Debasis Banerjee

Potential of Metal–Organic Frameworks for Separation of Xenon and Krypton

CONSPECTUS: The total world energy demand is predicted to rise significantly over the next few decades, primarily driven by the continuous growth of the developing world. With rapid depletion of nonrenewable traditional fossil fuels, which currently account for almost 86% of the worldwide energy output, the search for viable alternative energy resources is becoming more important from a national security and economic development standpoint. Nuclear energy, an emission-free, high-energy-density source produced by means of controlled nuclear fission, is often considered as a clean, affordable alternative to fossil fuel. However, the successful installation of an efficient and economically viable industrial-scale process to properly sequester and mitigate the nuclear-fission-related, highly radioactive waste (e.g., used nuclear fuel (UNF)) is a prerequisite for any further development of nuclear energy in the near future. Reprocessing of UNF is often considered to be a logical way to minimize the volume of high-level radioactive waste, though the generation of volatile radionuclides during reprocessing raises a significant engineering challenge for its successful implementation. The volatile radionuclides include but are not limited to noble gases (predominately isotopes of Xe and Kr) and must be captured during the process to avoid being released into the environment. Currently, energy-intensive cryogenic distillation is the primary means to capture and separate radioactive noble gas isotopes during UNF reprocessing. A similar cryogenic process is implemented during commercial production of noble gases though removal from air. In light of their high commercial values, particularly in lighting and medical industries, and associated high production costs, alternate approaches for Xe/Kr capture and storage are of contemporary research interest. The proposed pathways for Xe/Kr removal and capture can essentially be divided in two categories: selective absorption by dissolution in solvents and physisorption on porous materials. Physisorption-based separation and adsorption on highly functional porous materials are promising alternatives to the energy-intensive cryogenic distillation process, where the adsorbents are characterized by high surface areas and thus high removal capacities and often can be chemically fine-tuned to enhance the adsorbate-adsorbent interactions for optimum selectivity. Several traditional porous adsorbents such as zeolites and activated carbon have been tested for noble gas capture but have shown low capacity, selectivity, and lack of modularity. Metal-organic frameworks (MOFs) or porous coordination polymers (PCPs) are an emerging class of solid-state adsorbents that can be tailor-made for applications ranging from gas adsorption and separation to catalysis and sensing. Herein we give a concise summary of the background and development of Xe/Kr separation technologies with a focus on UNF reprocessing and the prospects of MOF-based adsorbents for that particular application.

Solution Processable MOF Yellow Phosphor with Exceptionally High Quantum Efficiency

An important aspect in the research and development of white light-emitting diodes (WLEDs) is the discovery of highly efficient phosphors free of rare-earth (RE) elements. Herein we report the design and synthesis of a new type of RE-free, blue-excitable yellow phosphor, obtained by combining a strongly emissive molecular fluorophore with a bandgap modulating co-ligand, in a three-dimensional metal organic framework. [Zn6(btc)4(tppe)2(DMA)2] (btc = benzene-1,3,5-tricarboxylate, tppe = 1,1,2,2-tetrakis(4-(pyridin-4-yl)phenyl)ethene, DMA = dimethylacetamide) crystallizes in a new structure type and emits bright yellow light when excited by a blue light source. It possesses the highest internal quantum yield among all RE-free, blue-excitable yellow phosphors reported to date, with a value as high as 90.7% (λex = 400 nm). In addition to its high internal quantum yield, the new yellow phosphor also demonstrates high external quantum yield, luminescent and moisture stability, solution processability, and color tunability, making it a promising material for use in phosphor conversion WLEDs.

