Showing papers by "Praveen K. Thallapally published in 2016"

Metal-organic framework with optimally selective xenon adsorption and separation.

Abstract: Nuclear energy is among the most viable alternatives to our current fossil fuel-based energy economy. The mass deployment of nuclear energy as a low-emissions source requires the reprocessing of used nuclear fuel to recover fissile materials and mitigate radioactive waste. A major concern with reprocessing used nuclear fuel is the release of volatile radionuclides such as xenon and krypton that evolve into reprocessing facility off-gas in parts per million concentrations. The existing technology to remove these radioactive noble gases is a costly cryogenic distillation; alternatively, porous materials such as metal-organic frameworks have demonstrated the ability to selectively adsorb xenon and krypton at ambient conditions. Here we carry out a high-throughput computational screening of large databases of metal-organic frameworks and identify SBMOF-1 as the most selective for xenon. We affirm this prediction and report that SBMOF-1 exhibits by far the highest reported xenon adsorption capacity and a remarkable Xe/Kr selectivity under conditions pertinent to nuclear fuel reprocessing.

Removal of TcO4− ions from solution: materials and future outlook

Abstract: Technetium mainly forms during artificial nuclear fission; it exists primarily as TcO4− in nuclear waste, and it is among the most hazardous radiation-derived contaminants because of its long half-life (t1/2 = 2.13 × 105 years) and environmental mobility. The high water solubility of TcO4− (11.3 mol L−1 at 20 °C) and its ability to readily migrate within the upper layer of the Earth's crust make it particularly hazardous. Several types of materials, namely resins, molecular complexes, layered double hydroxides, and pure inorganic and metal–organic materials, have been shown to be capable of capturing TcO4− (or other oxoanions) from solution. In this review, we give a brief description about the types of materials that have been used to capture TcO4− and closely related oxyanions so far and discuss the possibility of using metal–organic frameworks (MOFs) as next-generation ion-exchange materials for the stated application. In particular, with the advent of ultra-stable MOF materials, in conjunction with their chemical tunability, MOFs can be applied to capture these oxyanions under real-life conditions.

Zirconium-Based Metal-Organic Framework for Removal of Perrhenate from Water.

Abstract: The efficient removal of pertechnetate (TcO4–) anions from liquid waste or melter off-gas solution for an alternative treatment is one of the promising options to manage 99Tc in legacy nuclear waste. Safe immobilization of 99Tc is of major importance because of its long half-life (t1/2 = 2.13 × 105 yrs) and environmental mobility. Different types of inorganic and solid-state ion-exchange materials have been shown to absorb TcO4– anions from water. However, both high capacity and selectivity have yet to be achieved in a single material. Herein, we show that a protonated version of an ultrastable zirconium-based metal–organic framework can adsorb perrhenate (ReO4–) anions, a nonradioactive surrogate for TcO4–, from water even in the presence of other common anions. Synchrotron-based powder X-ray diffraction and molecular simulations were used to identify the position of the adsorbed ReO4– (surrogate for TcO4–) molecule within the framework.

Hybrid Ultra‐Microporous Materials for Selective Xenon Adsorption and Separation

Abstract: The demand for Xe/Kr separation continues to grow due to the industrial significance of high-purity Xe gas. Current separation processes rely on energy intensive cryogenic distillation. Therefore, less energy intensive alternatives, such as physisorptive separation, using porous materials, are required. Herein we show that an underexplored class of porous materials called hybrid ultra-microporous materials (HUMs) affords new benchmark selectivity for Xe separation from Xe/Kr mixtures. The isostructural materials, CROFOUR-1-Ni and CROFOUR-2-Ni, are coordination networks that have coordinatively saturated metal centers and two distinct types of micropores, one of which is lined by CrO4 (2-) (CROFOUR) anions and the other is decorated by the functionalized organic linker. These nets offer unprecedented selectivity towards Xe. Modelling indicates that the selectivity of these nets is tailored by synergy between the pore size and the strong electrostatics afforded by the CrO4 (2-) anions.

Removal of Pertechnetate-Related Oxyanions from Solution Using Functionalized Hierarchical Porous Frameworks.

Abstract: Efficient and cost-effective removal of radioactive pertechnetate anions from legacy nuclear waste is a key challenge to mitigate long-term nuclear waste storage issues. Traditional materials such as resins and layered double hydroxides (LDHs) were evaluated for their pertechnetate or its non-radioactive surrogate perrhenate removal capacity, but there is room for improvement in terms of capacity, selectivity and kinetics. A series of functionalized hierarchical porous frameworks were evaluated for their perrhenate removal capacity in the presence of other competing anions.

Kr/Xe Separation over a Chabazite Zeolite Membrane.

Abstract: Herein we demonstrate that chabazite zeolite SAPO-34 membranes effectively separated Kr/Xe gas mixtures at industrially relevant compositions. Control over membrane thickness and average crystal size led to industrial range permeances and high separation selectivities. Specifically, SAPO-34 membranes can separate Kr/Xe mixtures with Kr permeances as high as 1.2 × 10 –7 mol/m2 s Pa and separation selectivities of 35 for molar compositions close to typical concentrations of these two gases in air. In addition, SAPO-34 membranes separated Kr/Xe mixtures with Kr permeances as high as 1.2 × 10 –7 mol/m2 s Pa and separation selectivities up to 45 for molar compositions as might be encountered in nuclear reprocessing technologies. Molecular sieving and differences in diffusivities were identified as the dominant separation mechanisms.

