One-Step Mechanochemical Preparation of Magnetic Covalent Organic Framework for the Degradation of Organic Pollutants by Heterogeneous and Homogeneous Fenton-Like Synergistic Reaction

Abstract

The practical application of covalent organic frameworks (COFs) is limited because of the difficulties in rapid separation. This issue is expected to be solved with the emergence of magnetic nanoparticles. However, it remains challenging to quickly prepare magnetic COFs with high catalytic activity. In this study, a magnetic COF material (Fe3O4@TpMA) was prepared using a ball milling method based on grinding amino-functionalized magnetic nanoparticles (Fe3O4-NH2) and COFs (TpMA). The -C=N bond were as a bridge between Fe3O4 and COFs. Transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) characterizations showed that the doping of Fe3O4 nanoparticles did not destroy the structure of the COFs. In addition, Fe3O4@TpMA exhibited excellent superparamagnetic properties that were conducive to the magnetic separation of pollutants and catalysts. In the Fe3O4@TpMA+H2O2 system, 88.1% of methyl orange (MO) was degraded within 40 min. The degradation rate of MO in the Fe3O4@TpMA+H2O2 system was 4.2, 8.0, and 11.8 times that in the Fe3O4-NH2+H2O2, TpMA+H2O2, and mixed material (Fe3O4-NH2/TpMA)+H2O2 systems, respectively. Furthermore, experimental parameters such as pH, pollutant concentration, catalyst dosage, and H2O2 dosage played an important role in the degradation of MO. The Fe3O4@TpMA catalyst also achieved highly efficient degradation of MO under weakly acidic conditions (pH=6.38). The degradation mechanism is complex, involving the heterogeneous Fenton mechanism as the main step, and the homogeneous Fenton mechanism as the auxiliary step. This study aims to provide a new strategy for the preparation of magnetic COFs via mechanical grinding.

Keywords: Covalent organic frameworks (COFs), Magnetic nanoparticles (Fe3O4), Fenton-like reaction, Mechanical grinding method