Different behaviors in the transformation of PATP adsorbed on Ag or Au nanoparticles investigated by surface-enhanced Raman spectroscopy - a study of the effects from laser energy and annealing

Abstract

In order to explore the key role of surface plasmon resonance (SPR) and active (3)O2 for the chemical transformation to 4,4-dimercaptoazobenzene (DMAB) from p-aminothiophenol (PATP) adsorbed on Ag or Au NPs, we systematically investigated the laser wavelength and temperature dependent surface-enhanced Raman spectra of PATP capped Ag and Au NPs. DMAB can be easily observed at the 514.5nm laser for Ag NPs but at the 632.8nm laser for Au NPs, indicating that a suitable energy level is necessary for the formation of DMAB. The tendency is consistent with the wavelength dependent SPR properties of Ag or Au NPs accordingly. With the energy provided by annealing, the transformation of PATP to DMAB is much easier on Ag NPs at a lower temperature, and more DMAB can be observed at the same temperature, compared to the case of Au NPs under the same condition. It is mainly due to the active (3)O2 on Ag surfaces could be more easily formed than that on Au surfaces.

Keywords: Annealing effect; Chemical transformation; Laser energy effect; Surface-enhanced Raman spectroscopy.