Vacancies-rich MOFs-derived magnetic CoFe encapsulated in N-doped carbon nanotubes as peroxymonosulfate activator for p-arsanilic acid removal

A rational design of high-performance catalysts with peroxymonosulfate (PMS) activation and arsenic adsorption capacities for the removal of p -arsanilic acid ( p -ASA) is in high demand but remains a significant challenge. Herein, vacancies-rich metal–organic frameworks (MOFs) were constructed by room-temperature co-precipitation procedure, and the magnetic CoFe encapsulated in N -doped carbon nanotubes (CoFe- N -CNTs) were prepared using MOFs template by an annealing process under a nitrogen atmosphere. The synthesis conditions of CoFe- N -CNTs were optimized by tuning Fe/Co ratio and carbonization temperature. The CoFe- N -CNTs/PMS system showed favorable removal performance, achieving complete degradation of 46 μM p -ASA within 3 min and a total arsenic removal efficiency of 98% within 30 min at 0.1 g/L catalyst and 400 μM PMS. The degradation rate ( k obs ) and total arsenic removal efficiency towards p -ASA by CoFe- N -CNTs/PMS system were 6.7 and 2.7 times of those in the MOFs without vacancies-derived catalyst/PMS system, respectively. CoFe- N -CNTs/PMS system exhibited robust and efficient performance over a broad range of pH (4.5–9.0) and in different water matrices. Scavenging experiments and electron paramagnetic resonance (EPR) results demonstrated that non-radical singlet oxygen ( 1 O 2 ), sulfate radicals (SO 4 − ), hydroxyl radicals ( OH), and superoxide (O 2 − ) were involved in p -ASA decomposition. Electron transfer and direct oxidative transfer process (DOTP) also contributed to p -ASA degradation. High-performance liquid chromatography coupled with inductively coupled plasma mass spectrometry (HPLC-ICP-MS) analysis indicated that the arsenic moiety was cleaved from p -ASA in the form of As(III) and then rapidly oxidized to As(V). X-ray photoelectron spectroscopy (XPS) analysis indicated the removal of inorganic arsenic followed the mechanism of the inner-sphere complex. This study highlights the in-situ synthesis of CoFe- N -CNTs with outstanding activities for catalytic degradation and arsenic removal of organoarsenicals.