Fluorine Density Gradient Engineering in Triazine-Based Nanoporous Organic Polymers for Highly Selective SF ₆ Capture

Rational design of adsorbents for the greenhouse gas sulfur hexafluoride (SF₆) requires precise control over pore microenvironments to enhance host-guest interactions. While fluorination is known to improve SF₆ affinity, the quantitative impact of fluorine density on separation performance remains insufficiently understood. Here, we introduce a fluorine density gradient engineering strategy to systematically tune the fluorine content (0-16.34 wt %) within a robust triazine-based nanoporous polymer (TNOP) framework. Increasing fluorine density simultaneously enhances SF₆ uptake, isosteric heat of adsorption (<i>Q</i>_<i>st</i>), and SF₆/N₂ selectivity, with TNOP-5 (16.34 wt % F, 772 m² g^-1, ∼0.64 nm pore size) achieving a high selectivity of 108 at 298 K, significantly outperforming its nonfluorinated analog (77). Dynamic breakthrough experiments confirm high separation efficiency under practical flow conditions. Molecular simulations reveal that higher fluorine content strengthens dipole-induced and C-H···F interactions, with optimal performance emerging from the synergy between precise fluorine density and ultramicropore confinement. This work establishes fluorine density tuning as a practical and effective design principle for nanoporous adsorbents targeting challenging gas separations.