Sodalite Cages Research Articles

Dual‐Guest Functionalized Zeolitic Imidazolate Framework‐8 for 3D Printing White Light‐Emitting Composites

AbstractMetal–organic frameworks (MOFs) stand as a promising chemically active host scaffold for the encapsulation of functional guests, because they could enhance luminescent properties by molecular separation of fluorophores in the nanoscale pores of the MOF crystals. Herein, simultaneous nanoconfinement of two fluorophores is shown, namely, A) fluorescein and B) rhodamine B in the sodalite cages of ZIF‐8, constructed under ambient conditions through a simple one‐pot reaction. A novel Dual‐Guest@MOF system is reported, termed: A+B@ZIF‐8, which overcomes the intrinsic problem of aggregation‐caused quenching in the solid state to gain bright yellow emission under UV irradiation. Subsequently, this yellow emitter is combined with a blue‐emitting photopolymer resin, to yield a 3D printable luminescent composite material. A number of 3D printable composite objects for converting UV into warm white light emission are designed, achieving a high quantum yield of ≈44% in the solid state 3D printed form. This research instigates the bespoke application of a vast range of 3D printable Guest@MOF designer composites targeting energy‐saving lighting devices, smart sensors, and future optoelectronics.

Formation of luminescent silver-clusters and efficient energy transfer to Eu3+ in faujasite NaX zeolite

Faujasite (FAU) type zeolite is built from sodalite cages that joined by oxygen bridges between the hexagonal faces, and is characteristic of high cation exchange capacity and thermal stability. In this research, the FAU-NaX zeolite with Na/Si/Al molar ratio of 4.08:1.4:1.0 was prepared with template-free hydrothermal method and then confirmed with XRD analysis, based on which a series of Ag+ or/and Eu3+ loaded zeolites were obtained through the ion-exchange procedure. The PL spectra measurement indicated that after heat treatment at optimized temperatures between 400-600 ​°C, the Ag+ loaded zeolites showed strong green visible emission centered around 540–550 ​nm, which is due to the formation of Ag3n+ clusters. Furthermore, efficient energy transfer from silver-clusters to Eu3+ can be achieved in the Ag+/Eu3+ loaded zeolites, and the energy transfer efficiency that evaluated with silver-clusters lifetimes are 23.9%, 44.6%, 67.4% and 73.6%, respectively, in ZX-2Eu30Ag, ZX-5Eu30Ag, ZX-10Eu30Ag and ZX-20Eu30Ag. Besides, the XPS measurements implied that the loading of Eu3+ resulted in a further reduction of silver-clusters, which can also promote the formation of silver-clusters without heat treatment. This new class of metal-clusters and rare earth (RE) ions co-actived phosphors may offer interesting perspective applications in optoelectronics and lighting.

Synthesis and Characterization of a New Aluminogermanate Thiocyanate Aluminogermanate Sodalite Na8[AlGeO4]6(SCN)2

Thiocyanate enclathrated sodalite with aluminogermanate host framework was obtained by high temperature hydrothermal synthesis at 423 K. X-ray power diffraction, IR, ESR, TGA, SEM, and NMR spectroscopy on 27Al and 23Na nuclei were used to characterize this new sodalite. The crystal structure of aluminogermanate, Na8[AlGeO4]6(SCN)2 sodalite was refined from X-ray powder diffraction data in the space group P$$\bar {4}$$3n: a = 9.239 A, V = 788.630 A3, Rwp = 0.8515, Rp = 1.3241, and Al–O–Ge angle is 136.820°. The 27Al MAS NMR study confirms alternating Ge and Al ordering in sodalite framework. The recorded infrared spectrum show absorption band typical for the sodalite structure and frequency at 2200 cm–1 also clearly indicate the incorporation of thiocyanate anions in the sodalite cage. Thermogravimetric analysis has provided information on the extent of thiocyanate entrapment, stability within the sodalite cage and decomposition properties. SEM study shows the retention of cubical morphology of the thiocyanate enclathrated sodalite.

