LTA Topology Research Articles

Monitoring the dynamics of nanozeolite formation by combined in situ coherent small angle X-ray scattering techniques

Understanding the dynamics of zeolite formation is key to synthesising high-quality zeolitic materials with controllable properties, in order to develop more efficient and performant materials. X-ray photon correlation spectroscopy (XPCS) using coherent X-rays offers new possibilities for in situ observation of nano to micron-scale fluctuation dynamics during crystal growth. An in situ cell, which is capable of collecting time-resolved coherent X-ray scattering data under hydrothermal conditions has been developed and used to study, by in situ XPCS combined with small and wide angle X-ray scattering, zeolite formation and dynamics. Analysis of the results using two-time correlations enables to accurately identify the successive growth and crystallisation steps, revealing the dissolution process of the LTA topology during the SOD growth. This approach opens a powerful new avenue for studying the dynamics of nanomaterials formation, phase transitions and growth processes under in situ conditions that will enable profound insights into the nanoscale synthesis mechanisms.

Magnetic properties of bauxites and pre-fused hydrothermal product (zeolite)

Bauxites are deposits rich in aluminium and iron oxides/hydroxides, formed by the weathering of aluminosilicates rocks under warm and humid conditions. Due to their mineralogical composition, bauxites represent the primary source for aluminum and, subordinately, iron production. However, these sediments rich in Si and Al can be also used as raw material for the synthesis of zeolite with magnetic properties thanks to the high availability of Fe. In this work, three bauxite samples collected from Upper Cretaceous deposits of southern Italy were characterized for their magnetic parameters and used for the synthesis of zeolite with LTA topology (zeolite A). The results indicate differences in antiferromagnetic behaviour among the three raw materials. All the synthetic products, instead, display the same antiferromagnetic behaviour thus suggesting that the method used for the zeolite crystallization neutralizes the parameters responsible for raw bauxite magnetic differences.

Zeolite A with waste material: Morphological effect of laser treatments in air

The goal of this work is to investigate the action of femtosecond (fs) laser treatment performed under atmospheric conditions on morphology of zeolite A (LTA topology) synthesized with the addition of a waste material rich in iron such as red mud (RMFe-LTA) or introducing nanomagnetite (NMFe-LTA) during the hydrothermal synthesis. Both zeolite samples were analyzed by Scanning Electron Microscopy (SEM) technique. LTA zeolite formed using pure sources was assumed as reference. The results confirm that the presence of iron has a significant influence on laser-matter interactions affecting the morphology of the final treated synthetic material. Comparing to our previous data performed in vacuum conditions, these new results indicate that zeolite structure is generally preserved by fs laser treatment under atmospheric conditions although the presence of the Fe oxides distributed on the zeolite surfaces due to the use of red mud or in the form of nanomagnetite at specific locations, determines clear changes in treated zeolite morphology. However, the best performing results in terms of homogeneity of treatment and potential improvement of hydrophilic surface properties take places on zeolite formed with the addition of waste material (RMFe-LTA).

Lead, zinc, nickel and chromium ions removal from polluted waters using zeolite formed from bauxite, obsidian and their combination with red mud: Behaviour and mechanisms

Synthetic zeolites obtained combining natural sources (bauxite and obsidian), pure alumina/silica reagents, and waste material (red mud) were tested for heavy metals (i.e., Pb2+, Zn2+, Ni2+, Cr3+) removal. The adsorption capabilities of the formed sodalite, zeolite A and zeolite X (LTA and FAU topology, respectively), were compared through thermodynamic and kinetic experiments. Although all the newly-formed zeolites were able to remove the pollutant elements within 24 h, Zeolite X and sodalite synthesized combining obsidian (natural material as silica source) and red mud (waste material as alumina source) proved to be a better sorbent phase (qmax 20–25 mg g−1) compared to Zeolite A formed from treated bauxite (qmax 4–18 mg g−1). Their removal efficiency was also evaluated in polluted waters (wastewater treatment plant [WWTP] effluent, heavy metals mixture, native pH). Depending on synthesized zeolite type, the adsorption mechanism was accredited to ion exchange and precipitation mechanisms. The location of metal-ions inside the zeolite channels was defined by X-ray Powder Diffraction (XRPD) Rietveld analysis. Host–guest interactions among the framework oxygen atoms, co-adsorbed water molecules, and metal-ions were highlighted by the refined bond distances. Finally, magnetic characterization allowed the recognize of different magnetic properties as a function of raw materials used for zeolite synthesis.