Selective CO2 Adsorption in a Supramolecular Organic Framework

Abstract: Considering the rapidly rising CO2 level, there is a constant need for versatile materials which can selectively adsorb CO2 at low cost. The quest for efficient sorptive materials is still on since the practical applications of conventional porous materials possess certain limitations. In that context, we designed, synthesized, and characterized two novel supramolecular organic frameworks based on C-pentylpyrogallol[4]arene (PgC5 ) with spacer molecules, such as 4,4'-bipyridine (bpy). Highly optimized and symmetric intermolecular hydrogen-bonding interactions between the main building blocks and comparatively weak van der Waals interactions between solvent molecules and PgC5 leads to the formation of robust extended frameworks, which withstand solvent evacuation from the crystal lattice. The evacuated framework shows excellent affinity for carbon dioxide over nitrogen and adsorbs ca. 3 wt % of CO2 at ambient temperature and pressure.

Redox-Active Metal-Organic Composites for Highly Selective Oxygen Separation Applications.

Abstract: A redox-active metal-organic composite material shows improved and selective O2 adsorption over N2 with respect to individual components (MIL-101 and ferrocene). The O2 sensitivity of the composite material arises due to the formation of maghemite nanoparticles with the pore of the metal-organic framework material.

Noria: A Highly Xe‐Selective Nanoporous Organic Solid

Abstract: Separation of xenon and krypton is of industrial and environmental concern; the existing technologies use cryogenic distillation. Thus, a cost-effective, alternative technology for the separation of Xe and Kr and their capture from air is of significant importance. Herein, we report the selective Xe uptake in a crystalline porous organic oligomeric molecule, noria, and its structural analogue, PgC-noria, under ambient conditions. The selectivity of noria towards Xe arises from its tailored pore size and small cavities, which allows a directed non-bonding interaction of Xe atoms with a large number of carbon atoms of the noria molecular wheel in a confined space.

Simultaneous in Situ X-ray Diffraction and Calorimetric Studies as a Tool To Evaluate Gas Adsorption in Microporous Materials

Abstract: Combined application of in situ X-ray diffraction (XRD) and differential scanning calorimetry (DSC) is a novel technique for rapidly evaluating the suitability of microporous materials for postcombustion CO2 capture. Further, while many microporous materials show promise for CO2 capture, most are not evaluated in the presence of water vapor, a major component of postcombustion flue gas. As a demonstration of the versatility of XRD-DSC techniques, representatives of the classes of materials typically proposed for CO2 capture, zeolites, and metal–organic frameworks (MOFs) were studied: zeolite NaX, Ni-MOF-74 [Ni2(dobdc); dobdc = 2,5-dihydroxyterephthalate], ZIF-7 [ZIF: zeolitic imidazole framework, Zn(phim)2; phim: benzimidazole], and SBMOF-1 [Ca(sdb); sdb: 4,4′-sulfonyldibenzoate]. Although NaX and Ni-MOF-74 show very high affinity toward CO2 under idealized dry conditions, they are also very sensitive to the presence of water vapor and experience significant performance loss above 25% relative humidity (R...

Coordination Covalent Frameworks: A New Route for Synthesis and Expansion of Functional Porous Materials

Abstract: The synthetic approaches for fine-tuning the structural properties of coordination polymers or metal organic frameworks have exponentially grown during the past decade. This is due to the control over the properties of the resulting structures such as stability, pore size, pore chemistry and surface area for myriad possible applications. Herein, we present a new class of porous materials called Coordination Covalent Frameworks (CCFs) that were designed and effectively synthesized using a two-step reticular chemistry approach. During the first step, trigonal prismatic molecular building block was isolated using 4-aminobenazoic acid and Cr (III) salt, subsequently in the second step the polymerization of the isolated molecular building blocks (MBBs) takes place by the formation of strong covalent bonds where small organic molecules can connect the MBBs forming extended porous CCF materials. All the isolated CCFs were found to be permanently porous while the discrete MBB were nonporous. This approach would i...

Gas Sorption and Storage Properties of Calixarenes

Abstract: Calixarenes, a class of organic macrocyclic molecules have shown interesting gas sorption properties towards industrially important gases such as carbon dioxide, hydrogen, methane and acetylene. These macrocycles are involved in weak van der Waals interaction to form multidimensional supramolecular frameworks. The gas-diffusion and subsequent sorption occurs due to a cooperative behavior between neighboring macrocycles. Furthermore, the flexibility at the upper rim functional group also plays a key role in the overall gas uptake of calixarene. In this book chapter, we give a brief account of interaction and diffusion of gases in calixarene and selected derivatives.

Removal of TcO4‐ions from Solution: Materials and Future Outlook

Abstract: Technetium mainly forms during artificial nuclear fission; it exists primarily as TcO4− in nuclear waste, and it is among the most hazardous radiation-derived contaminants because of its long half-life (t1/2 = 2.13 × 105 years) and environmental mobility. The high water solubility of TcO4− (11.3 mol L−1 at 20 °C) and its ability to readily migrate within the upper layer of the Earth's crust make it particularly hazardous. Several types of materials, namely resins, molecular complexes, layered double hydroxides, and pure inorganic and metal–organic materials, have been shown to be capable of capturing TcO4− (or other oxoanions) from solution. In this review, we give a brief description about the types of materials that have been used to capture TcO4− and closely related oxyanions so far and discuss the possibility of using metal–organic frameworks (MOFs) as next-generation ion-exchange materials for the stated application. In particular, with the advent of ultra-stable MOF materials, in conjunction with their chemical tunability, MOFs can be applied to capture these oxyanions under real-life conditions.