Abstract
Coupling photocatalyst-coated optical fibers (P-OFs) with LEDs shows potential in environmental applications. Here we report a strategy to maximize P-OF light usage and quantify interactions between two forms of light energy (refracted light and evanescent waves) and surface-coated photocatalysts. Different TiO2-coated quartz optical fibers (TiO2-QOFs) are synthesized and characterized. An energy balance model is then developed by correlating different nano-size TiO2 coating structures with light propagation modes in TiO2-QOFs. By reducing TiO2 patchiness on optical fibers to 0.034 cm2/cm2 and increasing the average interspace distance between fiber surfaces and TiO2 coating layers to 114.3 nm, refraction is largely reduced when light is launched into TiO2-QOFs, and 91% of light propagated on the fiber surface is evanescent waves. 24% of the generated evanescent waves are not absorbed by nano-TiO2 and returned to optical fibers, thus increasing the quantum yield during degradation of a refractory pollutant (carbamazepine) in water by 32%. Our model also predicts that extending the TiO2-QOF length could fully use the returned light to double the carbamazepine degradation and quantum yield. Therefore, maximizing evanescent waves to activate photocatalysts by controlling photocatalyst coating structures emerges as an effective strategy to improve light usage in photocatalysis.
Highlights
Coupling photocatalyst-coated optical fibers (P-OFs) with LEDs shows potential in environmental applications
To test our hypothesis, we evaluate the ability of TiO2-coated quartz optical fibers (TiO2-QOFs), which have novel tunable surface “patches” of TiO2 layers, to promote evanescent wave generation to activate TiO2 (Fig. 1a) and degrade a refractory pollutant by photocatalytic generated hydroxyl radicals (HO) in bulk solution and pores in TiO2 coating layers (Fig. 1b)
From the experiments and model, we find that 91% of the radiant energy delivered to the low patchiness TiO2-QOFs propagates on the fiber surfaces as evanescent waves, and the behavior of evanescent waves interacting with the TiO2 coating results in a saving of 23% for the radiant energy delivered to the TiO2-QOFs
Summary
Coupling photocatalyst-coated optical fibers (P-OFs) with LEDs shows potential in environmental applications. As the area-specific TiO2 coating density decreased from TiO2-QOF-High to TiO2-QOF-Med to TiO2-QOF-Low, the generated evanescent wave energy (EE,g)—i.e., the sum of EE;dis[0] and EE,return,—increased from 0.44 to 0.56 to 0.69J, and the generated refracted light energy (ER,g)—i.e., the sum of ER;dis[0] and ER,reflect,—decreased from 0.32 to
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