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
Likun Chen,Kewen Xing,Qikai Shentu,Yifei Huang,Weiyang Lv,Yuyuan Yao
Developing single-atom Fenton-like catalysts with the maximum utilization of active sites present an attractive potential in environmental remediation. Herein, the single-atom Fe and N co-doped hollow carbon microsphere loaded g-C 3 N 4 catalyst (HFeNC-g-C 3 N 4 ) was prepared by an innovative cascade anchoring strategy using polystyrene as the hard template, iron phthalocyanine, polydopamine and urea as the Fe, N and C precursor, in which the in-situ generated g-C 3 N 4 could not only effectively anchor Fe atom to create the well-dispersed Fe-N x active sites, but also accelerate the electron transfer in peroxymonosulfate (PMS) activation. Taking advantages of such sequential protecting strategy, the as-synthesized HFeNC-g-C 3 N 4 catalyst with single-atom Fe-N x active sites, verified by XRD , XPS and HAADF-STEM, could work as an efficient Fenton-like catalyst for PMS activation, which achieved almost 100% removal of 4-chlorophenol (4-CP) in 5 min with the turnover frequency calculated to be 34.6 times higher than that of the homogeneous Fe 2+ catalyst. The mechanism of O 2 •- dominated radical combined with nonradical 1 O 2 pathway was confirmed by quenching experiments and ESR analysis, which might be interrelated to the improvement of pH adaptability and interference immunity of HFeNC-g-C 3 N 4 /PMS system. Overall, the present findings provided an innovation strategy for the synthesis of excellent single-atom Fe based catalyst in wastewater purification.
Cobalt-free Li and Mn-rich layered cathode materials are promising for next generation lithium ion batteries due to their high specific capacity and low cost. However, these materials are facing serious issues, such as structural collapse due to volume shrinkage during Ni 2+ oxidation to Ni 4+ and oxygen vacancy generation over 4.5V. In this work, we report a strategy to address the issue of volume shrinkage caused by structural deformation via constructing a large-size rigid frame by simultaneously doping inactive and large radius atoms of Cd and S. This strategy significantly reduces the volume shrinkage when fully delithiated relative to the pristine material. The Cd- and S-doped cathode materials present a highly reversible structure, which were determined by using HAADF-STEM and in-situ XRD characterization. The doped Cd and S atoms act as supporting atoms and synergistically enlarge the layer spacing of crystalline from 0.455 to 0.483 nm. The in-situ XRD monitors the structural changes in real time during charging and discharging processes, further verifying structural stability during cycling. Due to the unique structural properites, an initial capacity of 268.5 mAh g −1 at 0.1 C along with a good rate capacity of 153.8 mAh g −1 at 5 C were achieved. Also, a capacity of 243.4 mAh g-1 at 0.1 C over 80 cycles indicate good cyclic stability of the co-doped Li- and Mn-rich layered cathode.
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