Synergistic Adsorption and Degradation of Florfenicol for Water Remediation by Double-Layer Core–Shell Fe0/Fe3C-Based Biochar Without External Oxidants

Zero-valent iron-supported biochar (Fe0@BC) integrates multiple functions, including adsorption, complexation, and reduction, exhibiting promising application prospects for the removal and degradation of organic pollutants. However, it still faces challenges such as complex preparation processes and the irreversible deactivation of iron centers. Herein, a double-layer core–shell iron-based biochar composite (Fe0/Fe3C@BC) featuring a “zero-valent iron (Fe0) core–iron carbide (Fe3C) interlayer–graphitized carbon shell” structure was successfully synthesized via a one-step carbothermal reduction method. Furthermore, its synergistic adsorption and degradation mechanism toward florfenicol (FLO) in the absence of external oxidants was systematically investigated. The 4% FeBC-800 composite (0.5 g·L−1) demonstrated a rapid removal efficiency, eliminating 99.89% of FLO (100 mg·L−1) within 30 min, and exhibited exceptional durability by maintaining approximately 90% of its removal efficiency after four consecutive regeneration cycles. The adsorption behavior of FLO by 4% FeBC-800 fitted well with the pseudo-second-order kinetic model (R2 = 0.999) and the Langmuir isotherm model (R2 = 0.958). The primary adsorption mechanisms included pore filling, hydrogen bonding, surface complexation, and π-π electron donor–acceptor interactions. Interfacial electron transfer played a dominant role in the FLO degradation process. The degradation mechanism primarily involved reductive dechlorination and oxidative degradation via reactive oxygen species (ROS) generated from the activation of dissolved oxygen. This study provides a novel strategy for the development of advanced iron-based biochar materials for the highly efficient removal of persistent organic pollutants.