Harnessing Particle Size‐Control and DNA‐Oligo Functionalization in ZIF‐76 for Biological Applications

AbstractAdvanced therapeutics require novel nanocarriers to ensure their functionality is preserved during transit. Zeolitic imidazolate frameworks (ZIFs) have emerged as promising materials in this field owing to their combined biocompatibility, high porosity, and tunable chemistry. While a diverse family of ZIFs has been reported, few have been explored beyond the prototypical ZIF‐8. Herein, the size‐controlled synthesis of three distinct ZIF‐76 analogs is demonstrated, overcoming the unique synthetic challenges intrinsic to the lta topology and complex crystallization kinetics associated with the mixed linker approach. This assesses the materials’ platform effectiveness for intracellular delivery first by exploring the structural and colloidal stability in biologically relevant media. To circumvent particle aggregation, fluorescently labeled DNA oligonucleotides are post‐synthetically attached to the ZIF surface. This modification significantly improves the colloidal stability in media and facilitates particle internalization tracking. Finally, the particle‐cell interactions are assessed, revealing rapid cell membrane association with macrophages, but not lung epithelial cells, and ZIF accumulation within macrophages which increased over time. Importantly, this study outlines a generalized approach toward expanding the available library of ZIFs for biological applications, enabling the potential for targeted therapeutic delivery for intracellular infections treatment.

Efficiency in Ofloxacin Antibiotic Water Remediation by Magnetic Zeolites Formed Combining Pure Sources and Wastes

In this work, red mud (RM) and spinel iron oxide nanoparticles (SPIONs) were added to pure silica/alumina sources (SAs) and fly ash (FA) with the aim of synthesizing and investigating the magnetic behavior of different zeolites. SAs were used to synthesize zeolite with LTA topology (zeolite A) with the addition of both red mud and spinel iron oxide nanoparticles. FA and RM were mixed to synthesize sodalite whereas only FA with the addition of SPIONs was used to form zeolite with FAU-topology (zeolite X). All the synthetic products showed magnetic properties. However, zeolites with spinel iron oxide nanoparticles (zeolites A and X) showed ferromagnetic-like behavior. Sodalite was characterized by a reduction in saturation magnetization, whereas zeolite A with red mud displayed antiferromagnetic behavior. For the first time, all the synthetic products were tested for polluted water remediation by a persistent emerging contaminant, ofloxacin (OFL) antibiotic. The four zeolite types showed good adsorption affinity towards OFL under actual conditions (tap water, natural pH). All materials were also tested for OFL removal in real waters spiked with OFL 10 µg L−1. Satisfactory recoveries (90–92% in tap water, 83–87% in river water) were obtained for the two zeolites synthesized from industrial waste materials.

Expanding the ZIFs Repertoire for Biological Applications with the Targeted Synthesis of ZIF-20 Nanoparticles.

Owing to their facile synthesis, tailorable porosity, diverse compositions, and low toxicity, zeolitic imidazolate framework (ZIF) nanoparticles (NPs) have emerged as attractive platforms for a variety of biologically relevant applications. To date, a small subset of ZIFs representing only two topologies and very few linker chemistries have been studied in this realm. We seek to expand the bio-design space for ZIF NPs through the targeted synthesis of a hierarchically complex ZIF based on two types of cages, ZIF-20, with lta topology. This study demonstrates the rapid synthesis and size tunability of ZIF-20 particles across the micro and nanoregimes via microwave heating and the use of a modulating agent. To evaluate the utility of ZIF particles for biological applications, we examine their stability in biologically relevant media and demonstrate biocompatibility with A549 human epithelial cells. Further, the ability to encapsulate and release methylene blue, a therapeutic and bioimaging agent, is validated. Importantly, ZIF-20 NPs display a unique behavior relative to previously studied ZIFs based on their specific structural and chemical features. This finding highlights the need to expand the design space across the broader ZIFs family, to exploit a wider range of relevant properties for biological applications and beyond.

