High-valent iron-oxo species on pyridine-containing MWCNTs generated in a solar-induced H2O2 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 (FePcCl16), immobilized on pyridine-modified multiwalled carbon nanotubes (FePcCl16-Py-MWCNTs). In the catalyst, FePcCl16 worked as the active site, and the axial fifth ligand, 4-aminopyridine, was introduced to cleave H2O2 heterolytically. Inspired by the reaction mechanism of heme catalase and H2O2, the catalytic system was designed based on FePcCl16-Py-MWCNTs for oxidizing 4-chloro-3,5-dimethylphenol (PCMX) by H2O2 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 H2O2. 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 (•O2−), 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.