Key Takeaways & Executive Findings
- •• • PD-WY achieves iodine vapor uptake of 4.88 g g−1 at 75°C, surpassing many reported COFs; this high capacity is critical for reducing adsorbent volume in off-gas treatment systems. • • PD-WY exhibits rapid adsorption kinetics with K80% values of 3.25 g g−1 h−1 for I2 and 7.89 g g−1 h−1 for I3−, enabling fast decontamination in dynamic flow scenarios. • • In aqueous phase, PD-WY adsorbs 3.56 g g−1 of I3−, demonstrating effectiveness for water remediation; in organic phase, it captures 2.00 g g−1 of iodine in cyclohexane, showing versatility across media. • • The COFs maintain robust chemical resistance and thermal stability, essential for practical application under harsh nuclear waste conditions.
Abstract
Efficient sequestration of radioactive iodine species (I2, CH3I, I3−) is vital for nuclear safety and environmental protection. However, developing multifunctional adsorbents that remain effective under diverse conditions remains a significant challenge. Herein, we report two functionalized PD-COFs (PD-WS and PD-WY) with moderate crystallinity, outstanding thermal stability, and robust chemical resistance. They exhibit superior adsorption performance in both gas and liquid phases. Specifically, at 75°C, PD-WY achieves capacities of 4.88 g g−1 for I2, 1.55 g g−1 for CH3I, and 5.55 g g−1 for the I2/CH3I mixture, while high capacities are also retained at room temperature. In solution, PD-WY adsorbs up to 3.56 g g−1 of I3− in water and 2.00 g g−1 of iodine in cyclohexane. These COFs display rapid kinetics (K80% = 3.25 g g−1 h−1 for I2 and 7.89 g g−1 h−1 for I3−) and excellent selectivity. Mechanistic studies indicated that the excellent iodine affinity of PD-COFs arises from their rich electronic structures, abundant active sites, and charge transfer interactions. These findings position PD-COFs as highly promising adsorbents for nuclear waste treatment and environmental remediation.
1. Introduction
The management of radioactive iodine isotopes, particularly long-lived 129I and short-lived but bioavailable 131I, remains a critical bottleneck in nuclear waste treatment. These species exist in diverse forms—gaseous I2 and CH3I in off-gas streams, and molecular/ionic iodine (I2, I−, I3−) in aqueous environments. Their high volatility and mobility pose severe environmental and health risks. Conventional adsorbents such as activated carbons, zeolites, and metal-organic frameworks often suffer from limited multi-species capture capability, poor stability under harsh conditions, or slow kinetics, hindering their practical deployment.
This study addresses these limitations by engineering covalent organic frameworks (COFs) with thioether or vinyl functional groups, creating PD-WS and PD-WY. These materials combine high surface area, abundant active sites, and charge-transfer interactions to achieve exceptional iodine affinity. The reported performance metrics—including high uptake capacities, rapid kinetics, and selectivity across gas and liquid phases—demonstrate a significant advancement over existing sorbents, positioning PD-COFs as promising candidates for integrated nuclear waste treatment and environmental remediation.
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Yumei Luo, Yuancheng Qin, Cailing Ni, Chao Liu, Hewei Yan, Renjie Song, Jianping Zou (2026). Covalent Organic Frameworks Functionalized with Thioether or Vinyl Groups for Efficient and Rapid Capture of Multiple Iodine Pollutants. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-4044-3
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Frequently Asked Questions
What are the maximum adsorption capacities of PD-WY for different iodine species under varying conditions?
At 75°C, PD-WY achieves 4.88 g g−1 for I2 vapor, 1.55 g g−1 for CH3I, and 5.55 g g−1 for an I2/CH3I mixture. In aqueous solution, it adsorbs 3.56 g g−1 of I3−, and in cyclohexane, 2.00 g g−1 of iodine.
How do the adsorption kinetics of PD-COFs compare to existing iodine adsorbents?
PD-WY exhibits rapid kinetics with K80% values of 3.25 g g−1 h−1 for I2 and 7.89 g g−1 h−1 for I3−, indicating fast capture rates that are advantageous for continuous flow processes.
What structural features contribute to the high iodine affinity of PD-COFs?
The high affinity is attributed to rich electronic structures, abundant active sites from thioether and vinyl groups, and charge-transfer interactions with iodine species, enhancing binding and uptake.
Are PD-COFs stable under conditions relevant to nuclear waste treatment?
Yes, PD-COFs exhibit outstanding thermal stability and robust chemical resistance, essential for withstanding the harsh conditions encountered in nuclear waste streams.
How do PD-COFs perform in both gas and liquid phases, and what are the implications for practical applications?
PD-COFs demonstrate high adsorption capacities in both gas (I2, CH3I) and liquid (aqueous I3−, organic iodine) phases, making them versatile for capturing multiple iodine pollutants across different media, which is critical for comprehensive nuclear waste treatment.
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