From polymer precursors to metal oxides [Elektronische Ressource] : preparation and characterization of zinc oxide and ZnO-based mixed metal oxide nanoparticles / vorgelegt von Guangqiang Lu

Informations

• Publié par: johannes_gutenberg-universitat_mainz
• Publié le: 01 janvier 2007
• Nombre de lectures: 10
• Langue: English
• Poids de l'ouvrage: 11 Mo

Extrait

From Polymer Precursors to Metal Oxides:
Preparation and Characterization of Zinc Oxide and ZnO-Based
Mixed Metal Oxide Nanoparticles




Dissertation zur Erlangung des Grades
„Doktor der Naturwissenschaften“
am Fachbereich Chemie, Pharmazie und Geowissenschaftern
der Johannes-Gutenberg-Universität in Mainz




vorgelegt von


Guangqiang Lu
geboren in Anhui / P. R. China

Mainz, 2006
































Tag der mündlichen Prüfung: Dezember 11, 2006.



Die vorliegende Arbeit wurde im Zeitraum von

Oktober 2003 bis Oktober 2006 am Max-Planck-

Institut für Polymerforschung in Mainz unter der

Anleitung von Herrn Prof. Dr. G. Wegner

angefertigt.






































For my families
List of Abbreviations and Symbols

Chemicals
AA acrylic acid
BPO benzoylperoxide
ES5P zinc-loaded polymer sample using Span 60 as emulsifier
ES8P2 zinc-loaded polymer sample using Span 80 as emulsifier
MMO mixed metal oxide
PAA polyacrylic acid
PAA5K polyacrylic acid with molecular weight of 5000
PANH 5K ammonium polyacrylate with molecular weight of 5000 4
SDS sodium dodecyl sulphate
Span 60 sorbitane monostearate
Span 80 sobitan monooleate
ZnCoPA zinc-cobalt polyacrylate
ZnMgPA zinc-magnesium polyacrylate
ZnPA zinc polyacrylate
ZnPA5K zinc polyacrylate with molecular weight of 5000
ZnCoO zinc-cobalt oxide
ZnMgO zinc-magnesium oxide


Methods and related acronyms
AAS Atomic absorption spectroscopy
AFM Atomic force microscopy
CW-EPR Continuous wavelength-electron paramagnetic resonance spectroscopy
CELREF Free software used for refinement of XRD data
DLS Dynamic light scattering
DSC Differential scanning calorimetry
DTGA First-order differential TGA
EA Elementary analysis
EDX Energy dispersive X-ray spectroscopy
EPR Electron paramagnetic resonance spectroscopy
FTIR Fourier transfer infrared spectroscopy
IHRTEM High-resolution TEM
LS Light scattering
MAS-NMR NMR spectroscopy measured under rotation of the sample at magic angle of
o 54.7
PL Photoluminescence
31 31PNMR P nuclear magnetic resonance spectroscopy
SEM Scanning electron microscopy
SQUID Superconducting quantum interference device
TEM Transmission electron microscopy
TGA Thermogravimetric analysis
TG-MS TGA coupled with mass spectra
XRD X-ray diffraction
UV/Vis Ultraviolet / visible absorption spectroscopy
BSE Primary backscattered electrons
DMS Dilute magnetic semiconductor
DVLO Theory of colloidal stability developed by Derjaguin, Verwey, Landau and
Overbeek
FFT Fast Fourier transform
FWHM Full width at half maximum
HCP Hexagonal close packing
JCPDS Joint Committee on Powder Diffraction Standards
NBE Near-band-edge emission
SE Secondary electrons
SDC Shallow donor center
TADC Theory of average dielectric constant

