO, SiO2 Sol-gel 250
Silicon Nanocluster-mediated vapor-liquid- > 100
solid growth > 20
MnO2, Fe2O3, Cu2O, Pd, Electrodeposition on graphite
Cu, Au, Ag surface
Nanotubes
Gold Templated electroless deposition 250
Silica Sol-gel 250
Carbon High temperature: laser > 100
ablation, arc discharge, others
Nanorods
Gold Surfactant/seed mediated synthesis ~20
CdSe Surfactant/seed mediated synthesis 2-10
Cu Micellar growth 1.7-3.7
Se Crystal growth > 100
65. Synthesis of Au Nanorods
1. Formation of 4 nm “seed” by reduction of HAuCl4
HAuCl4 NaBH4
solution
+ Sodium citrate
2. Seed-mediated growth in the presence of cetyltrimethylammonium
bromide (CTAB) produces rod-like Au spheroids and nanorods
HAuCl4
Solution + ascorbic acid
in CTAB
3. Seed-mediated growth in the presence of cetyltrimethyammonium
bromide (CTAB) of rod-like Au nanoparticles leads to Au nanorods
HAuCl4
Solution
+ ascorbic acid
in CTAB
CTAB = cetyltrimethylammonium bromide (a surfactant)
66. Increase in Intensity of the Longitudinal
Plasmon Band with Increase in Nanorod
Concentration
Chem. Mater. 2003, 15, 1957
67. TEM Image of Au Nanorods Prepared
by a Seed-Mediated Growth Method
Aspect Ratio = 13
J. Phys. Chem. B. 2001, 105, 4065
68. Gold Nanoparticles with Increasing
Aspect Ratio
Increasing aspect ratio
1
18
Obare, S. O.; Jana, N. R.; Murphy, C. J. Unpublished results
69. Increase in Aspect Ratio of Au
Nanoparticles Shifts the Longitudinal
Plasmon Band to the NIR
Chem. Mater. 2003, 15, 1957
70. Calculated absorption spectra of Au nanoparticles
with Varying Medium Dielectric Constant
Link, S.; Mohamed, M. B.; El-Sayed, M. A. J. Phys. Chem. B. 1999, 103 (16), 3073-3077
71. Synthesis of Ag Nanorods and Nanowires
Formation of 4 nm “seed” by reduction of AgNO 3
AgNO3 NaBH4
solution
+ Sodium citrate Ag seed
Formation of Ag nanorods; aspect ratio was varied by changing the
seed
concentration; pH is higher ~ 11.8
AgNO3
solution + ascorbic acid NaOH
Formation of Ag nanowires; pH is low
AgNO3 + ascorbic acid
solution NaOH
CTAB = cetyltrimethylammonium bromide (a surfactant)
72. TEM Images of Silver Nanorods and
Nanowires
Chem. Commun. 2001, 617
73. Silver Nanoparticles with Increasing
Aspect Ratio
Increasing aspect ratio
1 10
Murphy, C. J.; Jana, N. R. Adv. Mater. 2002, 14, 80
74. Electrochemical Synthesis of
Nanoparticles
Synthesis of High Aspect Ratio Nanoparticles
Nanoporous Membrane Templated Fabrication
SEM image of typical
alumina membrane.
Typically membranes consists of
1. Anodized alumina
2. Track etch polycarbonate www. whatman.com
J. Vac. Sci. Technol. B 2003, 35, 1097
75. Nanowire Synthesis by Electrodeposition
Sputter Place membrane in
copper on aqueous solution of
bottom metal salt
Nanoporous alumina membrane
M+
Apply potential
e- -
e
M+(aq) + e- M(s)
Remove copper Dissolve alumina
with CuCl/HCl in warm .5 M
solution KOH
76. Current–Time Transient for the Deposition of 60 nm
Nickel Nanowires into a 6 µm Polycarbonate Template
Science 1993, 261, 1316
77. The Sol-Gel Process
M-O-R + H2O → MOH + R-OH (Hydrolysis)
M-OH + HO-M → M-OH + H2O (Condensation)
Sol Gel
Metal
Hydrolysis Gelling
Alkoxide
Solution
79. SEM Image of TiO2 Nanostructures
Prepared by the Sol-Gel Process
SEM image of TiO2 nanostructures obtained by immersing the template membrane in the
sol for (A) 5, (B) 25, and (C) 60 s.