The adsorption mechanisms of organic micropollutants on high-silica zeolites causing S-shaped adsorption isotherms: An experimental and Monte Carlo simulation study

The adsorption of organic micropollutants (OMPs) on high-silica zeolites is characterized by adsorption isotherms with various shapes. The occurrence of an S-shaped adsorption isotherm indicates the lack of adsorption affinity for OMPs at low, environmentally relevant equilibrium concentrations. In this study, S-shaped isotherms were observed during batch experiments with 2,4,6-trichlorophenol (TCP) and FAU zeolites. This is the first time that an S-shaped isotherm is reported for the adsorption of OMPs on high-silica zeolites. Monte Carlo (MC) simulations in the grand-canonical ensemble were used to obtain a better understanding of the mechanism of the S-shaped adsorption isotherms. From the MC simulation results, it was observed that multiple TCP molecules were adsorbed in the supercages of the FAU zeolites. It was found that the π-π interactions between TCP molecules give rise to the adsorption of multiple TCP molecules per supercage, and thus causing an S-shaped adsorption isotherm. Simulations also revealed that water molecules were preferentially adsorbed in the supercages and sodalite cages of the FAU zeolites. FAU zeolites with a higher Al content adsorbed a higher amount of water molecules and a lower amount of TCP, and showed less pronounced S-shaped isotherms.

Cage reactions in sodalites – A phenomenological approach using cellular automata

Abstract Three-dimensional cellular automata (CA) models for cage template reactions in sodalites are developed. The CA's basic structure of cells and their neighborhood relations in sodalites is defined by their body-centered cubic net of cages. They are connected via four- and six-ring windows, with transport mechanism only allowed via the six-ring windows. Cage reactions are encoded in the CA's transformation rules. Two reactions are modelled: The decomposition of the permanganate ion in the sodalite cage at elevated temperatures and the transformation of the nitrite sodalite to the carbonate nosean in a CO2 atmosphere. In both cases parameters are extracted which can be compared with experimental results, showing a good agreement. Advantageous features of such CA are: The possibility to extract the contributions of single reaction steps, easy examination of the influence of crystallite shapes. Furthermore, the influence of the reaction's confinement on the cages and their connections are naturally included in these models.

Selective catalytic reduction of NO by NH3 on cerium modified faujasite zeolite prepared from aluminum scraps and industrial metasilicate

This work was devoted to the study of the selective catalytic reduction of NO by NH3 on calcined and hydrothermal treated cerium loaded zeolite catalysts. The parent faujasite zeolite Na–F (Si/Al = 1.32 and SBET = 749 m2/g) used as support for the preparation of the catalysts was obtained from industrial sodium metasilicate and aluminum scraps. As expected, the NO conversion increases with increasing the percentage of cerium in the structure of the faujasite zeolite. Total NO conversion into N2 is reached at 400 °C at a space velocity of 250 000 h−1. The high conversion is due to the redox shift between Ce3+/Ce4+ and the strong acid sites related to the rare earth present in the framework that is the key in SCR of NO process. Moreover, the highest loaded cerium catalyst retains almost its activity after hydrothermal treatment at 850 °C. This higher loading is desirable for both activity and stability provided that two stages of preparation are used to put the Ce ions in the sodalite cages.

Oxygen condensation in ZIF-8 upon ‘gate opening’ structural transition

We report a wide Q-range neutron diffraction study on the absorption of oxygen molecules into deuterated ZIF-8 as the system is taken through its gate-opening transition by applying gas pressure at 85 K. The combination of the quantitative nature of the total neutron scattering technique and the modelling performed using the Empirical Potential Structure Refinement (EPSR) technique has allowed us to determine the behaviour of the absorbed fluid upon condensation within the pores with unprecedented detail. The results show that the number of oxygen molecules found inside the central core of the spherical pore of the sodalite cage does not vary as the gate-opening transition is induced. After going through the structural transition, there is a rearrangement of the molecules and the extra molecules entering the structure are instead pushed towards the window apertures in the open structure. These results help to provide a greater insight into the nature of the structural flexibility of ZIF-8 and to understand its gas sorption behaviour.

