Nanoparticles (from Greek nanos – dwarf) are or- ganic or inorganic solid
particles. The dimension of nanoparticles is not defined in a uniform manner.
Nanoparticle Technology
Definitions Nanotechnology wants to control the smallest structures built of atoms and molecules. It is connected with colloidal chemistry and physics, biology, medicine, pharmacy and engineering (materials and processes). Nanoparticles (from Greek nanos – dwarf) are organic or inorganic solid particles. The dimension of nanoparticles is not defined in a uniform manner.
a) particles in the sub micron range ( < 1 µm) , b) materials science : < 100 nm (nano scaled particles) c) pharmaceutics : < 500 nm, < 1000 nm = 1µm
Usually nanoparticles are dispersed in a continuous phase ( see dispersed systems).
Historical overview – Nanotechnology and nanoparticles 2697 BC
Tien-Lcheu: petroleum lamp soot for Indian ink used in China
400 BC
Lycurgus cup (with gold nanoscaled particles covered glass cup, British Museum London
1600
Manufacturing of church windows, shining red by colloidal gold nanoparticles
1857
Faraday
Synthesis of colloidal gold nanoparticles, colour effects
1915
Ostwald, Wolfgang
Colloids - „world of neglected dimensions“
1931
Ruska, Knoll
development of an electron microscope TEM, 1938 built commercially by Siemens
1942
Knöpfer
Aerosil process (Degussa) – pyrogenic silica, 1953 aluminium oxide, 1954 titanium dioxide
1959
Feynman
lecture on the prospects of miniaturisation, “There’s plenty of room at the bottom“
1968
Stöber, Fink, Bohn
Synthesis of monodisperse silica, described before in 1956 by Kolbe in PhD thesis
1974
Taniguchi, Norio
“Nanotechnology” for processing of separation, consolidation, and deformation of materials by one atom or one molecule
1985
Smalley, Curl, Kroto
Buckminster fullerenes, e.g. C60 carbon
1986
Binnig, Quate, Gerber
construction of an atomic force microscope AFM, 1981 Binnig, Rohrer construction of a scanning tunnelling microscope
1989
Eigler, Schweizer
IBM logo written with 35 Xe-atoms on Ni
1991
Iijima
Carbon nanotubes
Disperse Systems dispersed phase
continuous phase gaseous
gaseous
liquid
solid
bubbles
porous solids xerogels, aerogels, cryogels
liquid
solid
aerosol
fog
aerosol smoke
emulsion
porous solids with liquids
microemulsion
hydrogels, alcogels
nanoparticles
composite materials
Nanoparticles: Numerous fields of application • Ceramics for membranes
• Sun creams
• Batteries and fuel cells
• Electronics, lasers, displays
• Catalysis and electrolysis reactors
• Photochromic coatings
• Gas storage
• Automotive coatings
• Protective coating of plastic
• Bioceramics, drug carriers
surfaces • Thermal and scratch protection • Reflection avoidance in windows
• Magnetic nanoparticles for hydrothermal treatment of cancers
bioavailability quantum effect strong surface effects 10-9 m
10-6 m
0.001
0.01
0.1
1
10
100
1µm
1000 nm
polymers proteins metal powders viruses, DNA ceramics tobacco smoke aerosols nanoparticle for life sciences
Sizes and properties of nanoparticle materials
Properties of nanoparticles
The outstanding importance of nanoparticles and nano structured systems can be ascribed to :
1. particle size bioavailability : in water non soluble substances can be transported as nanoparticles in an organism of human beings (application in life sciences)
2. large specific surface area strong surface area effects (e.g. reactivity, high energy of surface area, adsorption, higher solubility, lower melting point etc.)
3. change of electronic properties quantum effects of particles < 10 nm, importance for electronic and optoelectronic application
Characterisation of nanoparticles Nanoparticles and nanopowders are characterised by : particle size (1 nm – 100 nm)
Laser diffraction
Optical spectroscopy
Light scattering
Transmission electron microscopy (TEM) Scanning electron microscopy (SEM) large specific surface area
Gas adsorption (BET – Brunauer, Emmett, Teller) (BJH – Barrett, Joyner, Halenda)
(electrostatic) stabilisation
Zeta - potential
Preparation of silica nanoparticles Process : Sol - Gel - Synthesis - Precipitation Chemical reactions : Hydrolysis - Polycondensation
Hydrolysis : suspension in ethanol
Si(OC2H5)4
+
4 H2O
Si(OH)4
+
4 C2H5OH
pH 11 - 12 (NH3)
Tetra ethyl orthosilicate (TEOS)
Silicon tetra hydroxide
Ethanol
Polycondensation : suspension in ethanol
Si(OH)4
nano- SiO2 (Sol) + pH 11 - 12 (NH3)
Silicon tetra hydroxide
Principles :
Silica
nucleation, nucleus growth, Ostwald ripening, (agglomeration) Controlled double jet precipitation (CDJP)
2 H2O
Principle of dynamic light scattering correlation function Laser
Optical Unit
g (τ)= e-2·D·K²·τ
Sample
Optics
Photo multiplier
D
diffusion constant
K
scattering light vector
τ
delay time
correlator
Stokes – Einstein – equation
Optical unit of photon correlation spectroscopy d= I(t)
g(τ )
small particle
large particle small particle
large particle time
Scattering light intensity – time – function
kB ⋅T 3⋅ π⋅η⋅ D
d
particle diameter
kB
Boltzmann constant
T
absolute temperature
η
dynamical viscosity
τ
auto correlation function
Particle size frequency distribution q0 (log d) in nm-1
Particle size distribution of titanium dioxide nanoparticles method: dynamic light scattering method 4.0
instrument : Zetamaster (Malvern)
3.0
