Tina M. Nenoff

Intrinsic broad-band white-light emission by a tuned, corrugated metal-organic framework.

Herein we report on the broad-band direct white-light originating from a single component emitter, namely a novel three-periodic metal-organic framework (MOF). This material features an unprecedented topology with (3,4)-connected nodes. The structure-function relationship in this system is driven by two complementary unique structural features: corrugation and interpenetration. Good correlation between simulated and experimental emission spectra has been attained, resulting in optimized color properties that approach requirements for solid-state lighting (SSL). Guided by the optimized calculated spectra, the tunability of the assembly was proven by the successful in-framework co-doping of Eu(3+). This resulted in significantly improved color properties, opening new paths for the rational design of alternative materials for SSL applications.

Capture of Volatile Iodine, a Gaseous Fission Product, by Zeolitic Imidazolate Framework-8

Here we present detailed structural evidence of captured molecular iodine (I(2)), a volatile gaseous fission product, within the metal-organic framework ZIF-8 [zeolitic imidazolate framework-8 or Zn(2-methylimidazolate)(2)]. There is worldwide interest in the effective capture and storage of radioiodine, as it is both produced from nuclear fuel reprocessing and also commonly released in nuclear reactor accidents. Insights from multiple complementary experimental and computational probes were combined to locate I(2) molecules crystallographically inside the sodalite cages of ZIF-8 and to understand the capture of I(2) via bonding with the framework. These structural tools included high-resolution synchrotron powder X-ray diffraction, pair distribution function analysis, and molecular modeling simulations. Additional tests indicated that extruded ZIF-8 pellets perform on par with ZIF-8 powder and are industrially suitable for I(2) capture.

Radioactive Iodine Capture in Silver-Containing Mordenites through Nanoscale Silver Iodide Formation

The effective capture and storage of radiological iodine ((129)I) remains a strong concern for safe nuclear waste storage and safe nuclear energy. Silver-containing mordenite (MOR) is a longstanding benchmark for iodine capture; however, the molecular level understanding of this process needed to develop more effective iodine getters has remained elusive. Here we probe the structure and distribution of iodine sorbed by silver-containing MOR using differential pair distribution function analysis. While iodine is distributed between gamma-AgI nanoparticles on the zeolite surface and subnanometer alpha-AgI clusters within the pores for reduced silver MOR, in the case of unreduced silver-exchanged MOR, iodine is exclusively confined to the pores as subnanometer alpha-AgI. Consequently, unreduced silver-containing zeolites may offer a more secure route for radioactive iodine capture, with the potential to more effectively trap the iodine for long-term storage.

Trapping Guests within a Nanoporous Metal–Organic Framework through Pressure-Induced Amorphization

The release of guest species from within a nanoporous metal-organic framework (MOF) has been inhibited by amorphization of the guest-loaded framework structure under applied pressure. Thermogravimetric analyses have shown that by amorphizing ZIF-8 following sorption of molecular I(2), a hazardous radiological byproduct of nuclear energy production, the pore apertures in the framework are sufficiently distorted to kinetically trap I(2) and improve I(2) retention. Pair distribution function (PDF) analysis indicates that the local structure of the captive I(2) remains essentially unchanged upon amorphization of the framework, with the amorphization occurring under the same conditions for the vacant and guest-loaded framework. The low, accessible pressure range needed to effect this change in desorption is much lower than in tradition sorbents such as zeolites, opening the possibility for new molecular capture, interim storage, or controlled release applications.

Synthesis, Characterization, and Ion Exchange Properties of Hydrotalcite Mg6Al2(OH)16(A)x(A‘)2-x·4H2O (A, A‘ = Cl-, Br-, I-, and NO3-, 2 ≥ x ≥ 0) Derivatives

A series of monovalent anion-containing hydrotalcites (HTCs) with the general formula Mg6Al2(OH)16(A)x(A‘)2-x·4H2O (A, A‘ = Cl-, Br-, I-, and NO3-, 2 ≥ x ≥ 0) have been studied. Samples were synthesized by three different methods:  ion exchange (IE), hydrothermal (HT), and recrystallization based on “memory effect” (ME). The physical, structural, and chemical characteristics and properties of the HTCs have been studied as a function of the synthetic methods and anions used. All three synthetic methods produced HTCs of good crystallinity and uniform particle size. When a second (A‘) or all four (Cl-, Br-, I-, NO3-) anions were present together with an A-HTC in an aqueous medium, the order of ion exchange preference was Br- > Cl- > NO3- > I-. When using one-pot synthetic methods (HT, ME), the same order of anion incorporation preference, Br- > Cl- > NO3- > I-, was observed.

Internal surface modification of MFI-type zeolite membranes for high selectivity and high flux for hydrogen.

