Enhancing Visible Light CO₂ Reduction via π-Electron Delocalization in Barbituric Acid-Modified Poly(triazine imide) Crystals

Poly(triazine imide) (PTI) holds significant promise for photocatalytic CO2 reduction by addressing the limitations of conventional carbon nitrides. However, its practical application remains constrained by a narrow visible-light absorption. Herein, we report a barbituric acid (BA)-mediated copolymerization strategy to engineer π-electron delocalization within the triazine framework for broadening light-harvesting spectrum and optimizing charge carrier transport. Under visible light irradiation (λ ≥ 400 nm), the optimized PTI-BA1.0 photocatalyst achieves a CO evolution rate of 10 μmol h–1 (333 μmol g–1 h–1) with 95% selectivity, representing a 5-fold enhancement over pristine PTI. Remarkably, the apparent quantum efficiency reaches 13.6% at 365 nm, underscoring its superior CO2 photoconversion capability. Mechanistic investigations via in situ diffuse reflectance infrared Fourier transform spectroscopy and density functional theory calculations elucidate the energetically favorable pathways for CO2 activation, reduction and CO desorption. This work not only provides a rational design strategy for modulating the optoelectronic properties of crystalline carbon nitride but also advances the development of high-performance photocatalysts for sustainable CO2 conversion.