Unidirectional ice-templating for aerogel adsorbents: Excellent pore structure and high CO2 capture performance for direct air capture

Abstract

The ultralow atmospheric partial pressure of CO2 (∼40 Pa) presents a significant challenge for direct air capture (DAC). In this study, high-performance porous aerogel adsorbents are prepared using the unidirectional freezing–ice-templating method. The dispersion of the mixed solution is effectively improved by particle size modulation, and functionalized materials with abundant gas channels are constructed by the rapid cooling of liquid N2. The adsorbents feature a cross-structure comprising monolayer active components and nanoscale layered carriers. The unique micro/mesoporous composite structure of the adsorbents facilitates gas-phase transport. When the functional group efficiency is increased by 5.8 times, the prepared adsorbents demonstrate excellent CO2 capture capacity (1.17 mmol/g and 148 mol/m3) and a low adsorption half-time (1.28 min). The unique cross-structure of the adsorbents renders them hydrophobic; thus, they show higher adsorption capacity at high humidity than other moisture swing adsorbents. At the molecular scale, quantum chemical calculations show that appropriate coordination between the active components and carriers enhance the water vapor hindering ability of the adsorbents. The developed aerogel adsorbents significantly expand the application scenarios for moisture swing adsorbents and enhance the efficiency of DAC.