Phase-pure Zeolite Research Articles

Właściwości i zastosowanie gruzińskiego naturalnego filipsytu

Oceanic and terrestrial sedimentary phillipsites make up very large reserves, but the use of this natural zeolite is not so wide comparing to clinoptilolite, and purpose of our study was to characterize the phillipsites of the Georgian deposits and highlight their possible application. It is shown that natural phillipsite can be used as a raw material for the synthesis of phase-pure zeolite NaX with Si/Al~1.5-1.7 in the form of octahedral crystallites with uniform micrometric (2-7 μm) dimensions, characterized by high specific surface area (590-770 m2/g) and volume of pores (0.58 cm3/g) including uniform zeolitic micropores and channels with an average diameter of 55 nm, which opens up the prospect of its use in catalysis. It has been established that natural phillipsite is a suitable carrier of bioactive metals: silver-, copper-, and zinc-containing micro-mesoporous materials have been prepared using ion-exchange reactions between zeolite and a salt of a transition metal; the products contain up to 235 mg/g of silver, 85 mg/g of copper, and 87 mg/g of zinc, and in the Kirby-Bauer disk-diffusion test show strong bacteriostatic activity against such microorganisms as gram-negative bacterium Escherichia coli, gram-positive bacteria Staphylococcus aureus and Bacillus subtilis, fungal pathogenic yeast Candida albicans and a fungus Aspergilus niger. The use of bactericidal materials obtained on the basis of natural phillipsite is possible both for water purification and disinfection, and as fillers in the production of polymeric materials, paper and cardboard.

Disclosing the enhanced NH3-SCR-DeNOx activity of Cu-containing zeolite Y prepared with 15-Crown-5

The phase-pure zeolite Y with a high n(Si)/n(Al) ratio is obtained with the cyclic polyether 15-Crown-5 as a structure-directing agent. In copper-exchanged for this new zeolite outperformed other Cu-containing zeolite Y counterparts during NH3-SCR-DeNOx with more than 80% NO conversion and more than 85% N2 selectivity in the temperature range of 100 – 500 °C. The presence of Cu+ species located in sodalite cages with elevated redox cyclability guarantees high activity and N2 selectivity up to 400 °C over CuY-Crown. Above 400 °C, a high activity and N2 selectivity are related to the accessibility of chemisorbed NH3 to the gaseous NO during the NH3-SCR-DeNOx.

Synthesis and characterisation of pure zeolite A from fly ash for removal of lead and cadmium

ABSTRACT The primary objective of the present study is synthesis a highly crystalline zeolite A of pure phase using fly ash obtained from a thermal power station located in South India. The mineral composition of fly ash promotes the synthesis of zeolites, which are subsequently used in the treatment of wastewater. The composition of fly ash namely SiO2, Al2O3, and Na2O are enhanced to 88.01% through pre-treatment of original fly ash using HCl of 20% wt. and solid/liquid ratio of 20 during zeolite synthesis. The pre-treated fly ash was effectively converted to zeolite A by adjusting varying synthesis parameters including silica/alumina (Si/Al) ratio (0.8–1.2), hydrothermal synthesis time (3–12 h), and sodium hydroxide to fly ash (NaOH/FA) ratio (0.64–1.2). The fusion-assisted hydrothermal synthesis technique was employed to successfully transform fly ash into a pure phase zeolite A with a crystallinity of 95.01% by optimising the synthesis parameters. X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), Burner-Emmett -Teller (BET), and Fourier transform infrared spectroscopy (FTIR) methods were used for characterisation of synthetic zeolite samples. The findings unveiled a single-phase zeolite A with an excellent cation exchange capacity (CEC) of 218.66 meq/g and a high BET surface area of 108.59 m2/g. The efficacy of zeolite A towards heavy metal removal was investigated using Pb+2 and Cd+2 ions through batch experiments. The adsorption of Pb+2 and Cd+2 obeyed pseudo-second-order kinetics and the Langmuir model was found to provide a better description of adsorption isotherm. Synthetic zeolite A exhibited remarkable removal capacities of 277.78 mg/g and 87.729 mg/g for lead and cadmium, respectively. The experimental findings of the present study showcased the conversion of fly ash into a potent zeolite material with significant potential for the remediation of heavy metal-contaminated wastewater.

