High-Performance CO₂ Capture from Air by Harnessing the Power of CaO- and Superbase-Ionic-Liquid-Engineered Sorbents

Direct air capture (DAC) of CO₂ by solid porous materials represents an attractive “negative emission” technology. However, state-of-the-art sorbents based on supported amines still suffer from unsolved high energy consumption and stability issues. Herein, taking clues from the CO₂ interaction with superbase-derived ionic liquids (SILs), high-performance and tunable sorbents in DAC of CO₂ was developed by harnessing the power of CaO- and SIL-engineered sorbents. Deploying mesoporous silica as the substrate, a thin CaO layer was first introduced to consume the surface-OH groups, and then active sites with different basicities (e. g., triazolate and imidazolate) were introduced as a uniformly distributed thin layer. The as-obtained sorbents displayed high CO₂ uptake capacity via volumetric (at 0.4 mbar) and breakthrough test (400 ppm CO₂ source), rapid interaction kinetics, facile CO₂ releasing, and stable sorption/desorption cycles. Operando diffuse reflectance infrared Fourier transformation spectroscopy (DRIFTS) analysis under simulated air atmosphere and solid-state NMR under ¹³CO₂ atmosphere demonstrated the critical roles of the SIL species in low-concentration CO₂ capture. The fundamental insights obtained in this work provide guidance on the development of high-performance sorbents in DAC of CO₂ by leveraging the combined advantages of porous solid scaffolds and the unique features of CO₂-philic ionic liquids.