Application of response surface methodology in optimizing MOF5@Fe3O4 catalyst for activating peroxymonosulfate in the degradation of reactive black 5 dye

Magnetic nanoparticles (Fe₃O₄) were loaded onto metal-organic framework (MOF-5) as an activator for peroxymonosulfate (PMS) in the decomposition of the dye reactive black 5 (RB5). Modeling and optimization of operational parameters were performed using response surface methodology coupled with central composite design (RSM-CCD). The maximum removal efficiency of RB5 was predicted under laboratory conditions, including pH of 11, catalyst dosage of 1 g/L, RB5 concentration of 10 mg/L, temperature of 50 °C, and reaction time of 60 min. High values of confidence coefficient (R²) and F-value indicated that the present model could explain most of the data and could also be used to predict efficiency within a design space. Also, the adsorption capacity was equal to 99.2 mg/g. The efficiency of the MOF-5@Fe₃O₄/PMS system in removing RB5 was higher than that of standalone systems such as adsorption and PMS. Stability tests revealed that the synthesized catalyst could be reused for six consecutive reaction cycles with a negligible decline in dye removal efficiency (<4.3 %) and total organic carbon (TOC) removal (<5.50 %). Trapping experiments using ethanol and tert-butyl alcohol scavengers confirmed the presence of sulfate (SO₄^•-) and hydroxyl (^•OH) radicals in dye decomposition. The removal efficiency of COD and the BOD₅/COD ratio improved with increasing catalytic time, reaching 87.93 % and 0.84, respectively, at 120 min. The LC₅₀ value of untreated and treated RB5 solutions was examined using Daphnia magna, and findings showed an increase in the LC₅₀ value of the treated solution.