Hydrothermal synthesis of zeolite A from K-feldspar and its crystallization mechanism

Assessment of acid catalytic properties of ferrosilicate MFI zeolite by methanol-to-hydrocarbon conversion

Four representative synthetic methods were employed to prepare Fe-containing siliceous MFI zeolites. The obtained Fe-MFI zeolites exhibited markedly different catalytic performances in the methanol-to-hydrocarbon (MTH) conversion reaction depending on the type of Fe incorporation within the siliceous framework. The catalytically active Brønsted acid sites were analyzed using pyridine adsorption experiments combined with Fourier transform infrared spectroscopy, providing characteristic signal intensities according to the acid-base interactions. Based on the MTH conversion results and acidity analyses, a suitable synthetic method was identified for the incorporation of Fe within the MFI zeolite framework. However, compared to other catalytic reactions, structural analyses by transmission electron microscopy, ultraviolet-visible spectroscopy, and X-ray absorption spectroscopy were much less conclusive.

The Removal of Strontium Ions from an Aqueous Solution Using Na-A Zeolites Synthesized from Kaolin

Sr2+ ions in an aqueous solution were removed using Na-A zeolites synthesized from kaolin, a natural mineral. Na-A zeolites with high crystallinity were synthesized using NaOH/kaolin mass ratios of 0.6 (ZK06) and 0.9 (ZK09). The adsorption reached equilibrium within 120 min. The adsorption data obtained from experiments for Sr2+ using ZK06 and ZK09 were appropriately analyzed with pseudo-second-order kinetic and Langmuir isotherm models. Comparing the maximum adsorption capacities (qm) of ZK06 and ZK09 for Sr2+, the highest values were obtained at 1.90 and 2.42 mmol/g, respectively. Consequently, the Na-A zeolites synthesized from kaolin can be evaluated as adsorbents with high adsorption capacities for the removal of Sr2+, proportional to the degree of their crystallinity.

Optimization of preparation of NaA zeolite from fly ash for CO2 capture

The green synthesis method of fly ash-based NaA zeolite was explored to reduce the synthesis cost and environmental hazards. For the prepared NaA samples, the effects of crystallization time, solid-liquid ratio, and Si/Al ratio were systematically studied. CO2 adsorption isotherm is used for adsorption model fitting analysis and adsorption selectivity determination. According to the experimental results, the optimized NaA zeolite synthesis conditions are as follows: the Si/Al ratio of NaA zeolite is 1.4, the solid-liquid ratio is 10, and the crystallization time is 6 h. The green synthesis method reported in this study can successfully prepare NaA zeolite and exhibit excellent CO2 adsorption performance, reaching 4.34 mmol/g, with high CO2 selective adsorption ability, reaching 89.2 for N2, 257.1 for O2, and 45.8 for CH4. The adsorbed CO2 can be released for further utilization, and NaA zeolite also has strong adsorption and regeneration performance, with a ten cycle adsorption capacity only decreasing by 1.17%. In addition, the use of cheap raw materials synthesis methods will promote the large-scale industry application of green synthesis technology in the future.

Study on adsorption of ammonia nitrogen by sodium-modified kaolin at calcination temperature

Natural kaolin (NK) is not used as a material for removal of ammonia nitrogen in wastewater because of its low ammonia adsorption capacity. In this study, sodium-modified kaolin adsorbent (NaCK) with high ammonia nitrogen adsorption capacity was prepared by NaOH modification of calcined NK, which was developed to address this problem. The adsorption properties were evaluated by batch static adsorption test. The results showed that when the initial concentration of ammonia nitrogen was 10 mg/L, pH = 8, and dosage of adsorbent was 1 g/L, the adsorption capacity of NaCK-600 for ammonia nitrogen was the best, reaching 6.23 mg/g, which was 34.6 times higher than that of NK (0.18 mg/g). Batch static adsorption test combined with adsorption kinetics, adsorption isothermal, and characteristic data showed that NaCK prepared at different temperatures had different adsorption mechanisms. Batch static adsorption test data of NaCK-600 was in good agreement with the pseudo-second-order model and Langmuir model, and the main mechanism of its adsorption of ammonia nitrogen was the ion exchange of NH4+ and Na+ in NaCK. After the third cycle, the removal rate of NaCK-600 was still up to 76.44%, which indicates that NaCK-600 has considerable potential for removal of ammonia nitrogen in wastewater and provides a new way for the application of kaolin in removal of ammonia nitrogen.

