The single Fe atom anchored to graphitic carbon nitride doped air-cathode for bioenergy generation and tetracycline degradation in microbial fuel cells

Microbial Fuel Cell (MFC) as a green energy technology that converts pollutants into electricity. In this study, Fe single atom catalysts (SACs) based on graphitic carbon nitride (g-C3N4) with Fe-N4 coordination structure are synthesized for the cathodic electrocatalysis of MFCs for the electrochemical degradation of tetracycline (TC) and the reduction of antibiotic resistance genes (ARGs). The synthesized SAFe-MCN catalysts have uniform and dispersed Fe SA sites with Fe-N4 stabilized structure. Their applications in MFCs achieve highly efficient and stable oxygen reduction reaction activity with the maximum power density up to 493.64 mW/m2. A degradation rate of 60.6 % is achieved in one cycle for a 40 mg/L high concentration of TC in MFC application, and the maximum power density reaches 707.04 mW/m2. Based on that, an oxidation step is proposed for the O2 reaction at the cathode by summarizing the catalytic mechanism of SAFe-MCN. The anodic microorganisms Achromobacter, Chitinophaga, Comamonas and Geobacter are identified to have the main degradation and electroproduction roles in MFCs, and the joint application of MFCs and SAFe-MCN prevents the outflow of ARGs to some extent. The Fe SAC made in this work has a Fe-N4 structure, which improves stability and catalytic activity, greatly improves cathode ORR performance, and better promotes pollutant degradation. It also offers direction for future studies on the application of single-atom cathodes.