Porous Silsesquioxane

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.

(ACS Appl. Mater. Interfaces 2018, 23, 19964-19973)