Photoelectrochemical Degradation of 4-Nitrothiophenol and In Situ Surface-Enhanced Raman Spectroscopy Monitoring Based on Au Nanoparticles Grown on Templated TiO₂

Coupled photoelectrochemistry and surface-enhanced Raman spectroscopy (SERS) provide a unique platform for monitoring photocatalyzed and photoelectrocatalyzed reactions. The combination of catalysis and detection platforms typically requires sophisticated synthesis procedures, which make them prohibitive to implement. In this work, we have designed and fabricated a controllable array of Au nanoparticles (NPs) on a templated TiO2 substrate for the simultaneous photoelectrochemical degradation and in situ electrochemical-SERS monitoring, where 4-nitrothiophenol (4NTP) was used as a molecular probe. The effect of the dimension of the Au NPs was studied, showing that the array of 42.2 nm diameter Au NPs exhibited the best degradation kinetics of 4NTP at 0.017 min–1 and the highest SERS response for detection and monitoring. Polarization modulation infrared reflection absorption spectroscopy and density functional theory calculations were further employed to understand the 4NTP response to the applied electric field. It was found that the angle of adsorbed 4NTP was highly dependent on the applied potential, resulting in changes in the effective dipole moment of the molecule. The implementation of this combined platform provides insights into surface reaction kinetics for photocatalyzed reactions on metal oxide surfaces.