Simultaneous Adsorption and Electron-Transfer Degradation of Tetracycline by Fe-Multivalence Decorated N-Doped Carbon Nanotubes in the Absence of Oxidants

Iron/nitrogen codoped biochar (FeNBC) composite with CNT as the main structure was prepared by a one-pot pyrolysis method. The specific surface area (SBET) of the FeNBC is 2.6 times that of nitrogen-doped biochar (NBC), and its adsorption performance is stronger and well conforms to the pseudo-second-order (PSO) adsorption model. Quenching experiments, electron paramagnetic resonance (EPR), probe conversion tests, and LC-MS analysis confirmed that FeNBC induced the generation of reactive oxygen species (ROS) and caused the chemical degradation of tetracycline (TC) in the absence of oxidants. Electrochemical experiments have confirmed that FeNBC has capacitance, redox properties, and electron transfer ability better than that of NBC. In terms of chemical structure, FeNBC has a higher degree of graphitization/aromatization, more C═O functional groups, and contains dispersed nZVI and Fe2+/F3+ nanoparticles. The experimental results also reveal that FeNBC has stronger electron donation/acceptation capability (EDC/EAC) and better electron transfer performance. The surface morphology and chemical structure characteristics of FeNBC are believed to be the fundamental reasons for its excellent electrochemical, adsorption, and catalytic performance. In addition, the study revealed that organic compounds act as external electron donors (EEDs) to promote O2•– generation, while they themselves are simultaneously oxidized, which is a mutually reinforcing coupling process with O2•– generation.