Preparation of waste chromium adsorbent based catalytic material and activation of PMS for degradation of 2, 4-D

In this study, a new catalytic material Fe-Ce@N-2-WA was successfully synthesized, which used waste chromium adsorbent as a precursor to effectively activate peroxymonosulfate (PMS) to degrade 2, 4-dichlorophenoxyacetic acid (2, 4-D). Under the typical conditions of Fe-Ce@N-2-WA dose of 0.1 g/L, PMS of 6 mM, and 2,4-D of 10 mg/L, the removal rate of 2,4-D of Fe-Ce@N-2-WA/PMS system reached >98 % within 60 min, and its rate constant k(s) was 0.0629 min(-1). Quenching experiment and electron paramagnetic resonance (EPR) confirmed that SO4 center dot- and O-1(2) were the main reactive oxygen species (ROSs) in the degradation process. Besides ROSs, electron transfer was another pathway for 2, 4-D degradation. Notably, nitrogen doping enhanced the electron transfer process in the reaction. Additionally, Fe-Ce@N-2-WA catalyst showed effectiveness over a wide pH range for 2,4-D removal. The degradation process was proposed through liquid chromatograph-mass spectrometer (LC-MS) and density functional theory (DFT) analyses, decarboxylation, de-chlorination and hydroxyl substitutions, as well as benzene ring cleavage were established in Fe-Ce@N-2-WA/PMS system. This study provides a convenient way to recycle waste adsorbents and provides a deeper understanding of the degradation mechanism of 2, 4-D in heterogeneous systems.