Photomicrobial
fuel cells can efficiently improve the power density
of microbial fuel cells (MFCs), but bimetallic spinel ferrite photoactive
material-based microbial devices have not been investigated yet. Herein,
a dissimilatory iron-reducing bacterium, Shewanella
putrefaciens CN32 (S. putrefaciens CN32), is selected as a model bacterium due to its possible enhanced
affinity with iron-containing photoactive materials. Three bimetallic
spinel ferrite nanoparticles, cobalt ferrite (CoFe2O4), nickel ferrite (NiFe2O4), and manganese
ferrite (MnFe2O4), were used to modify the surface
of S. putrefaciens CN32 for photo-MFCs,
showing that MnFe2O4 has the best catalytic
effect. Results reveal that these nanoparticle coatings on bacteria
not only enhance direct electron transfer mediated by outer membrane
c-type cytochromes (OMCs) while serving as conductive paths for charge
transport between bacteria and the electrode surface but also significantly
promote bacterial growth for increased flavin production from S. putrefaciens CN32. In addition, the extracellular
electron transfer can be greatly accelerated with the assistance of
photosensitive MnFe2O4 nanoparticles under visible
light. This work demonstrates that the photomicrobial anode can simultaneously
enhance both mediated and direct electron transfer processes and offers
universal significance for photo-bio-electrocatalysis.
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