Modulating the properties of g-C₃N₄through two-step annealing and ionic-liquid gating

The graphitic carbon nitride (g-C₃N₄) is an important optoelectronic and photocatalytic material; however, its application is limited by the high recombination rate of the electron-hole (e^--h⁺) pairs. In this work, we reported a novel strategy combining two-step annealing treatment and ionic-liquid (IL) gating technology for effectively regulating the properties of g-C₃N₄, especially largely reducing the recombination rate of the e^--h⁺pairs, which is evidenced by a remarkable reduction of the photoluminescence (PL) intensity. Firstly, g-C₃N₄samples with typical layered structure were obtained by annealing melamine with temperature of 600 °C. Further annealing of the samples at 600 °C with much longer time (from 4 h to 12 h) were found to effectively reduce the imperfections or defects, and thus the PL intensity (49% reduction). This large reduction of PL intensity is attributed to the improved interconnection of triazine units, the shortened charge transfer diffusion distances, and the reduced interlayer spacing, which facilitate electron relocation on the g-C₃N₄surface. Secondly, by post-treating the annealed sample with IL, the PL intensities were found to be further reduced, mainly due to the passivation of charged defect centers by IL. Additionally, applying an external electric field in an IL environment can significantly enhance the charged defect passivation. Overall, by utilizing electric field-controlled IL gating, defect states in g-C₃N₄were passivated, leading to a significant reduction in PL intensity and an extension of PL lifetime, thereby effectively decreasing the e^--h⁺recombination rate in the material. This study demonstrates a new approach for defect passivation, providing insights and strategies for modulating properties of advanced materials such as g-C₃N₄.