Directional Electron Transfer in Enzymatic Nano‐Bio Hybrids for Selective Photobiocatalytic Conversion of Nitrate

Semi-artificial photosynthetic system (SAPS) that combines enzymes or cellular organisms with light-absorbing semiconductors, has emerged as an attractive approach for nitrogen conversion, yet faces the challenge of reaction pathway regulation. Herein, we find that photoelectrons can transfer from the -C≡N groups at the edge of cyano-rich carbon nitride (g-C3N4-CN) to nitrate reductase (NarGH), while the direct electron transfer to nitrite reductase (cd1NiR) is inhibited due to the physiological distance limit of active sites (> 14 Å). By means of the directional electron transfer between g-C3N4-CN and extracted biological enzymes, the product of the denitrification reaction was switched from inert N2 to usable nitrite with an unprecedented selectivity of up to 95.3%. The converted nitrite could be further utilized by anammox microbiota and dissimilatory nitrate reduction to ammonia (DNRA) microorganisms, doubling the efficiency of total nitrogen removal (96.5 ± 2.3 %) for biological nitrogen removal and ammonia generation (12.6 mg NH4+-N L-1 h-1), respectively. Thus, our work paves an appealing way for the sustainable treatment and utilization of nitrate for ammonia fuel production by strategically regulating the electron transfer pathway across the biotic-abiotic interface.