80. SEM Image of MnO2 Nanostructures
Prepared by the Sol-Gel Process
SEM image of MnO2 fibers prepared in the 200-nm-pore-diameter alumina
template membrane
81. SEM Image of V2O5 Nanostructures
Prepared by the Sol-Gel Process
SEM images of the template-synthesized V2O5 microstructures
82. SEM Image of Co3O4 Nanostructures
Prepared by the Sol-Gel Process
SEM image of Co3O4 fibers prepared in the 200-nm-pore-diameter
alumina template membrane
83. Synthesis of Carbon Nanotubes
Synthesis of carbon 1993, Nature 1993, 363, 603
Iijima an coworkers first synthesized carbon
nanotubes involves high nanotubes via the thermal decomposition of
temperature approaches hydrocarbons.
High temperature decomposition of vapors such
as benzene or acetylene, in the presence of Co,
Fe, or Ni catalysts, formed single walled carbon
nanotubes.
1996, Science 1996, 273, 483
Laser Ablation method (Smalley and coworkers)
Method produced nanotubes formed into ropes of
100-500 carbon nanotubes, at yields of more than
70%.
A single walled carbon nanotube
2002, Nano Lett. 2002, 2, 1043
Carbon nanotubes are cylindrical Catalyst-free synthesis (Avouris and coworkers)
structures consisting of rolled-up Method developed for carbon nanotube synthesis
graphene sheets with fullerene on a silicon surface. Advantage is that catalyst
caps. removal is not necessary for purification.
84. Ligands and the Surfaces they are
Reported to Functionalize
Ligand Name Surface Proposed
modified linkage
R–S–H Thiols
Au, Ag, Cu, Hg, Fe
R–S–S–R Disulfides
R–C N Isocyanides Pt, Pd
Carboxylic acids Metal oxides
Phosphonates Metal oxides
Siloxanes Metal oxides
Hydroxamic acids Metal oxides
86. Applications of High Aspect Ratio
Nanoparticles
Several applications of high aspect ratio nanoparticles have been
shown, and many others continue to be unfolded
Applications is areas such as:
•Biology
•Gene therapy
•Bioseparations
•Separations
•Catalysis
•Sensing
•Electronics
•Optical applications
Etc.
87. Nanowire Synthesis by Electrodeposition
Sputter Place membrane in
copper on aqueous solution of
bottom metal salt
Nanoporous alumina membrane
M+
Apply potential
e- -
e
M+(aq) + e- M(s)
Remove copper Dissolve alumina
with CuCl/HCl in warm .5 M
solution KOH
88. Au-Ni-Au Nanorods Bound and Unbound
to Fluorescein-tagged Poly-His
Confocal fluorescence
image of Au-Ni-Au after
modification of Ni portion
with Fluorescein-tagged
poly-His
SEM image of Au-Ni-Au
Nanowires
Angew. Chemie. Int. Ed. 2004, 43, 3048
89. Exposure of Fluorescein-tagged Poly-His
Proteins to Au-Ni-Au Nanorods
Left: Fluorescein-tagged poly-His
solution
Right: Fluorescein-tagged poly-His
Solution after exposure to Au-Ni-Au
Nanorods Angew. Chemie. Int. Ed. 2004, 43, 3048
90. Separation of His-tagged Proteins
from a Non-His-tagged Structures
a. Solution of IgG protein (no
a b c His)-Green Alexa dye
mixed with His-tagged
protein-Red Alexa Dye
b. After exposure to Au-Ni-
Au; (non-His protein
remains in solution)
c. Separated Au-Ni-Au from a
in solution
Angew. Chemie. Int. Ed. 2004, 43, 3048
91. Smart Nanotubes for Bioseparations
and Biocatalysis
J. Am. Chem. Soc. 2002, 124, 11864
92. Smart Nanotubes for Bioseparations
and Biocatalysis
Nanotubes preferentially
reside in cyclohexane due to
Vial containing cyclohexane the outer hydrophobic
(upper) and water (lower) surface
Add nanotubes A
cyclohexane
H2 O
Nanotubes A. Dansylamide on inner void and C 18 on outer surfaces
Danyslamide dye fluoresces green J. Am. Chem. Soc. 2002, 124, 11864
93. Smart Nanotubes for Bioseparations
and Biocatalysis
Nanotubes preferentially
Vial containing cyclohexane reside in Aqueous phase due
(upper) and water (lower) to the outer hydrophilic