Utilization of electrolytic manganese residue to synthesize zeolite A and zeolite X for Mn ions adsorption

Extensive research is being carried out to efficiently utilize electrolytic manganese residue (EMR) and convert it into useful materials. In this paper, phase pure zeolite A (ZA) and zeolite X (ZX) were synthesized by EMR for the first time. The EMR-based zeolites were characterized by XRD, TG, SEM and BET, and their zero point charges were tested. Then, the adsorption capacities of ZA and ZX on Mn ions were studied. On the adsorbent concentration = 3.0 g/L and C0 = 439 mg/L, the adsorption capacities of ZA and ZX on Mn ion were 119.5 and 96.7 mg/g, respectively. In addition, the adsorption kinetics and isotherms of the adsorption process were discussed, and the adsorption mechanism was clarified by means of XRD, FTIR, SEM, and XPS. The appearance of Mn-O functional groups indicated that Mn ions did enter the binding sites of zeolites. Moreover, ZA and ZX were successfully regenerated in this work. Furthermore, the influence of coexisting cations was explored, and the maximum adsorption capacities of ZA and ZX were compared with other adsorbents, which proved the excellent adsorption of Mn ions by ZA and ZX. In conclusion, the synthesized ZA and ZX were low-cost adsorption materials with high adsorption capacity.

Preparation of Zeolite 4A for Adsorptive Removal of Methylene Blue: Optimization, Kinetics, Isotherm, and Mechanism Study

In this study, we have reported a facile preparation of zeolite 4A from Ethiopia kaolin for the adsorptive removal of methylene blue (MB) dye. The formation of highly crystalline and pure phase zeolite 4A with cubic morphology was confirmed by powder X-ray diffraction (XRD) and scanning electron microscope (SEM) analysis. The efficiency of zeolite 4A for abatement of MB was investigated at varying adsorption parameters. Response surface methodology coupled with Box Behnken Design (RSM-BBD) was employed to optimize adsorption parameters. High regression (R2 = 0.9947) and the low probability (p value <0.0001) values signify the validity of the quadratic model to predict the removal (%) of MB. The maximum MB removal (%) was 99.37% at the optimum combination of 50 mL of 10 mg/L of MB, 39.05 mg zeolite 4A, and 179.82 contact time (min). The adjusted R-square (R2adj) and standard deviations (SD) were validated the best fitting of pseudo-second-order kinetics and the Langmuir isotherm model for experimental values. The maximum adsorption capacity (Qmax) of zeolite 4A towards MB was found to be 44.35 mg g−1. Electrostatic interaction, hydrogen bond, and n to π bond formation are predicted to be the plausible interaction mechanism of MB to the surface of zeolite 4A. The Fukui function and vibration analysis based on the density functional theory (DFT) further strengthened the proposed mechanism.

INVESTIGATIONS ON HYDROTHERMAL SYNTHESIS PARAMETERS IN PREPARATION OF ZEOLITE W

Zeolite W crystals were synthesized via hydrothermal process, the influence of crystallization time, aging time and temperature, the molar ratios Al2O3/SiO2 and K2O/SiO2 on the crystalline final products were studied. The results revealed that well-developed twin-ball shaped morphology zeolite W crystals were obtained after 6 h of crystallization, the longer crystallization time would not result in substantial changes in crystal morphology and size of end products. However, the crystals transferred from twin-ball to bouquet-like in shape with increasing aging time, while the high aging temperature resulted in zeolite F developed. Also, the Al2O3/SiO2 and K2O/SiO2 molar ratios of the hydrogel had major influences on synthesis of pure form zeolite W. Well-crystallized pure phase zeolite W products were obtained with Al2O3/SiO2=0.20, which were composed of many square pillars crystals, with average width in the range of 0.2–0.5 μm and length approximately 10 μm. Mild alkalinity circumstance was in favor of zeolite W crystallization, when the K2O/SiO2 molar ratio was increased to 9.42, the product obtained was pure phase of zeolite LTJ.