Ionothermal synthesis and characterization of AlPO4 and AlGaPO4 molecular sieves with LTA topology

Abstract Aluminophosphate molecular sieves are recognized as very promising materials for catalysis, adsorption, and separation. This study presented an attempt to synthesize LTA-type AlPO4 and AlGaPO4 molecular sieves by an ionothermal method. The influences of the relevant synthesis parameters and various template removal methods were discussed. The optimum growth temperature, doses of ILs, and crystallization time were suggested. The two-step calcination method was recommended since the intact crystalline structure and microporosity of LTA-type AlPO4 were retained after template removal. Perfect cubic AlPO4-LTA molecular sieves were successfully prepared with an excellent micropore volume of 0.33 ml/g and water uptake of 0.38 g/g at P/P0 = 0.20. Moreover, an LTA-type AlGaPO4 molecular sieve was also successfully synthesized by an ionothermal method with partial Ga doping. Evident changes in morphology were found and could be ascribed to various crystal plane orientations. Ga-doped crystals subjected to template removal and water soaking showed worse thermal and hydrothermal stability. The microporosity and water sorption capacity of AlGaPO4-LTA also decreased greatly due to its sharply reduced stability and collapsed structure. After Ga doping, however, the materials became more hydrophilic, with slightly higher water uptake at low relative pressure. The materials also showed greater acidity strength at both Bronsted and Lewis acid sites.

Role of hydrogen bonding in the capture and storage of ammonia in zeolites

Ammonia is an important chemical compound used in a wide range of applications. This makes its capture, purification and recovery necessary. We combine experimental and molecular simulation techniques to identify the molecular mechanisms ruling the adsorption of ammonia in pure and high silica zeolites. To reproduce accurately the interaction between ammonia and the zeolites the development of a transferable set of Lennard-Jones parameters was needed. Adsorption isotherms were measured and also calculated using the new set of parameters for several commercial pure silica zeolites, including MFI, FAU, and LTA topologies. We found an anomalous behavior of the adsorption isotherm of ammonia in MFI, which can be explained through a monoclinic to orthorhombic structural phase transition. We also found that low concentration of extra-framework cations favors the adsorption of ammonia in these high silica zeolites. Using radial distribution functions and hydrogen bond analyses we identified ammonia clusterization as the key mechanism involved in the adsorption. Based on it, hydrophobic zeolites with large pores could be used for ammonia sequestration with lower cost than the currently used techniques.

A zeolite supramolecular framework with LTA topology based on a tetrahedral metal-organic cage.

An unprecedented zeolite supramolecular framework featuring truncated cuboctahedral and truncated octahedral cavities was self-assembled from tetrahedral metal-organic cationic cages and tetrahedral anions. This crystalline porous material could trap iodine and organic dye molecules, and its solid state spin-crossover behavior was affected by guest encapsulation.

Rational design, synthesis, characterization and catalytic properties of high-quality low-silica hierarchical FAU- and LTA-type zeolites

Despite the development of several synthetic strategies employing various templates as (pore) structure directing agents, the preparation of high-quality aluminum-rich hierarchical zeolites (designated as ZH) with Si/Al < 5 from its molecular precursors is still a challenge to the scientific community. For the first time, we report here, a successful synthesis methodology for the preparation of hierarchical zeolites, having FAU and LTA topologies with uniform micropores and mesopores by a rationally designed method. Here, a stable supramolecular self-assembly was achieved under the challenging synthesis conditions by tailoring the zeolitization process, viz., by a homogeneous nucleation and a multi-step crystallization. This has resulted in regular mesoporosity in FAU-type zeolites and a unique mesoporosity in LTA-type zeolites, hitherto not reported so far.

