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.

https://img62.chem17.com/1/20140715/635410323829886334962.pdf

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

Delaminated Fe2O3-Pillared Clay: Its Preparation, Characterization, and Activities for Selective Catalytic Reduction of No by NH3

Desulfurization of a commercial diesel fuel (2972 ppmw S) by different nickel(II)-exchanged faujasite zeolites was studied in a fixed-bed adsorber operated at ambient temperature and pressure The zeolites were prepared by both liquid-phase (LP) and solid-state (SS) ion-exchange (IE) methods In general, the adsorbents tested for total sulfur adsorption capacity at breakthrough followed the order:  Selexsorb CDX (alumina)/Ni(II)-Y (SSIE-500) > Selexsorb CDX (alumina)/Ni(II)-X (LPIE-RT) > Ni(II)-Y (SSIE-500) > Ni(II)-X (LPIE-RT) > Ni(II)-Y (LPIE-135) The best adsorbent, Selexsorb CDX (alumina)/Ni(II)-Y (SSIE-500) [layered bed of 25 wt % activated alumina followed by Ni(II)-Y] is capable of producing 19 cm3 of diesel fuel per gram of adsorbent with a weighted average content of 022 ppmw S These low-sulfur fuels are suitable for fuel cell applications The sorbents were fully regenerated in one step using air at 350 °C, which simplifies possible implementation for many applications GC−FPD results showed

Desulfurization of Diesel Fuels via π-Complexation with Nickel(II)-Exchanged X- and Y-Zeolites

Ab Initio molecular orbital calculations are performed at the B3LYP/6-31G(d)/HF/3-21G(d) calculation level on graphite and oxygen intermediates on and near the edges of graphite. The results are in agreement with experimental data for structural geometry parameters, vibrational frequencies, and, more importantly, bond energies. Three intermediates are studied:  semiquinone, carbonyl, and an off-plane, epoxy oxygen. The rate-limiting step for all gasification reactions by oxygen-containing gases is the breakage of C−C bonds to free CO from the semiquinone intermediate. The energy for this C−C bond is near 80 kcal/mol, which is close to the experimental activation energy for the reactions with CO2 and H2O. The C−C bond is weakened by 33% by the adjacent epoxy oxygen, to a bond energy of nearly 53 kcal/mol. This extent of weakening in the C−C bond energy coincides with the decrease in the experimental activation energy from 85 kcal/mol for the reactions with CO2 and H2O to 58 kcal/mol for the reaction with O...

Ab Initio Molecular Orbital Study of the Unified Mechanism and Pathways for Gas-Carbon Reactions†

An experimental feasibility study of using ultrasound to accomplish the dificult desorption of phenol from activated carbon and polymeric resin adsorbents is discussed. The desorption rates of activated carbon were found to significantly increase by ultrasound at 40 kHz and 1.44 MHz. Attrition of the activated carbon due to cavitation could be prevented by operating at a higher frequency and with an intensity below the threshold of the pulverization of carbon. According to the structural stability study of Amberlite XAD-4 and Dowex Optipore L-493 resins to withstand the abrasive cavitational effects of ultrasound at 40 kHz, the Dowex Optipore resin was stable under experimental conditions and phenol desorption rates were enhanced significantly with sonication. The ultrasonic desorption rates were favored by decreased temperature, aerated liquid medium, and increased ultrasound intensity. The desorption rates obtained without ultrasound appeared to be limited by pore diffusion, whereas those obtained in the presence of ultrasound were limited by surface reaction. The rate enhancement was due to an increase in diffusive transport within the pores caused by acoustic vortex microstreaming. The activation energy for desorption decreased with an increase in ultrasonic power density, thus making the ultrasound weaken the adsorption bond.

/pdf/desorption-by-ultrasound-phenol-on-activated-carbon-and-vnmp5nr933.pdf

Desorption by ultrasound: Phenol on activated carbon and polymeric resin

The Horvath-Kawazoe (HK) model is a widely used method for determining pore-size distribution in a microporous material from a single adsorption isotherm. The original model, however, suffers from conceptual flaws. The total interaction energy of the adsorbate is underestimated since the adsorbate-adsorbate interaction is incorrecty calculated. New corrected HK models proposed here for three pore geometries (slit, cylindrical, and spherical) can overcome these defects. Two other improvements have also been made in the new models. These assume that a filled micropore is composed of layers of adsorbate molecules which interact only with the molecular layers in the immediate vicinity. A better estimate of adsorbate-adsorbate-adsorbent interaction is obtained by utilizing actual distances between interacting molecules. The average interaction energy is calculated by a population-weighted average of the energy potential of the layers rather than by integration. This average potential approaches a nonzero value at large pore size, unlike that in the original model. Pore-size distributions predicted by the corrected HK models agreed significantly better with crystallographic data compared to the original model for both microporous and mesoporous sorbents.

/pdf/corrected-horvath-kawazoe-equations-for-pore-size-2drq6lfnvl.pdf

Ralph T. Yang

Papers

Delaminated Fe2O3-Pillared Clay: Its Preparation, Characterization, and Activities for Selective Catalytic Reduction of No by NH3

Desulfurization of Diesel Fuels via π-Complexation with Nickel(II)-Exchanged X- and Y-Zeolites

Ab Initio Molecular Orbital Study of the Unified Mechanism and Pathways for Gas-Carbon Reactions†

Desorption by ultrasound: Phenol on activated carbon and polymeric resin

Corrected Horvath-Kawazoe Equations for ´ Pore-Size Distribution