Hofmann-MOF derived nanoball assembled by FeNi alloy confined in carbon nanotubes as a magnetic catalyst for activating peroxydisulfate to degrade an ionic liquid

[Display omitted] •Hofmann MOF-derived FeNiC is used for the 1st time to activate PDS to degrade BMIM.•FeNiC consists of a unique nanoball assembled by carbon nantubes with FeNi alloy NPs.•FeNiC shows much higher catalytic activities than Fe3O4 for PDS activation.•FeNiC shows a lower activation energy of BMIM degradation than the reported values.•BMIM degradation pathway is elucidated through the theoretical (DFT) calculation. As ionic liquids (ILs) are increasingly consumed, release of ILs into water environment has posed risks to aquatic ecology due to their toxicities. Since 1-Butyl-3-methylimidazolium chloride (BMIMCl) represents the most typical IL, development of useful techniques to eliminate BMIM from water is urgent and critical. While SO4•−-based oxidation processes are useful for degrading BMIM, very few studies have been conducted using peroxydisulfate (PDS), and almost no studies exist for developing heterogeneous activation of PDS to degrade BMIM. Thus, the aim of this study is to develop a useful heterogeneous catalyst for the first time to activate PDS for degrading BMIM in water. Herein, a special catalyst is developed from a unique Hofmann-type MOF ([Fe]pyrazine[Ni(CN)4]) through carbonization to afford a nanoball assembled from carbon nanotubes (CNTs) with confinement of FeNi alloy nanoparticles. Such a FeNi@CNT (i.e., FeNiC) nanoball exhibits many advantageous features, including embedment of effective metals (Fe and Ni), strong magnetism, protection of FeNi by CNT, synergy of FeNi and CNT, and unique interwoven assembled structures, making FeNiC a promising heterogeneous catalyst for activating PDS to degrade BMIM. FeNiC is proven to exhibit a much higher catalytic activity (RSE = 0.0388) than Fe3O4 for PDS activation (RSE = 0.0155). FeNiC/PDS also shows a lower activation energy (i.e., 40.4 kJ/mol) for BMIM degradation then other reported values, revealing promising advantages of FeNiC. The activation mechanism as well as degradation pathway of BMIM degradation by FeNiC/PDS is also investigated here through theoretical DFT calculations and experimental evidences to provide valuable insights into degradation behaviors of BMIM using Hofmann MOF-derived catalysts.