Hydrogen Adsorption in a Zeolitic Imidazolate Framework with lta Topology

The adsorption of H2 in ZIF-76, a zeolitic imidazolate framework (ZIF) with lta topology, was investigated in a combined experimental and theoretical study. Each Zn2+ ion in the structure of this ZIF is coordinated to imidazolate and 5-chlorobenzimidazolate linkers in a 3:1 ratio. The X-ray crystal structure of ZIF-76 contains a large amount of structural disorder, which makes this a challenging material for modeling. We therefore chose to parametrize and simulate H2 adsorption in two distinct crystal structure configurations of ZIF-76 that differ by only the relative positions of one imidazolate and one 5-chlorobenzimidazolate linker. The simulated H2 adsorption isotherms for both structures are in satisfactory agreement with the newly reported experimental data for the ZIF, especially at low pressures. The experimental initial isosteric heat of adsorption (Qst) value for H2 in ZIF-76 was determined to be 7.7 kJ mol–1, which is comparable to that for other ZIFs and is fairly high for a material that does...

Hollow polycrystalline Y zeolite shells obtained from selective desilication of Beta-Y core-shell composites

Hollow polycrystalline Y zeolite spheres have been obtained by combining zeolite crystallization and selective dissolution steps. Beta-Y core shell composites were first obtained by hydrothermal recrystallization of a synthesis mixture containing as-made Beta crystals in the presence of Y zeolite seeds. Under such conditions, Beta zeolite crystals served not only as cores but they also progressively dissolved and provided the necessary Si species for the formation of the shell. The proportion of Beta zeolite remaining in the composite strongly depended on the composition of the solution, in particular the amount of Al and the alkalinity. It could not be decreased below 45–50 wt. % without formation of contaminating phases, mainly zeolites with GME, GIS and LTA topologies. Successive additions of Al could significantly reduce the amount of Beta zeolite in the composite but to the detriment of faujasite crystal size. Hollow shells with less than 10 wt. % Beta have been obtained by selective removal of Beta zeolite from a composite containing 20 wt. % Beta and obtained after two successive recrystallizations in the presence of aluminum. These shells are built up from faujasite nanocrystals with a high silicon content, making them potentially interesting in diffusion-limited catalytic reactions.

Intensified Biobutanol Recovery by using Zeolites with Complementary Selectivity.

A vapor-phase adsorptive recovery process is proposed as an alternative way to isolate biobutanol from acetone-butanol-ethanol (ABE) fermentation media, offering several advantages compared to liquid phase separation. The effect of water, which is still present in large quantities in the vapor phase, on the adsorption of the organics could be minimized by using hydrophobic zeolites. Shape-selective all-silica zeolites CHA and LTA were prepared and evaluated with single-component isotherms and breakthrough experiments. These zeolites show opposite selectivities; adsorption of ethanol is favorable on all-silica CHA, whereas the LTA topology has a clear preference for butanol. The molecular sieving properties of both zeolites allow easy elimination of acetone from the mixture. The molecular interaction mechanisms are studied by density functional theory (DFT) simulations. The effects of mixture composition, humidity and total pressure of the vapor stream on the selectivity and separation behavior are investigated. Desorption profiles are studied to maximize butanol purity and recovery. The combination of LTA with CHA-type zeolites (Si-CHA or SAPO-34) in sequential adsorption columns with alternating adsorption and desorption steps allows butanol to be recovered in unpreceded purity and yield. A butanol purity of 99.7 mol % could be obtained at nearly complete butanol recovery, demonstrating the effectiveness of this technique for biobutanol separation processes.

Critical Role of Dynamic Flexibility in Ge‐Containing Zeolites: Impact on Diffusion

Incorporation of germanium in zeolites is well known to confer static flexibility to their framework, by stabilizing the formation of small rings. In this work, we show that the flexibility associated to Ge atoms in zeolites goes beyond this static effect, manifesting also a clear dynamic nature, in the sense that it leads to enhanced molecular diffusion. Our study combines experimental and theoretical methods providing evidence for this effect, which has not been described previously, as well as a rationalization for it, based on atomistic grounds. We have used both pure‐silica and silico‐germanate ITQ‐29 (LTA topology) zeolites as a case study. Based on our simulations, we identify the flexibility associated to the pore breathing‐like behavior induced by the Ge atoms, as the key factor leading to the enhanced diffusion observed experimentally in Ge‐containing zeolites.

