The present study explores the use of carbon dots coated with Iron (II, III) oxide (Fe₃O₄) for its application as an anode in microbial fuel cells (MFC). Fe₃O₄@PSA-C was synthesized using a hydrothermal-assisted probe sonication method. Nanoparticles were characterized with XRD, SEM, FTIR, and RAMAN Spectroscopy. Different concentrations of Fe₃O₄- carbon dots (0.25, 0.5, 0.75, and 1 mg/cm²) were coated onto the graphite sheets (Fe₃O₄@PSA-C), and their performance in MFC was evaluated. Cyclic voltammetry (CV) of Fe₃O₄@PSA-C (1 mg/cm²) modified anode indicated oxidation peaks at −0.26 mV and +0.16 mV, respectively, with peak currents of 7.7 mA and 8.1 mA. The fluxes of these anodes were much higher than those of other low-concentration Fe₃O₄@PSA-C modified anodes and the bare graphite sheet anode. The maximum power density (Pmax) was observed in MFC with a 1 mg/cm² concentration of Fe₃O₄@PSA-C was 440.01 mW/m², 1.54 times higher than MFCs using bare graphite sheet anode (285.01 mW/m²). The elevated interaction area of carbon dots permits pervasive Fe₃O₄ crystallization providing enhanced cell attachment capability of the anode, boosting the biocompatibility of Fe₃O₄@PSA-C. This significantly improved the performance of the MFC, making Fe₃O₄@PSA-C modified graphite sheets a good choice as an anode for its application in MFC.

In this study, multifunctional lithium-doped bismuth ferrite [BiFe_1−xLi_xO₃]-graphene nanocomposites (x = 0.00, 0.02, 0.04, 0.06) were synthesized by a sol-gel and ultrasonication assisted chemical reduction method. X-ray diffraction and FESEM electron microscopy techniques disclosed the nanocomposite phase and nanocrystalline nature of [BiFe_1−xLi_xO₃]-graphene nanocomposites. The FESEM images and the EDX elemental mapping revealed the characteristic integration of BiFe_1−xLi_xO₃ nanoparticles (with an average size of 95 nm) onto the 2D graphene layers. The Raman spectra of the [BiFe_1−xLi_xO₃]-graphene nanocomposites evidenced the BiFe_1−xLi_xO₃ and graphene nanostructures in the synthesized nanocomposites. The photocatalytic performances of the synthesized nanocomposites were assessed for ciprofloxacin (CIP) photooxidation under UV-visible light illumination. The photocatalytic efficiencies of [BiFe_1−xLi_xO₃]-graphene nanocomposites were measured to be 42%, 47%, 43%, and 10%, for x = 0.00, 0.02, 0.04, 0.06, respectively, within 120 min illumination, whereas the pure BiFeO₃ nanoparticles were 21.0%. BiFe_1−xLi_xO₃ nanoparticles blended with graphene were explored as cathode material and tested in a microbial fuel cell (MFC). The linear sweep voltammetry (LSV) analysis showed that the high surface area of BiFeO₃ was attributed to efficient oxygen reduction reaction (ORR) activity. The increasing loading rates of (0.5–2.5 mg/cm²) [BiFe_1−xLi_xO₃]-graphene composite on the cathode surface showed increasing power output, with 2.5 and 2 mg/cm² achieving the maximum volumetric power density of 8.2 W/m³ and 8.1 W/m³, respectively. The electrochemical impedance spectroscopy (EIS) analysis showed that among the different loading rates used in this study, BiFeO₃, with a loading rate of 2.5 mg/cm², showed the lowest charge transfer resistance (R_ct). The study results showed the potential of [BiFe_1−xLi_xO₃]-graphene composite as a cost-effective alternative for field-scale MFC applications.