K⁺ Ion-Doped Mixed Carbon Nitride: A Daylight-Driven Photocatalyst and Luminophore for Enhanced Chemiluminescence

Photocatalytic production of reactive oxygen species from O₂ at the interface of the photocatalyst is significant to convert luminous energy like daylight into chemical energy and could be momentous for a reactive oxygen species-based chemiluminescence system. Herein, we synthesized a novel K⁺ ion-doped tri-s-triazine/triazine mixed carbon nitride (MCN), in which K⁺ ions were intercalated into the layers in a bridging manner. After a mild daylight treatment for 30 min, the MCN suspension could produce long-lifetime reactive oxygen species and further directly produce intense and stable chemiluminescence emission in the presence of luminol. In particular, the chemiluminescence intensity was 780 times that of H₂O₂-luminol, and MCN could be recycled several times in the chemiluminescence system. The mechanism results revealed a large number of reactive oxygen species that were generated from O₂ on the surface of MCN through a temperate photocatalytic process. In the theoretical calculation, the charge density of N interacting with K⁺ ions was significantly more negative than that at the corresponding position in graphitic carbon nitride, which was beneficial to the adsorption and activation of oxygen, and the narrower band gap suggested that the doping of K⁺ ions was conducive to the intramolecular charge transfer interaction. Then, the long-lifetime reactive oxygen species triggered the conversion of luminol into an excited-state intermediate, which further transferred energy to MCN, producing strong chemiluminescence emission. The K⁺ ion-doped MCN might conduct as an efficient photocatalyst for reactive oxygen species generation, recyclable catalysts, and luminophores in the photoinduced chemiluminescence system.