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12 pages, 3922 KiB

Open AccessArticle

A New Type of Acidic OH-Groups in the LTL Zeolite

by Alessandro Contini, Martin Jendrlin and Vladimir Zholobenko

Crystals 2024, 14(8), 745; https://doi.org/10.3390/cryst14080745 - 21 Aug 2024

Viewed by 1694

Acidic properties of ion-exchanged LTL zeolites have been studied using FTIR spectroscopy, complemented by X-ray powder diffraction, SEM-EDX, XRF and N₂ physisorption. Infrared spectra of the ion-exchanged zeolites show the presence of two intense bands of the bridging OH-groups: a narrow band [...] Read more.

Acidic properties of ion-exchanged LTL zeolites have been studied using FTIR spectroscopy, complemented by X-ray powder diffraction, SEM-EDX, XRF and N₂ physisorption. Infrared spectra of the ion-exchanged zeolites show the presence of two intense bands of the bridging OH-groups: a narrow band at ~3640 cm⁻¹ that is attributed to Si(OH)Al groups freely vibrating in 12 MR and a broad, intense band at ~3250 cm⁻¹ that is assigned to bridging OH groups forming hydrogen bond with neighbouring oxygen atoms, e.g., in six-membered rings. The former can be selectively removed by caesium or rubidium cations with up to 3 Cs⁺ or Rb⁺ per unit cell readily ion-exchanged into the LTL zeolite, replacing an equivalent number of acidic OH-groups or K⁺ cations within the structure. The cation migration of the larger cation, evaluated by the Rietveld refinement method, occurs mostly via the main 12 MR channels. By contrast, less than 1 Li⁺ or Na⁺ cation per unit cell can be introduced under similar conditions. Accordingly, the concentration of Si(OH)Al groups in back-exchanged NH₄-K-LTL with smaller cations (Li⁺, Na⁺) does not differ considerably from the concentration of Brønsted acid sites in the original NH₄-K-LTL. Lower concentrations of acid sites have been detected in the samples back-exchanged with Cs⁺, Rb⁺ and K⁺. In addition, the acidic properties of NH₄-LTL samples have been compared with a structurally related NH₄-MAZ zeolite. Full article

(This article belongs to the Special Issue Feature Papers on "Hybrid and Composite Crystalline Materials" 2023–2024)

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11 pages, 12067 KiB

Open AccessFeature PaperArticle

The Effect of Cation Exchange on the Pore Geometry of Zeolite L

by Lisa A. Price, Zöe Jones, Antony Nearchou, Gavin Stenning, Daniel Nye and Asel Sartbaeva

AppliedChem 2022, 2(3), 149-159; https://doi.org/10.3390/appliedchem2030011 - 15 Jul 2022

Cited by 3 | Viewed by 3368

Abstract

Zeolites with the LTL framework topology are attractive materials for use in optoelectronics, gas adsorption and as chemical reactors. This is due to their unique, one-dimensional (1D) channel systems which are large enough to act as hosts for organic dye molecules and other [...] Read more.

Zeolites with the LTL framework topology are attractive materials for use in optoelectronics, gas adsorption and as chemical reactors. This is due to their unique, one-dimensional (1D) channel systems which are large enough to act as hosts for organic dye molecules and other guest materials. Here, we use high-resolution X-ray diffraction to show the effect of cation exchange on the pore geometry of LTL-type zeolites. The nature of the exchanging cation is shown to influence the free access diameter, volume and water content of the 12-ring (12R) channel systems. As such, cation exchange can be used to tune the molecular sieving and adsorption properties of LTL-type zeolites. This offers new possibilities for these materials in technologically relevant applications. Full article

(This article belongs to the Special Issue Feature Papers in AppliedChem)

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19 pages, 2350 KiB

Open AccessArticle

A Comparative Analysis of In Vitro Toxicity of Synthetic Zeolites on IMR-90 Human Lung Fibroblast Cells

by Seung-Hye Yu, Manjesh Kumar, Il Won Kim, Jeffrey D. Rimer and Tae-Jung Kim

Molecules 2021, 26(11), 3194; https://doi.org/10.3390/molecules26113194 - 26 May 2021

Cited by 6 | Viewed by 4575

Abstract

Broad industrial application of zeolites increases the opportunity of inhalation. However, the potential impact of different types and compositions of zeolite on cytotoxicity is still unknown. Four types of synthetic zeolites have been prepared for assessing the effect on lung fibroblast: two zeolite [...] Read more.

