Synthesis of metallic Ag and semiconducting ZnS nanoparticles in self-assembled polyelectrolyte templates

1
Synthesis of metallic Ag and semiconducting ZnS
nanoparticles in self-assembled polyelectrolyte
templates

• M.Logar, B.Jancar and D.Suvorov

Institute Jožef Stefan, Advanced materials
department, Slovenia
2
Introduction

• Inorganic nanoparticle properties
• Large surface / volume ratio
• Quantum confinement effect

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

3
Polyelectrolyte multilayer (PEM) template
formation

• Layer-by-layer
• self- assembly method

Driving force for the multilayer buildup
Electrostatic interaction between appositively
charged polyelectrolyte
PAA
PAH
4

Properties of the PEM film

• type of the PE

• pH value of the PE assembly

Weak polyelectrolyte - PAA
COO- f (pH)

• Thickness controllable in nanometer range

pH3.5
250
200
pH3.0
150
PEM thickness (nm)
pH2.5
Substrate effect
100
50
0
0
5
10
15
number of polyelectrolyte bilayers
5
In-situ synthesis of inorganic nanoparticles

O
C
O- m
Metal salt solution
pH5.5
Metal ion
Ag, Zn 2
Reduction/sulfidication
Recharge
Inorganic nanoparticle
Ag, ZnS
6
In-situ Ag nanoparticle synthesis
pH 2.5 pH 3.0 pH 3.5
Ag nanoparticle
PEM film
PS substrate
HAADF - STEM image
7
Volume fraction and size of the Ag nanoparticles
in PEM are pH- dependent
Ag particle concentrations (particles/cm3)
Average Ag particle diameter (nm)
Ag volume fraction ()
pH value of PEM assembly
6.91018
4.51.5
2.5
33
5.21018
6.11.6
27
3.0
1.11018
7.42.5
22
3.5
8
UV-vis absorption spectrum
Red shift
Surface plasmon resonance effect
pH2.5
pH3
pH3.5
9
Volume fraction and size of the Ag nanoparticles
in PEM are n- dependent
Red shift
Ag particle concentrations (particles/cm3)
Average Ag particle diameter (nm)
Ag volume fraction ()
Number of the reaction cycles
6.91018
4.51.5
33
1.0
4.11018
6.71.6
65
3.0
10
In-situ ZnS nanoparticle synthesis
pH 2.5 n 1 da 3.2 0.3 nm
NaCl solution
20 nm
Zn acetate solution pH5.5
pH 3.0 n 1 da 4.1 0.9 nm
Zn 2
n
Na2S solution
ZnS nanoparticles in PEM
ZnS nanoparticle
20 nm
11
ZnS nanoparticle crystal structure
pH 2.5 n 2 da 3.7 0.4 nm
Wurtzite - hexagonal
100
110
111
202
Sphalerite - cubic
SAED pattern
BF TEM image
12
UV-vis absorption spectrum
Quantum confinement effect
Red shift
Red shift
pH
n
13
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