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

Abstract

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.