Effects of Cold Sintering on the Performance of Zeolite 13X as a Consolidated Adsorbent for Cesium

Cold sintering, a novel low-temperature consolidation technique, has shown promising results in various inorganic materials. However, the application of this technique to nanoporous materials for energy and environmental fields is not yet fully understood. This study investigates the effects of cold sintering on the relative densities, compressive strengths, chemical durabilities, crystal structures, specific surface areas, and adsorption capacities of zeolites. Cold sintering at 200 °C achieved 10 to 20% greater densification than conventional high temperature (700 °C) sintering; however, the original nanoporous structure of dry cold sintered zeolite was not maintained. Introducing liquid agents during the cold sintering process resulted in reduced degradation of the SSA and increased densification. Using NaOH as the liquid agent increased the solubility of elements in zeolite, which promoted chemical mobility and achieved the highest relative density (96.7 ± 2.8%). However, soluble layers between the particles led to fragmentation, making it unsuitable for aqueous applications. Using H₂O as the liquid agent resulted in a relative density of 90.4 ± 4.1% while maintaining the nanoporous properties and structural integrity of zeolite under water. The cesium adsorption capacity (19.0 ± 0.1 mg·g^-1) was similar to that of conventional zeolite ion exchangers, indicating that cold sintering with H₂O was an efficient, economical, and safer alternative to conventional high-temperature consolidation method. Our findings suggest that this cold sintering can be applied to other nanoporous materials, such as metal-organic frameworks and covalent organic frameworks, in separation, catalysis, and adsorption applications.

Magnetic Induction Assisted Heating Technique in Hydrothermal Zeolite Synthesis

The magnetic induction assisted technique is an alternative heating method for hydrothermal zeolite synthesis with a higher heat-transfer rate than that of the conventional convection oil bath technique. The research demonstrates, for the first time, the application of the magnetic induction heating technique with direct surface contact for zeolite synthesis. The magnetic induction enables direct contact between the heat source and the reactor, thereby bypassing the resistance of the heating medium layer. A comparative heat-transfer analysis between the two methods shows the higher heat-transfer rate by the magnetic induction heating technique is due to (1) eight-time higher overall heat-transfer coefficient, attributed to the absence of the resistance of the heating medium layer and (2) the higher temperature difference between the heating source and the zeolite gel. Thereby, this heating technique shows promise for application in the large-scale synthesis of zeolites due to its associated efficient heat transfer. Thus, it can provide more flexibility to the synthesis method under the non-stirred condition, which can create possibilities for the successful large-scale synthesis of a broad range of zeolites.

Quantum Dots of [Na4 Cs6 PbBr4 ]8+ , Water Stable in Zeolite X, Luminesce Sharply in the Green

Nanocrystals (NCs) of CsPbX₃ , X = Cl, Br, or I, have excellent photoluminescent properties: high quantum yield, tunable emission wavelengths (410-700 nm), and narrow emission band widths. CsPbBr₃ NCs show high promise as a green-emitting material for use in wide color gamut displays. CsPbBr₃ NCs have, however, not been commercialized because they are sensitive to moisture and heat. To avoid these problems, this work attempts to introduce CsPbBr₃ into five zeolites. The zeolite X product, Pb,Br,H,Cs,Na-X, shows superior stability toward moisture, maintaining its initial luminescence properties after being under water for more than a month. Its structure, determined using single-crystal X-ray crystallography, shows that quantum dots (QDs) of [Na₄ Cs₆ PbBr₄ ]⁸⁺ (not of CsPbBr₃ ) have formed. They are tetrahedral PbBr₄ ^2- ions (Pb-Br = 3.091(11) Å) surrounded by Na⁺ and Cs⁺ ions. Each fills the zeolite's supercage with its Pb²⁺ ion precisely at the center, a position of high symmetry. The peaks in the emission spectra of Pb,Br,H,Cs,Na-X and the CsPbBr₃ NCs are both at about 520 nm. The FWHM of Pb,Br,H,Cs,Na-X, however, is narrower than any previously reported for any of the CsPbBr₃ NCs, and for zeolite Y and the various mesoporous materials treated with CsPbBr₃ .

Impact of fly ash fractionation on the zeolitization process

Coal combustion product in the form of fly ash has been sieved and successfully utilised as a main substrate and a carrier of silicon and aluminium in a set of hydrothermal syntheses of zeolites. The final product was abundant in zeolite X phase (Faujasite framework). Raw fly ash as well as its derivatives, after being sieved (fractions: ≤ 63, 63-125, 125-180 and ≥ 180 µm), and the obtained zeolite materials were subjected to mineralogical characterisation using powder X-ray diffraction, energy-dispersive X-ray fluorescence, laser diffraction-based particle size analysis and scanning electron microscopy. The influence of fraction separation on the zeolitization process under hydrothermal synthesis was investigated. Analyses performed on the derived zeolite X samples revealed a meaningful impact of the given fly ash fraction on synthesis efficiency, chemistry, quality as well as physicochemical properties, while favouring a given morphological form of zeolite crystals. The obtained zeolites possess great potential for use in many areas of industry and environmental protection or engineering.

