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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. The control over the particle shape, size and concentration. Introduction.

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slide1

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

The control over the particle shape, size and concentration

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
polyelectrolyte multilayer pem template formation
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

slide4

Properties of the PEM film

  • type of the PE
  • pH value of the PE assembly

Weak polyelectrolyte - PAA

[COO- ]= f (pH)

  • Thicknesscontrollable in nanometer range

pH=3.5

250

200

pH=3.0

150

PEM thickness (nm)

pH=2.5

Substrate effect

100

50

0

0

5

10

15

number of polyelectrolyte bilayers

in situ synthesis of inorganic nanoparticles
In-situ synthesis of inorganic nanoparticles

O

C

O- m+

Metal salt solution

pH=5.5

Metal ion

Ag+, Zn 2+

Reduction/sulfidication

Recharge

Inorganic nanoparticle

Ag, ZnS

in situ ag nanoparticle synthesis
In-situ Ag nanoparticle synthesis

Ag acetate solution

pH=5.5

n

Ag+

Ag

nanoparticle

NaBH4 solution

pH = 2.5

pH = 3.0

pH = 3.5

Ag nanoparticle

PEM film

PS

substrate

HAADF - STEM image

volume fraction and size of the ag nanoparticles in pem are ph dependent

pH=2.5

pH=3.5

pH=3.0

Volume fraction and size of the Ag nanoparticles in PEM are pH- dependent

pH value of PEM assembly

Ag volume fraction (%)

Average Ag particle diameter (nm)

Ag particle concentrations

(particles/cm3)

2.5

4.5±1.5

6.9∙1018

33

3.0

27

6.1±1.6

5.2∙1018

3.5

22

7.4±2.5

1.1∙1018

uv vis absorption spectrum
UV-vis absorption spectrum

0,022

0,020

0,018

0,016

pH value of PEM assembly

SPR wavelenght

Λmax (nm)

FWHM (nm)

0,014

Absorbance [a.u.]/nm

0,012

0,010

2.5

110

440

0,008

3.0

427

97

0,006

3.5

414

90

0,004

0,002

0,000

200

400

600

800

Wavelenght [nm]

Red shift

Surface plasmon resonance effect

pH=2.5

pH=3

pH=3.5

volume fraction and size of the ag nanoparticles in pem are n dependent

4,0

3,5

3,0

Absorbance (arbitrary units)

2,5

n

2,0

1,5

1,0

0,5

0,0

200

400

600

800

1000

1200

Wavelength (nm)

pH=2.5

n=1

pH=2.5

n=3

Volume fraction and size of the Ag nanoparticles in PEM are n- dependent

Red shift

Number of the reaction cycles

Ag volume fraction (%)

Average Ag particle diameter (nm)

Ag particle concentrations

(particles/cm3)

1.0

33

4.5±1.5

6.9∙1018

3.0

65

6.7±1.6

4.1*1018

in situ zns nanoparticle synthesis
In-situ ZnS nanoparticle synthesis

pH = 2.5

n = 1

da= 3.2 ± 0.3 nm

NaCl solution

20 nm

Zn acetate solution

pH=5.5

pH = 3.0

n = 1

da= 4.1 ± 0.9 nm

Zn 2+

n

Na2S solution

ZnS nanoparticles in PEM

ZnS

nanoparticle

20 nm

slide11

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

slide12

UV-vis absorption spectrum

0.025

0.8

0.020

0.7

absorbance (a.u.)/ nm

0.6

0.015

0.5

absorbance (a.u.)

0.4

0.3

0.010

220

240

260

280

300

320

wavelength (nm)

0.2

0.1

0.0

220

240

260

280

300

320

wavelength (nm)

Quantum confinement effect

Red shift

Red shift

pH

n

conclusion s
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