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

Covalent-organic framework COF-1 and metal-organic frameworks HKUST-1 and MIL-101 were synthesized and studied for hydrogen storage at 77 and 298 K. Although MIL-101 had the largest surface area and pore volume among the three materials, HKUST-1 had the highest uptake (2.28 wt %) at 77 K. However, the H2 storage capacity at 298 K and high pressure correlated with the surface area and pore volume. The H2 storage in the COF and MOF materials assisted by hydrogen spillover, measured at 298 K up to a pressure of 10 MPa, have been examined for correlations with their structural and surface features for the first time. By using our simple technique to build carbon bridges, the hydrogen uptakes at 298 K were enhanced significantly by a factor of 2.6–3.2. The net uptake by spillover was correlated to the heat of adsorption through the Langmuir constant. Results on water vapor adsorption at 298 K indicated that COF-1 was unstable in moist air, while HKUST-1 and MIL-101 were stable. The results suggested that MIL-101 could be a promising material for hydrogen storage because of its high heat of adsorption for spiltover hydrogen, large surface area and pore volume, and stability upon H2O adsorption. 2007 American Institute of Chemical Engineers AIChE J, 54: 269–279, 2008

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Hydrogen storage in metal‐organic and covalent‐organic frameworks by spillover

New sorbents for the desulfurization of liquid fuels were developed using π-complexation. Vapor-phase adsorption isotherms were investigated to understand the interaction between benzene/thiophene and various kinds of sorbents, including Ag−Y, Cu−Y, Na−Y, H−USY, Na−ZSM-5, activated carbon, and modified activated alumina. Compared to Na−Y, Cu−Y and Ag−Y adsorbed significantly larger amounts of both thiophene and benzene at low pressures, as a result of π-complexation with Cu+ and Ag+. Molecular orbital calculations confirmed that the relative strengths of π-complexation lie in the order thiophene > benzene and Cu+ > Ag+. The experimental heats of adsorption for π-complexation are in excellent agreement with theoretical molecular orbital predictions. Na−ZSM-5 and activated carbon could also adsorb small amounts of thiophene and benzene at low pressures. The sorbent capacities for thiophene at the low pressure of 2.3 × 10-5 atm were 0.92 molecule/Cu+ and 0.42 molecule/Ag+ and followed the order Cu−Y and Ag−Y...

Ralph T. Yang

Papers

Hydrogen storage in metal‐organic and covalent‐organic frameworks by spillover

New Sorbents for Desulfurization by π-Complexation: Thiophene/Benzene Adsorption

Selective Catalytic Reduction of NO with NH3 on SO−24/TiO2 Superacid Catalyst

Hydrogen Spillover from a Metal Oxide Catalyst onto Carbon Nanotubes—Implications for Hydrogen Storage

Kinetic separation of methane—carbon dioxide mixture by adsorption on molecular sieve carbon