Jagadeswara R. Karra

Georgia Institute of Technology, Atlanta, GA, United States

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Publications (9)23.96 Total impact

  • Source
    Jagadeswara Reddy Karra, Himanshu Jasuja, You-Gui Huang, Krista Walton
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    ABSTRACT: Stability of metal-organic frameworks (MOFs) under humid environments is of particular interest for their potential commercial and industrial uses. In this work, water vapor adsorption experiments and subsequent structural analysis on the newly synthesized BTTB-based MOFs (BTTB = 4,4’,4’’,4’’’-benzene-1,2,4,5-tetrayltetrabenzoic acid) have been performed to investigate their stability under humid conditions. ZnBTTB and CdBTTB degrade completely after exposure to 90% relative humidity (RH). Instability of ZnBTTB is due to the four-coordinated zinc carboxylate system similar to MOF-5. Similarly, CdBTTB is also unstable as Cd2+ ions have coordination number of 4 when the MOF is activated (desolvated). Unlike ZnBTTB and CdBTTB, the structure of ZnBTTBBDC has not degraded significantly upon exposure to 90% RH. This partial structure retention is attributed to the higher nuclearity of the metal in the SBU of ZnBTTBBDC compared to ZnBTTB and CdBTTB. Water adsorption isotherms of CoBTTBAZPY and ZnBTTBAZPY show type V behavior due to free nitrogen sites analogous to mesoporous silicas and BPL activated carbon. The crystal structures of AZPY-based pillared MOFs show partial loss of crystallinity whereas BPY-based pillared MOFs remain stable after exposure to 90% RH. The greater stability of BPY-based MOFs is attributed to the higher extent of catenation, higher rigidity of the BPY linker, and absence of any hydrophilic sites.
    J. Mater. Chem. A. 11/2014;
  • Jagadeswara R. Karra, You-Gui Huang, Krista S. Walton
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    ABSTRACT: Three porous metal–organic frameworks {[Ni(H2BTTB)·(H2O)2]·(DIOX)2}n (1), {[Zn(H2BTTB)]·(DEF)3·(H2O)2}n (2), and {[Mg(H2BTTB)·(C2H5OH)2]·(DEF)4}n (3) based on the 4,4′,4″,4‴-benzene-1,2,4,5-tetrayltetrabenzoic acid (H4BTTB) ligand have been synthesized under solvothermal conditions (DIOX = dioxane). These three MOFs show structural diversities: compound 1 is a two-dimensional (2D) grid layer, compound 2 is a 2-fold interpenetrated 3D framework with a pillared-layer structure, and compound 3 is a noninterpenetrated 3D framework with a (4, 4)-connected binodal net. Compound 1 and compound 2 have BET surface areas of 391 and 447 m2/g, respectively; however, the surface area of compound 3 cannot be experimentally determined. All three MOFs have a higher adsorption preference for CO2 over N2 and CH4. Ideal adsorbed solution theory was used to estimate binary adsorption selectivities. Compound 2 shows the highest capacity for all three gases, whereas compound 1 shows the highest selectivity for CO2 over CH4 and N2. Compound 1 exhibits a selectivity of 30 for CO2 over N2 in equimolar mixtures.
    Crystal Growth & Design 02/2013; 13(3):1075–1081. · 4.69 Impact Factor
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    ABSTRACT: Metal–organic frameworks (MOFs) are attractive microporous materials for adsorption separations due to their extraordinary structures and impressive high surface areas. Catenation, or framework interpenetration, can significantly impact the crystal stability and improve the adsorption interactions. This interesting approach was used to obtain {[Cu3(BTB)2(H2O)3]⋅(DMF)9(H2O)2} (MOF-14) as a microporous material with a high surface area and large pore volume, which are desirable parameters for adsorption applications. Here, we report a detailed study of this catenated material with its gas adsorption properties. The potential for adsorption separations is evaluated by measuring pure-component adsorption isotherms for carbon dioxide, methane, and nitrogen. The Ideal Adsorbed Solution Theory (IAST) was used to evaluate adsorption selectivities of MOF-14 for CO2/CH4 and CO2/N2 equimolar mixtures. In addition, water adsorption and the impact of exposure on structural degradation are reported. Compared to other open-metal site MOFs, MOF-14 adsorbs significantly less water. This interwoven MOF is a promising competitor to other MOF materials in the gas separation field due to low interactions with water and high selectivity for CO2 over N2.