Synthesis and characterization of pure phase zeolite 4A from coal fly ash

This study was aimed at the synthesis of pure phase zeolite 4A from coal fly ash sourced from Nishat power plant in the Punjab province of Pakistan. Analysis of fly ash (FA) demonstrated that it can be used to produce low silicate type zeolites specifically zeolite 4A due to its Si/Al molar ratio of ∼2. The current investigation emphasized on the addition of induction time (before and after crystallization) to the fly ash extract of Si-Al-Na species that was extracted from fly ash. The induction time helped in catalysing primary and secondary gel formation during the synthesis leading to controlled formation of single phase with high crystallinity and small crystallite size. The physiochemical investigations of synthetic zeolite 4A by using various analytical techniques made the proposed process justified on comparison with commercial zeolite 4A. The X-Ray Diffraction (XRD) analysis for synthesize zeolite 4A confirmed only one crystallographic phase and small crystallite size with 82% crystallinity compared to reference zeolite with 75% crystallinity. Fourier-Transform Infrared spectroscopy (FTIR) spectra revealed the structural aspects of synthesis and reference zeolite by indicating the presence of identical structural units with same height and width of peaks. Morphological analysis by Scanning Electron Microscope (SEM) showed a well-defined cubic shape of synthesis zeolitic crystals. Surface area analyses by Brunauer–Emmett–Teller (BET) showed that synthesized zeolite possessed 122 m2/g surface area that is 3 times higher than reference zeolite of 36.3 m2/g. The synthesized zeolite was also found to have smaller particle size than reference zeolite. Thermal stability comparison of both zeolites was studied by non-isothermal Thermo Gravimetric Analysis-Differential Thermal Analysis (TGA-DTA) thermograms from 25 to 800 °C temperature and both the samples were found to be stable at 800 °C.

Synthesis and characterization of zeolite NaX from Bangka Belitung Kaolin as alternative precursor

The potential use of kaolin as silica and alumina precursor for the synthesis of zeolite NaX was investigated in this study. The synthesis involved three steps of reactions; the preparation of seed gel, the formation of feedstock gel using kaolin and the combination of overall gel followed by hydrothermal treatment at 105°C for 12 hours. Analysis using X-ray Diffraction (XRD) method indicated the transformation of kaolin into pure phase zeolite NaX with a small amount of kaolin was still visible. Detail microscopic analysis showed the morphology of zeolite X consisted of octahedral particles with a crystallite diameter of 20-30 µm. Analysis of surface acidity using pyridine as probe molecule indicated the zeolite X has high Brǿnsted acidity with 0.181 mmol/g of acid sites, significantly higher than Lewis acidity ~0.053 mmol/g. The N2 adsorption-desorption measurement indicated a type IV material with both microporous and mesoporous structures with an average pore size of 1.47 nm for micropore and 3.41 nm for mesoporous.

Synthesis of zeolites Na-A and Na-X from tablet compressed and calcinated coal fly ash.

Zeolites Na-A and Na-X are important synthetic zeolites widely used for separation and adsorption in industry. It is of great significance to develop energy-efficient routines that can synthesize zeolites Na-A and Na-X from low-cost raw materials. Coal fly ash (CFA) is the major residue from the combustion of coal and biomass containing more than 85% SiO2 and Al2O3, which can readily replace the conventionally used sodium silicate and aluminate for zeolite synthesis. We used Na2CO3 to replace the expensive NaOH used for the calcination of CFA and showed that tablet compression can enhance the contact with Na2CO3 for the activation of CFA through calcination for the synthesis of zeolites Na-A and Na-X under mild conditions. We optimized the control variables for zeolite synthesis and showed that phase-pure zeolite Na-A can be synthesized with CFA at reactant molar ratio, hydrothermal reaction temperature and reaction time of 1.3Na2O: 0.6Al2O3: 1SiO2: 38H2O at 80°C for 6 h, respectively, while phase-pure zeolite Na-X can be synthesized at 2.2Na2O: 0.2Al2O3: 1SiO2: 88H2O at 100°C for 8 h, respectively. The composition, morphology, specific surface area, vibration spectrum and thermogravimetry of synthesized Na-A and Na-X were further characterized.

