Destruction of Aqueous Phase Organic Pollutants Using Ultraviolet Light-Emitting Diodes and Photocatalysis

The photocatalytic degradation of dyes (Allura Red AC and Brilliant Blue FCF) in water using ultraviolet light-emitting diodes (UV-LED) and an immobilized titanium dioxide (TiO₂) as a photocatalyst was investigated using a novel bench-top Teflon® reactor. This reactor has been uniquely designed to contain low-powered UV-LEDs combined with TiO₂ immobilized substrates. A sol-gel method was used to anneal TiO₂ to three different substrates: standard microscope quartz slides, quartz cylinders, and borosilicate beads. Scanning electron microscopy (SEM), Raman spectroscopy, and mass comparisons techniques were performed for TiO₂ characterization. High-resolution images confirmed the presence and morphology of TiO₂ on the substrates. These analyses demonstrated the TiO₂ coating was uniform and predominantly had the anatase crystalline phase structure. The slide had the largest individual TiO₂ surface area of 0.187 mg cm⁻². Results indicated the size, shape, packing, and stirring properties were factors that determine overall photocatalytic properties and degradation inside the reactor. The adjusted rate constants for an ideal completely mixed batch reactor (CMBR) were 1.69 * 10⁻³, 5.39 * 10⁻³, and 4.46 * 10⁻³ min⁻¹ for the slides, beads, and cylinders, respectively. Beads were the best-performing substrate as determined by the greatest degradation rate for the model organic compound, Allura Red AC. The beads and cylinders showed 58 and 51% degradation of Allura Red AC, respectively. Actinometry experiments revealed cylinders had the largest fluence rate of 0.0782 J·L⁻¹ s⁻¹. Optimization of the sol-gel application method and reactor operating parameters was performed to maximize the degradation rate and the overall degradation of Allura Red AC. Electric energy per order (EEO) was calculated and optimized at 9.20, 10.5, and 12.7 kWh·m⁻³ order⁻¹ for the glass beads, cylinders, and slides, respectively. Graphical abstract ᅟ