Iodine capture using spirobifluorene-based covalent organic frameworks

Abstract

Two covalent organic framework materials based on rigid spirobifluorene units, DbSp-COF and BbSp-COF, were designed and synthesized for efficient capture of gaseous and solution phase iodine. Both DbSp-COF and BbSp-COF exhibit excellent thermal stability, retaining 77% and 90% residual mass at 800 °C, respectively. The materials show strong hydrophobicity with contact angles greater than 100°. Under 80% humidity, both DbSp-COF and BbSp-COF maintain over 85% of their adsorption performance. Under simulated nuclear fuel reprocessing conditions (75 °C, atmospheric pressure), the saturated adsorption capacities of DbSp-COF and BbSp-COF for gaseous iodine are 4.73 g·g⁻¹ and 4.48 g·g⁻¹, respectively. In a 500 mg·L⁻¹ iodine solution in cyclohexane, their maximum adsorption capacities are 569.3 mg·g⁻¹ and 585.7 mg·g⁻¹, respectively. Characterization results indicate that the adsorption mechanism involves charge transfer between iodine molecules and π-conjugated frameworks, forming I₃⁻/I₅⁻ polyiodides. After four cycles, the adsorption capacity decreases by less than 15%, highlighting their potential application in radioactive iodine treatment.