Supramolecular organic framework for iodine capture from seawater

Iodine is a crucial element in various industries, but it is one of the least abundant nonmetallic elements on Earth. Although seawater holds around 70% of the world's iodine reserves, its low concentrations—approximately 60 ppb—make extraction challenging. Additionally, radioactive iodine, which is released during nuclear accidents, presents significant long-term risks to marine ecosystems and human health. Therefore, there is an urgent need for effective strategies to both extract iodine from seawater and address radioactive iodine pollution.

Now, a team at Hainan University has developed a supramolecular organic framework (SOF) for iodine capture from seawater. This framework has demonstrated the ability to remove 79% of iodine pollution in a simulated contaminated environment. In natural seawater, it achieves an ultrahigh iodine adsorption capacity of 46 mg g⁻¹ within a 20-day extraction period. 

“The sustainable extraction of iodine from seawater is not only vital to meet the increasing global demand but also essential for mitigating the ecological risks posed by radioactive iodine pollution,” said lead author Ning Wang. “Innovative materials can contribute to the field by enhancing the selectivity and capacity for iodine extraction from seawater. Our findings showcase an effective strategy for fabricating multi-dimensional 3D SOF materials and also present a promising material for iodine capture from seawater.”

Wang is a professor in State Key Laboratory of Marine Resource Utilization in South China Sea, Hainan University.

Multi-dimensional space for iodine storage

Supramolecular organic frameworks (SOFs) are crystalline porous frameworks materials formed through weak noncovalent interactions, such as hydrogen bonding and π-π stacking. Compared to the other crystalline porous frameworks, SOFs possess abundant active sites, flexible storage space, and enhanced reversibility, making them ideal for storing target substances. In the study, the researchers developed a novel 3D SOF through the self-assembly of two adjustable compounds for highly efficient iodine recovery from seawater. This 3D SOF contains interconnected 1D channels and 2D interlayer spaces, providing ample iodine storage space for iodine, which enables it to achieve a high iodine adsorption capacity.

Selective Adsorption of Iodine

The researchers discovered that the 3D SOF exhibits an outstanding adsorption capacity for triiodide, one of the highest reported iodine adsorption capacities for non-covalent organic framework in aqueous conditions. The material also demonstrates impressive reusability, retaining over 88% of its initial adsorption capacity after six reuse cycles. Additionally, it achieved an ultrahigh iodine adsorption capacity in natural seawater.

The 3D SOF exhibits selective adsorption ability of triiodide in simulated nuclear-polluted seawater and iodide in natural seawater. this selectivity is attributed to the charge interactions of amine and pyridyl groups, as well as the binding affinity of aromatic rings.

“The extraction of iodine from marine resources and the management of iodine pollution requires a comprehensive understanding of both chemical and environmental processes.” Professor Wang said. “The various iodine species, such as iodides and iodates, and their complex interactions with other interfering ions in seawater, highlight the need for highly selective and efficient extraction methods. These methods are crucial for ensuring sustainable iodine recovery and the long-term mitigation of iodine pollution.”