Raman Spectroscopy for Characterizing Raman Spectroscopy for Characterizing Gold Nanoparticles on Polyaniline Gold Nanoparticles on Polyaniline (PANI) Thin Films(PANI) Thin Films

Yi-Hsiu Chen, Cai-Wei Lin, Chun-Guey Wu, and Yi-Hsiu Chen, Cai-Wei Lin, Chun-Guey Wu, and

Bor-Chen ChangBor-Chen Chang

Department of ChemistryDepartment of ChemistryNational Central UniversityNational Central UniversityChung-Li 32001, TAIWANChung-Li 32001, TAIWAN

AcknowledgementsAcknowledgements

Cai-Wei LinYi-Hsiu Chen (M.S. 2006)

Prof. Chun-Guey Wu

Students In Collaboration with

Financial Supports:National Science Council, TAIWANNational Central University

Pernigraniline Base (PNB)Violet

Emeraldine Base (EB)Blue

NH NH NH NHn

NH NH N Nn

H2N NH N N

n

H AA

N N N Nn

reductionoxidation

reductionoxidationacidbase

Protonated Emeraldine Salt (ES)Green

Leucoemeraldine Base (LEB)Pale Yellow

Polyaniline (PANI) StructuresPolyaniline (PANI) Structures

MacDiarmid and Epstein, Synth. Met. 29, E409 (1989)

Gold (Au) NanoparticlesGold (Au) Nanoparticles

Green OxidationsGreen Oxidations of primary alcohols of primary alcohols.. Catalysts: Catalysts: Au/TiOAu/TiO22 or Au-Pd/TiO or Au-Pd/TiO22. [G. J. Hutchings and co-. [G. J. Hutchings and co-

workers, workers, NatureNature 437437, 1132 (2005) and , 1132 (2005) and ScienceScience 311311, , 362 (2006).]362 (2006).]

We tried the oxidation of benzyl alcohol with We tried the oxidation of benzyl alcohol with Au/PANI as the catalyst. Au/PANI as the catalyst.

CH2OH CHO COOH

O2 O2

Benzyl Alcohol Benzaldehyde Benzoic Acid

Use HPLC to Monitor the OxidationUse HPLC to Monitor the Oxidation

HPLC Chromatogram

CH2OH

Benzyl Alcohol

CHO

Benzaldehyde

COOH

Benzoic AcidInternal Standard：

1,3,5-benzenetricarboxylic acid

HOOC

COOH

COOH

Catalysis StudyCatalysis Study

Au-CHClAu-CHCl33/PANI has a better catalytic activity /PANI has a better catalytic activity

than Au-Hthan Au-H22O/PANI.O/PANI. The temperature-dependency experiments The temperature-dependency experiments

(273K to 353K) show a smaller activation (273K to 353K) show a smaller activation energy of Au-CHClenergy of Au-CHCl33/PANI (ca. 6 kJ mol/PANI (ca. 6 kJ mol-1-1) than ) than

that of Au-Hthat of Au-H22O/PANI (ca. 23 kJ molO/PANI (ca. 23 kJ mol-1-1).).

Scanning Electron Microscopy (SEM) Images

0 100 200 300 400 500 6000

10

20

30

40

50

Diameter (nm)

249 ± 50 nm

0 10 20 30 40 50 600

10

20

30

40

50 31.4 ± 5.0 nm

Diameter (nm)

Au-H2O/PANI

Au-CHCl3/PANI

Au nanoparticles prepared in an aqueous solution.

Au nanoparticles prepared in a chloroform solution.

Questions?Questions? The size distributions in SEM images are The size distributions in SEM images are

INCONSISTENTINCONSISTENT with the catalytic activities.with the catalytic activities. SEM shows only the Au nanoparticles on surface and SEM shows only the Au nanoparticles on surface and

these particles may not be the real catalytic centers. these particles may not be the real catalytic centers. Small angle X-Ray diffraction (XRD) study shows Small angle X-Ray diffraction (XRD) study shows

the particle sizes of the embedded Au nanoparticles the particle sizes of the embedded Au nanoparticles are roughly the same for differently preparation are roughly the same for differently preparation methods.methods.

Why? Spectroscopy?Why? Spectroscopy?

400 600 800 1000 1200 1400 1600 1800

Raman shift (cm-1)

1513

1622

1621

1511 16

2015

81

1515

1582

Raman Spectra for Raman Spectra for Au-HAu-H22O/PANIO/PANI

Benzoid ring C＝ C stretch.

Quinoid ring C＝ C stretch.

C＝ N stretch.

EB

PNB

PNB

LEB

544

541

542

134412

43

1269

1208

1189

1542

1270

1196

1186

1542

1444

599

1473

1335

598

1445

1339

801

596

802

1240

(a) PANI

(b) Au-H2O/PANI before reaction

(c) Au-H2O/PANI after reaction

400 600 800 1000 1200 1400 1600 1800

Raman shift (cm-1)

1620

1587

1342

1208

1621

1516

1341

124511

90

1583

1445

1511

133912

69

1186

59654

2

1620

1581

1240

1542

Benzoid ring C＝ C stretch.

Quinoid ring C＝ C stretch.

C＝ N stretch.

EB

PNB

PNB

LEB

801

798

(a) PANI

(b) Au-CHCl3/PANI before reaction

(c) Au-CHCl3/PANI after reaction

Raman Spectra for Raman Spectra for Au-CHClAu-CHCl33/PANI/PANI

400 600 800 1000 1200 1400 1600 1800

After reaction

Before reaction

400 600 800 1000 1200 1400 1600 1800

Raman shift (cm-1) Raman shift (cm-1)

PANI

Au-H2O/PANI Au-CHCl3/PANI

The bonding between Au nanoparticles and PANI is stronger in Au-CHCl3/PANI than in Au-H2O/PANI.

SummarySummary

Gold nanoparticles prepared by different Gold nanoparticles prepared by different solvents exhibit distinctively different catalytic solvents exhibit distinctively different catalytic activities.activities.

Raman spectroscopy reveals the bonding Raman spectroscopy reveals the bonding differences between different gold differences between different gold nanoparticles.nanoparticles.

Anisotropy Raman spectroscopy? A probe of Anisotropy Raman spectroscopy? A probe of morphology? morphology?