Dual-site engineering of N vacancies and K single-atoms in C3N4: Enabling spatial charge transfer channels for photocatalysis

Graphitic carbon nitride (C 3 N 4 ) is a promising photocatalyst due to its suitable band gap and polymer properties, but its efficiency is limited by the poor separation of photoinduced electron/hole (e – /h + ) pairs. To address this issue, we propose creating N vacancies within the layers and bridging K single-atoms between the C 3 N 4 layers through the self-assembly of potassium citrate and melamine–urea monomers. The introduction of N vacancies disrupts the symmetry of C 3 N 4 , promoting electron transfer along the delocalized π-conjugated network, while the presence of K atoms provides channels for electron transfer between the layers by forming N K N bridges, thereby leading to significant enhancement in the separation and transfer of e – /h + pairs across spatial dimension. As expected, the co-modified C 3 N 4 , with N vacancies and K single-atoms (designated as CN-K-V N ), exhibits excellent photocatalytic performance, with reaction rate constant of 9.69 × 10 −2 min −1 (7.39 × 10 −2 min −1 in real water environment) for tetracycline, achieving 80% degradation of tetracycline within 20 min. The reaction mechanism, as well as the toxicity of the degradation intermediates, is deeply discussed. This study provides a strategy to enhance the spatial separation of electrons for photocatalyst, highlighting its significance role in photocatalysis. • Dual-site engineering of N vacancies and K single-Atoms in C 3 N 4 established efficient spatial channels for charge separation. • These N vacancies and K single-atoms enhance electron transfer both within planes and between layers, respectively. • The degradation and detoxification of TC were effectively achieved. • The TC degradation pathways were deeply studied through in-situ DRIFTS experiment and intermediate analysis.