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

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.