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

This critical review will be of interest to the experts in porous solids (including catalysis), but also solid state chemists and physicists. It presents the state-of-the-art on hybrid porous solids, their advantages, their new routes of synthesis, the structural concepts useful for their ‘design’, aiming at reaching very large pores. Their dynamic properties and the possibility of predicting their structure are described. The large tunability of the pore size leads to unprecedented properties and applications. They concern adsorption of species, storage and delivery and the physical properties of the dense phases. (323 references)

Hybrid porous solids: past, present, future

New materials capable of storing hydrogen at high gravimetric and volumetric densities are required if hydrogen is to be widely employed as a clean alternative to hydrocarbon fuels in cars and other mobile applications. With exceptionally high surface areas and chemically-tunable structures, microporous metal–organic frameworks have recently emerged as some of the most promising candidate materials. In this critical review we provide an overview of the current status of hydrogen storage within such compounds. Particular emphasis is given to the relationships between structural features and the enthalpy of hydrogen adsorption, spectroscopic methods for probing framework–H2 interactions, and strategies for improving storage capacity (188 references).

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Hydrogen storage in metal–organic frameworks

Separation of hydrocarbons with a microporous metal-organic framework

Advancement in hydrogen storage techniques represents one of the most important areas of today's materials research. While extensive efforts have been made to the existing techniques, there is no viable storage technology capable of meeting the DOE cost and performance targets at the present time. New materials with significantly improved hydrogen adsorption capability are needed. Microporous metal coordination materials (MMOM) are promising candidates for use as sorbents in hydrogen adsorption. These materials possess physical characteristics similar to those of single-walled carbon nanotubes (SWNTs) but also exhibit a number of improved features. Here, we report a novel MMOM structure and its room-temperature hydrogen adsorption properties.

Microporous metal organic materials: promising candidates as sorbents for hydrogen storage.

The reactions of Ln(NO3)3 (Ln = La, Er) with 1,4-phenylendiacetic acid (H2PDA) under hydrothermal conditions produce isostructural lanthanide coordination polymers with the empirical formula [Ln2(PDA)3(H2O)]·2H2O. The extended structure of [Ln2(PDA)3(H2O)]·2H2O consists of Ln-COO triple helixes cross-linked through the −CH2C6H4CH2− spacers of the PDA anions, showing 1D open channels along the crystallographic c axis that accommodate the guest and coordinated water molecules. Evacuation of [Er2(PDA)3(H2O)]·2H2O at room temperature and at 200 °C, respectively, generates [Er2(PDA)3(H2O)] and [Er2(PDA)3], both of which give powder X-ray diffraction patterns consistent with that of [Er2(PDA)3(H2O)]·2H2O. The porosity of [Er2(PDA)3(H2O)] and [Er2(PDA)3] is further demonstrated by their ability to adsorb water vapor to form [Er2(PDA)3(H2O)]·2H2O quantitatively. Thermogravimetric analyses show that [Er2(PDA)3] remains stable up to 450 °C. The effective pore window size in [Er2(PDA)3] is estimated at 3.4 A. Gas ad...

Porous lanthanide-organic frameworks: synthesis, characterization, and unprecedented gas adsorption properties.

Zeolites and related molecular sieves, which contain rigid frameworks and accessible internal channels and/or cages, have been dominating the porous material world for a long time, because of their widespread applications in catalytic and separation science.[1,2] Although there is an increasing demand for materials with tunable structures, the structural design of zeolites is limited by their requirement for If one Si atom causes pyramidalization, two of them should enhance the effect. We have calculated the Si2BH5 structure at various levels and found it to have a Cs structure (7) with a pyramidal boron atom. The corresponding C2v structure (8) with a planar boron center is found to be higher in energy. The calculated value of q is larger than that of 1. The energy differences are also found to be considerably higher (Table 5). The heavier group 14 elements, Ge and Sn, must also influence the pyramidalization of boron. Calculations at the B3LYP/LANL2DZ level show that q decreases as Si (14.18) is replaced by Ge (7.78) or Sn (6.58 ; Table 6). However, the inversion barrier increases in going from Si (0.7) to Ge (7.5) to Sn (12.7 kcalmol 1). The unexpected nonplanar arrangement of the tricoordinate boron center in 1 provides another demonstration of the many novel structural patterns that the heavier elements of the main group can contribute to the firstrow elements, and invites experimental verification.

RPM-1: A recyclable nanoporous material suitable for ship-in-bottle synthesis and large hydrocarbon sorption

A novel guest-free metal organic framework (GFMMOF) is synthesized and structurally characterized. It contains one-dimensional close-packed open channels with a pore diameter of 4.5 A. It demonstrates a remarkable thermal stability, a unique ability to separate methanol from dimethyl ether or water, and is among the microporous MOFs having the highest adsorbed hydrogen density (0.054 g/cm3 at 77 K and 1 atm).

Long Pan

Papers

Separation of hydrocarbons with a microporous metal-organic framework

Microporous metal organic materials: promising candidates as sorbents for hydrogen storage.

Porous lanthanide-organic frameworks: synthesis, characterization, and unprecedented gas adsorption properties.

RPM-1: A recyclable nanoporous material suitable for ship-in-bottle synthesis and large hydrocarbon sorption

Zn(tbip) (H2tbip= 5-tert-Butyl Isophthalic Acid): A Highly Stable Guest-Free Microporous Metal Organic Framework with Unique Gas Separation Capability