Effects of introduction of N on the structural and catalytic ozonation properties of Fe-MOF derivatives

Environmentally friendly and efficient heterogeneous catalysts are of great significance for refractory pollutant degradation via catalytic ozonation. Metal-organic framework (MOFs) with high specific surface area and porosity exhibited higher catalytic activity. However, poor stability and weak mechanical strength of MOFs hinder the further application. The properties of derivatives prepared with MOFs as precursors can be improved. In this work, Fe-MOFs (MIL-53(Fe) and NH₂-MIL-53(Fe)) and derivatives (Fe@C and Fe@NC) were prepared and the removal performance of hexazinone in Fe-MOFs/O₃ or derivatives/O₃ system was evaluated. Fe@NC has outstanding catalytic ability, the removal rate of hexazinone reached 86.37 % within 20 min in Fe@NC/O₃ system, and k_obs (0.0992 min⁻¹) was 16.89 times that of O₃ system. The high catalytic ability of Fe@NC was attributed to the introduction of N. The highly active Fe-N compound was formed on the Fe@NC surface, and the ability of electron transfer between Fe@NC and O₃ was promoted, thus improving the catalytic performance. Electron paramagnetic resonance, probe experiments, and density functional theory were combined to reveal the catalytic ozonation mechanism of Fe@NC and degradation pathway of hexazinone. Reactive oxygen species (•OH, •O₂⁻ and ¹O₂) were the important cause of the degradation of hexazinone and Lewis acid sites on Fe@NC surface were the main active sites for O₃ decomposition. The toxicity of hexazinone degradation intermediates was evaluated and degradation intermediates had lower toxicity than hexazinone. Moreover, Fe@NC showed excellent environmental adaptability, stability and reusability. This study provided technical support for MOFs derivatives application in catalytic ozonation.