Catalytic ozonation for degradation of sulfamethazine using NiCo₂O₄ as catalyst

In this study, spinel NiCo₂O₄ was prepared, characterized, and used for catalytic ozonation of SMT. The performance of NiCo₂O₄ in SMT mineralization was systematically evaluated. The results showed that NiCo₂O₄ could significantly enhance the mineralization of SMT over a wide initial pH range of 3.0-9.0. The mineralization rate of SMT increased with the increase in the dosage of NiCo₂O₄ and O₃ concentration, while the initial concentration of SMT (from 10 mg/L to 40 mg/L) had no obvious influence on the removal efficiency of TOC, indicating that the SMT mineralization was mainly affected by the mass transfer. Furthermore, according to the result of the determination of OH, NiCo₂O₄ could undoubtedly improve the generation of OH, the quenching test confirmed that OH played an important role in TOC removal in ozonation process. Moreover, the XPS spectra of as-prepared and used NiCo₂O₄ catalyst showed that Co ions might indirectly promote the catalytic ozonation process as the Lewis acid sites, while the Ni²⁺/Ni³⁺ cycle in the catalyst played a vital role in catalyzing ozone to generate free radicals and enhancing the mineralization capacity of NiCo₂O₄/O₃ system.