Highly Efficient and Reversible Iodine Capture in Hexaphenylbenzene-Based Conjugated Microporous Polymers

Yaozu Liao,Zihao Ren,Benjamin M Mills,Charl F J Faul,Jens Weber

doi:10.1021/acs.macromol.6b00901

Abstract

The effective and safe capture and storage of radioactive iodine (129I or 131I) is of significant importance during nuclear waste storage and nuclear energy generation. Here we present detailed evidence of highly efficient and reversible iodine capture in hexaphenylbenzene-based conjugated microporous polymers (HCMPs), synthesized via Buchwald–Hartwig (BH) cross-coupling of a hexakis(4-bromophenyl)benzene (HBB) core and aryl diamine linkers. The HCMPs present moderate surface areas up to 430 m2 g–1, with narrow pore size distribution and uniform ultramicropore sizes of less than 1 nm. Porous properties are controlled by the strut lengths and rigidities of linkers, while porosity and uptake properties can be tuned by changing the oxidation state of the HCMPs. The presence of a high number of amine functional groups combined with microporosity provides the HCMPs with extremely high iodine affinity with uptake capacities up to 336 wt %, which is to the best of our knowledge the highest reported to date. Two ...

Highlights

Microporous adsorbents for selective capture of micropollutants have received increasing interest in recent years.[1−4] Capture of volatile iodine (I2) is of special interest, since the long-lived radioactive iodine isotopes (e.g., 129I or 131I) need to be removed from exhaust fumes of nuclear power plants regularly.[2−4] fast removal of radioactive iodine is needed in the case of nuclear accidents, as iodine shows significant biouptake and can be accumulated in living matter
After treatment with 1.0 M anhydrous hydrazine/tetrahydrofuran in a glovebox, hexaphenylbenzene-based conjugated microporous polymers (HCMPs)-1 and -2 became gray while the HCMP-3 and -4 showed no obvious changes in color. This behavior indicated that the pristine HCMP-1 and -2 containing the π-electron-rich phenylenediamine group were sensitive to exposure to the reducing hydrazine
In an attempt to further identify the reasons for the differences in the iodine uptake capacity and UV−vis/NIR spectra of the different HCMPs, we explored the use of timedependent density functional theory (TD-DFT) calculations to provide additional insight

Summary

■ INTRODUCTION

Microporous adsorbents for selective capture of micropollutants have received increasing interest in recent years.[1−4] Capture of volatile iodine (I2) is of special interest, since the long-lived radioactive iodine isotopes (e.g., 129I or 131I) need to be removed from exhaust fumes of nuclear power plants regularly.[2−4] fast removal of radioactive iodine is needed in the case of nuclear accidents, as iodine shows significant biouptake and can be accumulated in living matter. The UV−vis spectra of all extracts showed two absorbance maxima at 291 and 360 nm, assigned to polyiodide anions (Figure S20).[4,54] The amount of iodine released from all the HCMPs adsorbents increased linearly with time, following pseudo-zero-order kinetics within the monitored time frame (70 min), which cannot be compared directly to the vapor adsorption/ desorption experiments. We believe that this release behavior is governed by host−guest interactions,[19] facilitating the regeneration of the adsorbent for reuse. These very high values make our adsorbents attractive materials for use as robust recyclable and reversible iodine uptake adsorbents

■ CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES