Remote and in-situ monitoring of plasmon-induced catalysis reaction by fiber SERS probes

Abstract

Monitoring chemical reaction processes is of great significance in the study of the reaction mechanisms, and the optimization or control of reaction conditions. In this work, we demonstrate a novel monitoring method of chemical reactions using fiber SERS probes. The high-performance fiber SERS probes are prepared by the laser-induced evaporation self-assembly method (LIESAM), where lots of Au-nanorod clusters are deposited on the fiber facet for providing large SERS enhancement factor and good hot electron catalytic property. The remote and in-situ monitoring of chemical reactions is achieved through simply dipping the probes into the reaction solution. Taking the classic reduction reaction from 4-nitrothiophenol (4-NTP) to 4-aminothiophenol (4-ATP) by sodium borohydride (NaBH₄) as an example, the time-resolved SERS spectra collected by probes clearly reflect the reduction procedure of the disappearance of 4-NTP, the formation of intermediate product 4,4′-dimercaptoazobenzene (4,4′-DMAB) and the emergence of the final product 4-ATP. In addition, a new Raman peak at 1366 cm⁻¹ is observed when the 4-NTP is reduced in an H₂ atmosphere generated by the hydrolysis of NaBH₄, corresponding the formation of a new intermediate product 4-nitrosothiophenol (4-NSTP). Also, the monitoring of the oxidation reaction from 4-ATP to 4,4′-DMAB is demonstrated using fiber SERS probes. Considering that all the SERS spectra are acquired with a portable Raman spectrometer and the fiber has a very low transmission loss, this work provides a good platform for remote, on-site and in situ monitoring of chemical reactions in liquid environments and thus finds important applications in scientific research and industrial scenarios.