surface
Add nanotubes B
cyclohexane
H2 O
Nanotubes B. Quinineurethan on inner and no silane on outer surfaces
Quinineurethan dye fluoresces blue J. Am. Chem. Soc. 2002, 124, 11864
94. Smart Nanotubes for Bioseparations
and Biocatalysis
Nanotubes A preferentially
reside in Organic phase while
Vial containing cyclohexane
nanotubes B reside in the
(upper) and water (lower)
aqueous phase
Add nanotubes A
cyclohexane Add nanotubes B
H2 O
Nanotubes A. Dansylamide on inner void and C 18 on outer surfaces
Nanotubes B. Quinineurethan on inner and no silane on outer surfaces
J. Am. Chem. Soc. 2002, 124, 11864
95. Multifunctional Nanorods for Gene Delivery
Nature Materials 2003, 2, 668
Goal of gene therapy: to introduce foreign cells into somatic cells to
supplement defective genes, or provide additional biological functions
H2N H2N
S-S S-S DNA*
HOOC OOC
Au Ni
HN-DNA* HN-DNA*
S-S S-S
OOC S-T OOC
HS-Transferrin
Observations
1. Nanorods were internalized into the cell but did not
enter the nucleus
2. GFP was observed in the nucleus indicating
delivery of the reporter gene to the nucleus
Human kidney cell 3. Au-S-T served to promote cellular uptake
4. Disulfide linkage acts as a cleavable point to
promote release of DNA within the cell
DNA* = DNA plasmids which encodes Green fluorescent Protein GFP
96. What is Nanoparticle
Engineering/Surface Modification
Tailored synthesis of core-shell nanoparticles
with defined morphologies and properties
shell
core
97. Why Surface Modification?
1. The shell can alter the charge, functionality, and
reactivity of the surface
2. The shell can enhance the stability and dispersibility
of the colloidal core
3. Magnetic, optical, or catalytic functions may be
readily imparted to the dispersed colloidal core
4. Encasing colloids in a shell of different composition
may also protect the core from extraneous chemical
and physical changes
98. Effects of Surface Modification
Chemical and Colloidal Stability
• Nanoparticle degradation through chemical etching
• Agglomeration caused by strong van der Waals attractive forces
Tuning of Physical Properties
For example, the optical properties of metal nanoparticles are
influenced by their environments. Controlled surface modification can
alter these properties
Control of Interparticle Interactions Within Assemblies
• Collective properties of nanoparticle assemblies are influenced to a
large extent by the separation between the particles.
• Coating the particles with a uniform shell of inert material could
control the distance between the particles
99. Types of Core-Shell Nanoparticles
• Metal-Polymer
• Metal-Metal
• Semiconductor- Semiconductor
• Semiconductor-Metal
• Metal - Semiconductor
100. Polymers on Metals
• Main reason is for nanoparticle stabilization
• Could also be used to assemble nanoparticles
• Examples:
– Chem. Mater. 1998, 10, 1214
– J. Am. Chem. Soc. 1999, 121, 8518
– Adv. Mater. 1999, 11, 34
– Adv. Mater. 1998, 10, 132
– Chem. Commun. 1998, 351
– Adv. Mater. 1999, 11, 131
– J. Am. Chem. Soc. 1999, 121, 10642
– Nano Lett. 2002, 2, 3
101. Sketch of the surface reactions involved in
the formation of a thin silica shell on citrate-
stabilized gold particles
Langmuir 1996, 12, 4329
102. UV-visible spectra of sodium citrate-
stabilized, 15 nm diameter gold colloids 1
day after addition of different amounts of
APS
APS: polymerization initiator
3-aminopropyltrimethoxysilane
Langmuir 1996, 12, 4329
103. 15 nm gold particles coated with thin
silica layers
18 hours after addition 42 h after addition 5 days after addition
of active silica
The silica shell keeps on growing, but eventually small silica particles also nucleate out
of the solution.
