Designing optimal core–shell MOFs for direct air capture

Abstract

Metal-organic frameworks (MOFs), along with other novel adsorbents, are frequently proposed as candidate materials to selectively adsorb CO2 for carbon capture processes. However, adsorbents designed to strongly bind CO2 nearly...

Overcoming the Entropy Penalty of Direct Air Capture for Efficient Gigatonne Removal of Carbon Dioxide

“…By this method, air blown over high surface area materials has CO 2 removed by adsorption to the surface; in a second phase, the high surface area materials undergo new conditions such as a higher temperature to promote desorption as a high-concentration CO 2 effluent stream. ,, These methods include additional processing costs such as regeneration of the binding site, compression, or purification of the effluent CO 2 -rich stream, and/or pretreating of the air input stream such as compression to enhance the rate or extent of adsorption. The operating conditions of adsorption systems are dictated by the material adsorbents, with engineered binding sites consisting of many structures including Lewis acids incorporated into high surface area materials such as resins, zeolites, carbons, or metal–organic frameworks (MOFs). − These newer materials combined with improved process designs can lower the energy requirements to ∼1600 kWh tCO 2 –1 (Figure b), albeit with lower concentrations of CO 2 in the effluent stream (70–80%) that lead to higher compression and injection costs, as well as higher material costs due to the engineering required for developing suitable binding sites …”

Review on Multidimensional Adsorbents for CO2 Capture from Ambient Air: Recent Advances and Future Perspectives

“…To obtain higher gravimetric and volumetric CO 2 uptake at 0.4 mbar, the strategy of replacing the ethylenediamine (EDA) molecule with the shortest diamine, hydrazine (N 2 H 4 ), 69 was proposed to graft small-pore [Mg 2 (adobdc)] (H 4 dobdc = 2,5-dihydroxyl-1,4-benzenedicarboxylic acid), which achieved a CO 2 uptake of 3.89 mmol g −1 at 0.4 mbar and 298 K, as well as more than 4.2 mmol g −1 adsorption/desorption working capacity under flue-gas conditions. Boone et al 70 designed MOFs with core−shell structures by utilizing the core for efficient CO 2 adsorption and the shell for slow water diffusion, which have advantages of high adsorption area and high CO 2 selectivity under humid conditions for the DAC process. Despite MOFs having shown remarkable performance in capturing CO 2 from the atmosphere, their ineffective regeneration and complicated synthesis processes hinder practical applications for DAC.…”

Implementation of a Core–Shell Design Approach for Constructing MOFs for CO2 Capture

“…Since it was practically impossible to synthesize and test all of the different core−shell MOF combinations (there are 1512 total possibilities with compositionally distinct core and shell domains), computational screening of these different MOFs was performed to determine adsorption and diffusivity of N 2 , CO 2 , and H 2 O at conditions relevant for DAC. 40 From these data, we identified potential shell MOFs that would allow rapid diffusion of CO 2 and slow diffusion of H 2 O, reasoning that such MOFs would limit H 2 O penetration to the core MOF. A UiO-67 derivative containing 2-amino-[1,1′-biphenyl]-4,4′dicarboxylate (Figure 2B), NH 2 -BPDC, was selected for the shell because it had the highest CO 2 diffusivity of 49.8 m 2 /s of the MOFs screened and a high CO 2 /H 2 O diffusion selectivity of 307.…”

“…The CO 2 capacity for (CyNH) 2 -UiO-67 is higher than that for NH 2 -UiO-67, which is consistent with our computational predictions. 40 Multigas Adsorption Studies. To evaluate the CO 2 capture performance of each MOF under multigas and humid conditions, we constructed a multigas manifold and sample holder for measuring the gas uptake using flow controllers and a gas chromatograph (GC) with a thermal conductivity detector (Scheme S1).…”