Zeolite imidazole framework-8-derived nitrogen-doped nanocarbon boosted Fenton-like oxidation: Another sustainable path for Fe(III)/Fe(II) circulation

Zeolite imidazole framework-8 (ZIF-8) is a promising template to obtain porous nanocarbons. In this study, microporous nitrogen-doped nanocarbons from the carbonization of ZIF-8 (ZCN) was prepared as an efficient metal-free catalyst to improve several micropollutants degradation in Fe(III)/H₂O₂ process. The sulfamethoxazole (SMX) ratio was increased from 20% to 100% with the addition of ZCN (50 ​mg/L) in Fe(III)/H₂O₂ within 20 ​min, and the working pH was endowed. The direct reduction for Fe(III) resulting from carbonyl on ZCN's surface was revealed. Hydroxyl radical (•OH) was determined to be the main reactive species, and the evolution of different Fe species during the reaction was discussed by monitoring the mass balance of Fe species. We found that part of the iron was bound to the surface of ZCN during the reaction. Additionally, the dissociative Fe was captured by ZCN to form Fe-N_x bonds. Surface-bound Fe with a lower energy barrier was more likely to react with H₂O₂ to generate Fe(II). Our work revealed that in addition to the direct reduction by ZCN, another catalytic reduction pathway for the sustainable conversion of Fe(III) to Fe(II) in the ZCN/Fe(III)/H₂O₂ process was operative.