Highly efficient microwave-assisted Fenton degradation of metacycline using pine-needle-like CuCo2O4 nanocatalyst

Abstract

The heterogeneous Fenton reaction was a powerful technique for degrading organics in wastewater. However, it usually took a long time to meet efficiency requirement. To solve this problem, herein, pine-needle-like CuCo2O4 was prepared and applied as a catalyst in a microwave-assisted Fenton reaction (MAFR) towards antibiotic metacycline (MTC). The optimized degradation condition was 500 μL of H2O2, 10.0 mg of catalyst, 50 mg/L of MTC, and 90 °C of temperature, under which MTC was degraded within 4.0 min. Dynamics data revealed that the activation energy of MAFR was 17.3 kJ/mol, which was much lower than that of the corresponding heterogeneous Fenton reaction (52.2 kJ/mol). Owing to the synergistic effect of combining Cu(II)/Cu(I) and Co(III)/Co(II) sites, the reaction rate constant of CuCo2O4 nanoneedles (7.2 × 10−1 min−1) was much higher than that of the CuO (1.3 × 10−1 min−1), Co3O4 (2.2 × 10−1 min−1), and mixed CuO + Co3O4 (1.5 × 10−1 min−1) references. CuCo2O4 nanoneedles could be easily separated from the reaction solution, and their degradation efficiency remained 86.4% after the 5th cycle. To study the catalytic mechanism, radical trapping experiments were performed, and the results revealed that OH played a dominating role in the degradation process. A possible degradation pathway of MTC was investigated, and it was determined that hydroxylation, de-alkylation, de-hydroxylation, and ring-opening reactions were involved for final inorganic molecules.