Carbazole-Based Hyper-Cross-Linked Polymers for Efficient Iodine Capture via Framework Engineering

Abstract Radioactive iodine released from nuclear waste processing poses significant environmental and safety risks. Developing cost-effective, high-performance adsorbents remains a challenge due to the inherent trade-off between physical porosity and chemical affinity. In this study, we apply a rational framework engineering strategy to construct three carbazole-based hyper-cross-linked polymers (NBU-HCP-1, NBU-HCP-2, and NBU-HCP-3). These materials are synthesized via a facile Friedel-Crafts knitting process using monomer 3, a multi-phenyl-extended carbazole derivative derived from inexpensive precursors. This synthetic control resulted in a materials series where the Brunauer–Emmett–Teller (BET) surface areas differ significantly (1137 to 206 m2 g–1), while the heteroatom density follows the exact reverse order, successfully decoupling physical porosity from chemical affinity for a systematic comparative study. Consequently, NBU-HCP-3 exhibits an iodine vapor capture capacity of 2.92 g g–1 at 75 °C and reaches 98% of its equilibrium capacity within 180 min. Notably, this performance exceeds that of NBU-HCP-1, despite the latter possessing a significantly higher BET surface area (1137 vs. 206 m2 g–1). X-ray Photoelectron Spectroscopy (XPS) analysis and density functional theory (DFT) calculations indicate that the dense N/O sites in NBU-HCP-3 generate a local electric field (ESP difference: 56.83 kcal mol–1), which facilitates charge-transfer interactions and stabilizes iodine as polyiodide species. This framework-polarity regulation strategy provides a scalable route for the design of efficient radionuclide capture materials.