In-Situ SERS Monitoring of SPR-Catalyzed Coupling Reaction of p-Nitroiodobenzene on Noble Metal Nanoparticles
Surface-enhanced Raman spectroscopy(SERS)derived from surface plasmon resonance(SPR)has become an effective tool for surface analysis because of its high sensitivity and surface specificity.Moreover,SPR can induce and stimulate the catalytic reaction on the surface of noble metal nanostructures.The combination of SERS and SPR is beneficial to in-situ monitoring of SPR catalytic reaction at the surface interface of noble metals.This paper used p-nitroiodobenzene(PNIB)as a probe molecule to demonstrate SERS's capability in characterizing catalytic coupling reactions.The effects of laser power,wavelength,and substrate on the catalytic coupling were investigated,and the mechanism of the coupling reaction was proposed preliminary.The results revealed that azo compound 1,2-bis(4-iodophenyl)diazene was produced by SPR-catalyzed coupling reaction of PNIB on the surface of gold nanoparticle monolayer film(Au MLF).The equilibrium of the reaction was reached with short duration by increasing laser power,i.e.,from 200 s at 3 mW to about 50 s at 15 mW.The coupling efficiency was increased to about doubled.On the Au@Ag nanoparticle film,the coupling efficiency is increased by about 10 times,and the coupling efficiency is significantly dependent on the excitation wavelength and SERS substrates.The reaction activity order of different substrate surfaces is Au@Ag(532 nm)＞Au@Ag(638 nm)＞Au(638 nm).It demonstrated that the hole-trapping agent sodium sulfite increase the coupling efficiency of the reaction by about an order of magnitude.It indicated that the reaction of PNIB coupling to 1,2-bis(4-iodophenyl)diazene catalyzed by SPR is a reduction reaction induced by hot electrons.
Surface-enhanced Raman spectroscopyp-NitroiodobenzeneSPR catalysisCoupling reactionNoble metal nanoparticles
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