Broad industrial application of zeolites increases the opportunity of inhalation. However, the potential impact of different types and compositions of zeolite on cytotoxicity is still unknown. Four types of synthetic zeolites have been prepared for assessing the effect on lung fibroblast: two zeolite L (LTL-R and LTL-D), ZSM-5 (MFI-S), and faujasite (FAU-S). The cytotoxicity of zeolites on human lung fibroblast (IMR-90) was assessed using WST1 cell proliferation assay, mitochondrial function, membrane leakage of lactate dehydrogenase, reduced glutathione levels, and mitochondrial membrane potential were assessed under control. Intracellular changes were examined using transmission electron microscopy (TEM). Toxicity-related gene expressions were evaluated by PCR array. The result showed significantly higher toxicity in IMR-90 cells with FAU-S than LTL-R, LTL-D and MFI-S exposure. TEM showed FAU-S, spheroidal zeolite with a low Si/Al ratio, was readily internalized forming numerous phagosomes in IMR-90 cells, while the largest and disc-shaped zeolites showed the lowest toxicity and were located in submembranous phagosomes in IMR-90 cells. Differential expression of TNF related genes was detected using PCR arrays and confirmed using qRT-PCR analysis of selected genes. Collectively, the exposure of different zeolites shows different toxicity on IMR-90 cells. Full article

(This article belongs to the Special Issue Zeolites and Mesoporous Materials: Properties and Applications)

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16 pages, 6115 KiB

Open AccessArticle

CHA-Type Zeolite Prepared by Interzeolite Conversion Method Using FAU and LTL-Type Zeolite: Effect of the Raw Materials on the Crystallization Mechanism, and Physicochemical and Catalytic Properties

by Toshiki Nishitoba, Takuya Nozaki, Sungsik Park, Yong Wang, Junko N. Kondo, Hermann Gies and Toshiyuki Yokoi

Catalysts 2020, 10(10), 1204; https://doi.org/10.3390/catal10101204 - 17 Oct 2020

Cited by 22 | Viewed by 4965

Abstract

The effect of the raw materials including parent zeolite as aluminosilicate sources and organic structure-directing agents (OSDAs) on the crystallization mechanism, and physicochemical and catalytic properties of the CHA-type aluminosilicate zeolite was investigated. For this purpose, the FAU-type and the LTL-type zeolites were [...] Read more.

The effect of the raw materials including parent zeolite as aluminosilicate sources and organic structure-directing agents (OSDAs) on the crystallization mechanism, and physicochemical and catalytic properties of the CHA-type aluminosilicate zeolite was investigated. For this purpose, the FAU-type and the LTL-type zeolites were used as raw material, and trymethyladamantyl ammonium hydroxide and tetraethyl ammonium hydroxide were used as OSDAs. We firstly found that the CHA-type aluminosilicate zeolite was crystallized from the combination of the LTL-type zeolite and tetraethyl ammonium hydroxide as raw materials. The crystallization behaviors were also monitored in detail. The crystallization was delayed by using the LTL-type zeolite as the starting material regardless of the type of OSDA because of the low solubility of the LTL-type zeolite compared to the FAU-type zeolite. We have found that the Al distribution in the CHA framework was dependent on the raw materials. Thus, the prepared CHA-type aluminosilicate zeolite from the LTL-type zeolite exhibited a high thermal stability and catalytic performance in the methanol to olefins reaction. Full article

(This article belongs to the Special Issue Microporous Zeolites and Related Nanoporous Materials: Synthesis, Characterization and Applications in Catalysis)

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9 pages, 2469 KiB

Open AccessCommunication

Designer Synthesis of Ultra-Fine Fe-LTL Zeolite Nanocrystals

by Fen Zhang, Yunhong Luo, Lei Chen, Wei Chen, Yin Hu, Guihua Chen, Shengyong You and Weiguo Song

Crystals 2020, 10(9), 813; https://doi.org/10.3390/cryst10090813 - 15 Sep 2020

Cited by 1 | Viewed by 3078

Abstract

Nanosized zeolites with larger external surface area and decreased diffusion pathway provide many potential opportunities in adsorption, diffusion, and catalytic applications. Herein, we report a designer synthesis of ultra-fine Fe-LTL zeolite nanocrystals under very mild synthesis conditions. We prepared Fe-LTL zeolite nanocrystals synthesized [...] Read more.

