Ionic liquid gating-induced defect passivation and enhanced photocatalytic performance in graphitic carbon nitride (g-C₃N₄) semiconductors

Ionic liquid gating (ILG) is an emergent technique for controlling multiple types of ionic doping and leads to numerous attractive physical properties in quantum materials. This study widens its intriguing applications in metal-free graphitic carbon nitride (g-C₃N₄) semiconductor which is distinct by various extrinsic defects (vacancies, interlayer defects, etc) and intrinsic defects (irregular melon chains, dangling bonds, etc.). Here, the efficient passivation of defects is realized in g-C₃N₄through combined electrostatic and electrochemical mechanisms. By optimizing the ionic liquid concentration and applying a negative electric field, the gated g-C₃N₄exhibit a changed local bonding environment, an increased bandgap, as well as a suppression of photoluminescence (PL) intensity over 80%. Our results demonstrate that the charged ions from the mixed electrolyte passivate the charged defect centers, redistribute the charges within the g-C₃N₄framework, leading to the improved photogenerated carries separation, which is verified by the enhanced photocatalytic efficiency of treated g-C₃N₄. In particular, the changes of the density of states near the Fermi level reflect ionic interaction induced defect passivation in g-C₃N₄, which plays a key role in regulating its PL properties. These findings provide novel insights in ILG mechanisms in layered porous materials and shed light on its potential prospects in other semiconductors with controlled defect engineering.