Programming interfacial electron transfer at Shewanella oneidensis – Magnetic biochar hybrids for selective tetracycline–ciprofloxacin co-removal

Antibiotic residues persist in waters and require effective, low-chemical remediation strategies. Here we create a contacted system that brings Shewanella oneidensis (MR-1) into controlled association with nitrogen doped magnetic biochar to promote interfacial electron transfer. In a mixed tetracycline-ciprofloxacin matrix, the contacted system was superior to the single biochar or microbial system. Meanwhile, the MR-1 activity was maintained within the range of 3–20 mg/L and pH 5–8, with the best performance near pH 5-6. Electrochemical and spectroscopic signatures are consistent with interfacial electron transfer from MR-1 to surface Fe centers, accompanied by Fe 3 ⁺/Fe 2 ⁺ redox cycling and coupling of adsorption with reduction. Dissolved Fe 2+ after reaction followed similar trends and increased with carrier loading, and excitation-emission matrices showed humic-like extracellular polymers that may assist electron shuttling. Electronic-structure analysis is consistent with the observed differences between tetracycline and ciprofloxacin, with tetracycline more readily accepting the first electron at chelating diketone sites, whereas the fluorinated moiety and associated bond stability may constrain ciprofloxacin conversion. Overall, the results suggest an interface-controlled route to antibiotic co-removal under mild conditions and provide design insights linking pollutant electronics, Fe site density, and operating pH to interfacial electron flow.