Insights into the mechanism of persulfate activation by hollow MOF-derived carbon: electron transfer-triggered non-radical oxidization for antibiotic removal

Abstract

Non-radical oxidation triggered by hollow MOF-derived carbon in persulfate-based AOPs shows potential for antibiotic wastewater remediation. However, the inherent relationship between the hollow structure and catalytic activity and the evolution mechanism involving the transformation from solid structures into hollow frameworks is not clear. Considering this, herein, hollow ZIF-8-derived carbon (HZC) was fabricated via TA etching and carbonization for the activation of PDS. The results indicated that HZC-800 exhibited an excellent antibiotic removal performance through electron-transfer mediated non-radical oxidation. Characterization studies revealed the key role of graphitic N in the catalytic reaction, which was linearly correlated with the kinetic constant (k) and a high graphitic N content enhanced the degradation of antibiotics. Further analysis suggested that the evolution mechanism from an ROS-dominated process in solid ZIF-8-derived carbon (ZC-800)/PDS to electron-transfer oxidation in HZC-800/PDS originated from the transformation into a hollow structure. Compared to solid ZC-800, hollow HZC-800 with a higher graphitic N and lower electron-withdrawing O group content exhibited an enhanced electron conductivity and was more conducive to PDS adsorption and forming activated PDS* for electron-transfer non-radical oxidation, reducing the direct activation of PDS into ROS. HZC-800 with a larger porosity and more defects facilitated the mass diffusion for antibiotic removal with great practicality. This study provides a new insight into the evolution mechanism for the transformation from solid structures into hollow structures and designing carbon catalysts for wastewater treatment.