NaA Zeolite Research Articles

Synthesis of ultra-small NaA zeolite nanocrystals at near room temperature

The NaA zeolite nanocrystalline aggregates composed of 6 nm ultra-small were synthesized for the first time by refluxing at near room temperature and atmospheric pressure. NaA zeolite samples had been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N2 adsorption-desorption isotherms. The XRD of the obtained samples at different synthesis temperatures demonstrated that their crystallinity was high. Furthermore, the SEM images of NaA zeolite synthesized at 30, 40 and 60 °C showed that its particle sizes were 130, 130 and 180 nm, respectively. Moreover, the TEM images confirmed that the NaA zeolite aggregates synthesized at 40 and 60 °C consisted of ultra-small crystals with a size of 6 nm, while the NaA zeolite synthesized at 30 °C was a single crystal. Compared with the previously reported synthetic zeolite crystals, the use of a reflux system under atmospheric pressure in this study not only synthesized the ultra-small zeolite nanocrystals (6 nm) with large specific surface area, but also avoided many safety issues brought by traditional synthesis methods under high autogenous pressure. Therefore, this study provides a precise and safe synthetic method for the development of ultra-small zeolite nanocrystals. Moreover, the large specific surface area makes them have great potential for development.

High photodegradation performance of ZnO nanoparticles supported on porous Zeolite Na-A: Effects of ZnO loading

Zeolite Na-A supported ZnO nanocomposites (ZnO/Zeolite Na-A NCs) were synthesized at low temperature (70 °C) via the sol-gel process and characterized for thermal, structural, morphological, adsorption, optical and bonding properties. Both XRD and microscopy imaging results indicated that the obtained nanopowders were crystalline in nature with no Zeolite Na-A structural collapse revealed. The synthesized ZnO nanoparticles occurred mainly on the surface of the Zeolite Na-A support and were more dispersed as compared to those of unsupported ZnO. The textural properties showed improved porosity and increased surface area. Photocatalytic activity for the ZnO/Zeolite Na-A was higher compared to that of unsupported ZnO which was attributed to the combined effects of both ZnO and zeolite aluminosilicate network. These effects were as result of the increased surface area, strong adsorption and enhanced ZnO dispersion hence suppressed charge recombination of the nanocomposites powders.

Characterizing crystalline phase transitions in zeolitization of coal fly ash using focused ion beam-scanning electron microscopy

Coal fly ash (CFA) accounts for a significant portion of coal ash, which is a by-product of thermal power plants. Herein, CFA collected in Korea was used to synthesize a zeolitic material via fusion and hydrothermal synthesis. The crystallographic characteristics of CFA, alkali-fused CFA, and synthesized zeolitic material from CFA (SZC) were investigated via cross-section analysis using focused ion beam-scanning electron microscopy (FIB-SEM) with energy-dispersive X-ray spectroscopy (EDS), which has not been attempted in previous studies. Cross-section milling and EDS line scan were performed using FIB-SEM to develop the existing analysis methods, focusing on the crystalline phase and chemical composition of the surface of synthetic materials. Following the alkali treatment, the amorphous CFA exhibited a biphase comprising both crystalline and amorphous phases. After the synthesis process, both the surface and the interior exhibited a uniform Na-A zeolite crystalline structure with sharp-edged cubes. Furthermore, the SZC comprised crystals of Na-A zeolite with a uniform structure and a Si/Al molar ratio of approximately 1.4.

NaA zeolite-clay composite membrane formulation and its use as cost-effective water softener

