Persulfate activation by Fe, N co-doped carbon: Effect of N-containing groups on electron structure of Fe-Nx sites

Iron and nitrogen co-doped carbon (Fe-N-C) with Fe-N_x and graphitic N sites shows great potential in persulfate (PS) activation for organic pollutants degradation. Fe-N_x and graphitic N sites were quantified by X-ray photoelectron spectroscopy (XPS) to determine their ratios. The interaction between Fe-N_x and graphitic N and the mechanism affecting the catalytic activity were systematically explored by combining experiments and theoretical calculations. The results indicated a significant synergistic effect between Fe-N_x and graphitic N. Especially, Fe-N-C with a 1:4 ratio of Fe-N_x to graphitic N owned the highest turnover frequency (TOF) value (1.59 ​× ​10⁻³ ​g ​m⁻² min⁻¹). The contributions of radical mechanism influenced TOF values of Fe-N-C-rx to a certain extent. Theoretical calculations proved that the coordination environment could regulate the electronic structure of active sites, thereby affecting catalytic activity. Fe-N-C with a ratio of 1:4 Fe-N_x to graphitic N had maximum adsorption energy (E_ads), O-O bond length (l_O-O) and the optimal d-band center value, which promoted adsorption and electron transfer with PS. The 2,4-Dichlorophenol (2,4-DCP) degradation behavior was also explored by combining Fukui functions and mass spectrometry analysis.