Nanosized zeolites with larger external surface area and decreased diffusion pathway provide many potential opportunities in adsorption, diffusion, and catalytic applications. Herein, we report a designer synthesis of ultra-fine Fe-LTL zeolite nanocrystals under very mild synthesis conditions. We prepared Fe-LTL zeolite nanocrystals synthesized using L precursor. The precursor is aging at room temperature to obtain zeolite L nuclei. In order to investigate more details of Fe-LTL zeolite nanocrystals, various characterizations including X-ray diffraction (XRD), inductively coupled plasma (ICP), diffuse reflectance ultraviolet-visible (UV-Vis) spectroscopy, confirm the tetrahedral Fe³⁺ species in the zeolite framework. Besides, scanning electron microscope (SEM), Fourier transform infrared spectrometer (FT-IR), dynamic light scattering (DLS) indicate that the average particle size of Fe-LTL zeolite crystals is approximately 30 nm. Thus, ultra-fine Fe-LTL zeolite with large external surface area and shorter diffusion pathway to the active sites might have great potential in the near future. Full article

(This article belongs to the Special Issue Zeolites)

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12 pages, 2926 KiB

Open AccessFeature PaperArticle

In-Situ Ellipsometric Study of the Optical Properties of LTL-Doped Thin Film Sensors for Copper(II) Ion Detection

by Dervil Cody, Tsvetanka Babeva, Violeta Madjarova, Anastasia Kharchenko, Sabad-e-Gul, Svetlana Mintova, Christopher J. Barrett and Izabela Naydenova

Coatings 2020, 10(4), 423; https://doi.org/10.3390/coatings10040423 - 24 Apr 2020

Cited by 7 | Viewed by 3918

Abstract

Optical sensors fabricated in zeolite nanoparticle composite films rely on changes in their optical properties (refractive index, n, and thickness, d) to produce a measurable response in the presence of a target analyte. Here, ellipsometry is used to characterize the changes [...] Read more.

Optical sensors fabricated in zeolite nanoparticle composite films rely on changes in their optical properties (refractive index, n, and thickness, d) to produce a measurable response in the presence of a target analyte. Here, ellipsometry is used to characterize the changes in optical properties of Linde Type L (LTL) zeolite thin films in the presence of Cu²⁺ ions in solution, with a view to improving the design of optical sensors that involve the change of n and/or d due to the adsorption of Cu²⁺ ions. The suitability of two different ellipsometry techniques (single wavelength and spectroscopic) for the evaluation of changes in n and d of both undoped and zeolite-doped films during exposure to water and Cu²⁺-containing solutions was investigated. The influence of pre-immersion thermal treatment conditions on sensor response was also studied. Due to the high temporal resolution, single wavelength ellipsometry facilitated the identification of a Cu²⁺ concentration response immediately after Cu²⁺ introduction, indicating that the single wavelength technique is suitable for dynamic studies of sensor–analyte interactions over short time scales. In comparison, spectroscopic ellipsometry produced a robust analysis of absolute changes in film n and d, as well as yielding insight into the net influence of competing and simultaneous changes in n and d inside the zeolite-doped films arising due to water adsorption and the ion exchange of potassium (K⁺) cations by copper (Cu²⁺). Full article

(This article belongs to the Special Issue Optical Thin Films and Structures: Design and Advanced Applications)

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16 pages, 3777 KiB

Open AccessArticle

Selective Conversion of Glucose to 5-Hydroxymethylfurfural by Using L-Type Zeolites with Different Morphologies

by María José Ginés-Molina, Nur Hidayahni Ahmad, Sandra Mérida-Morales, Cristina García-Sancho, Svetlana Mintova, Ng Eng-Poh and Pedro Maireles-Torres

Catalysts 2019, 9(12), 1073; https://doi.org/10.3390/catal9121073 - 16 Dec 2019

Cited by 18 | Viewed by 3952

Abstract

In the present work, the morphology of L-type zeolite (LTL topology) has been modified in order to evaluate the influence of several protonated-form LTL-zeolites with different morphologies on their stability and catalytic performance in the conversion of glucose into 5-hydroxymethylfurfural (5-HMF). Physico-chemical characterization [...] Read more.

