Implanted fiber-optic sensor for analyzing catalytic reactions and kinetics in Au/TiO2 systems

Abstract

In heterogeneous photocatalytic reactions, understanding the catalytic processes and its kinetics is crucial for catalyst design and performance evaluation. However, real-time monitoring the interface reaction such as pollutant degradation remains a challenge. In this study, the implantable optical fiber sensors with real-time catalytic monitoring capability were created by modifying the sensing surface with Au/TiO₂ heterojunction photocatalysts. As pollutants adsorb and degrade on the catalytic interface, surface refractive index changes occur. The evanescent field on the sensing surface covers the photocatalytic layer, enabling in situ and real-time monitoring of surface refractive index changes for catalytic reaction analysis. The flexible fiber-optic Surface Plasmon Resonance (SPR) sensors can be directly immersed in a pollutant solution Rhodamine 6 G (R6G) to monitor its degradation rate and kinetic processes. It reveals that the optimal size of Au nanoparticles (AuNPs) can facilitate efficient electron transfer at heterojunction catalysts. The time-resolved resonance wavelength shift further elucidates the degradation kinetics of photocatalysts with varying Au/TiO₂ composition. The fiber-optic sensor demonstrated comparable accuracy to conventional UV-Vis spectrophotometry in assessing TiO₂ photocatalytic degradation (84.13 % vs. 81.25 % efficiency, respectively), with a relative deviation less than 5 %. However, unlike the discrete data collected by traditional UV-Vis methods, the miniaturized and implantable fiber-optic SPR sensor can collect data every 0.25 s. It demonstrates real-time monitoring capability and enables more accurate evaluation of dynamic reaction processes. This in situ sensing strategy provides new insights into photocatalytic mechanisms and shows great potential for guiding catalyst design and optimization.