Dual Ligands Driving Pyrolytic Formation of Fe₃C@CNO Nanohybrids for the Reinforcement of Heterogeneous Fenton Chemistry

The controllable synthesis of Fe3C/C nanomaterials is of great significance for the development of efficient and stable Fenton catalysts. However, ligands may be a crucial factor affecting the pyrolytic formation of Fe3C/C. Herein, we dug into the roles of ligands in the thermal-induced growth of Fe3C@CNOs from an iron-cyanamide precursor. Comprehensive results of TG-DSC-MS, in situ XRD, in situ Raman, XPS, and XANES proved that O-based ligands (carboxy groups) act as the capping and reducing agents offering confinement effect and internal electron transfer for the iron center over 300-380 degrees C. Upon disintegration of Fe-O coordination, the N-containing ligands (triazine rings) from the condensation of hydrolytic cyanamide cut into the vacant orbits of the Fe center, followed by mediating the nucleation of carbonitride over 380-600 degrees C. Molecular dynamics (MD) further demonstrated phase transition from carbonitride to Fe3C/C within the intrinsic structure. These two ligands ensure the formation of the Fe3C/C structure, leading to an outstanding hydroxyl radical (OH) generation from H2O2 activation, concurrent with strong pH adaptability (pH 3-9) and limited iron leaching (0.45 mg/L). This study provides new insights into the ligands' effect on the controllable synthesis of Fe3C-based catalysts for the reinforcement of H2O2 activation.