Mechanism of Carbon Dioxide Adsorption in a Highly Selective Coordination Network Supported by Direct Structural Evidence

Understanding the interactions between adsorbed gas molecules and a pore surface at molecular level is vital to exploration and attempts at rational development of gasselective nanoporous solids. Much current work focuses on the design of functionalized metal–organic frameworks (MOFs) or coordination networks (CNs) that selectively adsorb CO2. [1–9] While interactions between CO2 molecules and the p clouds of aromatic linkers in MOFs under ambient conditions have been explored theoretically, no direct structure evidence of such interactions are reported to date. Here we provide the first structural insight of such interactions in a porous calcium based CN using single-crystal X-ray diffraction methods, supported by powder diffraction coupled with differential scanning calorimetry (DSC-XRD), in situ IR/Raman spectroscopy, and molecular simulation data. We further postulate that such interactions are responsible for the high CO2/N2 adsorption selectivity, even in the case of a high relative humidity (RH). Our data suggest that the key interaction responsible for such selectivity, the room-temperature stability and the relative insensitivity to the RH of the CO2-CN adduct, is between two phenyl rings of the linker in the CN and the molecular quadrupole of CO2. The specific geometry of the linker molecule results in a “pocket” where carbon from the CO2 molecule is placed between two centroids of the aromatic ring. Our experimental confirmation of this variation on theoretically postulated interactions between CO2 and a phenyl ring will promote the search for other CNs containing phenyl ring pockets. Selective adsorption and sequestration of CO2 from sources of anthropogenic emissions, such as untreated waste from flue gas and products of the water gas shift reaction, is important to mitigate the growing level of atmospheric CO2. [10] Current separation methods use absorption in alkanolamine solutions, which are toxic, corrosive, and require significant energy for their regeneration. Hence microporous solid-state adsorbents, such as zeolites, hybrid zeolite–polymer systems, porous organic materials, and MOFs are proposed as alternatives, especially in combination with pressure swing processes. Rather than relying solely on tuning the pore diameters of microporous materials to select between gases based on size (the kinetic diameters of CO2, CH4 and N2 are 3.30, 3.76 3.64 , respectively ) selective separation relies on differences in electronic properties, such as the quadrupole moment and polarizability. Attempts to produce MOFs or CNs with adsorption properties competitive with those of commercially established aluminosilicate zeolites, relies on strategies that include pore surface modification with strongly polarizing functional groups, such as amines 7, 9,15] and desolvating metals centers 8, 16] to produce low-coordinated sites suitable for CO2 adsorption. The amine-functionalized materials offer a high selectivity toward CO2 adsorption, but a low effective surface area and thus, a low total uptake capacity. Strong interactions with polarizing functional groups, as well as with open metal sites presents other drawbacks including an increase in the costs for material regeneration. Furthermore, water effectively competes with CO2 at low-coordinated cation sites, impeding the performance of frameworks in commercial flue gas. We recently described a porous framework, CaSDB (SDB: sulfonyldibenzoate, compound 1) with a high CO2/N2 selectivity. At 0.15 bar of CO2 and 0.85 bar of N2, a typical composition of flue gas mixture from power plants, the selectivity is in the range of 48 to 85 at 298 K. CaSDB shows a reversible uptake of CO2 of 5.75 wt% at 273 K and 1 bar pressure and 4.37 wt% at room temperature, with heats of adsorption for CO2 and N2 of 31 and 19 kJmol , respectively. The as-synthesized compound contains not coordinated water molecules and is easily activated for gas adsorption by heating to 563 K in vacuum; remarkably the activated framework does not readsorb water, even if exposed to a RH greater than [*] A. M. Plonka, W. R. Woerner, Prof. Dr. J. B. Parise Department of Geosciences, Stony Brook University Stony Brook, NY 11794-2100 (USA) E-mail: john.parise@stonybrook.edu

Systematic approach in designing rare-Earth-free hybrid semiconductor phosphors for general lighting applications.

As one of the most rapidly evolving branches of solid-state lighting technologies, light emitting diodes (LEDs) are gradually replacing conventional lighting sources due to their advantages in energy saving and environmental protection. At the present time, commercially available white light emitting diodes (WLEDs) are predominantly phosphor based (e.g., a yellow-emitting phosphor, such as cerium-doped yttrium aluminum garnet or (YAG):Ce(3+), coupled with a blue-emitting InGaN/GaN diode), which rely heavily on rare-earth (RE) metals. To avoid potential supply risks of these elements, we have developed an inorganic-organic hybrid phosphor family based on I-VII binary semiconductors. The hybrid phosphor materials are totally free of rare-earth metals. They can be synthesized by a simple, low-cost solution process and are easily scalable. Their band gap and emission energy, intensity, and color can be systematically tuned by incorporating ligands with suitable electronic properties. High quantum efficiency is achieved for some of these compounds. Such features make this group of materials promising candidates as alternative phosphors for use in general lighting devices.