Langmuir 1996, 12, 4329
104. Silica-Coated Au Nanoparticles
Langmuir 1996, 12, 4329
Transmission electron micrographs of silica-coated gold particles produced during the extensive
growth of the silica shell around 15 nm Au particles with TES in 4:1 ethanol/water mixtures. The
shell thickness are (a, top left) 10 nm, (b, top right) 23 nm, (c, bottom left) 58 nm, and (d, bottom
right) 83 nm
105. Influence of thin silica shells on the UV-
visible spectra of aqueous gold colloids
Experimental Calculated
Langmuir 1996, 12, 4329
106. Influence of thick silica shells on the UV-
visible spectra of ethanolic gold colloids
Experimental Calculated
Langmuir 1996, 12, 4329
107. Effect of Solvent Refractive Index on the
Color of Dispersions of 15 nm Gold Particles
with a 60 nm Silica Shell
The solvent refractive indices (left to right) are 1.45, 1.42, 1.39, and 1.36
Langmuir 1996, 12, 4329
108. Silica Coating of Silver Colloids
NaBH4
AgClO4 + sodium citrate 10 nm Ag nanoparticles
Ag + 3-aminopropyltrimethoxysilane + sodium silicate Ag@SiO2
nanoparticles
Silicate ion concentration
0.02 % 0.01 % 0.005 %
Langmuir 1998, 14, 3740
109. Emulsion Polymerization
Emulsion polymerization is a type of polymerization that takes place in an
emulsion typically incorporating water, monomer, and surfactant. The most
common type of emulsion polymerization is an oil-in-water emulsion, in
which droplets of monomer (the oil) are emulsified (with surfactants) in a
continuous phase of water.
In aqueous solution
surfactant
Monomer + free radical initiator → Polymer
110. Polymer-Coated Silver Nanoparticles
TEM images of silver particles: (A) uncoated particle, (B) polystyrene/methacrylate
coated particles, (C) polystyrene/methacrylate coated particles with a covalently bound
BSA layer, and (D) the same as panel C after exposure to gold colloids. Negative staining
by phosphotungstic acid used for all images
J. Am. Chem. Soc. 1999, 121, 10642
111. Preparation of Polymer-Coated
Functionalized Silver Nanoparticles
Extinction spectra of silver particles: (A) uncoated particles and (B) polystyrene coated
particles. Solid line: suspension in water. Dotted line: suspension in water, after 1 h in 1.8 M
NaCl
J. Am. Chem. Soc. 1999, 121, 10642
112. Synthetic Protocols for the Synthesis of Coupled
1D Nanoparticle Arrays
Procedures for (A) Ppy-
linked Au Colloids
Alkyldithiolate-Linked
Au Colloids
Ppy = poly(pyrrole)
Chem. Mater. 1998, 10, 1214
113. Au Colloids Linked by PPy
Transmission electron microscope images of 1D and near-
1D arrays of Au colloids linked by Ppy
Chem. Mater. 1998, 10, 1214
115. Energies of Various Semiconductors
TiO2
GaP
Energy (eV)
GaAs CdS
CdSe ZnO TiO2
WO3
1.4 3.0
2.25
1.7 2.5
3.2 3.2
3.2
Values at pH = 1
116. Inorganic Semiconductors
Trap states are caused by defects, such as vacancies, local
lattice mismatches, dangling bonds, or adsorbates at the
surface
117. Examples for Semiconductor-
Semiconductor Core-Shell Nanoparticles
Examples include:
ZnS on CdSe
CdS on CdSe
CdSe on CdS, etc
J. Phys. Chem. B. 1997, 101, 9463
J. Phys. Chem. B. 1998, 102, 1884
J. Phys. Chem. 1993, 97, 5333
J. Phys. Chem. 1996, 100, 6381
J. Phys. Chem. 1996, 100, 8927
J. Phys. Chem. 1996, 100, 13226
J. Phys. Chem. 1996, 100, 20021
118. CdSe Coated with ZnS Nanoparticles
Me2Cd + TOPSe CdSe
300 oC
(TMS)2/Me2Zn/TOP
∆T
ZnS
CdSe
J. Phys. Chem. 1996, 100, 468 TEM picture of (CdSe)ZnS nanocrystals
119. CdSe Coated with ZnS Nanoparticles
J. Phys. Chem. 1996, 100, 468
Absorption spectrum of the (CdSe)TOPO
(dotted line) and the (CdSe)ZnS Normalized fluorescence spectra of CdSe-TOPO
nanocrystals (solid line). The fluorescence (dotted line) and CdSe@ZnS (solid line) with
of the (CdSe)ZnS is also shown (solid line) 470 nm excitation
120. Observations on the Optical Characteristics
of CdSe/ZnS Nanoparticles
Fluorescence of CdSe-TOPO shows the broad tail, due to
surface traps.
