Abstract
<jats:p>Across various fields, interest in hybrid heterogeneous molecular materials is steadily increasing due to their tunability and versatility. Selective ammonia oxidation represents an attractive strategy for nitrogen-cycle closure, concomitantly generating proton equivalents relevant in hydrogen-related energy conversion processes. Here we report the first hybrid system capable of conducting photocatalytic ammonia oxidation (AO), consisting of a molecular ruthenium catalyst (RuBda; Bda = 2,2′ bipyridine 6,6′ dicarboxylate) covalently anchored onto graphitic carbon nitride (g C3N4, CN) and Sulfur-doped g C3N4 nanoparticles (10P, 50P). The resulting hybrid photocatalysts (CNRuBda, 10PRuBda, 50PRuBda) combine the light harvesting properties and robustness of C3N4 with the well-defined reactivity of Ru in the catalytic centre of the RuBda moiety. Covalent grafting via surface –NH2 defects enables high Ru loadings (up to 5.5 wt%) while preserving the structural integrity of the C3N4 framework. Electrochemical studies show that immobilised RuBda retains its intrinsic AO activity, exhibiting a ~0.33 V (vs NHE) cathodic shift of catalytic onset and turnover frequencies up to 5.6 s-1 (CNRuBda). Under Xe lamp irradiation, all hybrid catalysts oxidise NH3 to N2 and H+, with CNRuBda producing up to 9.09 µmol N2 in 3 h, a TOF of 1.55 × 10-3 s-1, and a cumulative TON of 44 over three cycles. Accompanying minor NO2- formation and background N2 evolution highlight the intrinsic complexity of AO. Overall, this work establishes the first proof-of-concept molecularly functionalised C3N4 photocatalysts for selective AO.</jats:p>