Three-dimensional hollow catalysts with edge-defective Fe-Nx sites and enhanced peroxymonosulfate activation performance: Preparation, applications, and mechanism

Abstract

Developing heterogeneous catalysts with high level of active site exposure is crucial for the activation of peroxymonosulfate. In this study, a series of high-performance Fe-N-C catalysts were obtained through the strategy of melamine-assisted pyrolysis. The morphology, specific surface area and pore structure of the catalysts can be adjusted by controlling the amount of melamine added during the pyrolysis process. Fe1-Nx-C obtained with a melamine to Fe-ZIF ratio of 1:1 exhibited the highest specific surface area (984.2 m2·g−1), pore volume (1.79 cm3·g−1) and reaction rate constant (0.055 min−1, 5.5 times that of Fe0-Nx-C). Furthermore, Fe1-Nx-C showed high stability and reusability in multiple cycles, maintaining high catalytic activity with pH range of 3–9. The addition of melamine can cause selective cleavage of C-N bonds, converting the central Fe-Nx sites into more active edge-defective Fe-Nx sites, thereby enhancing the catalytic activity. Quenching experiments and electron paramagnetic resonance (EPR) detection confirmed the dominance of 1O2 in the degradation of Bisphenol AF (BPAF). Two possible pathways for BPAF degradation were proposed based on liquid chromatography-mass spectrometry (LC-MS) and density functional theory (DFT) calculations. This study provides a new way to design and construct Fe-N-C catalysts with ideal pore structures, and enhance the accessibility of active sites inside the catalysts.