Enhancing acid orange II degradation in ozonation processes with CaFe₂O₄ nanoparticles as a heterogeneous catalyst

This study used CaFe₂O₄ nanoparticles as a catalyst for ozonation processes to degrade Acid Orange II (AOII) in aqueous solution. The study compared heterogeneous catalytic ozonation (CaFe₂O₄/O₃) with ozone treatment alone (O₃) at different pH values (3-11), catalyst dosages (0.25-2.0 g L^-1), and initial AOII concentrations (100-500 mg L^-1). The O₃ alone and CaFe₂O₄/O₃ systems nearly completely removed AOII's color. In the first 5 min, O₃ alone had a color removal efficiency of 75.66%, rising to 92% in 10 min, whereas the CaFe₂O₄/O₃ system had 81.49%, 94%, and 98% after 5, 10, and 20 min, respectively. The O₃ and CaFe₂O₄/O₃ systems degrade TOC most efficiently at pH 9 and better with 1.0 g per L CaFe₂O₄. TOC removal effectiveness reduced from 85% to 62% when the initial AOII concentration increased from 100 to 500 mg L^-1. The study of degradation kinetics reveals a pseudo-first-order reaction mechanism significantly as the solution pH increased from 3 to 9. Compared to the O₃ alone system, the CaFe₂O₄/O₃ system has higher k values. At pH 9, the k value for the CaFe₂O₄/O₃ system is 1.83 times higher than that of the O₃ alone system. Moreover, increasing AOII concentration from 100 mg L^-1 to 500 mg L^-1 subsequently caused a decline in the k values. The experimental data match pseudo-first-order kinetics, as shown by R² values of 0.95-0.99. AOII degradation involves absorption, ozone activation, and reactive species production based on the existence of CaO and FeO in the CaFe₂O₄ nanocatalyst. This catalyst can be effectively recycled multiple times.