(120c) Nano-Confined CO2 Sorbents for High-Efficiency CO2-Capture

CO₂ capture and sequestration are among the prime challenges of our time, as the need to reduce atmospheric concentrations of this greenhouse gas has become evident.  Among the most mature CO₂ capture technologies are liquid amine-based processes; however, even these applications are hampered by high cost and large energy penalty. Grafting or supporting liquid amines on solid supports offers a promising avenue to overcome some of these limitations. In particular, embedding amines into microporous solids constitutes a simple, flexible approach.

In the present project, we are investigating the application of this embedding approach to a novel class of CO₂ sorbents, so-called phase-change sorbent materials. An aminosilicone sorbent (“GAP-0”) that has recently shown great promise as a CO₂ sorbent due to its high sorbent capacity and its ability to change from a liquid to a solid upon CO₂ sorption, was chosen as a model compound and embedded into porous silica shells. The resulting material has the advantage of a well-defined particle size, suppressed agglomeration, and fast CO₂ transport. Furthermore, on a fundamental level, the impact of nanoconfinement on phase transitions of materials is poorly understood to-date and the present system poses a well-defined model system for such studies.

 GAP-0 was loaded into silica “nanobubbles” with ~30 nm diameter via a straight-forward wet impregnation method. The walls of these nanobubbles are ~10 nm thick and highly porous with average pore diameters of ~8Å. After characterization of the material, the CO₂ adsorption capability of the sorbent was studied via Thermo-Gravimetric Analysis (TGA) during cyclic CO₂ uptake and release over a temperature range between 45-90^oC.

Results to-date show that nanoencapsulated GAP-0 does indeed adsorb and desorb CO₂ effectively. However, the GAP-0 compound exhibited unexpected volatility over the temperature range of the experiments, leading to a loss of sorbent material over time. These losses were reduced via optimization of uptake and release conditions (time, temperature), but multi-cycle experiments still showed continual loss of CO₂ sorption capacity. Current work is extending the demonstrated approach onto other aminosilicone-based phase-change sorbent materials.