Molecular Screening of Metal−Organic Frameworks for CO₂ Storage

Abstract

We report a molecular simulation study for CO2 storage in metal-organic frameworks (MOFs). As compared to the aluminum-free and cation-exchanged ZSM-5 zeolites and carbon nanotube bundle, IRMOF1 exhibits remarkably higher capacity. Incorporation of Na(+) cations into zeolite increases the capacity only at low pressures. By variation of the metal oxide, organic linker, functional group, and framework topology, a series of isoreticular MOFs (IRMOF1, Mg-IRMOF1, Be-IRMOF1, IRMOF1-(NH2)4, IRMOF10, IRMOF13, and IRMOF14) are systematically examined, as well as UMCM-1, a fluorous MOF (F-MOF1), and a covalent-organic framework (COF102). The affinity with CO2 is enhanced by addition of a functional group, and the constricted pore is formed by interpenetration of the framework; both lead to a larger isosteric heat and Henry's constant and subsequently a stronger adsorption at low pressures. The organic linker plays a critical role in tuning the free volume and accessible surface area and largely determines CO2 adsorption at high pressures. As a combination of high capacity and low framework density, IRMOF10, IRMOF14, and UMCM-1 are identified from this study to be the best for CO2 storage, even surpass the experimentally reported highest capacity in MOF-177. COF102 is a promising candidate with high capacity at considerably low pressures. Both gravimetric and volumetric capacities at 30 bar correlate well with the framework density, free volume, porosity, and accessible surface area. These structure-function correlations are useful for a priori prediction of CO2 capacity and for the rational screening of MOFs toward high-efficacy CO2 storage.

The first porous MOF with photoswitchable linker molecules

“…The solvent was removed under vacuo and the product was chromatographically separated with ethyl acetate over silica gel. [Zn 2 (NDC) 2 (1)] (CAU-5). CAU-5 was formed in a solvothermal reaction in 0.2-0.5 ml glass vials (Biotage).…”

“…The crystalline orange product was filtered and washed three times with 1 ml DMF. The product was dried at room temperature in air followed by activation in an isothermal oven at 80 • C. Elemental analysis of the activated sample [Zn 2 (NDC) 2 (Fig. S2 †).…”

“…Structure determination and refinement CAU-5 [Zn 2 (NDC) 2 (1)] crystallizes to form air-stable orange rods (0.07 ¥ 0.07 ¥ 0.12 mm 3 ). The single-crystal XRD measurement was performed on a STOE IPDS diffractometer.…”

“…Depending on the size of the dicarboxylic acid it should be possible to fine tune the pore size of the MOF in order to allow the incorporation of the azo-functionalized 4,4¢-bipyridine linker molecule. 30 Here we present the synthesis of the switchable azo-linker molecule 3-azo-phenyl-4,4¢-bipyridine (1), its use in the synthesis of the new porous MOF [Zn 2 (NDC) 2 (1)] named CAU-5 (CAU = Christian-Albrechts-University) and the switching properties of both.…”

Comparative Molecular Simulation Study of CO2/N2 and CH4/N2 Separation in Zeolites and Metal−Organic Frameworks

“…In the meantime, such research can contribute to guide the development of new nanoporous materials for CO 2 capture and natural gas storage. 46,51,66,67 In this work, Henry coefficients and isosteric heats of adsorption at infinite dilution, and the adsorption isotherms of CO 2 and CH 4 in the 10 materials as a function of pressure up to 6 MPa were calculated, as shown in Table 4 and Figure 9, respectively. The figures up to 6 MPa may not be practical for some applications; however, the results obtained can be used for future reference from both scientific and practical points of view for comparing the adsorption capacities between MOFs and zeolites.…”