Supporting Porous Metal–Organic Frameworks on Carboxylated-Wood Sponges for Direct Air Capture and Highly Selective CO2/CH4 Separation

Abstract

To effectively mitigate the global warming problem caused by excessive CO₂ emissions, the implementation of direct air capture (DAC) technology has emerged as one of the most promising strategies for capturing CO₂ from the atmosphere. The key to DAC technology hinges on the development of high-performance solid sorbent materials that demonstrate high CO₂ adsorption capacity and gas separation selectivity, particularly under low CO₂ partial pressure conditions. Herein, we have successfully developed a class of MOF@carboxylated wood sponge (MOF@CWS) hybrid sorbents, capable of efficient CO₂ capture from low-concentration (less than 10,000 ppm) CO₂ sources, achieved by embedding the porous MOF into carboxylated wood sponges (CWS) substrate via an in situ growth route. Within the MOF@CWS series, the CO₂ uptake capacity of Mg-MOF-74@CWS is 3.61 and 2.65 mmol/g at 1 bar, 273 and 298 K, respectively, significantly higher than those of CWS and HKUST-1@CWS. Moreover, this material exhibited outstanding DAC performance, with the CO₂ sorption capacity at 273 K up to 0.56 mmol/g from ambient air (ca. 400 ppm of CO₂), surpassing most other solid sorbents. The obtained Mg-MOF-74@CWS also demonstrated exceptional CO₂/CH₄ separation performance, primarily due to the unique pore structure and augmented interaction between the CO₂ molecules and the hybrid sorbents. The results of this study indicate that Mg-MOF-74@CWS has potential as an efficient solid sorbent for the DAC of CO₂.