The present study describes the exchange of calcium and magnesium ions through an active layer of zeolite Na-A deposited on flat porous support made from clay. Microfiltration membrane's supports are prepared by uniaxial pressing dry mixture of clay, and 3% w/w activated carbon then sintered to 1000 °C. The zeolite Na-A (LTA) layer is deposited on the clay support using the hydrothermal method. An increase in the specific surface area and the pore volume and a decrease in pore diameter after deposition of the zeolite Na-A on the support is observed. SEM analysis of the zeolite Na-A shows well-defined cubic crystals with sizes between 1.3 and 2.4 μm. The efficiency of the zeolite membrane for the exchange of calcium and magnesium ions with the sodium (Na) within the zeolite-A cavities was evaluated by filtration tests of solutions containing chlorides salts of the two metals using a flow loop adjusted for dead-end filtration. The obtained results show that the Na+ ions of Zeolite-A were completely exchanged with Ca2+ and Mg2+ and that the maximum retention on the zeolite membrane reached 93.3% and 72.1% for Ca2+ and Mg2+ ions, respectively after 30 min of filtration. The electrochemical impedance spectroscopy (EIS) has shown an electron transfer increase of the membrane paste electrode exchanged with Ca2+, Mg2+ as single ions or as mixture, with a preference for Ca2+ compared to Mg2+, indicating that a combination of exchange and size exclusion mechanisms must be used to explain the membrane behavior. These properties make the zeolite Na-A membrane a suitable material that could be used effectively in the softening of hard water.

Synthesis of NaA zeolite via the mesoscale reorganization of submolten salt depolymerized kaolin: A mechanistic study

Deep understanding of the formation mechanism is crucial to the rational design and controllable synthesis of zeolites with desired pore architecture and acidity. Herein, we take the synthesis of NaA zeolite from a submolten salt depolymerized kaolin (SMS-K) as an example to elucidate the formation mechanism of NaA zeolite. By using SMS-K as sole Si and Al sources, a highly pure and crystalline NaA zeolite with superior ion exchange ability was synthesized. By using various ex-situ and in-situ characterizations and studying the crystallization kinetics, a plausible formation mechanism of NaA zeolite via the mesoscale reorganization of SMS-K was proposed. The results indicate that the reorganization of SMS-K into NaA zeolite follows the solid-phase transformation route. Upon being mixed with H2O, SMS-K that is mainly composed of silicate monomers and chain/ring microstructures is in-situ transformed rapidly into mesoscale intermediates containing double four-membered rings and β cages, sufficient stirring during aging generates more mesoscale intermediates. During the subsequent crystallization process, the mesoscale intermediates are further self-assembled into NaA nanoparticles when theirs amount reaches a maximum, and finally the nanoparticles grow into well-shaped cubic NaA zeolite particles with smooth surfaces through layer spreading. Our work provides the theoretical foundation for the design and green synthesis of zeolites directly from the natural minerals.

Influence of regeneration conditions on cyclic CO2 adsorption on NaA zeolite at high pressures

This work aimed to determine the influence of different regeneration conditions on CO2 adsorption on NaA zeolite at high pressures through cyclic processes. To reach this goal, NaA characterization, high-pressure adsorption isotherms, heat of adsorption and working capacities for CO2/NaA system were performed. NaA zeolite characterization showed a high crystalline and stable microporous structure with 0.43 nm pore diameter and 247 m² g-1 specific area. CO2 adsorption isotherms are strongly favorable, showing adsorption uptakes equal to 4.73, 4.54 and 4.44 mol kg-1 (c.a. 20 wt%) at 40 bar and 20, 30 and 40 °C, respectively. Jensen-Seaton model fits experimental data and was used to determine CO2/NaA heats of adsorption from 10 to 40 kJ mol-1, which are characteristic of physisorption process. This was corroborated by constant working capacity for all regeneration processes, reaching 1.44, 3.27, and 4.27 mol kg-1 for REG-1 (1 bar, 30 °C), REG-2 (vacuum, 30 °C) and REG-3 (vacuum, 150 °C) regeneration processes, respectively. The working capacity simulation showed a strong influence of pressure and practically insensitive to adsorption temperature from 20° to 40°C. Therefore, NaA zeolite is a regenerative material showing a high potential for utilization in high pressure cyclic adsorption processes, such as fixed and fluidized beds, for CO2 separation when pressure and temperature are changed in blowdown/regeneration step.