Simple preparation of high concentration Nd3+-modified NaY zeolites with lower desorption activation energy of water

High concentration Nd3+-modified zeolite NaY with 22.6 wt% Nd element contained has been successfully prepared by a simple re-doping method via 4-fold ion-exchange and subsequent calcination treatments. This re-doping method not only provides a way to incorporate as high contend Nd cations within zeolite, but also proves the ion migration theory from experimental prospective. The obtained Nd-NaY zeolites are characterized by X-ray powder diffraction (XRD), Inductive coupled plasma (ICP), Scanning electron microscopy (SEM), etc, illustrating the Nd3+ cations can migrate into the sodalite cages from supercages, which leads to the lattice distortion of zeolite structure. With the addition of more Nd3+ ions, the average pore of the Nd-NaY zeolites has increased slowly while the specific surface area decreases. We found the values of reduce desorption activation energy (Ed) of water decrease gradually with the introduction of Nd3+ cations when it used as adsorptive materials. When the Nd3+ content of zeolite reaches 22.6 wt %, the value of Ed of water decreases to 154.7 kJ/mol. This research provides highly application value to reduce water molecules desorption activity energy as potential adsorptive materials in rotary dehumidification wheel.

Electronic and mechanic properties of a new cubic boron nitride

The current work introduces a new type of cubic boron nitride with a special sodalite cage structure, named Cubic-B6N6, based on the first principle of density functional theory (DFT). After determining the lattice parameters at the lowest energy state, the phonon spectra and elastic constants were calculated to demonstrate the dynamical and mechanical stability of the structure, respectively. Cubic-B6N6 possesses its bulk modulus of 274.0 GPa, shear modulus of 258.5 GPa, Young’s modulus of 675.8 GPa and Poisson's ratio of 0.09, indicating its large hardness. The electronic band structure indicates that Cubic-B6N6 is an insulator with a wide indirect band gap of 5.97 eV (HSE06). Moreover, XRD and Raman spectra are calculated to predict the experimental characteristics of Cubic-B6N6. Due to the large bulk modulus and large band gap, Cubic-B6N6 may provide potential super-hard and electronic resistance applications.

Structural and Photophysical Characterization of Ag Clusters in LTA Zeolites

Ag clusters (AgCLs) confined within Na-exchanged Linde type A zeolites are studied by X-ray absorption and steady-state and time-resolved photoluminescence spectroscopies in a coordinated effort to elucidate the photophysical properties and link them to the precise cluster structure. The hydrated sodalite cage contains mostly tetrahedral [Ag4(H2O)4] clusters located at the center of the sodalite cages, whereas octahedral Ag6 clusters coordinated with the zeolite framework oxygen (OF) [Ag6(OF)14] are formed upon dehydration. The time-dependent density functional theory and electron spin resonance reports suggest that both Ag4 and Ag6 clusters have formally a double positive charge of 2+. Time-resolved spectroscopy shows that at room temperature, the emission of the hydrated sample decays with 3.4 ns from a state with the same multiplicity as the ground state. Upon dehydration, the entire excited-state dynamics speeds up to 1.2 ps. The microsecond-scale lifetimes observed at 77 K suggest the occurrence of t...

Hydrogen Storage, Magnetism and Electrochromism of Silver Doped FAU Zeolite: First-Principles Calculations and Molecular Simulations.

The complex configuration, H2 adsorption binding energy, magnetic, and optical properties of FAU zeolites with Ag cations loaded by ion exchange in the vacant dielectric cavities were investigated by employing the first-principles calculations with all-electron-relativistic numerical atom-orbitals scheme and the Metropolis Monte Carlo molecular simulations. The visible absorption spectrum peaked at distinct wavelengths arranging from red or green to blue colors when changing the net charge load, due to the produced various redox states of Ag cations exchanging at multiple Li+-substituted sites. The spin population analyses indicate the ferrimagnetic coupling between Al–O–Si framework and Ag cations originates from the major ferromagnetic spin polarization in Ag cation cluster coordinating with sodalite cages, with the net spins appreciably depending on the Ag content and exchange site. The H2 adsorption capacities and binding energies represent significant dependence on the content, location, and electronic property of Ag cations introduced into the FAU zeolites. The evident decrease of H2 adsorption binding energy with increased loading concentration demonstrates repulsive interaction between H2 molecules and heterogeneous adsorption configuration on Ag cations. The adsorption sites of H2 sorted by the binding energy with different adsorption configurations were correlated with exchange sites of Ag cations under different Ag loading to comprehend the H2 adsorption mechanism.

