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