Sulfate Radical-Mediated Degradation of Sulfadiazine by CuFeO2 Rhombohedral Crystal-Catalyzed Peroxymonosulfate: Synergistic Effects and Mechanisms

Copper-iron bimetallic oxides have shown great potential for powerful radical production by activating peroxides. In this work, CuFeO2 rhombohedral crystals (RCs) were synthesized and used as heterogeneous catalysts for peroxymonosulfate (PMS) activation under various conditions. Sulfadiazine, a widely used veterinary sulfonamide, was used as a target pollutant to evaluate the efficiency of this combination. The results showed that of all the catalysts tested, the CuFeO2 RCs had the greatest reactivity. Under conditions of 0.1 g L(-1) CuFeO2 RCs and 33.0 μM PMS, the nearly complete degradation of sulfadiazine occurred within 24 min. A synergistic catalytic effect was found between solid Cu(I) and Fe(III), probably due to the accelerated reduction of Fe(III). The two activation stages that produced different radicals (hydroxyl radicals followed by sulfate radicals) existed when solid Cu(I) was used as the catalyst. The CuFeO2 RCs had a higher PMS utilization efficiency than CuFe2O4, probably because the Cu(I)-promoted reduction of solid Fe(III). A total of 10 products were identified, and their evolution was explored. On the basis of the evidence of oxidative product formation, we proposed four possible pathways of sulfadiazine degradation.