Porous Silsesquioxane

Capturing the Invisible: A Breakthrough in Volatile Iodine Adsorption Using Porous Silsesquioxane–Imine Frameworks

Nuclear power continues to be a major pillar in the global transition toward cleaner energy. However, managing its byproducts—especially radioactive isotopes like volatile iodine—remains one of the industry's most pressing challenges. Volatile iodine species, including isotopes such as iodine-129 (with a half-life of 15.7 million years) and iodine-131 (a shorter-lived yet highly radiotoxic isotope), are major concerns due to their mobility, volatility, and potential long-term impact on human health and the environment.

A recent study published in ACS Applied Materials & Interfaces introduces a new class of materials—Porous Silsesquioxane–Imine Frameworks (PSIFs)—that demonstrate exceptional promise in capturing these elusive pollutants. This research not only presents a technical innovation but also marks a significant step forward in sustainable nuclear waste management.

Porous Silsesquioxane–Imine Frameworks (PSIFs)

PSIF are a porous hybrid material that combines two key structural components:

• Silsesquioxane Units: These are cage-like silica-based molecules that offer structural rigidity and excellent thermal stability.

• Imine Linkages: These organic bonds form through the condensation of amines and aldehydes, creating a flexible and tunable network.

By linking these two components, the team developed PSIFs—materials with large surface areas, chemical flexibility, and high thermal resilience.

Porous Silsesquioxane-Imine Frameworks (PSIF), constructed by a condensation of octa(3-aminopropyl)silsesquioxane cage compound (OAS-POSS) and selected multitopic aldehydes. The resulting PSIFs possess 3D micro-mesoporous structures with permanent porosity and high thermal stability. The resulting PSIFs are permanently porous (Brunauer-Emmet-Teller (BET) surface areas up to 574 m²/g), thermally stable and present a combination of micro-, meso- and macropores in their structures. Porous properties can be controlled by the strut length and rigidity of linkers.

Schematic representation of the synthesis of PSIF-1–5; bifunctional and trifunctional prolinkers used in the synthesis (ACS Appl. Mater. Interfaces 2018, 23, 19964-19973)

Electrical energy production and consumption is in the focal point of worldwide discussion. Increasing global emission of greenhouse gases forces the utilization of energy sources other than fossil fuels. In this view, nuclear power is still one of the major alternatives, however, volatile radioactive waste (e.g. ¹²⁹I, ¹⁴CO₂, ⁸⁵Kr, ³H) generated from nuclear fuel raises many concerns and constitutes a major challenge for present technologies. One of the biggest issues is the generation of highly volatile radioactive iodine-containing species. The influence of I₂ on the human body is related to the proper function of thyroid gland, which is responsible for fundamental biological functions. In this regard, effective capture and storage of radioactive iodine-129, because of its long radioactive half-life (1.57×10⁷ years), high volatility, and harmful effects on humans and the environment, still requires finding of more efficient solutions. From a practical perspective, adsorption of I₂ vapor onto a solid adsorbent has many advantages over traditional liquid scrubbing methods.

The presence of a high number of imine functional groups in combination with silsesquioxane cores results in extremely high I₂ affinity with uptake capacities up to 485%wt, which is the highest reported to date. . In addition, PSIF-1a could be recycled at least 4 times while maintaining 94% I₂ uptake capacity. Kinetic studies of I₂ desorption show two strong binding sites with apparent activation energies of 77.0 kJ/mol and 89.0 kJ/mol.

The modular design of PSIFs opens the door to customization for other pollutants. By altering the functional groups in the imine linkages or tweaking the structure of the silsesquioxane cages, researchers could create new variants aimed at capturing gases like sulfur dioxide, carbon dioxide, or even organic vapors.

This flexibility makes PSIFs a platform technology—not just a one-trick material.

Moreover, their stability and regenerability make them attractive not only for nuclear applications but also for broader use in industrial emissions control, air purification systems, and chemical manufacturing.

This study represents a leap forward in the design of advanced materials for environmental remediation. PSIFs stand out as a smart, scalable, and sustainable solution to one of nuclear energy’s thorniest problems: the safe containment of volatile iodine.

By harnessing the synergy between robust inorganic cages and adaptable organic linkers, the researchers have created a material that not only solves a practical problem but also sets a new standard for what porous materials can achieve in real-world applications.

As we push forward into an energy-hungry future, innovations like this remind us that with the right materials science, we can turn even the most dangerous pollutants into manageable challenges.

Read the full study: Porous Silsesquioxane–Imine Frameworks as Highly Efficient Adsorbents for Volatile Iodine (ACS Appl. Mater. Interfaces 2018, 23, 19964-19973)