Antibacterial Application of Ag-Loaded Zn-Hybrid NaA Zeolite with High Ag Loading Amount

Antibacterial Application of Ag-Loaded Zn-Hybrid NaA Zeolite with High Ag Loading Amount

Effective removal of fluorine ions in phosphoric acid by silicate molecular sieve synthesized by hexafluorosilicic acid

Silicone zeolite prepared from hexafluorosilicic acid is a good adsorbent for fluoride removal. The morphology and structure of the prepared composites were characterized by XRD, FT-IR and BET. XRD images showed that fluorine was adsorbed on the surface of zeolite and the FT-IR spectra showed that there are different kinds of silicon and aluminum in silica-based zeolite. Therefore, through the studied of regeneration-adsorption cycle of zeolite, fluoride desorption and regeneration mechanism of zeolite defluorination was explained, and the adsorption performance and regeneration adsorption performance of zeolite defluorination were evaluated. The effects of phosphoric acid concentration, operating condition and specific surface area of zeolite and Si/Al ratio of zeolite on adsorption performance were investigated. Silicate molecule sieve shows strong adsorption capacity for fluoride (F-), and the adsorption capacity reached 352.46 mg/g under the optimal conditions. The Freundlich and Langmuir isotherm models for aluminosilicate MCM-41 and NaA zeolite which experimental data of F- adsorption on in phosphoric acid were fitted to investigate the adsorption mechanism. In the mechanism of anion adsorption, F- or SiF62- is bound by electrostatic adsorption of hydroxyl on the surface of adsorbent with anion adsorption. The adsorbed SiF62− ions can be regenerated when the environmental pH increases to value higher than that of zero charge point of zeolite. There is a competitive adsorption between OH– and F- with negative charge, which reduces the adsorption efficiency of adsorbent for F-. The NaA zeolite regenerated with NH3·H2O showed better fluorine re-adsorption performance.

Possibilities of Using Zeolites Synthesized from Fly Ash in Adsorption Chillers

Adsorption chillers produce cold energy, using heat instead of electricity, thus reducing electrical energy consumption. A major industrial waste, fly ash, can be converted to zeolite and used in adsorption chillers as an adsorbent. In this research, three different types of zeolites were synthesised from fly ash via a hydrothermal reaction in an alkaline solution (NaOH). The obtained samples (Na-A zeolites) were modified with K2CO3 to increase the water adsorption capacity of these samples. Phase and morphology analyses shows that desired zeolites formed properly but other crystalline phases also exist along with nonporous amorphous phases. The determined specific surface areas for Na-A zeolite (12 h) and Na-A zeolite (24 h) are 45 m2/g and 185 m2/g respectively, while the specific surface area for synthesized 13X zeolite is almost negligible. Water-isotherm for each of these samples was measured. Considering the application of adsorption chillers, average adsorption capacity was very low, 1.73% and 1.27%, respectively, for the two most probable operating conditions for synthesized 13X zeolite, whereas no water was available for the evaporation from Na-A zeolite (12 h) and Na-A zeolite (24 h). This analysis implies that among the synthesized materials only 13X zeolite has a potential as an adsorber in sorption chillers.

Sorption and Spatial Distribution of 137Cs, 90Sr and 241Am on Mineral Phases of Fractured Rocks of Nizhnekansky Granitoid Massif

The sorption behavior and spatial microdistribution of Cs-137, Sr-90 and Am-241 onto the surface of a fractured rock sample from the R-11 borehole of the exocontact zone of the Nizhnekansky granitoid massif were studied. The sorption efficiency of the fractured sample increases in the row of Sr < Cs < Am, where americium is the most retained radionuclide. Based on the image processing of radiograms and scanning electron microscopy data, the mineral relative sorption efficiency (RSE) values were determined to quantify the contribution of the mineral phases of the fractured sample to radionuclide retention. It was established that cesium and strontium are predominantly retained in cracks filled with secondary mineral chlorite. Zeolite is a less effective sorbent with respect to cesium and strontium. Americium sorption is uniform over the whole surface of the fractured sample, with close RSE values for all mineral phases (RSE ~1). The behavior of cesium in heterogeneous and monomineral systems of crushed mineral phases of quartz, biotite and zeolite NaA imitating minerals of the fractured rock sample R-11 was determined. It was shown that the fraction of the sorbed cesium in a heterogeneous system of two mineral phases—biotite and quartz—was larger than the sum of sorption values for the same separated mineral phases. Based on the models of radionuclide sorption on illite–smectite minerals, it was able to estimate the depth of the penetration of solution into the fractured rock sample R-11. The variations of penetration depths for solutions of specific radionuclide into the fractured rock sample were established.