MFI-type zeolite membranes were modified by depositing molecular silica at a small number of active sites in the internal surface by in situ catalytic cracking of silane precursor. The limited silica deposition reduced the effective size of the zeolitic channels that dramatically enhanced the H(2) selectivity without causing a large increase in H(2) transport resistance. The modified zeolite membrane achieved an extraordinary H(2)/CO(2) permselectivity of 141 with a high H(2) permeance of 3.96 x 10(-7) mol/m(2) x s x Pa at 723 K. The effect of pore modification on the gas transport behavior was studied on the basis of single gas permeation data.

Effect of pressure, membrane thickness, and placement of control volumes on the flux of methane through thin silicalite membranes: A dual control volume grand canonical molecular dynamics study

The flux of methane through the straight channels of thin silicalite membranes is studied via dual control volume grand canonical molecular dynamics. The adsorption layers on the surfaces of the thin membranes are found to provide a significant resistance to the flux of methane. This strong surface effect for thin membranes requires that the control volumes (where insertions and deletions are performed) must be placed far enough away from the membrane surface that they do not overlap with the surface adsorption layer. The permeance (flux/pressure drop) of methane through the surface layer is shown to be insensitive to both the average pressure and the pressure drop. In contrast, the permeance through the interior of the membrane increases with decreasing average pressure. These results are explained using a model which treats the transport through the surface barrier as driven by the pressure gradient and transport through the zeolite as driven by the chemical potential gradient. A new force field named D...

(CN4H7)2·Zn3(HPO3)4, a three-dimensional framework zincophosphite: an example of template–template co-operation?

Abstract The hydrothermal synthesis and single crystal structure of (CN 4 H 7 ) 2 ·Zn 3 (HPO 3 ) 4 are reported. This phase is built up from a network of vertex-linked ZnO 4 and HPO 3 building units encapsulating the extra-framework animoguanidinium cations. A new type of three-dimensional network for the inorganic component of the structure arises, which contains polyhedral 4-, 6-, 8-, 12- and 16-rings. There are close (∼3.6 A), side-on, template–template contacts similar to those seen between pairs of guanidinium cations in molecular compounds. Crystal data: (CN 4 H 7 ) 2 ·Zn 3 (HPO 3 ) 4 , M r =666.30, monoclinic, space group P 2 1 / n (No. 14), a =10.2589 (4) A, b =29.5851 (12) A, c =13.7578 (5) A, β =103.303 (1)°, V =4063.6 (5) A 3 , Z =8, T =298 (2) K, R ( F )=0.0399, wR ( F 2 )=0.0792.

Nanoconfined Water in Magnesium-Rich 2:1 Phyllosilicates

Inelastic neutron scattering, density functional theory, ab initio molecular dynamics, and classical molecular dynamics were used to examine the behavior of nanoconfined water in palygorskite and sepiolite. These complementary methods provide a strong basis to illustrate and correlate the significant differences observed in the spectroscopic signatures of water in two unique clay minerals. Distortions of silicate tetrahedra in the smaller-pore palygorskite exhibit a limited number of hydrogen bonds having relatively short bond lengths. However, without the distorted silicate tetrahedra, an increased number of hydrogen bonds are observed in the larger-pore sepiolite with corresponding longer bond distances. Because there is more hydrogen bonding at the pore interface in sepiolite than in palygorskite, we expect librational modes to have higher overall frequencies (i.e., more restricted rotational motions); experimental neutron scattering data clearly illustrates this shift in spectroscopic signatures. It follows that distortions of the silicate tetrahedra in these minerals effectively disrupt hydrogen-bonding patterns at the silicate-water interface, and this has a greater impact on the dynamical behavior of nanoconfined water than the actual size of the pore or the presence of coordinatively unsaturated magnesium edge sites.

Vapor Phase Transport Synthesis of Zeolites from Sol-Gel Precursors

A study of zeolite crystallization from sol-gel precursors using the vapor phase transport synthesis method has been performed. Zeolites (ZSM-5, ZSM-48, Zeolite P, and Sodalite) were crystallized by contacting vapor phase organic or organic-water mixtures with dried sodium silicate and dried sodium alumino-silicate gels. For each precursor gel, a ternary phase system of vapor phase organic reactant molecules was explored. The vapor phase reactant mixtures ranged from pure ethylene diamene, triethylamine, or water, to an equimolar mixture of each. In addition, a series of gels with varied physical and chemical properties were crystallized using the same vapor phase solvent mixture for each gel. The precursor gels and the crystalline products were analyzed via Scanning Electron Microscopy, Electron Dispersive Spectroscopy, X-ray mapping, X-ray powder diffraction, nitrogen surface area, Fourier Transform Infrared Spectroscopy, and thermal analyses. The product phase and purity as a function of the solvent mixture, precursor gel structure, and precursor gel chemistry is discussed.