Galvanic replacement approach for bifunctional polyacrylonitrile/Ag-M (M = Au or Pd) nanofibers as SERS-active substrates for monitoring catalytic reactions

SERS has been applied to monitor different types of catalytic reactions on the surface of metal NPs in recent years, which requires bifunctional metal structures with plasmonic properties as well as catalytic activity. Monitoring catalytic reactions with SERS technology in previous reports was usually performed in metal solution, using metal electrodes or on a glass/silica substrate with an immobilized metal. Here, we report a general approach for preparing novel SERS-active substrates which are used to monitor catalytic reactions. The polyacrylonitrile (PAN)/Ag-M (M = Au or Pd) bimetallic nanofibrous mats are prepared through galvanic replacement reactions of Ag with Au or Pd on the surface of electrospun PAN/Ag nanofibers. The composition of Ag and Au or Pd could be tuned by changing the concentration of the metal solution used for replacement. The PAN/Ag0.60Au0.40 and PAN/Ag0.90Pd0.10 bimetallic nanofibrous mats exhibit both excellent SERS and catalytic activities. The reduction of 4-nitrothiophenol (4-NTP) to the corresponding to 4-aminothiophenol (4-ATP) on PAN/Ag0.60Au0.40 and PAN/Ag0.90Pd0.10 bimetallic nanofibrous mats are monitored by SERS technology. The SERS signals of the reaction intermediate, 4,4'-dimercapto-azobenzene(4,4'-DMAB), are observed as the reaction proceeds with time.