ZnO/ZnFe2O4/zeolite composite catalyst for peroxymonosulfate oxidation and photocatalysis

Magnetic ZnO/ZnFe2O4/Zeolite (ZFZ) catalysts were prepared by a solvothermal-microwave method and used for advanced oxidation processes. Careful investigations indicate ZFZ has a core-shell structure with ZnO/ZnFe2O4 nanoparticles covered on the surface of Na-A zeolite. The specific saturation magnetization of ZFZ is up to 15.276 emu/g, which is sufficient for efficient magnetic separation. Experiments on advanced oxidation degradation of Rhodamine B indicate that ZFZ have remarkable catalytic activity for peroxymonosulfate oxidation. The degradation rate increased more than 3 times under UV-light irradiation, suggesting that ZFZ has stronger photocatalysis. The highest decomposition rate could reach 98.55 %. And after 5 cycles, a 79.11 % degradation rate still remained.

Bifunctional core-shell structure NaA zeolite@mesoporous-silica/curcumin nanocomplexes for removing heavy metals and reduction of Cadmium-induced damage

Heavy metals had been reported to bioaccumulate in many organs and adversely affect the functions of these organs. Therefore, it was of great significance to develop bifunctional drug carrier, which could remove heavy metals and load curcumin with multiple protective properties. Newly designed drug carrier combining a core of NaA zeolite and a mesoporous silica (MS) shell has been developed, which the core is used to remove heavy metals, the outer shell loads drugs, and explore the dual functions. In this work, Curcumin-loaded on an amino modified NaA@MS-0.2 (NaA@MS-0.2-N-Cur) are 220 nm sized and have a mesoporous silica shell of 30 nm thickness. The cumulative drug release from NaA@MS-0.2-N-Cur were 14.1 and 43.0% in pH 7.4 and pH 1.2 PBS. NaA@MS-0.2-N-Cur released in 100 mL of pH 1.2 PBS containing 100 mg/L Cd2+, the cumulative drug release rate was 43.9%, the sorption rate of Cd2+ was 79.7%, and the sorption capacity of Cd2+ was 109.5 mg/g. Taken together, these results suggested that core-shell structure nanocomplexes are bifunctional and its cumulative drug release rate increased in pH 1.2 PBS. And this drug carrier has great potential for protecting the body from damage for heavy metal.

Preparation of NaA zeolite with fly ash and its adsorption properties for lead ions

Preparation of NaA zeolite with fly ash and its adsorption properties for lead ions

МОРФОЛОГІЯ ТА ТЕРМІЧНА СТІЙКІСТЬ СИНТЕТИЧНОГО ЦЕОЛІТУ, МЕХАНОХІМІЧНО МОДИФІКОВАНОГО КАТІОНАМИ Ca, Zn I Mn(II)

An important direction of new technologies of corrosion protection of metals is the use of inhibitory pigments in the composition of paints and varnishes, which are tolerant to the environment, have high efficiency and can replace chromates. Promising anti-corrosion pigments for paints and varnishes are ion-exchange substances, in particular modified zeolites, which will provide optimal selective resistance to aggressive environmental influences. In this work the dispersion and morphology of complex pigments based on synthetic zeolite and monophosphates of calcium, zinc and manganese are investigated. It was found that the modification of zeolites by metal monophosphates by mechanochemical method in a ball mill for 60 min at a speed of 200 rpm leads to decrease in fraction to 2.0 μm by ~44%… 64% and an increase from 2.0 to 10.0 μm by ~60%. The fraction up to 2.0 μm is represented by particles of irregular globular shape > 10.0 μm - agglomerates. Thermogravimetric studies have shown that all synthesized complex pigments are characterized by thermal stability. Thermolysis is characterized by 4 stages, which correspond to the removal of physically adsorbed water, chemically sorbed water, dehydroxylation of the surface by cleavage of OH groups, and phase transitions. Modification with metal monophosphates increases the thermal stability of pigments in the sequence Na-A: Ca(H2PO4)2 - Na-A: Zn(H2PO4)2 - Na-A: Mn(H2PO4)2. Thermolysis of samples in the temperature range from 15 to 700 °С is took place during four stages, most intensively at temperatures up to 400 °С. During mechanochemical dispersion of zeolites with calcium, zinc and manganese monophosphates, the amount of physically adsorbed water increases by ~18… ~41%, and chemically sorbed water decreases by ~19… ~41%. The specific surface area of zeolite Na-A: Ca(H2PO4)2 increases by ~8%, and Na-A: Zn(H2PO4)2 and Na-A: Mn(H2PO4)2 decreases by ~50% and ~22%, respectively. This may be due to the radii of the metal cations and the fraction content up to 2.0 μm when grinding zeolites. Based on the obtained results, the synthesized zeolites can be recommended for further studies of their inhibitory properties as pigments in the composition of paints and varnishes.

