Insights into novel phosphorus-doped biochar for tetracycline removal: Non-radical oxidation and adsorption

Heteroatom doping has been widely recognized as an emerging and promising strategy for material enhancement and the degradation of organic pollutants. However, most heteroatom doping biochars are used to activate, for example, PMS to generate reactive oxygen species (ROS) to degrade organic pollutants instead of investigating their own ability to produce ROS. Herein, phosphorus-doping biochars (PBC) were synthesized at various temperatures for adsorption and degradation of tetracycline (TC). Compared to the pristine biochar (BC-800), PBC-800 exhibited significant enhancements in the specific surface areas (1307.30 m²·g⁻¹), porosity (0.94 cm³·g⁻¹) and higher removal efficiency (1.25 times higher than BC-800). The abundance of functional groups in the PBC-800 such as electron-rich ketone functional groups (CO), phosphorus-oxygen moieties (P-O), and defective sites within the carbon matrix, have been identified to play crucial roles in TC degradation. The free radical quenching and analysis of electron paramagnetic resonance (EPR) indicated that the presence of persistent free radicals (PFRs) on PBC also influenced the TC removal, and the possible non-radical pathways were proposed. The density functional theory (DFT) calculations proved that PBC-800 exhibited the highest adsorption energy as well as the lowest energy gap between triplet O₂ and ¹O₂, suggesting that the existence of P was conducive to the production of ¹O₂. This study laid the groundwork for the development of biochars and provided a novel insight into the design of green biomass for effective removal of antibiotics in the future.