A green approach to develop zeolite-thymol antimicrobial composites: analytical characterization and antimicrobial activity evaluation

In this work, the development, analytical characterization and bioactivity of zeolite-thymol composites, obtained using wet, semi-dry and dry processes, were carried out in order to obtain sustainable and powerful antimicrobial additives. FT-IR, XRD, DSC, TGA, SEM and B.E.T. analyses were carried out to gain comprehensive information on the chemical-physical, thermal, and morphological features of the composites. GC-MS analyses allowed quantifying the active molecule loaded in the zeolite, released by the functionalized composites and its stability over time. Among the three procedures, the dry approach allowed to reach the highest thymol loading content and efficiency (49.8 ± 1.6% and 99.6 ± 1.2%, respectively), as well as the highest composite specific surface area value, feature which promises the best interaction between the surface of the composite and the bacterial population. Therefore, the bioactive surface of composites obtained by this solvent-free method was assayed for its antimicrobial activity against four microbial strains belonging to Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and Candida albicans species. The higher antimicrobial activity produced by the solvent-free composite in comparison with that of pure thymol, at the same thymol concentration, was ascribed to the large interfacial contact between the composite and the bacterial target. This feature, together with its enhanced storage stability, suggested that this composite could be employed as effective additives for the development of antimicrobial biointerfaces for food, home and personal care applications.

Low-cost Y-type zeolite/carbon porous composite from coal gasification fine slag and its application in the phenol removal from wastewater: fabrication, characterization, equilibrium, and kinetic studies

As an industrial solid waste, coal gasification fine slag (CGFS), which consists of many elements, such as silicon, aluminum, and carbon, could be used as an important resource. Therefore, this solid waste was used as a raw material to prepare high-value-added adsorption material for the treatment of industrial wastewater in this study. A hydrothermal synthesis method was applied to convert CGFS into a Y-type zeolite/carbon porous composite. The effects of time and temperature on the synthesis were studied. XRD, SEM, and other techniques were used to analyze the material and its physicochemical properties. Additionally, the adsorption performance of the material for phenol was studied. The results showed that the composite has better adsorption capacity for phenol than CGFS. The Freundlich model and pseudo-second-order kinetics well fitted the adsorption behavior of the composite, which demonstrated that the adsorption of phenol was dominated by chemical adsorption.

Two-step hydrothermal synthesis and conversion mechanism of zeolite X from stellerite zeolite

We investigated the conversion mechanism of stellerite zeolite to zeolite X under two-step hydrothermal conditions. To elucidate the conversion mechanism, solid products were separated from the mixtures at different crystallization times and characterized by XRD, FESEM, FT-IR, Raman, solid-state NMR, XRF, and TEM. The results indicate that in this reaction process, the Si, Al, and Na in the gel solid phases were continuously dissolved and transformed into the gel-liquid-phase. When the concentration of each component reached supersaturation in the gel-liquid-phase, Si, Al, and Na were transferred to the surface of the gel-solid-phase, and nucleation and crystallization occurred on the surface. Abundant nuclei were formed during the second hour of the crystallization. As the crystallization time increased, the nuclei rapidly grew into zeolite X crystals, and the relative crystallinity of zeolite X reached a maximum when the crystallization time reached 4 h. These phenomena indicate that the formation mechanism of zeolite X is a liquid-phase conversion mechanism.

