Efficient capture of gaseous, aqueous iodine, near-sunlight white light emission and iodine sensing in 12-connected and [Pb6]-cluster based MOFs

Abstract

The radioactive iodine as highly harmful fission waste from nuclear power production features fifteen-million years radiation period and easy diffusion, yet its efficient treatment and sensing is greatly challenged by the operation concentration as low as several ppm in gaseous and aqueous medium. A (3,12)-connected and [Pb₆(µ₄-O)₂(COO)₈] based MOFs of [Pb₆(μ₄-O)₂(pia)₄]·4DMF (1) was rationally constructed as a multifunctional materials for iodine capture and sensing, which possesses the highest void fraction of 34.4 % among all known cluster based Pb-MOFs. Microwave-assistant solvothermal reaction facilitates gram-scale synthesis of 1 with yield of 82 % within 4 h. The 1D round channels sized at 1.0 nm coupled with high structure stability of the MOFs contribute to accommodate iodine. 1 can rapidly capture iodine vapor at 70 °C in 6 h with fully utilized nanopores, resulting in a high iodine packing density of 3.52 g cm⁻³ closely matching that of iodine single crystal. Particularly, the MOFs of 1 exhibits long-lasting adsorption to iodine vapor at extremely low concentration of 120 ppm, as well as efficient capture of I₂ in 1.0 × 10^-4 M aqueous solution with removal percentages of 67.1 % in only 20 min, driven by synergistic host–guest interactions. The MOFs is further discovered as a single-phase white-emitting phosphor with quite broad fluorescence spectrum covering the entire visible region, benefited from the multiple Pb···Pb interactions and change-transfer between the metal and ligand. White light emitting diodes can be created by coating commercial blue LEDs with phosphor 1, generating pure white chromaticity coordinates of (0.313, 0.338), a near daylight color temperature of 6420 K, a high color rendering index of 85 and light maintenance up to 120 °C. The migration of iodine into the channels of 1 led to obvious fluorescence quenching. As the combined result, 1 presents a rare and instructive multifunctional MOFs that exhibiting efficient capture to low-concentration iodine in gaseous/aqueous condition and fluorescent detection to iodine.