Symbols
β Heating rate (in Ch.2)
Full width at half maximum (in Ch.4)
η Viscosity
η Reduced Viscosity red
λ Wavelength (nm)
λem Emission wavelength
λexc Excitation wavelength
II-6µm Micrometer (10 m)
-9nm Nanometer (10 m)
Π Osmotic pressure
∆p Laplace pressure
∆νa-s Frequency difference of carboxylate antisymmetric and symmetric stretching
oθ Angle ( )
ζ Zeta-potential
κ Debye length (in Ch.2)
Susceptibility (in Ch.4)
a Lattice parameter
c Concentration (in Ch.2)
Lattice parameter (in Ch.4)
f Filling factor
g g-factor of EPR (in Ch.2, 4)
Shape factor (in Ch.5)
t Time
tM 3d-transition metal ions
x Composition of mixed metal oxide
Ea Activation energy
L Crystallite size or coherence length hkl
M Magnetization
M Number averaged molecular weight n
N Avogadro’s number A
O Interstitial Oxygen i
R Hydrodynamischer Radius h
TTemperature
T Curie temperature C
T Peak Temperature of DTGA P
V Oxygen vacancies O
V Zinc vacancy Zn
Zn Zinc interstitial i
III Abstract
Abstract

We report on a strategy to prepare metal oxides including binary oxide and mixed metal
oxide (MMO) in form of nanometer-sized particles using polymer as precursor. The process
consists of wet chemistry, precipitation and pyrolysis three steps, which starts from aqueous
solution to form a metal polyacrylate precursor under mild preparation conditions. The metal
polyacrylate precursor is purified by precipitation into a nonsolvent. The polymer precursor
could be redissolved and loaded with different kinds of metal ions. The purified cation-loaded
complex in dry form is calcined at relatively low temperature to give nanosized crystals of
binary oxide or MMO powders. The composition of the precursor polymer defines the
stoichiometry of the mixed metal oxide. Moreover, the polymer-metal salt solution can also
be processed by spin coating, drop casting or similar procedure to obtain polymer precursor
films for production of nanocrystalline metal oxide films.

We chose zinc oxide as the model system to prove the concept of this strategy due to the
simple (hexagonal) crystal structure of zinc oxide and its increasing interests in industrial
application and fundamental research. The zinc polyacrylate (ZnPA) precursor is amorphous
as confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM).
Dynamic light scattering (DLS) results reveal that zinc cations mainly form intra-polymer
complexes with polyacrylate. Viscosity and UV results show that the precursor was
effectively purified during precipitation into the nonsolvent acetone, which proves that the
zinc source of ZnO formation is the polymer precursor and not the free zinc ion or other zinc-
containing species.
The transformation from polymer precursor via degradation, nucleation followed by
crystallization into ZnO crystal during pyrolysis was investigated by means of XRD,
thermogravimetric analysis (TGA) and FTIR spectroscopy. The XRD results show that the
oprecursor remains amorphous when heated even over 370 C, while the polymer precursor
from Pechini method and some zinc salts like zinc nitrate hexahydrate, zinc acetate dihydrate
oconvert to zinc oxide at about 300 C. The TGA results exhibit three weight loss stages in the
o o opyrolysis process i.e. 150-260 C , 260-350 C and 350-460 C. By combination with mass
spectra (MS), it is revealed that the main weight loss is due to escape of H O and CO . The 2 2
as-synthesized ZnO consists of mainly individual particles with a diameter around 40 nm with
a narrow size distribution as shown by scanning electron microscopy (SEM). Due to Oswald
oripening, the particles grow to 100 nm at 650 C. The effects of various parameters like
I Abstract
polymer molecular weight and zinc content in the precursor on the crystal morphology were
studied too. The as-synthesized ZnO surface absorbs some organic groups like OH- and C-O
indicated from FT-IR spectra. The photoluminescence (PL) and electron paramagnetic (EPR)
properties of the material are investigated, too. It is generally assumed that the PL emission
originates from oxygen defect centres located on the particle surface or in the bulk.

Employing this method, ZnO nanocrystalline films are fabricated via pyrolysis of a zinc
polyacrylate precursor film on solid subst