Electrochemical reduction of SPR-catalysate 4,4′-dimercaptoazobenzene at [BMIm]BF4/Ag interface probed by SERS

Abstract The surface plasmon resonance (SPR) catalyzed reaction has attracted considerable attention due to its promising application in heterogeneous catalysis. The acquirements on mechanism of the conversion reaction are still in challenge. It was found that the cyclic conversion of para-aminothiophenol (PATP) and 4,4′-dimercaptoazobenzene (DMAB) was critically dependent on the interfacial environments, such as hydrogen, oxygen and water, which were of the fundamental issues in electrochemistry. Here, the in situ surface enhanced Raman spectroscopy (SERS) combined with electrochemical control was developed to investigate the cyclic conversion of PATP and DMAB at the interface of [BMIm]BF 4 /Ag electrode and to probe the interfacial structure of water. The surface-catalyzed coupling reaction of PATP commonly occurred to produce DMAB in a fast rate with the illumination of laser. The results revealed that water played the vital role in the reduction of DMAB. The expected reduction of DMAB was absent in the extremely negative potential due to the lack of the free water at the interface in the “dried” [BMIm]BF 4 . The similar experiments were performed in the [BMIm]BF 4 /H 2 O mixtures with the water molar fraction of 0.01, 0.1, 0.3, 0.5, 0.7 and 0.9 respectively. The trace water in the [BMIm]BF 4 /H 2 O mixture ( x w x w  = 0.7–0.9). By this strategy, the electrochemical reduction of DMAB could be served as the probe to monitor the water structure in the [BMIm]BF 4 /H 2 O mixtures, and it was believed that SERS could be developed as the powerful tool for monitoring the interfacial reaction and to resolve the interfacial structure in RTILs, particularly for the water structure.