In the present work, the morphology of L-type zeolite (LTL topology) has been modified in order to evaluate the influence of several protonated-form LTL-zeolites with different morphologies on their stability and catalytic performance in the conversion of glucose into 5-hydroxymethylfurfural (5-HMF). Physico-chemical characterization of the LTL-based catalysts has revealed that the three types of morphologies (needle, short rod and cylinder) are active, providing complete glucose conversion and high 5-HMF yield values. The addition of CaCl₂ had a positive influence on the catalytic performance. It was found that morphology influences the textural and acid properties of LTL-zeolites, and hence their catalytic performance. The best catalytic results have been obtained with the NEEDLE-LTL, showing nanoparticles with a length of 4.46 μm and a width of 0.63 μm, which attains a 5-HMF yield of 63%, at 175 °C after 90 min of reaction, and a glucose conversion of 88%. The reusability study has revealed a progressive decrease in 5-HMF yield after each catalytic cycle. Different regeneration methods have been essayed without recovering the initial catalytic activity. The presence of organic molecules in micropores has been demonstrated by TG analysis, which are difficult to remove even after a regeneration process at 550 °C. Full article

(This article belongs to the Special Issue Sustainable Catalytic Conversion of Biomass for the Production of Biofuels and Bioproducts)

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12 pages, 1841 KiB

Open AccessArticle

Zeolite Nanocrystals Protect the Performance of Organic Additives and Adsorb Acid Compounds during Lubricants Oxidation

by Moussa Zaarour, Hussein El Siblani, Nicolas Arnault, Philippe Boullay and Svetlana Mintova

Materials 2019, 12(17), 2830; https://doi.org/10.3390/ma12172830 - 3 Sep 2019

Cited by 7 | Viewed by 3256

Abstract

Zeolite nanocrystals were used as proactive agents to extend the lifetime of commercial lubricants by protecting the performance additives from depletion and adsorbing the acid formed during oxidation. The nanosized zeolites were introduced into four lubricants and subjected to oxidation (90 °C and [...] Read more.

Zeolite nanocrystals were used as proactive agents to extend the lifetime of commercial lubricants by protecting the performance additives from depletion and adsorbing the acid formed during oxidation. The nanosized zeolites were introduced into four lubricants and subjected to oxidation (90 °C and 150 °C). A strong affinity towards protection of zinc dialkyldithiophosphate (ZDDP) additive was demonstrated by ³¹P NMR (nuclear magnetic resonance) and FTIR (fourier-transform infrared) spectroscopy even after heating at 150 °C for 24 h. FTIR profiles of lubricants aged in the presence of LTL (Linde Type L zeolite) showed lower oxidation degree while the formed oxidation products (aldehydes, ketones, and acids) were adsorbed on the zeolite crystals acting as scavengers. Full article

(This article belongs to the Collection Porous Materials and Nanozeolites)

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13 pages, 3837 KiB

Open AccessArticle

Photoactive Nanomaterials Inspired by Nature: LTL Zeolite Doped with Laser Dyes as Artificial Light Harvesting Systems

by Leire Gartzia-Rivero, Jorge Bañuelos and Iñigo López-Arbeloa

Materials 2017, 10(5), 495; https://doi.org/10.3390/ma10050495 - 4 May 2017

Cited by 19 | Viewed by 5747

Abstract

The herein reported work describes the development of hierarchically-organized fluorescent nanomaterials inspired by plant antenna systems. These hybrid materials are based on nanostructured zeolitic materials (LTL zeolite) doped with laser dyes, which implies a synergism between organic and inorganic moieties. The non-interconnected channeled [...] Read more.

The herein reported work describes the development of hierarchically-organized fluorescent nanomaterials inspired by plant antenna systems. These hybrid materials are based on nanostructured zeolitic materials (LTL zeolite) doped with laser dyes, which implies a synergism between organic and inorganic moieties. The non-interconnected channeled structure and pore dimensions (7.1 Å) of the inorganic host are ideal to order and align the allocated fluorophores inside, inferring also high thermal and chemical stability. These artificial antennae harvest a broad range of chromatic radiation and convert it into predominant red-edge or alternatively white-light emission, just choosing the right dye combination and concentration ratio to modulate the efficiency of the ongoing energy transfer hops. A further degree of organization can be achieved by functionalizing the channel entrances of LTL zeolite with specific tailor-made (stopcock) molecules via a covalent linkage. These molecules plug the channels to avoid the leakage of the guest molecules absorbed inside, as well as connect the inner space of the zeolite with the outside thanks to energy transfer processes, making the coupling of the material with external devices easier. Full article

(This article belongs to the Special Issue Green Chemistry - both precursors and processes - to Hierarchical Materials)

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