Optimal preparation of low-cost and high-permeation NaA zeolite membrane for effective ethanol dehydration

In this work, low-cost and high permeation NaA zeolite membrane was successfully prepared on kaolinite support by in-situ crystallization using secondary growth method. The effect of synthesis conditions including temperature and time of crystallization, and water ratio was studied aiming to improve the quality and the performance of the membrane. The prepared membrane was thoroughly characterized using many techniques such as X-ray diffraction, scanning electron microscopy infrared spectroscopy, Brunauer-Emmett-Teller specific surface area and zeta potential to investigate the layer deposition. The prepared membrane exhibits high permeation flux of 8.49 kg m −2 h−1 and separation factor of 10900 for the dehydration of 90 wt% ethanol by pervaporation at 75 °C.

N-Cetyltrimethylammonium Bromide-Modified Zeolite Na-A from Waste Fly Ash for Hexavalent Chromium Removal from Industrial Effluent

Chromium ions released into aquatic environments pose major environmental risks, particularly in developing countries. Here, a low-cost N-cetyltrimethylammonium bromide (CTAB)-modified fly ash-based zeolite Na-A (CTAB@FZA) was prepared for the treatment of industrial wastewater contaminated with Cr(VI). CTAB@FZA was evaluated using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM), which showed that CTAB intercalation and coating of the modified zeolite were successful. The effects of influencing variables on the removal of Cr(VI) using CTAB@FZA were also evaluated, including pH, initial concentration, time, temperature, and coexisting ions. Fast adsorption equilibrium was observed after less than 10 min, and CTAB@FZA had a maximum adsorption capacity of 108.76 mg/g and was substantially greater than that of pristine FZA following modification. Furthermore, isothermal and kinetic data demonstrated that Cr(VI) adsorbed onto homogeneous surfaces via rate-limiting monolayer Langmuir adsorption, and according to thermodynamic data, the sorption of the targeted pollutant was exothermic and spontaneous. The application of CTAB@FZA to industrial wastewater treatment yielded Cr(VI) concentrations that were below the USEPA standards. Overall, the findings demonstrated that CTAB@FZA is an effective, promising, and economical adsorbent for the treatment of Cr(VI)-polluted water.

The influence of separately and combined bentonite and kaolinite as binders for pelletization of NaA zeolite from coal fly ash

Pelletization of zeolitic materials is required to facilitate their practical industrial and commercial applications. Zeolite-NaA was synthesized from fly ash by the fusion method and shaped into spherical granules. Bentonite, kaolinite, and a combination of bentonite with kaolinite were tested as binders with different contents from 5 to 10 wt%. The pellet formation was optimized. The physicochemical properties of binders, zeolite powder, and zeolite granular were characterized by X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), nitrogen adsorption/desorption isotherm, and scanning electron microscopy (SEM) among other techniques. Deformation and breakage behavior of spherical granulates by compression was also studied. The best performance was obtained by the pellet with 10% bentonite with satisfactory mechanical strength and water resistance. The XRD and SEM results revealed NaA zeolite granular with a typical cubic shape and high crystallinity formed on the surface of bentonite. This result presents a potential use of the coal fly ash to obtain pelletized NaA zeolite following the principles of circular economy and the sustainable development goals (SDGs), particularly SDG 12.

Effect of membrane performance variability with temperature and feed composition on pervaporation and vapor permeation system design for solvent drying.

