Characterization of an Isostructural MOF Series of Imidazolate Frameworks Potsdam by Means of Sorption Experiments with Water Vapor

Abstract

Sorption measurements of water vapor on an isoreticular series of Imidazolate Frameworks Potsdam (IFP), based on penta-coordinated metal centers with secondary building units (SBUs) connected by multidentate amido-imidate-imidazolate linkers, have been carried out at 303.15 K. The isotherm shapes were analyzed in order to gain insight into material properties and compared to sorption experiments with nitrogen at 77.4 K and carbon dioxide at 273.15 K. Results show that water vapor sorption measurements are strongly influenced by the pore size distribution while having a distinct hysteresis loop between the adsorption and desorption branch in common. Thus, IFP-4 and -8, which solely contain micropores, exhibit H4 (type I) isotherm shapes, while those of IFP-1, -2 and -5, which also contain mesopores, are of H3 (type IV) shape with three inflection points. The choice of the used linker substituents and transition metals employed in the framework has a tremendous effect on the material properties and functionality. The water uptake capacities of the examined IFPs are ranging 0.48 mmol g−1 (IFP-4) to 6.99 mmol g−1 (IFP-5) and comparable to those documented for ZIFs. The water vapor stability of IFPs is high, with the exception of IFP-8.

Modelling adsorption based on an isoreticular MOF‐series of IFPs–Part I: Collection of physical properties and single component equilibria

“…[7][8][9][10]12] The light scattering experiments carried out on the untreated samples and those treated with dispersion agents prove that all IFPs form agglomerates during synthesis. [11] Thus, after F I G U R E 6 Absolute loads of CO 2 on all imidazolate framework Potsdam (IFP) samples for the assumption V occ ¼ V p,Σ approximated with the extended Langmuir (EL) (-) and dual site Langmuir (DSL) (---) models breaking the agglomerates, the mean diameter, d 50,3 , is reduced by a factor of 2.5 (for IFP-4) up to a factor of 20 (for IFP-3), which is also indicated by significant left shifts of the volume density and sum distributions, q 3 and Q 3 , respectively (see Figures S1 and S2, SI). This is in good agreement with the SEM images (see Figure S3, SI), which show that the crystals tend to form superordinate structures, whereby IFP-5 exhibits the smallest of these with a median value of 22.53 μm.…”

“…Most of the IFPs can be synthesized in gram scale amounts under lab scale conditions at low costs and show similar hydrothermal stability to zeolitic imidazolate frameworks (ZIFs). [11] For more detailed information on material synthesis and chemical backgrounds, the reader is referred to the related literature. [7][8][9][10]12]…”

“…[1,6] One MOF series that has proven to be a hydrothermally stable species are the imidazolate frameworks Potsdam (IFP). [7][8][9][10][11] IFPs are structurally identical compounds, which have been modified in numerous ways by varying linker substituents and transition metals. This allows for the analysis of the influence of different metal centres and functional groups on phenomenological and physicochemical material properties.…”

Modelling adsorption based on an isoreticular MOF‐series of IFPs—Part II: Dynamic adsorption in fixed beds

“…This phenomenon is primarily to be attributed to the different particle radii. [9,38] Additionally, in the case of IFP-3, the isotherm slope occurs to be extremely flat in comparison, [9] which further amplifies the mass transport resistance according to the Darken equation (Equation ( 32)). In order to shed more light on whether the separation is kinetic-or equilibrium-driven, the respective saturation curves of the adsorbents are shown comparatively for CO 2 and CH 4 in Figure 6, where the saturation reflects the ratio of actual loading to equilibrium loading.…”

“…The terms for micro-and mesopore diffusion are weighted according to their volume fractions, determined from the pore size distributions, [9,38] with the micropore fraction, φ μ , and the resulting mesopore fraction, 1 À φ μ .…”