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.
In this work, a magnetic CoFe alloy and Co supported on mesoporous carbon with abundant defects (CoFe–Co/MC) was prepared by a sol–gel method combined with calcination and applied to activate peroxymonosulfate (PMS) and efficiently remove bensulfuron methyl (BSM) from water. CoFe–Co/MC could degrade 95% of BSM, while Co or Fe without supported mesoporous carbon could only provide degradation efficiencies below 10%, indicating that the introduction of mesoporous carbon could effectively enhance catalytic activity. Moreover, the dissolution of Co2+ from CoFe–Co/MC is only 0.22 mg L−1, which is about 20% of Co/MC, indicating that the bimetallic composite effectively inhibits the dissolution. The results of radical scavenger and EPR experiments demonstrated that 1O2 played the leading role in degradation process, while SO4˙− and small amounts of ˙OH and O2˙− were also involved in the degradation. The results of p-BQ scavenger and N2 atmosphere experiments showed that 1O2 mainly originated from the interaction between carbon defects and dissolved oxygen. The degradation performance of the CoFe–Co/MC/PMS system, carbon defect content and 1O2 content all increased with the increase of pyrolysis temperature, which demonstrated that adjusting pyrolysis temperature can regulate carbon defect content and 1O2 content, further improving catalytic activity. Possible BSM degradation pathways of CoFe–Co/MC/PMS were investigated in detail. This research provides new insights into the design and construction of metal–carbon catalysts rich in carbon defects and reveals how to regulate carbon defect content, 1O2 content and catalytic performance.
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