Spatial confinement of nitrogen through carboxyl-induced hydrogen bond networks in covalent organic frameworks for efficient overall ammonia photosynthesis

Covalent organic frameworks (COFs) have gained attention as promising candidates for photocatalytic nitrogen (N2) reduction to ammonia (NH3) due to their highly ordered structures and customizable molecule design. However, their efficiency in photocatalytic NH3 synthesis is limited by the generally weak affinity for N2. Inspired by spatial confinement effects, hydrophilic carboxyl groups were incorporated into a diketopyrrolopyrrole-based COF ( DPPCOOH-COF ) to form a localized hydrogen bond network that retains N2near the active sites. This structural modification significantly boosts N2adsorption and activation on COFs and lowers the energy cost for NH3 production, facilitating a more efficient reaction pathway. Remarkably, DPPCOOH-COF achieves a record NH3 production rate of 521.37 mu mol g-1 h-1 without any sacrificial agents, outperforming its structural counterpart, DPPC-COF, which lacks carboxyl groups. This study provides the first successful demonstration of COFs enabling overall NH3 photosynthesis, presenting a molecular-level design approach that effectively addresses solid-liquid-gas interactions within photocatalytic processes.