Enhanced persulfate activated sono-catalytic degradation of brilliant green dye by magnetic CaFe2O4 nanoparticles: Degradation pathway study, assessment of bio-toxicity and cost analysis

Abstract In this study, CaFe2O4 nanoparticles were successfully synthesized by a chemical precipitation technique and applied in persulfate (PS) activated sono-assisted degradation of brilliant green (BG) dye from aqueous medium. Vibrating-sample magnetometer (VSM) analysis revealed that CaFe2O4 nanoparticles have manifested magnetic properties, which aided in effortless separation of nanoparticles from aqua matrix after treatment. More than 99% BG dye degradation was observed under dye concentration of 50 mg/L, catalyst dose of 0.5 g/L, PS dose of 200 mg/L and in an ultrasound (US) irradiation time of 15 min. However, US alone treatment had shown BG degradation of only 40.7% whereas the efficiency was enhanced to ∼89% upon addition of CaFe2O4 in US system. The PS activated sono-catalytic dye degradation (US + CaF + PS) process was optimized using response surface methodology (RSM) with four experimental variables, i.e., CaFe2O4 catalyst dose, PS dose, dye concentration, and sonication time. The quadratic model developed using RSM was found to be successful in optimizing the process variables (R2∼0.983). The scavenging effects observed with sodium chloride and sodium sulphate on US + CaF + PS process have reduced BG removal efficiency from 98% to 93% and 89%, respectively, which affirmed that the free radicals play the fundamental role in BG degradation. In US + CaF + PS process, BG dye (m/z ∼ 385) was degraded to simpler products having m/z ratio of 215, 113 and 73. Moreover, the microtox bioassay results indicated that the formed intermediate products were non-toxic in nature, i.e., toxicity of BG dye reduced from 90.58 to 1.24% after treatment with US + CaF + PS system. The treatment cost of BG dye solution varied between 131.85 and 922.02 USD/Kg of BG dye removed; however, the RSM based model has predicted the optimal BG dye removal of 99.57% with treatment cost of 330.82 USD/Kg of BG dye removed. Finally, the outcome of reusability study revealed that the synthesized nanoparticles were recyclable with a removal efficiency of 80.1% even after five consecutive cycles.