Application of Fe_0.66Cu_0.33@Al(OH)₃ catalyst from fluidized-bed crystallizer by-product for RB5 azo dye treatment using visible light-assisted photo-Fenton technology

This study aims to explore the reusability of wastewater treatment by-product for photo-Fenton process to treat an organic pollutant model. The optimal condition, reactive oxygen species (ROS), and kinetic approach in photo-Fenton process was discussed. The Metal oxide crystal pellets from are a by-product of the Fluidized-Bed Crystallization (FBC) process and can be used as a catalyst in the Photo-Fenton process. Electroplating wastewater containing iron and copper was treated via the FBC process using granulated Al(OH)₃ as carrier seeds. The binary oxide of FeOOH and Cu₂O on the Al(OH)₃ surface (Fe_0.66Cu_0.33@Al(OH)₃) was identified as the FBC by-product after characterization using FTIR and XPS analysis. In the photo-Fenton process, visible light from a fluorescence lamp with a wavelength of 400–610 nm was chosen as an irradiation source. Oxalic acid was added as chelating agent to form photosensitive iron oxalate species and hydrogen peroxide was applied as oxidant to generate active radical to decolorize and mineralize RB5 synthesized solution (100 mg/L). The operating conditions including the oxalic acid to pollutant ratio ([OA]₀/[RB5]₀) of 4.5–13.0, reaction pH (pHr) of 3–7 and initial to theoretical hydrogen peroxide molar ratio [H₂O₂]₀/[ H₂O₂]_theoretical of 35%–120% were optimized. Under the optimal conditions, pH_r = 5.0; [H₂O₂]₀/[RB5]₀ at 75% stoichiometric and [OA]₀/[RB5]₀ = 9, the RB5 is almost completely decolorized after 210 min of operation and the mineralization efficiency is 58%. The contribution of •OH, O₂^•-, and O₂¹ to the Photo-Fenton system was determined using ESR analysis with the addition of DMPO and TEMP as spin trap agents. The kinetic analysis reveals the observed rate constants k_RB5, k_OA and k_R from fitting are 0.0120, 0.0054 and 0.0001 M⁻¹s⁻¹, respectively.