    Journal of Colloid and Interface Science 10/2012; 392:331–336. · 3.55 Impact Factor
  • Angewandte Chemie International Edition 01/2011; 50(2):436-40. · 11.34 Impact Factor
  • Jagadeswara R. Karra, Krista S. Walton
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    ABSTRACT: Atomistic grand canonical Monte Carlo simulations were performed to understand the interplay of factors (pore size, heat of adsorption, open metal sites, electrostatics, and ligand functionalization) contributing to adsorption of CO2, CO, and N2 in MOFs. Four MOFs—IRMOF-1, IRMOF-3, Cu-BTC, and Zn2[bdc]2[dabco]—were chosen for comparison. Binary mixtures (CO2/CO) and (CO2/N2) containing 5%, 50%, and 95% CO2 were examined. CO2 is preferentially adsorbed over CO and N2 in all MOFs. Cu-BTC displays higher selectivities for CO2 over CO at lower pressures and CO2 over N2 at all pressures for all mixtures due to the increase in electrostatic interactions of CO2 with the exposed copper sites. However, IRMOF-3 shows surprisingly high selectivities for CO2 over CO for 50% and 95% mixtures at higher pressures due to the presence of amine-functionalized groups and high pore volume. CO2 selectivities increase with increasing CO2 concentration in the gas mixtures at total pressures above 5 bar. On the basis of the results obtained, it can be concluded that construction of smaller pore size MOFs relative to sorbate size with embedded open metal sites or functionalized groups can lead to greater enhancement of these adsorption separation systems.
    The Journal of Physical Chemistry C. 08/2010; 114(37).
  • Jagadeswara R. Karra, Krista Walton
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    ABSTRACT: A better understanding of how key structural features affect adsorption properties of guest molecules is necessary for the development of simple heuristics that can lead to the design of new MOFs with high gas adsorption capacities and improved selectivities for specific gas separations. This study is an effort to understand the interplay of different factors (pore size, heat of adsorption, open metal sites, electrostatics and ligand functionalization) contributing to adsorption in MOFs. Two MOFs, Cu-BTC and Zn2[bdc]2[dabco] were synthesized and characterized using powder X-ray diffraction experiments and nitrogen adsorption at 77K. Adsorption isotherms for CO2 and CO were measured gravimetrically at room temperature. GCMC simulations were performed to calculate adsorption of CO and CO2 for the synthesized MOFs and two other MOFs IRMOF-1 and IRMOF-3. Heats of adsorption for each component in all four MOFs were also computed. Binary mixture (CO2/CO) simulations were performed for 5%, 50%, and 95% CO2 mixtures and adsorption selectivities were calculated. Simulations show that all the MOFs are selective for CO2 over CO. Cu-BTC displays higher selectivities for CO2 over CO at lower pressures for all mixtures due to the increase in electrostatic interactions of CO2 with the exposed copper sites. IRMOF-3 shows surprisingly higher selectivities for CO2 over CO for 50% and 95% mixtures at higher pressures due to the presence of amine functionalized groups. These results and their implications for enhancement of adsorption separation systems will be discussed.
    2009 AIChE Annual Meeting; 11/2009
  • Jagadeswara R. Karra, Krista S. Walton
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    ABSTRACT: A critical step in developing adsorption-based technologies is the identification/synthesis of adsorbents that provide the proper adsorption capacities, selectivities, or reactivities for the application. It is well known that metal sites in porous materials have a tremendous influence on the resulting adsorption properties. Metal-organic frameworks (MOFs) are a recent addition to the classes of porous materials and have the potential for providing a flexible platform for developing designer adsorbents. MOFs are synthesized by self assembly of organic ligands and metal oxide clusters and possess pore sizes and chemical functionalities that can be manipulated by modifying the metal group or organic linker. Several MOFs have open metal sites (coordinatively unsaturated) that are built into the pore walls in a repeating, regular fashion. These metal sites have been shown to impart catalytic activity to the materials and also have the potential to enhance general adsorption properties. In this work, we explore the effect of open metal sites in Cu-BTC on adsorption selectivities of carbon monoxide- and carbon dioxide-containing mixtures. Molecular modeling results and experimental results will be discussed.
