In situ surface-enhanced Raman spectroscopic monitoring electrochemical and surface plasmon resonance synergetic catalysis on dehydroxylation of PHTP at Ag electrodes

Surface plasmon resonance (SPR)-driven heterogeneous catalytic reactions have attracted considerable interests. However, the application of SPR was restricted in few types of surface reaction; the extension of SPR-catalyzed reaction still remains significant challenge. The introduction of additional external fields is expected to generate the synergetic effect for improving the performance of SPR catalytic reaction. Herein, the roughened Ag electrode played as a substrate for introducing the second external field, that is, electrochemical control. A probe molecule, p-hydroxythiophenol (PHTP), was preanchored onto Ag electrodes and surface-enhanced Raman spectroscopy was employed to monitor the surface processes. It demonstrated that the PHTP underwent the dehydroxylation reaction to produce the thiophenol (TP) by the appropriate excitation line and potentials. It disappeared on Ag roughened electrodes without electrochemical control or on a smooth charged surface attached with shell-isolated nanoparticles. It suggested that the dehydroxylation reaction was contributed by the synergetic effects of localized SPR and applied potential. The results revealed that the efficiency of dehydroxylation was critically depended on wavelength and power of laser, potential, as well as solution pH. The hydrogen sources were essential for dehydroxylation and protonated hydroxyl group promoted the process for producing TP, thus, the dehydroxylation of PHTP was more favorable in acidic solution than that in a neutral case, while it was inhibited completely in alkaline environment. With the appropriate potential, the size of the nanostructures on Ag electrode surface and the corresponding surface plasmon band resulted in the higher efficiency with matched laser wavelength at about 532 nm. The synergetic effects of SPR and potential allowed the extension of the SPR catalysis to a new catalogue of surface reaction, that is, dehydroxylation. It was beneficial to develop the SPR catalysis as a promising approach in the surface chemistry.