Tailoring the Intermediate Energy Level Density to Enhance the Visible and Near-Infrared Photocatalytic Activity of...

Poly(heptazine imides) (PHI) possesses a wide bandgap, which restricts its light absorption range and leads to low photocatalytic activity. In this work, an intermediate energy level was introduced into PHI via the 2p orbitals of doped carbon. By modulating the carbon doping concentration, the density distribution of this intermediate energy level was optimized. Experimental results show that introducing a low-density intermediate level can temporarily trap carriers, thereby prolonging carrier lifetime and suppressing non-radiative recombination, which enhances visible-light photocatalytic activity. Meanwhile, introducing an appropriate amount of high-density intermediate levels can act as a stepping stone for electron transitions, enabling efficient capture of low-energy photons in the near-infrared region and thus activating near-infrared photocatalytic hydrogen production activity, with a rate reaching up to 4.3 μmol·h^-1. This study clarifies the regulatory mechanism of intermediate energy level density on photocatalytic performance from the perspectives of non-radiative recombination suppression and band structure modulation, offering important insights into the design of broadband-responsive semiconductor photocatalysts.