Understanding and Steering Nitrogen Fate in Photocatalytic Nitrate Reduction

Photocatalytic nitrate reduction is assessed through nitrate conversion, although the reaction can redistribute nitrogen among nitrite, nitric oxide (NO)‐derived intermediates, nitrous oxide (N 2 O), dinitrogen (N 2 ), ammonia/ammonium (NH 3 /NH 4 + ), and emerging C–N products. The environmental and resource value of the process depends on nitrogen fate rather than nitrate disappearance alone. This review establishes a product‐centred framework for understanding and steering that fate. We first consolidate the nitrogen network across surface, liquid, and gas phases, and distinguish primary selectivity from the final product distribution after secondary conversion and phase transfer. We then relate product formation to three coupled levels: nitrate entry, branching of NO‐derived intermediates, and branch completion; surface functions governing adsorption, intermediate binding, cooperative sites, and active hydrogen; and the photochemical redox environment, including charge delivery and the oxidation half‐reaction. Evidence from model systems, real waters, and time‐resolved operation shows why high selectivity under one condition cannot be treated as an intrinsic catalyst property. On this basis, N 2 ‐oriented treatment requires verified removal without nitrite, ammonium, or N 2 O leakage, whereas NH 3 ‐oriented conversion requires product preservation, capture, and a favourable process balance. Connecting working‐interface chemistry with water‐matrix effects, reactor operation, and product recovery provides a route from empirical nitrate removal to deliberate nitrogen management.