Abstract
This work presents sodium poly(heptazine imide) (NaPHI)-based materials, synthesized in a NaCl medium, as highly effective platforms for CO(2) capture. High crystallinity-an often-overlooked aspect in PHI frameworks-is identified as a key factor governing CO(2) adsorption capacity in microporous structures. Thermogravimetric analysis and manometric studies reveal a CO(2) uptake of ≈3.8 mmol g(-1), at 1 bar and 25 °C, surpassing most reported PHI-based adsorbents under similar conditions. Exchanging Na(+) with K(+) or Rb(+) preserves CO(2) adsorption performance, whereas Cs(+) incorporation induces structural distortion, greatly reducing CO(2) adsorption capacity in PHI. These materials exhibit excellent cyclic stability (20 cycles) without degradation and CO(2) adsorption capacity loss. Notably, at flue gas-relevant temperature (100 °C), NaPHI attains a CO(2) capacity of 2.1 mmol g(-1), doubling the performance of benchmark Zeolite 13X (1.1 mmol g(-1)). Ideal Adsorbed Solution Theory confirms remarkable CO(2)/N(2) selectivity (≈3.8 mmol g(-1) vs typical N(2) adsorption of 0.3 mmol g(-1)), a critical property for postcombustion CO(2) capture. These findings position PHI-based materials as a disruptive platform for CO(2) adsorption, offering 1) straightforward synthesis from readily available precursors, 2) promising scalability, and 3) outstanding performance.