Electrochemical and Plasmonic Photochemical Oxidation Processes of para-Aminothiophenol on a Nanostructured Gold Electrode

Abstract

The analysis of plasmonic photoelectrochemical reactions on nanostructured noble metal electrodes is an attractive field, but little is known about the detailed competition between the photochemical and electrochemical reaction processes, product selectivity, and synergistic kinetics. In this work, para-aminothiophenol (PATP), as a probe molecule in surface-enhanced Raman spectroscopy (SERS), was used to investigate electrochemical and photochemical oxidation on nanostructured gold electrodes. Using electrochemical SERS (EC-SERS) and density functional theory (DFT) calculations, the sophisticated oxidation process and the selectivity of PATP oxidation (electrochemical oxidation and photochemical oxidation) under different conditions were determined. Moreover, based on the provided oxidation pathways of PATP on the gold electrode, the oxidation kinetics of PATP was studied by COMSOL simulation and a spectroscopic tool. The increasing rate constant of cationic radical formation due to hot holes at a high laser power has induced the selective generation of photochemical products. This work built a system to modulate the reaction selectivity and will inspire photoelectrochemical kinetic research in other plasmonic metal electrode–adsorbate systems of nanostructures.

Reversible Plasmonic Switch in a Molecular Oxidation Catalysis Process

“…27 Concerning plasmonically mediated oxidation catalysis, in most cases, the PNPs were themselves the catalyst 16,17,19,21,22,30 with only a few exceptions 26,31 �many times utilizing high lightintensity. So far, most reported cases concern plasmonic systems coupled with semiconductors, 32−35 electrochemical and/or photochemical oxidations, 36,37 or gas-phase processes at high temperatures. 38 In the present work, we report the study of a wellcharacterized oxidation catalysis process, performed by a molecular catalyst, LMn II , where L is a Schiff base ligand, 39 in the presence of Ag 0 @SiO 2 PNPs.…”

“…Concerning plasmonically mediated oxidation catalysis, in most cases, the PNPs were themselves the catalyst ,,,,, with only a few exceptions , many times utilizing high light-intensity. So far, most reported cases concern plasmonic systems coupled with semiconductors, − electrochemical and/or photochemical oxidations, , or gas-phase processes at high temperatures …”

Revisit of the plasmon-mediated chemical transformation ofpara-aminothiophenol

“…26–31 SERS spectra of pATP measured on a metal surface are known to be significantly different from the normal Raman spectrum of the molecule; several unexpected peaks are observed in the Raman fingerprint region between 800–1600 cm −1 . There are two competitive mechanisms proposed to explain the origin of these anomalous peaks: the plasmon-mediated reaction 32–37 and the Herzberg–Teller (HT) type vibronic coupling effect. 38–43 The former is due to the fact that frequencies of these peaks are quite resemble to those of aromatic azo compounds in trans configuration.…”

“…Indeed, there are several reports on photo-induced evolution of these peaks during SERS experiments, which has strongly supported this mechanism. 26,37 On the other hand, the latter is based on the fact that the relative intensities of the anomalous peaks vary resonantly with the excitation photon energy; when the excitation photon energy is close to the energy difference between the Fermi level of the substrate metal and the LUMO of pATP, the resonant electronic transition between these two states, i.e. , charge-transfer (CT) resonance, is weakly allowed via the HT-type vibronic coupling, leading to the resonant intensity gain in the coupled vibration modes.…”

“…Importantly, the similarity between the SERS spectrum of pATP and that of trans -DMAB has been examined only in the fingerprint region between 800–1600 cm −1 , where group vibrations of molecules appear. 32–37 It is necessary to confirm it in a wider range of frequencies to exclude the possibility of coincidental similarity between them. In low-frequency region below 400 cm −1 including so-called terahertz (THz) region, surface-adsorbate (external) vibrations or large-amplitude vibrations are present although SERS detection of such low-frequency vibrations is still challenging.…”