The presence of water in organic solvents and biofuels can complicate their production and reuse because many hydrophilic solvents form difficult-to-separate mixtures with water (e.g., azeotropes). Pervaporation (PV) and vapor permeation (V⋅P) remove water from such mixtures via selective solution-diffusion transport through a membrane material. A recent article reviewed design factors that impact the effectiveness of PV/V⋅P solvent dehydration processes (J. Chem. Technol. Biotechnol 95: 495-512 (2020)). For the sake of simplicity, the earlier work assumed constant membrane permeabilities. The objective here is to explore the impact of variable permeabilities on predictions of PV/V⋅P system performance. A multiparameter expression relating permeability to process conditions was incorporated into the spreadsheet calculators from the previous work. Use of the expression was demonstrated with literature ethanol/water PV data for a NaA zeolite material and two poly (vinyl alcohol) (PVA) membranes. The variable permeabilities of the membranes yielded membrane area requirements that were 20-30% different from those calculated using permeances fixed at either end of the target water range. The impact of composition-dependent permeabilities was most pronounced on the fraction of ethanol transferred to the permeate for the NaA membrane. The inclusion of membrane permeabilities that vary with fluid composition and temperature noticeably altered predictions of the membrane area required to carry out water removal from ethanol by PV and of the transfer of ethanol to the permeate stream. Unless a PV/V⋅P process is expected to operate at a constant temperature and in a narrow concentration range, process performance estimates would be improved by inclusion of concentration- and temperature-dependent permeabilities or permeances.

On the Optimization of Ni/A and Ni/X Synthesis Procedure toward Active and Selective Catalysts for the Production of CH4 from CO2

Herein, optimization of zeolite NaA/NaX synthesis conditions in order to obtain the final product with high surface area and pore volume was investigated. An optimal synthesis condition was 5 days aging time and crystallization time of 9 h with the co-addition of cetyltrimethylammonium bromide (CTAB) and heptane. All those optimal synthesis conditions provided mixed phase between zeolite NaA and NaX, and addition of those organic phases improved the surface area and pore volume of the final synthesized zeolite. The role of CTAB and heptane on increasing the surface area of zeolite was studied by in situ small-angle X-ray scattering (SAXS). The SAXS results evidenced that small nucleation precursor was formed upon the addition of organic phase, and this nucleation precursor can provide zeolite with high-characteristic XRD signals of mixed phase of zeolite A and X after the crystallization process. The synthesized zeolite obtained from optimal synthesis condition with high surface area was further used as a catalyst support by impregnating with 5, 10, 15, and 20wt%Ni for catalyzing CO2 methanation reaction. The results found that 15wt%Ni/zeolite expressed the highest catalytic activity with high CH4 selectivity and stability. This was due to high dispersion of Ni species on catalyst surface and high metal-support interaction between Ni and zeolite. These results indicated that the mixed phase zeolite support can be a potential catalyst support for this reaction.

Interfacial nanoarchitectonics for accelerated growth of zeolite via enlarging gel-liquid interfacial area using rotating packed bed

Typically, silica-alumina zeolites are hydrothermally synthesized in the sodium-rich dense hydrogel systems with a relatively long crystallization time in industry. The fast and economical synthesis of silica-alumina zeolites is still a big challenge. Herein, we develop a universal method to tackle this issue using the rotating packed bed (RPB). An interesting phenomenon is found that gel-liquid interfacial areas in the zeolite precursor are obviously enlarged when RPB is employed, and thus the following crystallization rates of zeolites are greatly improved, especially for the initial nucleation process. Also, we successfully control the growth rates of silica-alumina zeolite by adjusting the gel-liquid interfacial areas. Furthermore, we find that the transfer rate of OH− and hydrated sodium ions from liquid part to gel phase is enhanced by RPB in the initial nucleation process, which greatly promotes the nucleation rate of zeolites. The density functional theory (DFT) calculations demonstrate that hydrated sodium ions can induce the dehydrogenation of Si–OH to generate reactive oxygen radicals, thus lowering the energy barrier of the polymerization reaction and consequently accelerating the nucleation process. Moreover, NaY, NaZSM-5, and NaA zeolites with larger surface areas and more pore volumes are successfully synthesized by this RPB-enhanced-interface strategy, and their crystallization processes are all greatly accelerated.