Bioinspired Fe Single-Atom Nanozyme Synergizes with Natural NarGH Dimer for High-Efficiency Photobiocatalytic Nitrate Conversion

Nitrate reduction is of paramount importance for both the restoration of natural ecosystems and the sustainable development of chemical industries but faces challenges in the rate-limiting step of nitrate-to-nitrite conversion. Herein, we demonstrate a semiartificial photobiosynthetic platform that synergistically combines cyano-rich carbon nitride (C₃N₄)- supported Fe single-atom nanozymes (Fe/C₃N₄-CN), which mimic the electron transfer function of the NarI subunit, with native NarGH dimers for efficient light-driven nitrate reduction. Under visible light irradiation, the photobiocatalyst exhibits a state-of-the-art capability for nitrate conversion with nearly 100% nitrite selectivity and an unprecedented reaction kinetic constant (k) that far exceeds those of all reported visible-light-driven photocatalysts, corresponding to a 68.9-fold enhancement over the isolated C₃N₄ photocatalysts. The synergized enzymatic catalytic efficiency (k_cat/K_M(app)) reaches 1.81 × 10⁶ M^-1 min^-1, far exceeding those of reported biological enzymes and enzyme-mimicking nanomaterials for nitrate conversion. Mechanistic studies at the atomic and molecular levels reveal that Fe single atoms and -C≡N groups on C₃N₄ mimic the heme b_D and heme b_P in the NarI subunit, forming a unique electron transfer chain between the biotic-abiotic interface that enables efficient nitrate reduction. This work represents an inspiring approach to overcome the kinetic bottleneck of nitrate-to-nitrite conversion, providing essential nitrite for sustainable anammox reactions and reducing energy consumption for ammonia production.