    2008 AIChE Annual Meeting; 11/2008
  • Krista S. Walton, Jagadeswara R. Karra
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    ABSTRACT: Metal-organic frameworks represent a new direction in porous materials research that could lead to the creation of designer-specific multifunctional materials for adsorption applications. The rich field of coordination chemistry provides a versatile platform from which these materials may be assembled from an almost infinite set of building blocks. The key to developing these materials for use in adsorption separations and gas storage is to obtain a fundamental understanding of their adsorption properties. In this work, we examine the effect of pore size, unsaturated metal sites, and functionalized ligands on the adsorption of carbon dioxide, carbon monoxide, and methane at various temperatures. The specific objective here is to determine the governing structure/property relationships for MOFs that contribute to favorable adsorption properties for polar and nonpolar molecules. Three MOFs were synthesized, and adsorption isotherms were measured. The first material, Cu-BTC, possesses open metal sites and interconnected pores. The other two MOFs were synthesized from a mixed-ligand system of benzene-dicarboxylic acid and triethylenediamine. From this system, we formed a zinc MOF (1) and an isostructural copper MOF (2), which possess two interconnected channels with dimensions of 7.5 x 7.5 angstrom and 4.8 x 3.2 angstrom. In this paper, we will discuss MOF synthesis methods and adsorption equilibrium measurements for CO2, CO, and CH4. We will also compare our findings with previously reported MOF results to strengthen the development of structure/property relationships. Recommendations for design of MOFs for trace contaminate applications will be discussed.
    2008 AIChE Annual Meeting; 11/2008
  • Jagadeswara R Karra, Krista S Walton
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    ABSTRACT: Atomistic grand canonical Monte Carlo simulations were performed in this work to investigate the role of open copper sites of Cu-BTC in affecting the separation of carbon monoxide from binary mixtures containing methane, nitrogen, or hydrogen. Mixtures containing 5%, 50%, or 95% CO were examined. The simulations show that electrostatic interactions between the CO dipole and the partial charges on the metal-organic framework (MOF) atoms dominate the adsorption mechanism. The binary simulations show that Cu-BTC is quite selective for CO over hydrogen and nitrogen for all three mixture compositions at 298 K. The removal of CO from a 5% mixture with methane is slightly enhanced by the electrostatic interactions of CO with the copper sites. However, the pore space of Cu-BTC is large enough to accommodate both molecules at their pure-component loadings, and in general, Cu-BTC exhibits no significant selectivity for CO over methane for the equimolar and 95% mixtures. On the basis of the pure-component and low-concentration behavior of CO, the results indicate that MOFs with open metal sites have the potential for enhancing adsorption separations of molecules of differing polarities, but the pore size relative to the sorbate size will also play a significant role.
    Langmuir 08/2008; 24(16):8620-6. · 4.38 Impact Factor

Publication Stats

36 Citations
23.96 Total Impact Points

Institutions

  • 2011–2012
    • Georgia Institute of Technology
      • School of Chemical & Biomolecular Engineering
      Atlanta, GA, United States
  • 2008–2009
    • Kansas State University
      • Department of Chemical Engineering
      Kansas, United States