Nanoparticle Technology

Transcription

1 Nanoparticle Technology

2 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).

3 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. C 60 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

4 Disperse Systems dispersed continuous phase phase gaseous liquid solid gaseous bubbles porous solids xerogels, aerogels, cryogels liquid aerosol fog emulsion microemulsion porous solids with liquids hydrogels, alcogels solid aerosol smoke nanoparticles composite materials

5 Nanoparticles: Numerous fields of application Ceramics for membranes Batteries and fuel cells Catalysis and electrolysis reactors Gas storage Protective coating of plastic surfaces Thermal and scratch protection Reflection avoidance in windows Sun creams Electronics, lasers, displays Photochromic coatings Automotive coatings Bioceramics, drug carriers Magnetic nanoparticles for hydrothermal treatment of cancers

6 bioavailability quantum effect strong surface effects 10-9 m 10-6 m µm nm polymers proteins metal powders viruses, DNA ceramics tobacco smoke aerosols nanoparticle for life sciences Sizes and properties of nanoparticle materials

7 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

8 Characterisation of nanoparticles Nanoparticles and nanopowders are characterised by : particle size (1 nm 100 nm) Laser diffraction Light scattering Optical spectroscopy 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

9 Preparation of silica nanoparticles Process : Sol - Gel - Synthesis - Precipitation Chemical reactions : Hydrolysis - Polycondensation Hydrolysis : Polycondensation : suspension in ethanol Si(OC 2 H 5 ) H 2 O Si(OH) C 2 H 5 OH ph (NH 3 ) Tetra ethyl orthosilicate (TEOS) Silicon tetra hydroxide Ethanol suspension in ethanol Si(OH) 4 nano- SiO 2 (Sol) + 2 H 2 O ph (NH 3 ) Silicon tetra hydroxide Silica Principles : nucleation, nucleus growth, Ostwald ripening, (agglomeration) Controlled double jet precipitation (CDJP)

10 Principle of dynamic light scattering Laser Optics Sample Photo multiplier Optical Unit correlator correlation function g (τ)= e -2 D K² τ D diffusion constant K scattering light vector τ delay time I(t) Optical unit of photon correlation spectroscopy small particle large particle time g( τ ) large particle small particle Scattering light intensity time function auto correlation function τ Stokes Einstein equation d d = k B T 3 π η D particle diameter k B Boltzmann constant T absolute temperature η dynamical viscosity

11 Particle size distribution of titanium dioxide nanoparticles Particle size frequency distribution q0 (log d) in nm Particle diameter in nm method: dynamic light scattering method instrument : Zetamaster (Malvern) detector angle 90 wave length 630 nm temperature 25 C Particle size distribution of titanium dioxide after peptization within 24 hours Mean particle diameter: d m, 3 = 18.6 nm (volume density) d m, 0 = 12.0 nm (number density)

12 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

13 Stabilisation of titanium dioxide nanoparticles in suspension 40 Zeta - Potential in mv Zeta - Potential in mv 0 0,0 0,5 1,0 1,5 2,0 2,5 ph - value of suspension Zeta potential of TiO 2 ranging from + 20 mv to + 40 mv for a ph < 3.0

14 Stabilisation of titanium dioxide nanoparticles in suspension OH 2 + OH O - + H + OH Ti +OH - OH + + OH Ti 2 OH 2 O - O - acid base Ti OH 2 + OH O - Zeta potential of TiO 2 ranging from + 20 mv to + 40 mv for a ph < 3.0

15 Processes for the production of nanoparticles Production processes in a liquid phase in a gaseous phase Precipitation process in homogeneous solution in surfactant based systems Aerosol process Flame hydrolysis Spray pyrolysis Sol - gel process Hydrothermal process

16 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) AgNO 3 KBr ions 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)

17 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

18 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

19 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

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21 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)

22 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(OC 2 H 5 ) H 2 O ph (NH 3 ) Si(OH) C 2 H 5 OH tetraethylorthosilicate silicon tetra hydroxide ethanol polycondensation : ethanolic suspension Si(OH) 4 ph (NH 3 ) SiO H 2 O silicon tetra hydroxide silica principle: nucleus formation, followed by growth reaction and Ostwald ripening, controlled double jet precipitation CDJP ammonia / water ethanol 0,2 M tetraethylorthosilicate ethanol tetraethylorthosilicate / ethanol particle 500 nm 10 μm products : titanium (IV) oxide, aluminium oxide, zirconium (IV) - oxide nuclear power materials ThO 2, UO 2, PuO 2 advantages: often mono disperse, spherical particles of controlled size disadvantages: reactions have to be carried out with low particle concentrations, low production output

23 Sol - gel synthesis / precipitation reaction Image (transmission electron microscopy) of Stöber particles (silica) Image (scanning electron microscopy) of Stöber particles (silica)

24 Morphology of nanoparticles Si(OH) 4 Dimers ph < 7 or ph 7-10 with salts Cycles Particles 1 nm ph 7 10 without salts 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

25 Sol - gel process dehydratisation chemical reaction chemical reaction drying Aerosil Precursor Sol Gel Aerogel coating dipping organic suspension surfactants drying spherical particle in gel structure Xerogel Calcination Calcination Calcination thin layer structure powder ceramics C.J. Brinker, G.W. Scherer : Sol - Gel Science

26 Aerosol processes Images (transmission electron microscopy) of different oxides, produced by direct oxidation in an arc