High-valent iron-oxo species on pyridine-containing MWCNTs generated in a solar-induced HO activation system for the removal of antimicrobials.

The overuse of antimicrobials has resulted in serious damage to the ecosystem and human health. Therefore, the development of an efficient, stable, and reusable catalyst to eliminate antimicrobials under mild conditions is highly desired. Drawing inspiration from the metabolism of drugs by the enzymes in the human body, such as heme catalase, we developed a simulated enzyme catalyst, perchloride iron phthalocyanine (FePcCl), immobilized on pyridine-modified multiwalled carbon nanotubes (FePcCl-Py-MWCNTs). In the catalyst, FePcCl worked as the active site, and the axial fifth ligand, 4-aminopyridine, was introduced to cleave HO heterolytically. Inspired by the reaction mechanism of heme catalase and HO, the catalytic system was designed based on FePcCl-Py-MWCNTs for oxidizing 4-chloro-3,5-dimethylphenol (PCMX) by HO activation. The results showed that the catalytic activity of the system was significantly increased under simulated solar light irradiation, which can promote electron transfer for heterolytic cleavage of HO. The enzyme-like catalyst achieved much higher catalytic activity than the Fenton reaction when the pH was close to neutral. It turned out that the main active species was high-valent iron-oxo (Fe(Ⅳ) = O) rather than hydroxyl radial (•OH) or superoxide radical (•O), different from most mechanisms. Ultraperformance liquid chromatography-high-definition mass spectrometry showed that the substrate was degraded to small molecule acids by Fe(Ⅳ) = O active species and further mineralization indicated by total organic carbon. The catalytic system exhibited highly efficient, stable, recyclable catalytic performance under mild conditions and did not cause secondary pollution to the environment. This study of a simulated enzyme catalytic system offers important insight into sewage treatment.