The Use of POSS-Based Nanoadditives for Cable-Grade PVC: Effects on its Thermal Stability

Plasticized–Poly(vinyl chloride) (P-PVC) for cables and insulation requires performances related to outdoor, indoor and submarine contexts and reduction of noxious release of HCl-containing fumes in case of thermal degradation or fire. Introducing suitable nanomaterials in polymer-based nanocomposites can be an answer to this clue. In this work, an industry-compliant cable-grade P-PVC formulation was added with nanostructured materials belonging to the family of Polyhedral Oligomeric Silsesquioxane (POSS). The effects of the nanomaterials, alone and in synergy with HCl scavenging agents as zeolites and hydrotalcites, on the thermal stability and HCl evolution of P-PVC were deeply investigated by thermogravimetric analysis and reference ASTM methods. Moreover, hardness and mechanical properties were studied in order to highlight the effects of these additives in the perspective of final industrial uses. The data demonstrated relevant improvements in the thermal stability of the samples added with nanomaterials, already with concentrations of POSS down to 0.31 phr and interesting additive effects of POSS with zeolites and hydrotalcites for HCl release reduction without losing mechanical performances.

Preparation of Zeolite X by the Aluminum Residue From Coal Fly Ash for the Adsorption of Volatile Organic Compounds

In China, coal fly ash is a large-scale solid waste generated by power plants. The high value utilization of coal fly ash has always been a hot research issue in China for these years. In this paper, the synthesis of zeolite X using aluminum residue from coal fly ash can not only realize the resource utilization of waste, but also achieve the effect of energy saving and emission reduction. Zeolite X prepared by hydrothermal synthesis method have been found to have higher purity and better crystallinity by chemical composition analysis. By comparing and analyzing the adsorption performance of zeolite X and activated carbon on volatile organic compounds, it is found that the adsorption capacity of zeolite X is higher than that of activated carbon, and it has stronger stability. This indicates that the zeolite X synthesized by this environmentally friendly and economical method has a good application prospect in adsorbing volatile organic compounds.

One-Step Hydrothermal Synthesis of Zeolite X Powder from Natural Low-Grade Diatomite

Zeolite X powder was synthesized using natural low-grade diatomite as the main source of Si but only as a partial source of Al via a simple and green hydrothermal method. The microstructure and surface properties of the obtained samples were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), wavelength dispersive X-ray fluorescence (XRF), calcium ion exchange capacity (CEC), thermogravimetric-differential thermal (TG-DTA) analysis, and N₂ adsorption-desorption technique. The influence of various synthesis factors, including aging time and temperature, crystallization time and temperature, Na₂O/SiO₂ and H₂O/Na₂O ratio on the CEC of zeolite, were systematically investigated. The as-synthesized zeolite X with binary meso-microporous structure possessed remarkable thermal stability, high calcium ion exchange capacity of 248 mg/g and large surface area of 453 m²/g. In addition, the calcium ion exchange capacity of zeolite X was found to be mainly determined by the crystallization degree. In conclusion, the synthesized zeolite X using diatomite as a cost-effective raw material in this study has great potential for industrial application such as catalyst support and adsorbent.

Sorption of Cu(II) Ions on Chitosan-Zeolite X Composites: Impact of Gelling and Drying Conditions

Chitosan-zeolite Na-X composite beads with open porosity and different zeolite contents were prepared by an encapsulation method. Preparation conditions had to be optimised in order to stabilize the zeolite network during the polysaccharide gelling process. Composites and pure reference components were characterized using X-ray diffraction (XRD); scanning electron microscopy (SEM); N₂ adsorption-desorption; and thermogravimetric analysis (TG). Cu(II) sorption was investigated at pH 6. The choice of drying method used for the storage of the adsorbent severely affects the textural properties of the composite and the copper sorption effectiveness. The copper sorption capacity of chitosan hydrogel is about 190 mg·g(-1). More than 70% of this capacity is retained when the polysaccharide is stored as an aerogel after supercrititcal CO₂ drying, but nearly 90% of the capacity is lost after evaporative drying to a xerogel. Textural data and Cu(II) sorption data indicate that the properties of the zeolite-polysaccharide composites are not just the sum of the properties of the individual components. Whereas a chitosan coating impairs the accessibility of the microporosity of the zeolite; the presence of the zeolite improves the stability of the dispersion of chitosan upon supercritical drying and increases the affinity of the composites for Cu(II) cations. Chitosan-zeolite aerogels present Cu(II) sorption properties.