Photocatalytic degradation of Reactive Red 22 in aqueous solution by UV-LED radiation

Photocatalytic processes using TiO2 as a catalyst have attracted extensive attention for decomposition of organic contaminants. The determination of optimum reactor design and operational conditions are the major concerns for the development and potential application of the photocatalytic process. Various photoreactor types, photocatalyst arrangements, light sources, and operation conditions were reported. This study was focused on the application of the ultraviolet light emitting diode (UV-LED) as the UV light source for the photocatalytic decomposition of Reactive Red 22 (RR 22). The temporal behavior of the photocatalytic decomposition of RR 22 in aqueous solution by the UV-LED/TiO2 with a rectangular planar fixed-film reactor operated in a recirculation mode was studied under various conditions including initial dye concentration, periodic illumination, light intensity, and arrangements of TiO2 coating. The decomposition of RR 22 in aqueous solution by TiO2 photocatalytic processes with the UV-LED was found to be technically feasible with a high TiO2 coated weight (1.135 g) and low pH value (pH 2). A Langmuir—Hinshelwood-type kinetic equation was adequate for modeling the photocatalytic decomposition of RR 22 by the UV-LED/TiO2 photocatalytic processes. The experimental results indicated that the photonic efficiency with periodic illumination was much higher than those with continuous illumination. The photonic efficiencies with the quartz–liquid–catalyst (QLC) arrangement were higher than those with the quartz–catalyst–liquid (QCL) arrangement for experiments conducted at lower applied light intensity; however, the photonic efficiencies for these two arrangements were nearly identical for experiments conducted at higher light intensities.