Raman Spectroscopy for Characterizing Gold Nanoparticles on Polyaniline

Raman Spectroscopy for Characterizing Gold Nanoparticles on Polyaniline (PANI) Thin Films Yi-Hsiu Chen, Cai-Wei Lin, Chun-Guey Wu, and Bor-Chen Chang Department of Chemistry National Central University Chung-Li 32001, TAIWAN

Acknowledgements Students Yi-Hsiu Chen (M. S. 2006) In Collaboration with Cai-Wei Lin Financial Supports: National Science Council, TAIWAN National Central University Prof. Chun-Guey Wu

Polyaniline (PANI) Structures Pernigraniline Base (PNB) Violet oxidation reduction Emeraldine Base (EB) Blue base oxidation acid Protonated Emeraldine Salt (ES) Green reduction Leucoemeraldine Base (LEB) Pale Yellow Mac. Diarmid and Epstein, Synth. Met. 29, E 409 (1989)

Gold (Au) Nanoparticles n n Green Oxidations of primary alcohols. Catalysts: Au/Ti. O 2 or Au-Pd/Ti. O 2. [G. J. Hutchings and coworkers, Nature 437, 1132 (2005) and Science 311, 362 (2006). ] We tried the oxidation of benzyl alcohol with Au/PANI as the catalyst. O 2 Benzyl Alcohol O 2 Benzaldehyde Benzoic Acid

Use HPLC to Monitor the Oxidation Internal Standard： Benzyl Alcohol 1, 3, 5 -benzenetricarboxylic acid HPLC Chromatogram Benzoic Acid Benzaldehyde

Catalysis Study Au-CHCl 3/PANI has a better catalytic activity than Au-H 2 O/PANI. n The temperature-dependency experiments (273 K to 353 K) show a smaller activation energy of Au-CHCl 3/PANI (ca. 6 k. J mol-1) than that of Au-H 2 O/PANI (ca. 23 k. J mol-1). n

Scanning Electron Microscopy (SEM) Images Au-H 2 O/PANI 31. 4 ± 5. 0 nm Au nanoparticles prepared in an aqueous solution. Diameter (nm) Au-CHCl 3/PANI Au nanoparticles prepared in a chloroform solution. 249 ± 50 nm Diameter (nm)

Questions? n n The size distributions in SEM images are INCONSISTENT with the catalytic activities. SEM shows only the Au nanoparticles on surface and these particles may not be the real catalytic centers. Small angle X-Ray diffraction (XRD) study shows the particle sizes of the embedded Au nanoparticles are roughly the same for differently preparation methods. Why? Spectroscopy?

Quinoid ring C＝C stretch. 1620 1581 1511 1542 1582 1622 1513 1445 EB PNB 1473 1515 1542 1621 1444 1335 1270 1196 1208 598 (c) Au-H 2 O/PANI after reaction 1339 1240 1269 599 544 802 (b) Au-H 2 O/PANI before reaction 1189 1243 801 596 542 (a) PANI 541 C＝N stretch. 1186 Raman Spectra for Au-H 2 O/PANI Benzoid ring C ＝C stretch. LEB

Quinoid ring C＝C stretch. 1620 1583 1621 1581 1511 1542 1587 1620 1245 1341 1342 (c) Au-CHCl 3/PANI after reaction 1208 798 (b) Au-CHCl 3/PANI before reaction 1190 1516 1445 1339 801 596 542 (a) PANI 1240 1269 1186 Raman Spectra for Au-CHCl 3/PANI Benzoid ring C ＝C stretch. C＝N stretch. EB PNB LEB

Au-H 2 O/PANI Au-CHCl 3/PANI The bonding between Au nanoparticles and PANI is Before reaction stronger in Au-CHCl 3/PANI than in Au-H 2 O/PANI. After reaction Raman shift (cm-1)

Summary Gold nanoparticles prepared by different solvents exhibit distinctively different catalytic activities. n Raman spectroscopy reveals the bonding differences between different gold nanoparticles. n Anisotropy Raman spectroscopy? A probe of morphology? n