Fig. 3. Color and TOC degradation efficiency for AOII by ozone alone (a and b) and CaFe₂O₄ nanocatalytic ozone (c and d) at various solution pH values. Conditions: [AOII] = 200 mg L⁻¹, catalyst dosage = 1.0 g, contact time = 50 min, and reaction temperature = 25 ± 2 °C.