Harnessing Evanescent Waves in UV-Irradiated TiO2-Coated Quartz Optical Fibers Improves Pollutant Degradation in Water

Abstract

Coupling TiO2-coated quartz optical fibers (TiO2-QOFs) with LEDs shows potential in degrading organics in water. Conventional TiO2-QOFs with thick and compact coatings are inefficient to degrade organic pollutants due to refraction losses. The research focuses on manipulating coating strategies to increase the generation of evanescent waves, which react more efficiently with the coated TiO2, which shows a crystal structure at anatase/rutile of 85/15. Through the use of dip-coating methods, TiO2 can be effectively deposited on quartz optical fibers, leveraging the principle of electrostatic attraction. By decreasing TiO2 dip-coating concentrations from 200 to 10 mg/L, dip-coating duration from 2 to 0.5 h, and coating cycles from 3 to 1, TiO2 patchiness on quartz fibers was reduced by 50–60%, enhancing the formation of more interspaces between the fiber surfaces and the coatings, which in turn allowed over 90% of evanescent waves in the TiO2-QOFs. The evanescent wave-dominated TiO2-QOFs irradiated by 275 nm UV-LED exhibited methylene blue degradation rate constants at around 0.03 h−1 and quantum yields greater than unity, indicating a highly efficient interaction between the evanescent wave and the surface coatings. These findings offer significant insights into optimizing the utilization of evanescent waves in TiO2-QOFs for pollutant degradation by regulating the coating structures.