Effective sensing of RDX via instant and selective detection of ketone vapors

Two new luminescent metal–organic frameworks (LMOFs) were synthesized and examined for use as sensory materials. Very fast and effective sensing of RDX was achieved by vapor detection of a cyclic ketone used as a solvent in the production of plastic explosives. The effects of porosity and electronic structure of the LMOFs on their sensing performance were evaluated. We demonstrate that the optimization of these two factors of an LMOF can significantly improve its sensitivity and selectivity. We also elucidate the importance of both electron and energy transfer processes on the fluorescence response of a sensory material.

Vapor phase detection of nitroaromatic and nitroaliphatic explosives by fluorescence active metal–organic frameworks

The detection of explosives using chemical sensors is of paramount importance. Recent studies based on luminescent metal–organic frameworks (MOFs) have shown that these materials can be effective detectors of high explosive substances. In the current study, we describe the explosive sensing properties of a series of zinc-based fluorescence active MOFs (or FAMs) built on prototypical paddle-wheel secondary building units.

Anionic Gallium-Based Metal−Organic Framework and Its Sorption and Ion-Exchange Properties

A gallium-based metal-organic framework Ga(6)(C(9)H(3)O(6))(8)·(C(2)H(8)N)(6)(C(3)H(7)NO)(3)(H(2)O)(26) [1, Ga(6)(1,3,5-BTC)(8)·6DMA·3DMF·26H(2)O], GaMOF-1; BTC = benzenetricarboxylate/trimesic acid and DMA = dimethylamine], with space group I43d, a = 19.611(1) Å, and V = 7953.4(6) Å(3), was synthesized using solvothermal techniques and characterized by synchrotron-based X-ray microcrystal diffraction. Compound 1 contains isolated gallium tetrahedra connected by the organic linker (BTC) forming a 3,4-connected anionic porous network. Disordered positively charged ions and solvent molecules are present in the pore, compensating for the negative charge of the framework. These positively charged molecules could be exchanged with alkali-metal ions, as is evident by an ICP-MS study. The H(2) storage capacity of the parent framework is moderate with a H(2) storage capacity of ~0.5 wt % at 77 K and 1 atm.

From 1D Chain to 3D Network: A New Family of Inorganic–Organic Hybrid Semiconductors MO3(L)x (M = Mo, W; L = Organic Linker) Built on Perovskite-like Structure Modules

MO3 (M = Mo, W) or VI-VI binary compounds are important semiconducting oxides that show great promise for a variety of applications. In an effort to tune and enhance their properties in a systematic manner we have applied a designing strategy to deliberately introduce organic linker molecules in these perovskite-like crystal lattices. This approach has led to a wealth of new hybrid structures built on one-dimensional (1D) and two-dimensional (2D) VI-VI modules. The hybrid semiconductors exhibit a number of greatly improved properties and new functionality, including broad band gap tunability, negative thermal expansion, largely reduced thermal conductivity, and significantly enhanced dielectric constant compared to their MO3 parent phases.

Effect of ligand geometry on selective gas-adsorption: the case of a microporous cadmium metal organic framework with a V-shaped linker.

A microporous cadmium metal organic framework is synthesized and structurally characterized. The material possesses a 3-D framework with a 1-D sinusoidal chain and shows high selectivity for CO2 over N2. The selectivity is attributed to CO2 interacting with two phenyl rings of a V-shaped linker as estimated by the in situ XRD-DSC study.

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

Efficient and cost-effective removal of radioactive pertechnetate anions from 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 perrhenate (the non-radioactive surrogate) 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.