detector angle
90 °
wave length
630 nm
temperature
25 °C
2.0
Particle size distribution of titanium dioxide after peptization within 24 hours 1.0
Mean particle diameter: 5 10 50 Particle diameter in nm
100
dm, 3 = 18.6 nm (volume density) dm, 0 = 12.0 nm (number density)
Determination of the zeta – potential for nanoparticle characterisation
cathode
anode
Charge distribution around a moving particle in an electrical field
laser beams
interference pattern scattering light detector
particle
Detection of particle velocity in an interference pattern system of two lasers
Stabilisation of titanium dioxide nanoparticles in suspension
Zeta - Potential in mV
40
Zeta - Potential in mV
30
20
10
0 0,0
0,5
1,0
1,5
2,0
2,5
pH - value of suspension Zeta potential of TiO2 ranging from + 20 mV to + 40 mV for a pH < 3.0
Stabilisation of titanium dioxide nanoparticles in suspension
OH2+ + H+ OH2+
Ti
OH2+
O-
OH
OH2+
OH
Ti
acid
OH
+OHO-
Ti
base OH
O-
Zeta potential of TiO2 ranging from + 20 mV to + 40 mV for a pH < 3.0
O-
Processes for the production of nanoparticles
Production processes
in a liquid phase
Precipitation process
in a gaseous phase
Aerosol process
• in homogeneous solution
• Flame hydrolysis
• in surfactant based systems
• Spray pyrolysis
Sol - gel process Hydrothermal process
Chemical and physical processes for nano particle synthesis Process:
precipitation – in homogeneous solution synthesis of silver bromide
Chemical reaction: (gelatine)
Ag+ +
Br -
AgBr Silver
bromide
Principle: precipitation (Controlled double jet precipitation CDJP - technique)
AgNO3
ions KBr
complex and cluster formation embryos cluster formation nuclei growth primary particle growth, coagulation, ... colloids Precipitation homogeneous solution - controlled double jet precipitation CDJP nucleus formation, followed by growth reaction and Ostwald ripening Particle size:
AgBr : 7 nm - 60 nm, particle system dependent a lot of syntheses on a laboratory scale
T. Sugimoto : J. Colloid Interface Sci. 150 (1992) 208 - 225
Precipitation reactions in homogeneous solution
AgBr – nanoparticle, produced by CDJ - technique at pBr 2,0 (a), 2,8(b), 4,0 (c)
Images (scanning electron microscopy) of typical monodisperse nanoscale oxides by conversion of metal alkoxides in alcoholic solution
Precipitation reactions in homogeneous solution
Images (transmission electron microscopy left - scanning electron microscopy right) of CdS – nanoparticles, produced in homogeneous solution at 26°C by CDJ - technique
Image (scanning electron microscopy) of PbS – nanoparticles, produced in homogeneous solution at 26°C by CDJ - technique
Precipitation reactions in homogenous solutions
Scanning electron microscopy image of aluminium(III)-oxide, 100°C, left Transmission electron microscopy image of chromium(III)-oxide, 75°C, right, produced by precipitation reaction in homogeneous solution
Images (scanning electron microscopy) of zinc oxide, 90°C, pH 8,8 (left) and 150°C, pH 13,3 (right), produced by precipitation reaction in homogeneous solution
Precipitation reactions in surfactant based systems
Images (scanning electron microscopy) of mullite (aluminium silicate) and barium titanate, produced by precipitation in surfactant based systems (microemulsion)
Image (transmission electron microscopy) of silica, produced by precipitation in surfactant based systems (microemulsion)
Chemical and physical processes for nanoparticle synthesis
process:
sol - gel process / precipitation synthesis of silica (Kolbe (1956), Stöber, Fink, Bohn (1968))
chemical reaction : hydrolysis :
ethanolic suspension
Si(OC2H5)4 + 4 H2O
pH 11 – 12 (NH3)
tetraethylorthosilicate
Si(OH)4 + 4 C2H5OH silicon tetra hydroxide ethanol
polycondensation : Si(OH)4
ethanolic suspension
SiO2
pH 11 – 12 (NH3)
silicon tetra hydroxide
+
2 H2O
silica
principle: nucleus formation, followed by growth reaction and Ostwald ripening, controlled double jet precipitation CDJP
ammonia / water ethanol
0,2 M tetraethylorthosilicate ethanol particle 500 nm – 10 μm
tetraethylorthosilicate / ethanol
products : titanium (IV) – oxide , aluminium oxide, zirconium (IV) - oxide nuclear power materials ThO2, UO2, PuO2 advantages:
often mono disperse, spherical particles of controlled size
disadvantages: reactions have to be carried out with low particle concentrations, low production output
Sol - gel synthesis / precipitation reaction
Image (transmission electron microscopy) of Stöber particles (silica)
Image (scanning electron microscopy) of Stöber particles (silica)
Morphology of nanoparticles Si(OH)4 Dimers pH < 7 or pH 7 - 10 with salts
Cycles Particles
pH 7 – 10 without salts
1 nm 5 nm 10 nm 30 nm 3 – dimensional gel network
100 nm Sol (Stöber – Particles) Brinker, C.J.; Scherer, G.W. : Sol-Gel-Science, The Physics and Chemistry of Sol-Gel-Science, Academic Press, San Diego, 1990
Sol - gel process dehydratisation chemical reaction Precursor
Aerosil
chemical reaction Sol
drying Gel
coating
organic suspension
dipping
surfactants
spherical particle in gel structure
Calcination
thin layer structure
Aerogel drying
Xerogel
Calcination
Calcination
powder
ceramics
C.J. Brinker, G.W. Scherer : Sol - Gel Science
Aerosol processes
Images (transmission electron microscopy) of different oxides, produced by direct oxidation in an arc
