Reconstruction of umbite framework variants by atomistic simulations using XRD and sorption data

The interest in the synthesis of new microporous metal silicates (e.g., umbite) has significantly increased during the last decades, driven by their ability to discriminate molecules based on their size, shape, or polarity. In the present work, different isomorphously substituted Zr-, Sn- and Ti-umbite crystals are reconstructed from powder XRD patterns. Then, the simulated structures are used as input to an algorithm for the determination of adsorption properties of small gas molecules in umbite crystals. In this way, guidance to optimize umbite structures with improved sieving properties can be provided. H2, NH3, and CO2 are examples of gases that are studied here. Our simulations have shown that the cell volume of Ti-umbite is smaller than the corresponding cell volume of Zr-umbite, in agreement with literature experimental data. This observation is fully aligned with our adsorption measurements, according to which Zr-umbite adsorbs considerably larger amounts (40 mg/g) of NH3, compared to those adsorbed by Ti-umbite at 50 °C (7 mg/g). The same methodology, which involves reconstruction from XRD spectra and sorption simulation, can also be applied to other metal substitutions in the umbite framework.