There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

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

The escalating level of atmospheric carbon dioxide is one of the most pressing environmental concerns of our age. Carbon capture and storage (CCS) from large point sources such as power plants is one option for reducing anthropogenic CO(2) emissions; however, currently the capture alone will increase the energy requirements of a plant by 25-40%. This Review highlights the challenges for capture technologies which have the greatest likelihood of reducing CO(2) emissions to the atmosphere, namely postcombustion (predominantly CO(2)/N(2) separation), precombustion (CO(2)/H(2)) capture, and natural gas sweetening (CO(2)/CH(4)). The key factor which underlies significant advancements lies in improved materials that perform the separations. In this regard, the most recent developments and emerging concepts in CO(2) separations by solvent absorption, chemical and physical adsorption, and membranes, amongst others, will be discussed, with particular attention on progress in the burgeoning field of metal-organic frameworks.

Carbon Dioxide Capture: Prospects for New Materials

Solvothermal assembly of a semirigid tetrahedral carboxylate ligand tetrakis[4-(carboxyphenyl)oxamethyl]methane acid (H4X) with Cd(II) ion in different solvent systems yields three novel metal−organic framework isomers (1−3) based on different secondary building units (SBUs). Although all three frameworks have the same dia (diamondoid) topology, complexes 1 and 3 are noncentrosymmetric and complex 2 is centrosymmetric. One of the networks (1) shows cross-linked 3-fold interpenetration of the single dia net and exhibits permanent porosities, as confirmed by Brunauer−Emmett−Teller (BET) and selective CO2 adsorption.

Metal−Organic Framework Isomers with Diamondoid Networks Constructed of a Semirigid Tetrahedral Linker

The crystal structures of the molecular complexes of sym-trinitrobenzene (TNB) with acridine, 1,10-phenanthroline and phenazine are discussed. In all three cases, the structures are held together by C–H⋯O and π⋯π interactions, and TNB forms hydrogen bonded dimers and tapes that are not found in its native crystal structure. Acridine and 1,10-phenanthroline yield 1 ∶ 1 complexes that have very similar structures. The related molecule phenazine, however, gives a different 2 ∶ 3 complex in which guest exchange, as seen in other recently reported examples, is not observed. A case is made for the reporting of such ‘low yield’ supramolecular reactions because they still provide valuable information about the packing characteristics of organic molecules.

C-H···O hydrogen bonds in molecular complexes of 1,3,5-trinitrobenzene with some N-heterocycles

Three novel crystalline forms of cucurbit[6]uril (CB[6], 1) have been identified by fine control of the mixing process of a hydrochloride solution of CB[6] with ethanol. The form that exists in nanoplate particles shows permanent porosity upon desolvation and the highest CO2 uptake (15 wt%) at 298 K and 1 bar among any known solid-state forms of CB[6].

Identification of solid-state forms of cucurbit[6]uril for carbon dioxide capture

http://manuscript.elsevier.com/S0378775322001835/pdf/S0378775322001835.pdf

Praveen K. Thallapally

Papers

Metal−Organic Framework Isomers with Diamondoid Networks Constructed of a Semirigid Tetrahedral Linker

C-H···O hydrogen bonds in molecular complexes of 1,3,5-trinitrobenzene with some N-heterocycles

Identification of solid-state forms of cucurbit[6]uril for carbon dioxide capture

In situ anodic electrodeposition of two-dimensional conductive metal-organic framework@nickel foam for high-performance flexible supercapacitor

Role of hydrocarbons in pore expansion and contraction of a flexible metal–organic framework