Synthesis of Germanosilicate Molecular Sieves from Mono- and Di-Quaternary Ammonium OSDAs Constructed from Benzyl Imidazolium Derivatives: Stabilization of Large Micropore Volumes Including New Molecular Sieve CIT-13

A series of monoquaternary and diquarternary benzyl-imidazolium derivatives are prepared and used as organic structure direction agents (OSDAs) in germanosilicate syntheses. The goal of this work is to create new multidimensional large pore zeolites. For the OSDA made and tested, we looked for relationships based upon stereochemistry from the benzyl ring as part of each structure. Several known molecular sieves with the *BEA, BEC, IWS, or LTA topologies are obtained. Molecular modeling is carried out with the goal of understanding: (a) the product selectivity correlation with the OSDA and the zeolite obtained, and (b) why differential rates of crystallization are observed for isomers that lead to different zeolite products. Additionally, a new molecular sieve denoted CIT-13 is prepared and shown to possess intersecting 14- and 10-membered ring pores, which gives confidence to the soundness of this approach for OSDA construction to yield new multidimensional large pore zeolites. CIT-13 is the first molecul...

A highly efficient zeolitic imidazolate framework catalyst for the co-catalyst and solvent free synthesis of cyclic carbonates from CO2

A zeolitic imidazolate framework possessing LTA topology is investigated for its catalytic potential in the synthesis of cyclic carbonates from CO2 and epoxides. The synthesized ZIF-22 was chemically and thermally stable and was analyzed using multiple physico-chemical characterizations such as XRD, FT-IR, FE-SEM, XPS, TGA, ICP-OES and EA. ZIF-22 was found to afford excellent heterogeneous catalysis with high turnover frequencies (TOF) and selectivity, outperforming the activities exhibited by the previously reported ZIF catalysts. Parameter studies were carried out with various temperature, CO2 pressure, catalyst amount and reaction time and the catalyst was found to have reusable properties over three times with negligible or no loss in catalytic activity.

Chemical Control of Thermal Expansion in Cation-Exchanged Zeolite A

Variable-temperature powder X-ray diffraction studies have been used to monitor dramatic changes in the thermal expansion properties of zeolites with the LTA topology on changing the pore contents. Detailed structural analysis was performed on dehydrated Li-, Na-, K-, Rb-, and Cs-exchanged zeolite A and a comparison made with their purely siliceous analogue ITQ-29. Mean thermal expansion coefficients were also determined for the hydrated alkali-metal-exchanged forms. Thermal expansion behavior ranging from negative to positive was observed as different monovalent cations were included in the zeolite pores. Cation-induced strain to the zeolite framework has been shown to play a significant role in the thermal expansion mechanism of LTA-zeolites. Atomic-scale mechanisms behind the thermal expansion behavior have been deduced for ITQ-29, dehydrated Ag-A, and dehydrated Na-A systems.

The effect of extra framework species on the intrinsic negative thermal expansion property of zeolites with the LTA topology

X-Ray powder diffraction studies have been used to measure the thermal expansion properties of three zeolites with the LTA topology and provide details of the underlying structural changes. Siliceous ITQ-29 and dehydrated and hydrated silver zeolite A have large negative, moderate negative and positive thermal expansion coefficients, respectively.

Acidic Properties of Cage-Based, Small-Pore Zeolites with Different Framework Topologies and Their Silicoaluminophosphate Analogues

Acidic properties of cage-based, small-pore aluminosilicate zeolites with CHA, AFX, RHO, LEV, ERI, and LTA topologies and their silicoaluminophosphate (SAPO) analogues were measured by means of an ammonia IRMS (infrared/mass spectroscopy)-TPD (temperature-programmed desorption) method. All SAPO molecular sieves studied here showed weaker Bronsted acid strength (11–26 kJ mol–1 lower in the heat of ammonia desorption) than their aluminosilicate counterparts. The density functional theory (DFT) calculations of the ammonia desorption energy were in good agreement with experiments; the difference in the energy of ammonia desorption was less than 10 kJ mol–1. DFT also showed that the introduction of Al into the SiO2 framework to form aluminosilicate zeolites resulted in large changes to the distance between atoms close to the acid site, while Si substitution into the AlPO4 framework to form SAPO materials predominantly modified the angles between atoms relatively far from the acid site. The introduction of Al i...