Sn Doping Enhances Light Absorption of Lanthanum Poly(Heptazine Imide) for Efficient Photocatalytic Hydrogen Evolution

ABSTRACT

Lanthanum poly(heptazine imide) (La‐PHI) is a novel, highly crystalline PHI material. However, its visible‐light absorption remains weak due to the limited contribution of La ³⁺ to the band structure of PHI. Considering that the ionic radius of Sn ²⁺ is comparable to that of La ³⁺ , Sn ²⁺ can stably occupy the identical sites within the PHI framework. Meanwhile, the 5p orbitals of Sn ²⁺ can effectively hybridize with the N 2p orbitals, thereby introducing intermediate energy levels. Experimental results demonstrate that Sn ²⁺ doping generates an intermediate level at approximately 2.30 eV within the forbidden band, effectively broadening the light absorption range. Through optimizing the Sn ²⁺ doping amount, the photocatalytic activity of the obtained sample under 420 < λ < 780 nm is 5.3 times that of the original La‐PHI. This study indicates that Sn ^{2 +} doping is an effective strategy for extending the light absorption range, and the introduction of intermediate levels provides new insights into the design of highly efficient PHI‐based photocatalysts.