CdSe/ZnS fluorescence spectrum has a flat baseline; this
indicates that the ZnS reduces the traps present on the CdSe
(TOPO) surface
Fluorescence of CdSe (CdSe/ZnS) was stable for months
compared to uncapped CdSe
No reduction in the CdSe quantum yield was observed for
months with the CdSe/ZnS nanoparticles
J. Phys. Chem. 1996, 100, 468
121. Synthesis of HgS/CdS Core-Shell
Nanostructures
J. Phys. Chem. 1993, 97, 5333
HgScore CdSshell
HgCl2 + H2S + sodium polyphosphate → HgS
HgS + Cd(ClO4)2 + H2S → HgS/CdS
CdScore HgSshell
Cd(ClO4)2 + H2S + sodium polyphosphate → CdS
CdS + HgCl2 + H2S → CdS/HgS
Note: Due to the much lower solubility of HgS compared with CdS
particles result in an exchange of Cd2+ by Hg2+
(CdS)n + mHgCl2 → (CdS)n-m(HgS)m + mCdCl2
122. CdS/HgS Mixed Colloids
J. Phys. Chem. 1993, 97, 5333
HgS nanoparticles HgS coated with CdS
123. Absorption Spectra of Core-Shell CdS
on HgS Nanoparticles
J. Phys. Chem. 1993, 97, 5333
A = HgS
124. Fluorescence Spectra of Core-Shell
CdS on HgS Nanoparticles
HgS nanoparticles do not
fluoresce
CdS coated HgS nanoparticles
fluoresce:
Possibly due to
removal of traps for
nonradiative recombinations
or
Fluorescence could
arise from band to
band recombination in
HgS core
J. Phys. Chem. 1993, 97, 5333
129. Pt/Au Core-Shell Nanoparticles
J. Phys. Chem. B. 2000, 104, 2201-2203
Absorption spectra of Pt nanoparticles
before and after deposition of various
amounts of gold. Overall Pt
concentration is 1 x 10-4 M
Concentration of Pt:Au is given on the Absorption spectra of Au nanoparticles
curves before and after deposition of various
amounts of Pt. Overall Au concentration:
3 x 10-4 M Molar of Au:Pt is given on the
curves
131. Metal-Semiconductor Core-Shell
Nanoparticles
Metals can be used as templates to make hollow semiconductor
nanostructures
Fabrication of composite nanoparticles with a large electronic
capacitance, i.e. a large difference in the Fermi level of the core relative
to the conduction band edge of the shell will enable electrons to diffuse
through the shell and be trapped in the core for a long time
Examples:
Au/CdSe: J. Mater. Res. 1998, 13, 905-908
Au/CdS: J. Phys. Chem. B. 1997, 101, 7675
Ag/TiO2: Langmuir 2000, 16, 2731-2735
Au/TiO2: J. Phys. Chem. B. 2000, 104, 10851
TiO2/Ag: Langmuir 1999, 15, 7084-7087
ZnO/Au: J. Phys. Chem. B. 2003, 107, 7479-7485
133. Synthesis of CdS-Capped Au
Nanoparticles
High T
NaAuCl4 + sodium citrate Au nanoparticles (~ 20 nm)
MNA = 2-mercaptonicotinic acid
J. Phys. Chem. B. 1997, 101, 7675
134. Absorption Spectra of Au/CdS
Nanocomposites
Absorption properties
of Au/CdS are not the
result of a simple
addition of the
spectra of two
nanoclusters, but
rather an influence of
the CdS on the Au.
Au
Au/CdS
Au/MNA
CdS
J. Phys. Chem. B. 1997, 101, 7675
135. Emission Spectra of Au/CdS
Nanocomposites
Emission quenching of CdS is
indicative of the occurrence of
electron transfer from excited CdS
into the Au core.
Conduction band energy for CdS =
- 1.0 V vs. NHE
Fermi level of Au = + 0.5 V vs. J. Phys. Chem. B. 1997, 101, 7675
NHE
Editor's Notes
Aromatic organic compounds make useful chromophores for receptor design, but metal nanoparticles are emerging as importanat colorimetric reporters due to their high extinction coefficients. Gold nanoparticle for examples display plasmon absorption bands that depend on their shape and size, and degree of aggregation. By varying the size of gold nanospheres we can change their color from orange to red. These particles can be used as optical reporters by functionalizing their surface. We have seen in the previous experiment how we have developed Li selective ligands based on Phen, and he ligand form a 2:1 complex with Li.
Aromatic organic compounds make useful chromophores for receptor design, but metal nanoparticles are emerging as importanat colorimetric reporters due to their high extinction coefficients. Gold nanoparticle for examples display plasmon absorption bands that depend on their shape and size, and degree of aggregation. By varying the size of gold nanospheres we can change their color from orange to red. These particles can be used as optical reporters by functionalizing their surface. We have seen in the previous experiment how we have developed Li selective ligands based on Phen, and he ligand form a 2:1 complex with Li.