Porous pillar[6]arene-based polymers for reversible iodine capture

Abstract

Iodine in nuclear waste can cause serious environment pollution and health risks, and has thus driven more development of materials for iodine capture. Herein, a novel porous pillar[6]arene-based polymer (P-P6APs) was easily prepared as a supramolecular adsorbent for iodine via a one-step crosslinking reaction between per-hydroxylated pillar[6]arene and decafluorobiphenyl. Nitrogen adsorption tests demonstrated that this material possessed a satisfactory surface area (S _BET = 366 m² g^-1) and pore diameter (3.8 nm), which was due to the macrocyclic scaffolds. Compared with commercially available activated carbon, P-P6APs exhibited superior adsorption efficiency toward volatile iodine not only in the solution phase (water and n-hexane) but also in the gas phase. This outcome was mainly ascribed to nonspecific adsorption by the pore structure of the crosslinked material coupled with multiple intermolecular binding sites of the macrocyclic scaffold. Moreover, this supramolecular absorbent was recyclable and could be reused 5 times with no obvious loss of performance.

Scheme 1. Pillar[6]arene-based polymer networks derived from nucleophilic aromatic substitution reactions. Left: Synthesis of the high-surface-area porous P-P6APs from P6A-OH and DFB. Right: Schematic of the P-P6APs structure.

Fig. 1. (a) FT-IR spectra of P6A-OH, P-P6APs and DFB. (b) Nitrogen adsorption/desorption isotherm of P-P6APs. (c) The cumulative pore volume (pore diameter) of P-P6APs obtained via a Barrett–Joyner–Halenda analysis. (d) SEM image of P-P6APs.

Fig. 2. (a) Photograph showing solution color change when 6.0 mg of P-P6APs was placed in I₂/KI (aq) (250 ppm). (b) Time-dependent UV/vis absorption spectra of I₂/KI (aq) (250 ppm) upon addition of P-P6APs (6.0 mg). (c) Time-dependent I₂ uptake efficiency based on the absorption peak at 286 nm after adding P-P6APs, AC and MPs. (d) Iodine adsorption efficiency of P-P6APs after the same material is recycled 5 times in I₂/KI (aq).

Fig. 3. (a) Photograph showing color change when 24.0 mg of P-P6APs was placed in an iodine/n-hexane solution (1 mM). (b) Time-dependent UV/vis absorption spectra of an iodine/n-hexane solution (1 mM) upon addition of P-P6APs (24.0 mg). (c) Time-dependent I₂ uptake efficiency based on the absorption peak at 520 nm after adding P-P6APs, AC and MPs. (d) Iodine adsorption efficiency of P-P6APs after the same material was recycled 5 times in an iodine/n-hexane solution.

Fig. 4. Photos of P-P6APs (a) before and (b) after exposure to iodine vapor for 11 h. (c) Time-dependent I₂ vapor uptake efficiency of P-P6APs, AC and MPs at 80 °C. (d) Iodine adsorption efficiency of P-P6APs after the same material is recycled 5 times for iodine vapor capture.