Amino-Functionalized MIL-101(Fe)-NH2 as Efficient Peracetic Acid Activator for Selective Contaminant Degradation: Unraveling the Role of Electron-Donating Ligands in Fe(IV) Generation

Peracetic acid-based advanced oxidation processes (PAA–AOPs), which generate various reactive radicals, have garnered substantial attention for degradation emerging contaminants (ECs). However, nonselective radical-based PAA–AOPs often suffer from interference by water matrix components, causing low contaminants removal efficiency. This study explores the use of amino-(NH₂)-functionalized metal–organic frameworks (MIL-101(Fe)-NH₂) as heterogeneous catalysts for PAA activation, enabling the generation of high-valent iron- (Fe)–oxo species (Fe(IV)) capable of efficiently degrading ECs (80−100%, within 30 min). The Fe(II) clusters in MIL-101(Fe)-NH₂, modulated by electron-donating −NH₂ groups, play a pivotal role in Fe(IV) generation. Scavenger and probe experiments confirmed Fe(IV) as the primary reactive species responsible for ECs degradation. Density functional theory calculations demonstrated that the four-electron transfer to generate Fe(IV) has lower free energy than the two-electron transfer to generate organic radicals (e.g., CH₃COO^• and CH₃C(O)OO^•). Furthermore, thermodynamically unfavorable CH₃COO^• desorption further promotes Fe(IV) generation. The PAA/MIL-101(Fe)-NH₂ system efficiently degraded SMX (k_app= 121.2−287.2 M⁻¹s⁻¹) and other ECs (k_app= 40−432 M⁻¹s⁻¹) with minimal interference from water matrix components and excellent reusability. This study demonstrates that MIL-101(Fe)-NH₂ is a robust catalyst for PAA activation and provides a novel approach for selectively generating Fe(IV) for ECs degradation.