A pinboard by
Peyman Moghadam

Post-doc, University of Cambridge


Computer simulations discover a new world-record material for oxygen storage

Current advances in materials science have resulted in the rapid emergence of thousands of functional materials in recent years. This clearly creates multiple opportunities for their potential application, but it also creates the following challenge: how does one identify the most promising structures, among the thousands of possibilities, for a particular application? Due to practical constraints, experimental trial-and-error discovery is simply not fast enough, and therefore more efficient alternatives must be developed to accelarate the discovery and deployment of new adsorbent materials. This work presents a rare case of computer-aided material discovery, in which we complete the full cycle from computational screening of porous materials for oxygen storage (application in the development of oxygen tanks for patients with respiratory problems), to identification, synthesis and measurement of oxygen adsorption in the top-ranked structure. We introduce an interactive visualisation concept to analyse over a 1000 unique structure-property plots in 4 dimensions and delimit – for the first time – the relationships between structural properties and oxygen adsorption performance at different pressures for 2,932 already-synthesised porous materials. We also report a new world-record holding material for oxygen storage, UMCM-152, which delivers 22.5% more oxygen than the best known material to date. All of the graphs presented in this work can be reproduced online at http://aam.ceb.cam.ac.uk/mof-explorer.


Application of Consistency Criteria To Calculate BET Areas of Micro- And Mesoporous Metal–Organic Frameworks

Abstract: Metal–organic frameworks (MOFs) can exhibit exceptionally high surface areas, which are experimentally estimated by applying the BET theory to measured nitrogen isotherms. The Brunauer, Emmett, and Teller (BET)-estimated nitrogen monolayer loading is thus converted to a “BET area,” but the meaning of MOF BET areas remains under debate. Recent emphasis has been placed on the usage of four so-called “BET consistency criteria.” Using these criteria and simulated nitrogen isotherms for perfect crystals, we calculated BET areas for graphene and 25 MOFs having different pore-size distributions. BET areas were compared with their corresponding geometrically calculated, nitrogen-accessible surface areas (NASAs). Analysis of simulation snapshots elucidated the contributions of “pore-filling” and “monolayer-formation” to the nitrogen adsorption loadings in different MOF pores, revealing the origin of inaccuracies in BET-calculated monolayer loadings, which largely explain discrepancies between BET areas and NASAs. We also find that even if all consistency criteria are satisfied, the BET calculation can significantly overestimate the true monolayer loading, especially in MOFs combining mesopores (d ≥ 20 Å) and large micropores (d = 10–20 Å), due to the overlap of pore-filling and monolayer-formation regimes of these two kinds of pores. While it is not always possible to satisfy all consistency criteria, it is critical to minimize the deviation from these criteria during BET range selection to consistently compare BET areas of different MOFs and for comparing simulated and experimental BET areas of a given MOF. To accurately assess the quality of a MOF sample, it is best to compare experimental BET areas with simulated BET areas rather than with calculated NASAs.

Pub.: 11 Dec '15, Pinned: 29 Jun '17

Carbohydrate-mediated purification of petrochemicals.

Abstract: Metal-organic frameworks (MOFs) are known to facilitate energy-efficient separations of important industrial chemical feedstocks. Here, we report how a class of green MOFs-namely CD-MOFs-exhibits high shape selectivity toward aromatic hydrocarbons. CD-MOFs, which consist of an extended porous network of γ-cyclodextrins (γ-CDs) and alkali metal cations, can separate a wide range of benzenoid compounds as a result of their relative orientation and packing within the transverse channels formed from linking (γ-CD)6 body-centered cuboids in three dimensions. Adsorption isotherms and liquid-phase chromatographic measurements indicate a retention order of ortho- > meta- > para-xylene. The persistence of this regioselectivity is also observed during the liquid-phase chromatography of the ethyltoluene and cymene regioisomers. In addition, molecular shape-sorting within CD-MOFs facilitates the separation of the industrially relevant BTEX (benzene, toluene, ethylbenzene, and xylene isomers) mixture. The high resolution and large separation factors exhibited by CD-MOFs for benzene and these alkylaromatics provide an efficient, reliable, and green alternative to current isolation protocols. Furthermore, the isolation of the regioisomers of (i) ethyltoluene and (ii) cymene, together with the purification of (iii) cumene from its major impurities (benzene, n-propylbenzene, and diisopropylbenzene) highlight the specificity of the shape selectivity exhibited by CD-MOFs. Grand canonical Monte Carlo simulations and single component static vapor adsorption isotherms and kinetics reveal the origin of the shape selectivity and provide insight into the capability of CD-MOFs to serve as versatile separation platforms derived from renewable sources.

Pub.: 26 Mar '15, Pinned: 29 Jun '17