Controllable Preparation of Cubic Zeolite A and Application of Langmuir Model in Carbon Dioxide Adsorption

A large amount of remaining fly ash has been piled up or landfilled, which not only a waste of land resources but also results in a series of environmental problems. Therefore, using fly ash to produce high value-added products is a win-win development orientation between human beings and nature. In this study, zeolite A is successfully synthesized using a hydrothermal method using fly ash. Additionally, it is at 1.0 mol·L⁻¹ of the alkali concentration that the crystallinity of zeolite A reaches the maximum value, about 96.6%. FTIR research shows that the main secondary structural unit D4R vibration band of zeolite A appears at 555 cm⁻¹. The results of the SEM study indicate the structure of zeolite A is cubic. The TEM results show that the crystal structure of the zeolite A belongs to the body-centered cubic structure. Meanwhile, the positively charged sodium ions cooperate with the silicon oxygen tetrahedron and the aluminum oxygen tetrahedron to form the zeolite A skeleton. Carbon dioxide adsorption equilibrium study shows that the maximum adsorption capacity of zeolite A of 46.5 mL·g⁻¹ is significantly higher than the maximum adsorption capacity of commercial-grade zeolite 4A of 39.3 mL·g⁻¹. In addition, the application of the Langmuir model in the adsorption of carbon dioxide by commercial-grade zeolite 4A and zeolite A is studied, which not only extends the application of zeolite A, but can be further extended to other zeolite materials as well. Meanwhile, the adsorption process belongs to the Langmuir model, which is a single layer adsorption on an ideal surface.

Core-shell Fe3O4@zeolite NaA as an Adsorbent for Cu2

Here, using Fe3O4@SiO2 as a precursor, a novel core-shell structure magnetic Cu2+ adsorbent (Fe3O4@zeolite NaA) was successfully prepared. Several methods, namely X-ray diffraction (XRD), Fourier transform infrared spectrometer (FTIR), Transmission electron microscope (TEM), Brunauer Emmett Teller (BET) and vibrating sample magnetometry (VSM) were used to characterize the adsorbent. A batch experiment was conducted to study the Cu2+ adsorption capacity of Fe3O4@zeolite NaA at different pH values, contact time, initial Cu2+ concentration and adsorbent does. It is found that the saturated adsorption capacity of Fe3O4@zeolite NaA on Cu2+ is 86.54 mg/g. The adsorption isotherm analysis shows that the adsorption process of Fe3O4@zeolite NaA to Cu2+ is more consistent with the Langmuir model, suggesting that it is a monolayer adsorption. Adsorption kinetics study found that the adsorption process of Fe3O4@zeolite NaA to Cu2+ follows the pseudo-second kinetics model, which means that the combination of Fe3O4@zeolite NaA and Cu2+ is the chemical chelating reaction. Thermodynamic analysis shows that the adsorption process of Fe3O4@zeolite NaA to Cu2+ is endothermic, with increasing entropy and spontaneous in nature. The above results show that Fe3O4@zeolite NaA is a promising Cu2+ adsorbent.

Synthesis of Zeolite 4A from Kaolin and Its Adsorption Equilibrium of Carbon Dioxide

Zeolite 4A was successfully prepared by hydrothermal synthesis using low-grade kaolin as a raw material. The properties of the synthesized zeolite 4A were characterized by means of X-ray diffraction (XRD), Fourier transform infrared (FTIR), 29Si magic-angle spinning (MAS)-nuclear magnetic resonance (NMR) and 27Al MAS-NMR, X-ray fluorescence (XRF), scanning electron microscopy (SEM)-energy-dispersive spectrometry (EDS), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET), thermogravimetry (TG)-differential thermal analysis (DTA), and carbon dioxide adsorption analysis. The textural properties of the synthesized zeolite 4A was further studied by BET analysis technique. The thermal stability analysis showed that the heat resistance of the synthesized zeolite 4A is up to 940 °C. In addition, it is found that the Langmuir model has the best agreement with the adsorption equilibrium data for carbon dioxide by synthesized zeolite 4A and commercial zeolite 4A. Meanwhile, the carbon dioxide adsorption analysis confirmed that the maximum equilibrium adsorption amount of carbon dioxide on synthesized zeolite 4A is 59.3820 mL/g, which is higher than the 55.4303 mL/g of the commercial zeolite 4A.

