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

In Pursuit of Carbon Neutrality: Progresses and Innovations in Sorbents for Direct Air Capture of CO2

Direct air capture (DAC) is of immense current interest, as a means to facilitate CO2 capture at low concentrations (∼400 ppm) directly from the atmosphere, with the aim of addressing global warming caused by excessive anthropogenic CO2 production. Traditionally, DAC of CO2 has relied on amine scrubbing and metal carbonate /hydroxide solutions. However, recent years have seen notable progress in DAC sorbents, with key advancements aimed at improving efficiency, capacity, and regenerability while reducing energy consumption. This review delivers an exhaustive analysis of contemporary developments in DAC sorbents, addressing the innovations in material design and consequent performance enhancement. The limitations of the sorbents have also been discussed, with future perspectives for improving sustainable CO2 capture strategies. We anticipate that this overview will help lay the groundwork for further development and large-scale implementation of sustainable sorbents and cutting-edge technologies toward attaining carbon neutrality.

Thermodynamic regulation of carbon dioxide capture by functionalized ionic liquids

Carbon dioxide capture has attracted worldwide attention because CO2 emissions cause global warming and exacerbate climate change. Ionic liquids (ILs) have good application prospects in carbon capture due to their excellent properties, which provide a new chance to develop efficient and reversible carbon capture systems. This paper reviews the recent progress in CO2 chemical absorption by ILs, such as N-site, O-site, C-site, and multi-site functionalized ILs. The application of thermodynamic regulation methods in CO2 capture is discussed in detail. Among them, the methods of enthalpy regulation are mainly introduced, for which different regulatory targets are proposed for single sites and multiple sites. Furthermore, the strategies of achieving entropy compensation through the design of spatial configurations are discussed. Particular attention is paid to the application of thermodynamic regulation in direct air capture (DAC) due to its great significance. The methods to improve the absorption kinetics are also outlined. Finally, the future development of carbon capture by functionalized ILs is proposed.

Ionic Pairs-Engineered Fluorinated Covalent Organic Frameworks Toward Direct Air Capture of CO2

The covalent organic frameworks (COFs) possessing high crystallinity and capability to capture low-concentration CO2 (400 ppm) from air are still underdeveloped. The challenge lies in simultaneously incorporating high-density active sites for CO2 insertion and maintaining the ordered structure. Herein, a structure engineering approach is developed to afford an ionic pair-functionalized crystalline and stable fluorinated COF (F-COF) skeleton. The ordered structure of the F-COF is well maintained after the integration of abundant basic fluorinated alcoholate anions, as revealed by synchrotron X-ray scattering experiments. The breakthrough test demonstrates its attractive performance in capturing (400 ppm) CO2 from gas mixtures via O─C bond formation, as indicated by the in situ spectroscopy and operando nuclear magnetic resonance spectroscopy using 13C-labeled CO2 sources. Both theoretical and experimental thermodynamic studies reveal the reaction enthalpy of ≈-40 kJ mol-1 between CO2 and the COF scaffolds. This implies weaker interaction strength compared with state-of-the-art amine-derived sorbents, thus allowing complete CO2 release with less energy input. The structure evolution study from synchrotron X-ray scattering and small-angle neutron scattering confirms the well-maintained crystalline patterns after CO2 insertion. The as-developed proof-of-concept approach provides guidance on anchoring binding sites for direct air capture (DAC) of CO2 in crystalline scaffolds.

Dual-Tuning Azole-Based Ionic Liquids for Reversible CO2 Capture from Ambient Air

A strategy of tuning azole-based ionic liquids for reversible CO2 capture from ambient air was reported. Through tuning the basicity of anion as well as the type of cation, an ideal azole-based ionic liquid with both high CO2 capacity and excellent stability was synthesized, which exhibited a highest single-component isotherm uptake of 2.17 mmol/g at the atmospheric CO2 concentration of 0.4 mbar at 30 °C, even in the presence of water. The bound CO2 can be released by relatively mild heating of the IL-CO2 at 80 °C, which makes it promising for energy-efficient CO2 desorption and sorbent regeneration, leading to excellent reversibility. To the best of our knowledge, these azole-based ionic liquids are superior to other adsorbent materials for direct air capture due to their dual-tunable properties and high CO2 capture efficiency, offering a new prospect for efficient and reversible direct air capture technologies.

Minimal Kinetic Model of Direct Air Capture of CO2 by Supported Amine Sorbents in Dry and Humid Conditions

Dilute concentration (∼400 ppm) and humidity are two important factors in the direct air capture (DAC) of CO2 by supported sorbents. In this work, a minimal DAC CO2 adsorption-kinetics model was formulated for supported amine sorbents under dry and humid conditions. Our model fits well with a recent DAC experiment with supported amine sorbent in both dry and humid conditions. Temperature and flow rate effects on breakthrough curves were quantitatively captured, and increasing temperature led to faster CO2 adsorption kinetics. Moisture was shown to broaden the breakthrough curve with slower CO2 adsorption kinetics but significantly improve the uptake capacity. The present minimal model provides a versatile platform for kinetic modeling of the DAC of CO2 on supported amine and other chemisorption systems.