TiO2-coated quartz optical fibers (TiO2-QOFs) coupled with UV-LEDs enable the photocatalytic degradation at the needed locations where light is inaccessible. However, there is still room for improvement in energy utilization since a portion of refracted light is dissipated out without being used. This work investigates quantum yields of carbamazepine (CBZ) degradation by three TiO2-QOFs coated with 0.0015~0.0257 mg/cm TiO2, and explores the relationship between light transmission in the TiO2-QOF interface and the different quantum yields. When degrading CBZ in water, the amounts of radiant energy dissipated into TiO2 layers decreased by ~25.3% with decreasing TiO2 from 0.0257 to 0.0015 mg/cm at the same degradation efficiency, and the amounts changed with changing of the external media (water vs. air). These findings suggest the involvement of evanescent waves, which return to the optical fibers if not used. A model was built to describe the radiant energy of refracted light and evanescent waves as functions of the coverage of TiO2 layers on the fiber surface (A) and the average interspace distance between surfaces of the optical fibers and coated TiO2 layers (Z). A decrease of ~92% in A and an increase of ~6 times in Z reduced the radiant energy of refracted light by ~92% and increased that of evanescent waves dissipated into the TiO2 layers by ~6.5 times. The model also showed that the quantum yield by the evanescent wave can be 1.35 times higher than that by the refracted light. These findings suggest that loading less TiO2 onto the optical fiber surface reduces A and increases Z, which in-return promotes the generation of evanescent waves and reduces light refraction. The radiant energy of evanescent waves, if not used, returns to the optical fibers and thus gives a higher quantum yield and enhances the energy efficiency in pollutant degradation by TiO2-QOFs.

Evanescent waves generated in TiO2-coated quartz optical fibers coupled with UV-LEDs improve quantum yields of pollutant degradation

2019 Fall National Meeting

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