Preparation of Fe/S Modified Biochar Cathode and Its Mechanism for Promoting Ceftriaxone Sodium Removal in an Electro-Fenton System

The efficient cathode material helps to improve the removal of antibiotics in the electro-Fenton (EF) system. The simultaneous doping of transition metals and heterogeneous non-metallic elements in biochar electrodes can enhance the performance of EF systems, but the catalytic mechanism for EF needs to be further explored. In this study, novel Fe/S-doped biochar cathodes derived from marine algae (MA) were prepared to investigate the removal rate of ceftriaxone sodium (CS) and the underlying mechanisms. The results indicated that the Fe/S modified MA (Fe/S/MA) biochar cathode showed the highest CS removal rate (71.23%) in the EF system when treating 20 mg/L CS solution containing 8 mg/L Fe²⁺ at pH 4. Scanning electron microscopy and X-ray photoelectron spectroscopy analyses revealed that this cathode provided more iron and sulfur active sites for catalyzing the oxygen reduction reaction to produce H₂O₂, enhanced surface porosity, and improved CS removal rate. Electrochemical tests demonstrated this cathode possessed high electrocatalytic capacity, rapid charge transfer capability, and low electrode resistance. This suggested that it can provide more oxygen reduction reaction sites to promote ∙OH generation and enhance Fe²⁺ regeneration for improving CS removal. This study demonstrates the Fe/S/MA biochar cathode in the EF system shows great potential for the removal of antibiotics.