Showing papers by "Praveen K. Thallapally published in 2012"

Progress in adsorption-based CO2 capture by metal–organic frameworks

Abstract: Metal–organic frameworks (MOFs) have recently attracted intense research interest because of their permanent porous structures, large surface areas, and potential applications as novel adsorbents The recent progress in adsorption-based CO2 capture by MOFs is reviewed and summarized in this critical review CO2 adsorption in MOFs has been divided into two sections, adsorption at high pressures and selective adsorption at approximate atmospheric pressures Keys to CO2 adsorption in MOFs at high pressures and low pressures are summarized to be pore volumes of MOFs, and heats of adsorption, respectively Many MOFs have high CO2 selectivities over N2 and CH4 Water effects on CO2 adsorption in MOFs are presented and compared with benchmark zeolites In addition, strategies appeared in the literature to enhance CO2 adsorption capacities and/or selectivities in MOFs have been summarized into three main categories, catenation and interpenetration, chemical bonding enhancement, and electrostatic force involvement Besides the advantages, two main challenges of using MOFs in CO2 capture, the cost of synthesis and the stability toward water vapor, have been analyzed and possible solutions and path forward have been proposed to address the two challenges as well (150 references)

Highly Selective Carbon Dioxide Uptake by [Cu(bpy-n)2(SiF6)] (bpy-1 = 4,4′-Bipyridine; bpy-2 = 1,2-Bis(4-pyridyl)ethene)

Abstract: A previously known class of porous coordination polymer (PCP) of formula [Cu(bpy-n)2(SiF6)] (bpy-1 = 4,4′-bipyridine; bpy-2 = 1,2-bis(4-pyridyl)ethene) has been studied to assess its selectivity toward CO2, CH4, N2, and H2O. Gas sorption measurements reveal that [Cu(bpy-1)2(SiF6)] exhibits the highest uptake for CO2 yet seen at 298 K and 1 atm by a PCP that does not contain open metal sites. Significantly, [Cu(bpy-1)2(SiF6)] does not exhibit particularly high uptake under the same conditions for CH4, N2, and, H2O, presumably because of its lack of open metal sites. Consequently, at 298 K and 1 atm [Cu(bpy-1)2(SiF6)] exhibits a relative uptake of CO2 over CH4 of ca. 10.5:1, the highest value experimentally observed in a compound without open metal sites. [Cu(bpy-2)2(SiF6)] exhibits larger pores and surface area than [Cu(bpy-1)2(SiF6)] but retains a high CO2/CH4 relative uptake of ca. 8:1.

Porous organic molecular materials

Abstract: Most nanoporous materials with molecular-scale pores are composed of directional covalent or coordination bonds, such as porous metal–organic frameworks and organic network polymers. By contrast, nanoporous materials comprised of discrete organic molecules, between which there are only weak non-covalent interactions, are seldom encountered. Indeed, the majority of organic molecules pack efficiently in the solid state to minimize the void volume, leading to nonporous materials. In recent years, a large number of nanoporous organic molecular materials (crystalline or amorphous) were discovered and their porosity was confirmed by gas adsorption. All of these materials were compiled in this highlight. In addition, advantages of porous organic molecular materials over porous networks are discussed.

Selective CO2 Capture from Flue Gas Using Metal–Organic Frameworks―A Fixed Bed Study

Abstract: It is important to capture carbon dioxide from flue gas, which is considered one of to be the main cause of global warming. CO2/N2 separation by novel adsorbents is a promising method for reducing ...

Metal-organic frameworks for removal of Xe and Kr from nuclear fuel reprocessing plants.

Abstract: Removal of xenon (Xe) and krypton (Kr) from process off-gases containing 400 ppm Xe, 40 ppm Kr, 78% N2, 21% O2, 0.9% Ar, 0.03% CO2, and so forth using adsorption was demonstrated for the first time. Two well-known metal–organic frameworks (MOFs), HKUST-1 and Ni/DOBDC, which both have unsaturated metal centers but different pore morphologies, were selected as novel adsorbents. Results of an activated carbon were also included for comparison. The Ni/DOBDC has higher Xe/Kr selectivities than those of the activated carbon and the HKUST-1. In addition, results show that the Ni/DOBDC and HKUST-1 can adsorb substantial amounts of Xe and Kr even when they are mixed in air. Moreover, the Ni/DOBDC can successfully separate 400 ppm Xe from 40 ppm Kr and air containing O2, N2, and CO2 with a Xe/Ke selectivity of 7.3 as indicated by our breakthrough results. This shows a promising future for MOFs in radioactive nuclide separations from spent fuels.

Switching Kr/Xe Selectivity with Temperature in a Metal–Organic Framework

Abstract: Krypton (Kr) and xenon (Xe) adsorption on two partially fluorinated metal–organic frameworks (FMOFCu and FMOFZn) with different cavity size and topologies are reported. FMOFCu shows an inversion in sorption selectivity toward Kr at temperatures below 0 °C while FMOFZn does not. The 1D microtubes packed along the (101) direction connected through small bottleneck windows in FMOFCu appear to be the reason for this peculiar behavior. The FMOFCu shows an estimated Kr/Xe selectivity of 36 at 0.1 bar and 203 K.

