Molten salt-mediated cyano group augmentation and morphology modulation in carbon nitride for boosting photocatalytic activity

Abstract

Graphitic carbon nitride (g-C₃N₄) is recognized as one of the excellent candidates of green photocatalysts due to its unique merits such as low cost, facile synthesis and suitable energy band structure. Herein, we report a systematically optimized carbon nitride catalyst (U1T5-CN-K) with integrated cyano group augmentation and morphology modulation, which is synthesized by the synergistic combination of potassium-ion (K⁺) molten-salt method and precursor regulation. It is verified that the molten-salt method using KCl facilitates the doping of K⁺ and the formation of cyano (–CN) groups. On this basis, the accomplished morphology modulation through precursor regulation significantly enhances the specific surface, which is responsible for the synergistic interplay with K⁺ dopants, thereby markedly elevating the exposed active sites and crystallinity. The K⁺ primarily enhance the oxygen (O₂) adsorption capacity and act as electron capture sites based on the experimental characterization and theoretical calculations, thereby effectively suppressing the recombination of photogenerated carriers. Meanwhile, the –CN groups directly or indirectly promote proton (H⁺) and O₂ absorption, thereby advancing the reaction progress. The obtained catalysts exhibit remarkably enhanced spatial charge separation efficiency and reaction kinetics in photocatalytic reactions, delivering a high hydrogen peroxide (H₂O₂) production rate of 13.7 mmol g⁻¹ h⁻¹. Moreover, they demonstrate an improved degradation rate of tetracycline hydrochloride (TH), which is ∼12 times that of their pristine counterpart. The present work provides some valuable insights into the synergistic mechanism by combining group augmentation and morphology modulation for boosting the photocatalytic performance of g-C₃N₄ materials.