Synthesis of metallic Ag and semiconducting ZnS nanoparticles in self-assembled polyelectrolyte...
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Transcript of Synthesis of metallic Ag and semiconducting ZnS nanoparticles in self-assembled polyelectrolyte...
Synthesis of metallic Ag and semiconducting ZnS nanoparticles in self-assembled polyelectrolyte
templates
M.Logar, B.Jančar and D.Suvorov
Institute Jožef Stefan, Advanced materials department, Slovenia
Introduction
Inorganic nanoparticle properties Large surface / volume ratio Quantum confinement effect
The control over the particle shape, size and concentration
In-situ nanoparticle synthesis methodology
- nanoparticles are synthesized in-situ in polymer template
- the surrounding polymer chains limits particle aggregation
- the size and volume fraction of the particles in composite films is manipulated by varying the synthesis conditions
Polyelectrolyte multilayer (PEM) template formation
Layer-by-layer
self- assembly method
Electrostatic interaction between appositively charged polyelectrolyte
Driving force for the multilayer buildup
PAA PAH
type of the PE pH value of the PE assembly
Thickness controllable in nanometer range
pH=2.5
pH=3.0
pH=3.5
Substrate effect
0
50
100
150
200
250
0 5 10 15
number of polyelectrolyte bilayers
PE
M t
hic
knes
s (
nm
)
Properties of the PEM film
Weak polyelectrolyte - PAA
[COO- ]= f (pH)
=
=
Metal salt solution
Reduction/sulfidicationRecharge
Metal ion
Inorganic nanoparticle
pH=5.5
In-situ synthesis of inorganic nanoparticles
Ag, ZnS
Ag+, Zn 2+
CO
O- m+
In-situ Ag nanoparticle synthesis
n
Ag
nanoparticle
Ag+
NaBH4 solution
=
=
Ag acetate solution
pH=5.5
HAADF - STEM image
pH = 2.5
pH = 3.0
pH = 3.5
PEM film
PS substrate
Ag nanoparticle
Volume fraction and size of the Ag nanoparticles in PEM are pH- dependent
1.1∙10187.4±2.5223.5
5.2∙10186.1±1.6273.0
6.9∙10184.5±1.5 332.5
Ag particle concentrations(particles/cm3)
Average Ag particle diameter (nm)
Ag volume fraction (%)
pH value of PEM assembly
pH=2.5
pH=3.0
pH=3.5
UV-vis absorption spectrum
pH=2.5
pH=3
pH=3.5
Red shift
3.5
97
FWHM (nm)SPR wavelenghtΛmax (nm)
pH value of PEM assembly
90414
4273.0
110 4402.5
200 400 600 800
0,000
0,002
0,004
0,006
0,008
0,010
0,012
0,014
0,016
0,018
0,020
0,022
Ab
sorb
an
ce [
a.u
.]/n
m
Wavelenght [nm]
Surface plasmon resonance effect
n
200 400 600 800 1000 1200
0,0
0,5
1,0
1,5
2,0
2,5
3,0
3,5
4,0
Ab
so
rba
nc
e (
arb
itra
ry u
nit
s)
Wavelength (nm)
Volume fraction and size of the Ag nanoparticles in PEM are n- dependent
pH=2.5
n=1
4.1*10186.7±1.6653.0
6.9∙10184.5±1.5331.0
Ag particle concentrations(particles/cm3)
Average Ag particle
diameter (nm)
Ag volume fraction (%)
Number of the reaction cycles
pH=2.5
n=3
Red shift
In-situ ZnS nanoparticle synthesis
n
ZnS
nanoparticle
Zn 2+
Na2S solution
=
=
Zn acetate solution
pH=5.5
NaCl solution
pH = 2.5
n = 1
da= 3.2 ± 0.3 nm
ZnS nanoparticles
in PEM
pH = 3.0
n = 1
da= 4.1 ± 0.9 nm
20 nm
20 nm
pH = 2.5
n = 2
da= 3.7 ± 0.4 nm
SAED pattern
BF – TEM image
Wurtzite - hexagonal
Sphalerite - cubic
[100]
[110]
[111]
[202]
ZnS nanoparticle crystal structure
UV-vis absorption spectrum
220 240 260 280 300 320
0.010
0.015
0.020
0.025
ab
so
rba
nc
e (
a.u
.)/
nm
wavelength (nm)
pH n
Red shift Red shift
220 240 260 280 300 3200.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
ab
so
rba
nc
e (
a.u
.)
wavelength (nm)
Quantum confinement effect
Conclusions
The thickness of PEM template is controlled in nanometer range by: pH value of the PE solution and number of adsorbed layers
With the In-situ synthesis method the control over the
inorganic particle volume fraction and size is obtained by: pH value of the PEM assembly and number of the reaction cycles - By increasing the pH value and number of the reaction cycles larger size and lower volume fraction of inorganic nanoparticles in composite films were obtained
Control over the optical properties of the composite film