Selective Metal Cation Capture by Soft Anionic Metal–Organic Frameworks via Drastic Single-Crystal-to-Single-Crystal Transformations

Abstract: Flexible anionic metal–organic frameworks (MOFs) are transformed into neutral heterobimetallic systems via single-crystal-to-single-crystal processes invoked by cation insertion. These transformations are directed by cooperative bond breakage and formation, resulting in expansion or contraction of the 3D framework by up to 33% due to the flexible nature of the organic linker. These MOFs displays highly selective uptake of divalent transition-metal cations (e.g., Co2+ and Ni2+) over alkali-metal cations (Li+ and Na+).

Progress in Adsorption‐Based CO2 Capture by Metal—Organic Frameworks

Abstract: Metal–organic frameworks (MOFs) have recently attracted intense research interest because of their permanent porous structures, large surface areas, and potential applications as novel adsorbents. The recent progress in adsorption-based CO2 capture by MOFs is reviewed and summarized in this critical review. CO2 adsorption in MOFs has been divided into two sections, adsorption at high pressures and selective adsorption at approximate atmospheric pressures. Keys to CO2 adsorption in MOFs at high pressures and low pressures are summarized to be pore volumes of MOFs, and heats of adsorption, respectively. Many MOFs have high CO2 selectivities over N2 and CH4. Water effects on CO2 adsorption in MOFs are presented and compared with benchmark zeolites. In addition, strategies appeared in the literature to enhance CO2 adsorption capacities and/or selectivities in MOFs have been summarized into three main categories, catenation and interpenetration, chemical bonding enhancement, and electrostatic force involvement. Besides the advantages, two main challenges of using MOFs in CO2 capture, the cost of synthesis and the stability toward water vapor, have been analyzed and possible solutions and path forward have been proposed to address the two challenges as well (150 references).

Insights into the Temperature‐Dependent “Breathing” of a Flexible Fluorinated Metal–Organic Framework

Abstract: The framework expansion and contraction upon carbon dioxide uptake was studied in a partially fluorinated metal-organic framework, FMOF-2. The results show framework expansion and contraction (breathing) as a function of pressure and temperature. Even at temperatures as low as -30 °C, two phase transitions seem to take place with a pressure step (corresponding to the second transition) that is greatly dependent on temperature. This behavior is described by the model proposed by Coudert and co-workers showing that the material seems to undergo two phase transitions that are temperature-dependent. The isosteric heats of adsorption at high pressures show a minimum that is concurrent with the region of CO(2) loadings where the second pressure step occurs. It was deduced that these lower enthalpy values are a consequence of the energy cost related to the expansion or reopening of the framework. Lastly, the large and reversible breathing behavior may be a product of the combination of the high elasticity of zinc (II) coordination and the apparent high flexibility of the V-shaped organic building block.

Initial proof-of-principle for near room temperature Xe and Kr separation from air with MOFs

Abstract: Materials were developed and tested in support of the U.S. Department of Energy, Office of Nuclear Energy, Fuel Cycle Technology Separations and Waste Forms Campaign. Specifically, materials are being developed for the removal of Xenon and krypton from gaseous products of nuclear fuel reprocessing unit operations. During FY 2012, Three Metal organic framework (MOF) structures were investigated in greater detail for the removal and storage of Xe and Kr from air at room temperature. Our breakthrough measurements on Nickel based MOF could capture and separate parts per million levels of Xe from Air (40 ppm Kr, 78% N2, 21% O2, 0.9% Ar, 0.03% CO2). Similarly, the selectivity can be changed from Xe > Kr to Xe < Kr simply by changing the temperature in another MOF. Also for the first time we estimated the cost of the metal organic frameworks in bulk.

Engineering Report on the Fission Gas Getter Concept

Abstract: In 2010, the Department of Energy (DOE) requested that a Brookhaven National Laboratory (BNL)-led team research the possibility of using a getter material to reduce the pressure in the plenum region of a light water reactor fuel rod. During the first two years of the project, several candidate materials were identified and tested using a variety of experimental techniques, most with xenon as a simulant for fission products. Earlier promising results for candidate getter materials were found to be incorrect, caused by poor experimental techniques. In May 2012, it had become clear that none of the initial materials had demonstrated the ability to adsorb xenon in the quantities and under the conditions needed. Moreover, the proposed corrective action plan could not meet the schedule needed by the project manager. BNL initiated an internal project review which examined three questions: 1. Which materials, based on accepted materials models, might be capable of absorbing xenon? 2. Which experimental techniques are capable of not only detecting if xenon has been absorbed but also determine by what mechanism and the resulting molecular structure? 3. Are the results from the previous techniques useable now and in the future? As part of the second question, the project review team evaluated the previous experimental technique to determine why incorrect results were reported in early 2012. This engineering report is a summary of the current status of the project review, description of newly recommended experiments and results from feasibility studies at the National Synchrotron Light Source (NSLS).

Gas Storage and Separation in Supramolecular Materials

Abstract: This chapter provides an overview of gas storage and separation applications using Porous Materials. Due to space constraints, we focused our discussion on Organic, Inorganic and Hybrid materials in other words metal organic frameworks. Keywords: gas storage; separation; porous materials; metal-organic framework