Design and Testing Model Cobalt Catalysts for Reactions Involving CO2 and H2O

In this work, we developed experimental model of cobalt heterogeneous catalyst, inserting the active phase into a nanoporous material ordered with the purpose of structurally elucidating the processes that occur during the interaction of the model with molecules. We synthesized the models by inserting cobalt species into a Faujasite zeolite and performed detailed studies of the complexes formed in the interaction of these models with water and carbon dioxide emphasizing electron densities. Regarding the interaction of Faujasite with water, X-ray diffraction showed the physical adsorption of a dense monomolecular film in the nanoporous space. There was no evidence of water entering the sodalite cage. The cell parameter increased with the degree of hydration for Faujasite containing cobalt (CoY). In the case of dehydrated material, cobalt occupied the sites within the hexagonal prism (I) and the sodalite cage (I′). The carbon dioxide adsorbs bridges between adjacent compensation cations located in II. We te...

Porosity Properties of the Conformers of Sodalite-like Zeolitic Imidazolate Frameworks

The conformational isomers of zeolitic imidazolate frameworks (ZIFs) can have their own unique porosity and structural stability. We report that a new sodalite-like ZIF (termed β-ZIF-65(Zn)) is polymorphous with as the existing ZIF-65(Zn) (Zn(nIm)2, nIm = 2-nitroimidazolate) but has a different linker conformation in the six-membered rings of sodalite cages. This conformational isomerism leads to distinctive permanent porosity for each conformer, which has been verified by gas adsorption measurements. In addition, variable-temperature X-ray diffraction analyses indicate that β-ZIF-65(Zn) is more resistant to displacive phase transitions than ZIF-65(Zn). The activated β-ZIF-65(Zn) conformer adsorbs 2.8 times more benzene than the activated ZIF-65(Zn) at P/ P0 = 0.3 and 298 K. This work suggests that other types of ZIF conformers can be discovered.

Ultrastabilization of Zeolite Y Transforms Brønsted-Brønsted Acid Pairs into Brønsted-Lewis Acid Pairs.

Two pairs of Brønsted acid sites have been identified in H,Na-Y zeolite, located in the supercage and in the sodalite cage, which upon ultrastabilization (dealumination) are transformed into pairs of Brønsted and Lewis acid sites. This mild postsynthetic modification step is an important process for converting this material into an active catalyst for large-scale commercial reactions. Pairing structures and their transformations have been investigated using 1 H double-quantum NMR spectroscopy experiments for dehydrated zeolite, H,Na-Y, and its ultrastabilized form, H,Na-USY. This approach enables the detection of pairs of Brønsted and Lewis acid sites with unprecedented 1 H resolution and distinguishing them from isolated acid sites. The dealumination is also detected by static 27 Al solid-state NMR experiments.

Origin of the bright photoluminescence of few-atom silver clusters confined in LTA zeolites.

Silver (Ag) clusters confined in matrices possess remarkable luminescence properties, but little is known about their structural and electronic properties. We characterized the bright green luminescence of Ag clusters confined in partially exchanged Ag-Linde Type A (LTA) zeolites by means of a combination of x-ray excited optical luminescence-extended x-ray absorption fine structure, time-dependent-density functional theory calculations, and time-resolved spectroscopy. A mixture of tetrahedral Ag4(H2O) x2+ (x = 2 and x = 4) clusters occupies the center of a fraction of the sodalite cages. Their optical properties originate from a confined two-electron superatom quantum system with hybridized Ag and water O orbitals delocalized over the cluster. Upon excitation, one electron of the s-type highest occupied molecular orbital is promoted to the p-type lowest unoccupied molecular orbitals and relaxes through enhanced intersystem crossing into long-lived triplet states.

Promotional effects of cerium modification of Cu-USY catalysts on the low-temperature activity of NH3-SCR

A series of ceria-modified Cu-USY catalysts were prepared by a co-impregnation method and tested towards the selective reduction of NOx with NH3. A 5Cu-8Ce-USY catalyst with 8 wt% Ce content showed optimum low-temperature activity, and the widest NO conversion temperature window (160–410 °C) of operation, which these features are related to the enhanced redox ability and Cu+ species concentration in the sodalite cage compared to the Cu-USY catalyst. In addition, Lewis acid sites on the surface of Cu-Ce-USY catalysts were found to play a key role for its excellent SCR performance. The ceria-modified Cu-USY catalysts with enhanced low-temperature (120–170 °C) deNOx performance make them highly promising candidates for practical applications in controlling NOx emissions.

