Developing high-efficient hybrids carbon catalysts for PMS-based advanced oxidation process (AOPs) are crucial in the field of environmental remediation. In this work, novel carbon nanocubes (xFe‒N‒C) with three-dimensional porous structure and abundant well-dispersed FeN x sites were obtained via a skillful cage-encapsulated-precursor pyrolysis strategy. The as-synthesized xFe‒N‒C exhibited superb activity for phenol degradation by activating peroxymonosulfate (PMS). Besides, the catalytic system not only possessed good recycling performance, wide pH adaptation and relatively low activation energy, but also had high resistance to environmental interference. Singlet oxygen ( 1 O 2 ) dominated non-radical process was responsible for phenol degradation rather than traditional radical pathways. Impressively, the doping level of Fe could regulate FeN x contents in catalysts, and the catalytic activity of xFe‒N‒C was greatly enhanced with increasing FeN x contents. Based on density functional theory calculations (DFT), the introduction of FeN x sites regulated the electronic structure of catalysts. Such electron-deficient Fe center acted as electron acceptor to receive electrons transmitted by the adsorbed PMS , thus generating highly reactive 1 O 2 for rapid phenol oxidation. This work provides a new insight into the innovation in transition metal-nitrogen hybrid carbon catalysts and highlights the pivotal roles of FeN x sites in 1 O 2 generation during PMS activation process.
Numerous efforts have been devoted to realizing the high loading and full utilization of single-atom catalysts (SACs). As one of the representative methods, atom migration-trapping (AMT) is a top-down strategy that converts a certain volume of metal nanoparticles (NPs) or metal-based precursors into mobile metal species at high temperature, which can then be trapped by suitable supports. In this study, high-loading iron single atoms anchored onto carbon matrix/g-C3N4hybrid supports were obtained through a single-atom migration-trapping method based on metal–organic framework (MOF) pyrolysis. It is confirmed, by high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM), X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS), that the Fe(acac)3precursor is reduced to Fe single atoms (SAs), which are not only anchored onto the original N-doped carbon (NC), but also onto g-C3N4, with an Fe-N coordination bond. Further electrochemical results reveal that Fe-C3N4-0.075 possesses a better half-wave potential of 0.846 V and onset potential of 0.96 V compared to Fe-N-C, the product obtained after pyrolysis of Fe(acac)3@ZIF-8. As opposed to SAs prepared by the pyrolysis process only, SAs prepared by AMT are commonly anchored onto the surface of the supports, which is a simple and effective way to make full use of the source metal and prepare SACs with higher exposing active sites.Keywords:atom migration-trapping;single-atom catalysts;metal–organic frameworks
High light adsorption and fast charge separation are crucial for photo-Fenton catalytic activity of MOFs. Herein, bottom-up design was proposed to fabricate polypyrrole (PPy C ) nanowires in MIL-88B(Fe) cages as photo-Fenton catalyst for Sulfamethoxazole (SMX) efficient degradation. Pyrrole was prior anchored into MIL-88B(Fe) cluster via Fe-N coordination, and then the additional monomer pyrrole was further triggered bottom-up polymerization in confined cages of MIL-88B(Fe) and formed PPy C @Py-MIL(Fe) composite. These PPy C nanowires were dispersed in Py-MIL(Fe) cages and tightly connected with MOFs clusters via Fe-N bonding. Characterization proved that: (1) Interfacial Fe-N can significantly promote the efficient electron transport from PPy C nanowires to Py-MIL(Fe), enhance optical absorption property, and construct strong Lewis acidic sites and ligand vacancies in PPy C @Py-MIL(Fe). (2) The confined PPy C nanowire via Fe-N connection remarkably promote photo-generated electron-hole separation, Fe 2+ |Fe 3+ redox ability of MOF, and improved photo-electric corrosion ability. As a result, it significantly enhanced the photo-Fenton catalytic performance for SMX degradation. Catalytic oxidation was attributed to the generation of ‧OH species that oxidized 93% SMX in 60 min, showing ultra-rapid degradation and TOC removal rates of 33.7 min −1 ·mg·g −1 and 8.68 min −1 ·mg·g −1 respectively, which was about 4–220 times higher than those reported state-of-the-art catalysts. Additionally, the PPy C @Py-MIL(Fe) catalyst showed minimal loss in catalytic activity even after recycling for 10 times, exhibiting good recycling stability compared to many MOFs. Systematic analysis shown that in-situ anchored growth of polypyrrole in confined porous cages of MOF can effectively enhance the catalytic activity and stability of MIL-88B(Fe), and has great development potential applications for photo-Fenton catalytic degradation of organic pollutants.
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