Crystalline metal-organic frameworks (MOFs) are formed by reticular synthesis, which creates strong bonds between inorganic and organic units. Careful selection of MOF constituents can yield crystals of ultrahigh porosity and high thermal and chemical stability. These characteristics allow the interior of MOFs to be chemically altered for use in gas separation, gas storage, and catalysis, among other applications. The precision commonly exercised in their chemical modification and the ability to expand their metrics without changing the underlying topology have not been achieved with other solids. MOFs whose chemical composition and shape of building units can be multiply varied within a particular structure already exist and may lead to materials that offer a synergistic combination of properties.

The Chemistry and Applications of Metal-Organic Frameworks

New materials hold the key to fundamental advances in energy conversion and storage, both of which are vital in order to meet the challenge of global warming and the finite nature of fossil fuels. Nanomaterials in particular offer unique properties or combinations of properties as electrodes and electrolytes in a range of energy devices. This review describes some recent developments in the discovery of nanoelectrolytes and nanoelectrodes for lithium batteries, fuel cells and supercapacitors. The advantages and disadvantages of the nanoscale in materials design for such devices are highlighted.

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Nanostructured materials for advanced energy conversion and storage devices

Adsorptive separation is very important in industry. Generally, the process uses porous solid materials such as zeolites, activated carbons, or silica gels as adsorbents. With an ever increasing need for a more efficient, energy-saving, and environmentally benign procedure for gas separation, adsorbents with tailored structures and tunable surface properties must be found. Metal–organic frameworks (MOFs), constructed by metal-containing nodes connected by organic bridges, are such a new type of porous materials. They are promising candidates as adsorbents for gas separations due to their large surface areas, adjustable pore sizes and controllable properties, as well as acceptable thermal stability. This critical review starts with a brief introduction to gas separation and purification based on selective adsorption, followed by a review of gas selective adsorption in rigid and flexible MOFs. Based on possible mechanisms, selective adsorptions observed in MOFs are classified, and primary relationships between adsorption properties and framework features are analyzed. As a specific example of tailor-made MOFs, mesh-adjustable molecular sieves are emphasized and the underlying working mechanism elucidated. In addition to the experimental aspect, theoretical investigations from adsorption equilibrium to diffusion dynamics via molecular simulations are also briefly reviewed. Furthermore, gas separations in MOFs, including the molecular sieving effect, kinetic separation, the quantum sieving effect for H2/D2 separation, and MOF-based membranes are also summarized (227 references).

Selective gas adsorption and separation in metal–organic frameworks

Metal–Organic Frameworks for Separations

Kenji Sumida, David L. Rogow, Jarad A. Mason, Thomas M. McDonald, Eric D. Bloch, Zoey R. Herm, Tae-Hyun Bae, Jeffrey R. Long

Carbon Dioxide Capture in Metal–Organic Frameworks

BaxSr1−xO/MgO nano-composite sorbents for tuning the transition pressure of oxygen: Application to air separation

Two pressure swing adsorption (PSA) cycles are used to produce a high-purity H2 from an H2-lean mixture containing strongly adsorbable gases. Zeolite 5A is used as the sorbent. The use of an evacuation step in the cycle is found necessary for this difficult separation. In addition, a new vacuum purge step is found efficient and a promising step for commercial application. A bidisperse pore diffusion model along with a simple algorithm is developed for the cycle performance. The model is simpler than all previous bidisperse pore models due to two justified simplifying assumptions: parabolic concentration profiles in crystal and pellet, and a double volume-average technique. The effects of both micropore and macropore diffusion resistances on the cyclic separation are found to be small but significant. A basic understanding of the transient adsorber dynamics is obtained through the bidisperse pore diffusion model.

Zeolite psa cycles for producing a high-purity hydrogen from a hydrogen-lean mixture.

Bulk gas separation of binary and ternary mixtures by pressure swing adsorption.

Synergism between Manganese and Cobalt on Mn–Co Oxides for the Catalytic Combustion of VOCs: A Combined Kinetics and Diffuse Reflectance Infrared Fourier Transform Spectroscopy Study

Binary gaseous diffusion coefficients in a nuclear graphite (H-451) along with the pore volume distribution were measured. The diffusion models of Johnson and Stewart and of Wakao and Smith were applied to this material. Diffusion coefficients predicted by the latter model were higher than the measured values at a ratio ranging from 1.2 to 1.6, whereas this ratio was about 4 to 5 with the former model. The models were also applied to other graphites whose diffusion and pore data were available in the literature. The predicted diffusion coefficients were all higher than the experimental data and the model by Wakao and Smith was consistently better. These results were compared with the literature data on commercial catalysts and inferences were drawn for the differences in the characteristics of diffusion in these two types of materials.

Ralph T. Yang

Papers

BaxSr1−xO/MgO nano-composite sorbents for tuning the transition pressure of oxygen: Application to air separation

Zeolite psa cycles for producing a high-purity hydrogen from a hydrogen-lean mixture.

Bulk gas separation of binary and ternary mixtures by pressure swing adsorption.

Synergism between Manganese and Cobalt on Mn–Co Oxides for the Catalytic Combustion of VOCs: A Combined Kinetics and Diffuse Reflectance Infrared Fourier Transform Spectroscopy Study

Gaseous diffusion in carbon with particular reference to graphite