Tailoring the Energy Level Depth and Density To Regulate the Visible and Near-Infrared Photocatalytic Activity of Poly(heptazine imide)

Very few studies have focused on and elucidated the mechanism by which the energy level depth and density regulate the visible and near-infrared photocatalytic activity. By altering the alkalinity during the thermal polymerization process of PHI, defective PHI (named NCCN-x, where x represents the amount of NH₄Cl added) was synthesized, and the number of defects was controlled, thereby regulating the density of deep and shallow energy levels. Experiments have demonstrated that the introduction of an appropriate amount of deep energy levels has a positive effect on broadening the light absorption range, thus generating near-infrared light activity. Meanwhile, the introduction of shallow energy levels enhances visible light activity by extending the carrier lifetime and suppressing nonradiative recombination. Our work clarifies the mechanism by which energy level depth and density affect photocatalytic activity, which is conducive to the regulation of visible and near-infrared light activity.