From Structured Solvents to Hybrid Materials (SS2HM) for Chemically Selective Capture and Electromagnetic Release of CO2: Mechanisms, Stability and Interfaces

Deep eutectic solvents (DESs) and nanoparticle organic hybrid materials (NOHMs) are structured solvents that demonstrate high CO2 solubilities and selectivities, good thermal stabilities, and extremely low vapor pressures. The unique chemical and structural turnabilities of DESs and NOHMs enable their rational design for the direct air capture of CO2 and energy-efficient solvent regeneration without thermal heating. Further, DESs and NOHMs are excellent candidates for encapsulation within polymeric thin films (e.g., core-shell), creating hybrid materials with multi-scale, large surface-area interfaces for CO2 transport and capture while maintaining the simultaneous benefits of liquid solvents and solid sorbents. However, the design rules for DESs and NOHMs are a knowledge gap that inhibits their broader adoption as DAC materials. The present research addresses this knowledge gap through synergistic experimental and computational approaches to understand the reaction mechanisms, thermodynamics, and the coupled kinetic and transport behaviors of DESs and NOHMs as they absorb CO2 for direct air capture (DAC), and regenerate CO2 upon electromagnetic irradiation. Through this work, the understanding of these fundamental underpinnings enables control and prediction of associated energetics ultimately leading to the rational design of new solvents, composite materials, and improved energy-efficiency in DAC technologies. Furthermore, determining the impact of the environmental factors such as temperature, humidity, and oxygen on working CO2 capacity, reaction rates, and energetics allows for informed decisions about the cost and implementation of DAC with these new materials. To achieve the research aims, this research explores encapsulated and neat structured solvents, measures working CO2 capacities by absorption and regeneration by dielectric heating, employs advanced neutron and X-ray scattering techniques for structure determination, leverages 2D nuclear magnetic resonance spectroscopy techniques for transport studies, usees thermal analysis including differential scanning calorimetry and thermal gravimetric analysis coupled with mass spectrometry to evaluate stability, and applies a suite of computational methods, including density functional theory, molecular dynamics, multiscale sampling, and machine learning, to study mechanisms and molecular descriptors. These studies are directed to answer the following scientific questions: How does the solvent composition (number of functional groups, steric accessibility, and basicity) impact measurable macroscopic CO2 capacity and binding energy?; What are the molecular descriptors that govern CO2 binding energies and can they be used for predicting CO2 capacities in DESs and NOHMs?; How does the composition-dependent structural heterogeneity (domain sizes and extent of H-bonding) impact CO2 transport? How does the solid-liquid interface impact the orientation of functional groups in DESs and NOHMs and influence CO2 transport and solvent regeneration mechanisms? What are the individual effects of environmental factors and the interplay among these factors that define CO2 capacity, selective transport, and regeneration stability? Can CO2 bound to DESs and NOHMs be activated and released via electromagnetic-based regeneration? How do the power, temperature, and irradiation time impact CO2 release and desorption in capsules?