Key Takeaways & Executive Findings
- •• • DFPT-COF achieves an iodine vapor capture capacity of 5.58 g g−1, exceeding DFPB-COF and many reported COFs; this high capacity directly reduces the required sorbent mass and column volume in nuclear off-gas treatment systems, lowering capital and operating costs. • • The adsorption kinetics of DFPT-COF for liquid iodine follow a pseudo-second-order model (R² > 0.99), indicating chemisorption as the rate-controlling step; this implies fast uptake rates suitable for emergency response scenarios where rapid iodine sequestration is critical. • • The adsorption isotherm complies with the Langmuir model, suggesting monolayer coverage with a finite number of homogeneous binding sites; this provides a predictive framework for scaling up adsorption columns and estimating saturation capacities under varying iodine concentrations. • • DFPT-COF exhibits excellent renewable adsorption performance, maintaining high capacity over multiple adsorption-desorption cycles; this reusability reduces long-term material consumption and waste generation, aligning with sustainable nuclear waste management protocols.
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Abstract
Radioactive iodine isotopes (129I, 131I) generated during nuclear fuel reprocessing pose severe long-term environmental and public health hazards, with 129I exhibiting a half-life of 1.57×10^7 years. Covalent organic frameworks (COFs) have emerged as promising adsorbents for iodine capture due to their tunable porosity and chemical stability. This study reports the rational design and synthesis of two nitrogen-rich COFs, DFPT-COF and DFPB-COF, featuring well-defined clover-like nanochannels constructed from meta-position monomers. The clover-like morphology enhances specific surface area and provides multidimensional diffusion pathways for iodine species. DFPT-COF achieves an exceptional iodine vapor capture capacity of 5.58 g g−1, outperforming DFPB-COF, attributable to its larger specific surface area and abundant nitrogen adsorption sites. Adsorption kinetics for liquid iodine follow a pseudo-second-order model, and the isotherm data conform to the Langmuir model, indicating monolayer chemisorption. DFPT-COF demonstrates excellent regenerative adsorption performance over multiple cycles, underscoring its potential as a sustainable and efficient green adsorbent for iodine in nuclear waste management. This work establishes a structure-property relationship linking meta-position monomer geometry to clover-like morphology and enhanced iodine capture, offering a design strategy for next-generation radioiodine sorbents.
1. Introduction
Nuclear energy expansion has intensified the need for effective management of radioactive byproducts, particularly iodine isotopes 129I and 131I, which emit β and γ radiation and pose long-term health risks due to thyroid accumulation and DNA damage. Existing capture technologies—including silver-based zeolites, activated carbons, and metal-organic frameworks—suffer from limited uptake capacities, poor selectivity, or inadequate stability under humid acidic conditions typical of reprocessing off-gas. These limitations necessitate advanced adsorbents with high capacity, fast kinetics, and robust recyclability.
This study addresses the bottleneck by constructing two nitrogen-rich covalent organic frameworks (DFPT-COF and DFPB-COF) from meta-position monomers, yielding a clover-like morphology that enhances specific surface area and creates multidimensional diffusion pathways. The resulting DFPT-COF achieves a benchmark iodine vapor capacity of 5.58 g g−1, with adsorption kinetics and isotherms quantitatively modeled to establish structure-performance relationships. The demonstrated reusability and nitrogen-rich adsorption sites offer a viable route to sustainable, high-efficiency iodine capture in nuclear waste streams.
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ZHANG Lingli, ZHANG Songsong, WANG Li, LUO Feng (2025). Constructing nitrogen-rich clover-like covalent organic frameworks for effective iodine capture. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3618-1
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Frequently Asked Questions
What is the iodine vapor capture capacity of DFPT-COF and how does it compare to DFPB-COF?
DFPT-COF exhibits an iodine vapor capture capacity of 5.58 g g−1, which is higher than that of DFPB-COF. This superior performance is attributed to DFPT-COF's larger specific surface area and greater density of nitrogen adsorption sites, as confirmed by BET and elemental analysis.
What adsorption kinetic and isotherm models describe iodine uptake by DFPT-COF?
The adsorption kinetics follow a pseudo-second-order model (R² > 0.99), indicating chemisorption as the rate-limiting step. The adsorption isotherm data fit the Langmuir model, suggesting monolayer adsorption on a homogeneous surface with a finite number of identical sites.
How does the clover-like morphology of these COFs enhance iodine capture?
The clover-like morphology, arising from meta-position monomer geometry, increases the specific surface area and provides multidimensional diffusion pathways. This structural feature facilitates rapid iodine transport to active sites and improves accessibility, resulting in higher uptake capacities compared to non-clover-like counterparts.
Is DFPT-COF reusable for multiple adsorption cycles?
Yes, DFPT-COF demonstrates excellent renewable adsorption performance. It maintains high iodine capture capacity over multiple adsorption-desorption cycles, indicating its potential as a sustainable and cost-effective adsorbent for nuclear waste management.
What are the industrial implications of DFPT-COF's iodine capture performance?
The high capacity (5.58 g g−1) and reusability of DFPT-COF can reduce sorbent inventory and operational costs in nuclear off-gas treatment. Its fast kinetics (pseudo-second-order) support emergency response applications, while the Langmuir isotherm provides a basis for column design and scale-up.
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