Determination of faujasite-type zeolite thermal conductivity from measurements on porous composites by laser flash method

An approach of determining thermal conductivity of zeolite is introduced, due to the lack of its thermal properties data for heat transfer calculations in adsorption and catalytic applications. Faujasite (FAU) as one of the important zeolites, whose framework consists of sodalite cages with pores formed by 12-membered rings, was chosen as model zeolite. Pellet-shaped samples made of FAU-type zeolite and binder pseudoboehmite were prepared with different binder fractions and porosities. Apparent thermal conductivity was determined using laser flash method. Results showed that the use of pseudoboehmite increased material’s heat capacity, thermal diffusivity and conductivity, and the apparent thermal conductivity of porous composites decreased with porosity. The thermal conductivity of FAU-type zeolite at 20 °C and 1 atm. was found to be 0.10 W/(m·K) by extrapolating measurement results.

Electronic, Optical, and Lattice Dynamical Properties of Tetracalcium Trialuminate (Ca₄Al₆O13).

The electronic, optical, and lattice dynamical properties of tetracalcium trialuminate (Ca4Al6O13) with a special sodalite cage structure were calculated based on the density functional theory. Theoretical results show that Ca4Al6O13 is ductile and weakly anisotropic. The calculated Young’s modulus and Poisson ratio are 34.18 GPa and 0.32, respectively. Ca4Al6O13 is an indirect-gap semiconductor with a band gap of 5.41 eV. The top of the valence band derives from O 2p states, and the bottom of conduction band consists of Ca 3d states. Transitions from O 2p, 2s states to empty Ca 4s, 3d and Al 3s, 3p states constitute the major peaks of the imaginary part of the dielectric function. Ca4Al6O13 is a good UV absorber for photoelectric devices due to the high absorption coefficient and low reflectivity. The lattice vibration analysis reveals that O atoms contribute to the high-frequency portions of the phonon spectra, while Ca and Al atoms make important contributions to the middle- and low-frequency portions. At the center of the first Brillouin zone, lattice vibrations include the Raman active modes (E, A1), infrared active mode (T2), and silentmodes (T1, A2). Typical atomic displacement patterns were also investigated to understand the vibration modes more intuitively.

Identification of Intermediates during the Hydration of Na8[AlSiO4]6(BH4)2: A Combined Theoretical and Experimental Approach.

Tetrahydroborate sodalites have been discussed as possible materials for reversible hydrogen storage. In order to access the suitability of Na8[AlSiO4]6(BH4)2, its reaction with water was investigated theoretically and experimentally. Density functional theory (DFT) calculations at the generalized gradient approximation (GGA) level were performed to identify the reaction intermediates. We compared experimental IR spectra and 11B NMR chemical shifts with theoretical results for selected molecules in the sodalite cage. Furthermore, the free energies of reaction of the intermediates with respect to Na8[AlSiO4]6(BH4)2, gaseous water, and molecular hydrogen at different temperatures were also calculated.

Selective synthesis of FAU-type zeolites

In the present work, parameters influencing the selectivity of the synthesis of FAU-zeolites from diatomite were studied. The final products after varying synthesis time were characterized by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction and gas adsorption. It was found that high concentrations of NaCl could completely inhibit the formation of zeolite P, which otherwise usually forms as soon as maximum FAU crystallinity is reached. In the presence of NaCl, the FAU crystals were stable for extended time after completed crystallization of FAU before formation of sodalite. It was also found that addition of NaCl barely changed the crystallization kinetics of FAU zeolite and only reduced the final FAU particle size and SiO2/Al2O3 ratio slightly. Other salts containing either Na or Cl were also investigated. Our results suggest that there is a synergistic effect between Na+ and Cl−. This is attributed to the formation of (Na4Cl)3+ clusters that stabilize the sodalite cages. This new finding may be used to increase the selectivity of syntheses leading to FAU-zeolites and avoid the formation of undesirable by-products, especially if impure natural sources of aluminosilica are used.