Selective synthesis of zeolites A and X from two industrial wastes: Crushed stone powder and aluminum ash

Crushed stone powder and aluminum ash are industrial wastes, and effective utilization of these wastes has been highly expected. Since the main components of the two wastes are Si, Al and O, those wastes can be used as starting materials for synthesis of zeolites of which some types have been commercialized as catalysts and ion-exchangers. In this study, zeolites A and X well-known as practical materials were successfully synthesized with high purity using the two industrial wastes by a mild process based on two hydrothermal treatments with intermediate acid treatment. In the first hydrothermal treatment at 150 °C, quartz in the crushed stone powder was dissolved and acid-soluble hydroxysodalite (Na₈(AlSiO₄)₆(H₂O)₂(OH)₂) with Si/Al = 1 and sodium aluminosilicate (Na₆(AlSiO₄)₆) were formed. Those compounds were dissolved with HCl aq. solution. The zeolites were successfully synthesized from the second hydrothermal treatment of the yellow dried filtrates at 80 °C in NaOH aq. solution. In the process proposed, removal of Ca from the crushed stone powder was effective to formation of zeolites A and/or X. Selective synthesis of zeolites A and X was achieved by controlling the acid treatment conditions. Furthermore, the effect of the drying condition of the filtrate obtained after the acid treatment was also investigated on the differences in the product phase.

Preparation, characterization, and performance of 4A zeolite based on opal waste rock for removal of ammonium ion

In this study, 4A zeolite was prepared from opal waste rock by hydrothermal method and applied in ammonium ion adsorption. To optimize synthesis conditions, the effect of crystallization time (1–8 h), crystallization temperature (65–115°C), Na2O/SiO2 (0.6–2.0), H2O/Na2O (20–70), and SiO2/Al2O3 (1.0–3.5) was investigated. X-ray diffraction, scanning electron microscope imaging, cation exchange capacity, static water adsorption, Fourier transform infrared spectroscopy, and N2 adsorption–desorption isotherm were used for assessing properties of 4A zeolite. Adsorption experiments were performed by 1.0 g l−1 4A zeolite with NH4+ solution (5–300 mg l−1) for 4 h at room temperature. The experiment results revealed with a crystallization time of 3 h, a crystallization temperature of 85°C, Na2O/SiO2=1.0, H2O/Na2O = 40, and SiO2/Al2O3=2.0, the 4A zeolite synthesized had excellent performance with cation exchange capacity of 2.93 mmol (g dry zeolite)−1 and static water adsorption of 22.3%. The adsorption process was described by Freundlich model (R2>0.99) and the maximum adsorption capacity could reach to 53.11 mg g−1. The experimental results provided a novel approach for the utilization of opal waste rock, which is produced during the mining of opal-rich palygorskite, and for the synthesis of 4A zeolite and the removal of ammonium ion.

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.

Controllable synthesis of (NH4)Fe2(PO4)2(OH)·2H2O using two-step route: Ultrasonic-intensified impinging stream pre-treatment followed by hydrothermal treatment

(NH₄)Fe₂(PO₄)₂(OH)·2H₂O samples with different morphology are successfully synthesized via two-step synthesis route - ultrasonic-intensified impinging stream pre-treatment followed by hydrothermal treatment (UIHT) method. The effects of the adoption of ultrasonic-intensified impinging stream pre-treatment, reagent concentration (C), pH value of solution and hydrothermal reaction time (T) on the physical and chemical properties of the synthesised (NH₄)Fe₂(PO₄)₂(OH)·2H₂O composites and FePO₄ particles were systematically investigated. Nano-seeds were firstly synthesized using the ultrasonic-intensified T-mixer and these nano-seeds were then transferred into a hydrothermal reactor, heated at 170 °C for 4 h. The obtained samples were characterized by utilising XRD, BET, TG-DTA, SEM, TEM, Mastersizer 3000 and FTIR, respectively. The experimental results have indicated that the particle size and morphology of the obtained samples are remarkably affected by the use of ultrasonic-intensified impinging stream pre-treatment, hydrothermal reaction time, reagent concentration, and pH value of solution. When such (NH₄)Fe₂(PO₄)₂(OH)·2H₂O precursor samples were transformed to FePO₄ products after sintering at 650 °C for 10 h, the SEM images have clearly shown that both the precursor and the final product still retain their monodispersed spherical microstructures with similar particle size of about 3 μm when the samples are synthesised at the optimised condition.