Porous Silsesquioxane-Imine Frameworks (PSIF)

​In the quest for efficient and sustainable methods to capture volatile pollutants, a  study titled "Porous Silsesquioxane–Imine Frameworks as Highly Efficient Adsorbents for Volatile Iodine" offers promising insights. Published in ACS Applied Materials & Interfaces, this research introduces a novel class of porous materials designed to effectively adsorb volatile iodine, a significant concern in nuclear waste management.

Volatile iodine is primarily released during the reprocessing of spent nuclear fuel and in the event of nuclear accidents. Its ability to travel long distances and bioaccumulate in the human thyroid makes it particularly dangerous. Current iodine capture technologies—like silver-doped zeolites, activated carbons, and MOFs (metal-organic frameworks)—have varying degrees of success but suffer from drawbacks including limited capacity, high cost, thermal instability, or difficulty in regeneration.

Hence, there's an urgent need for adsorbent materials that are not only efficient and selective but also economical, scalable, and thermally stable.

Enter Porous Silsesquioxane–Imine Frameworks (PSIFs)

The research team tackled this challenge by designing and synthesizing a new type of 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) was designed and synthesized by imine condensation approach starting from 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. These aerogels were tested in sorption of I₂ vapor. For PSIF-1a I₂ uptake of 481%wt was obtained, which is the highest value reported to date. Preferential interaction of I₂ with PSIFs can be attributed to the cooperative interactions of POSS cages and imine moieties in the porous framework.

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