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

Graphitic carbon nitride (C₃N₄) 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 C₃N₄ layers through the self-assembly of potassium citrate and melamine–urea monomers. The introduction of N vacancies disrupts the symmetry of C₃N₄, 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 C₃N₄, 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 minutes. 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.