Synthesis of Phase-Pure Zeolite Sodalite from Clear Solution Extracted from Coal Fly Ash

The formation of zeolite sodalite (SOD) as a by-product in the synthesis of zeolite X from clear solution extracted from fused South African coal fly ash has recently been studied. However, the present study shows that zeolite X as well as zeolite A should be seen as intermediate structures and that phase-pure sodalite can be obtained by increasing crystallization time and temperature. To investigate the transition from zeolites A and X into SOD, the crystallization was conducted at 70, 80, and 90°C for different times. In addition to structural and chemical analyses by XRD and ICP, respectively, a detailed morphological characterization of the synthesis products by scanning electron microscopy (SEM) was undertaken in order to investigate the effect of the crystallization conditions on different crystal morphologies of zeolite SOD.

Seeding-free synthesis of zeolite FAU membrane for seawater desalination by pervaporation

In this study, dense and phase-pure zeolite FAU membrane has been prepared on α-Al2O3 tube using a seeding-free synthesis strategy. 3-aminopropyltriethoxysilane (APTES) acts as a molecular linker for anchoring the FAU precursors onto the support surface to promote the nucleation and the formation of a thin, well intergrown zeolite FAU membrane. The obtained membranes are employed for desalination of seawater by pervaporation. With the increase of the synthesis time from 12 h to 24 h at 75 °C, the water fluxes of the zeolite FAU membranes reduce from 4.22 kg m−2 h−1 to 3.42 kg m−2 h−1 at 75 °C due to the increase of the thickness of the zeolite FAU membranes, while the ions rejections increase from 99% to 99.9%. For the zeolite FAU membrane which was prepared at 75 °C for 20 h, with increasing the feed temperature from 30 °C to 90 °C, the water fluxes increase from 0.96 kg m−2 h−1 to 5.64 kg m−2 h−1, and all the ions rejections of the zeolite FAU membrane are above 99.8%. Note that the zeolite FAU membranes show high separation performances for seawater desalination, even for desalination of 10 wt% seawater, the developed zeolite FAU membranes are very promising in seawater desalination.

Static in-situ hydrothermal synthesis of small pore zeolite SSZ-16 (AFX) using heated and pre-aged synthesis mixtures

The conditions of static in-situ hydrothermal synthesis were optimized to prepare crystalline, pure phase and template-free small pore zeolite SSZ-16 (AFX) particles. The type of silica source and prolonged ageing process at an elevated temperature were decisive in obtaining pure phase zeolite SSZ-16 particles under static conditions and conventional heating. Colloidal and fumed silica-based synthesis mixtures were successful in forming the zeolite SSZ-16. The zeolite particle size was reduced from 46 to 5 μm when the fumed silica was replaced by colloidal silica. Uniform, fine-grained and fully crystalline zeolite SSZ-16 particles were synthesized only from the colloidal silica-based mixtures that were aged at 80 °C for 7 days. The elevated temperature of the ageing stage is supposed to promote nucleation of viable nuclei leading to the reduction of the induction period. The two cycle calcination procedure with maximal temperature of 550 °C, ensured the removal of template molecules from the bulk phase of zeolite SSZ-16 particles. Carbonaceous residua were observed in zeolite subsurface region and mainly in the core shell morphology of zeolite SSZ-16 particles. The phase purity of zeolite SSZ-16 particles was checked by XRD and sorption properties were determined by N2 adsorption at −196 °C. Zeolite SSZ-16 particles showed the micropore volume of 0.24 cm3/g and BET surface area of 496 m2/g.

Synthesis of zeolite A from coal fly ash using ultrasonic treatment – A replacement for fusion step

The synthesis of zeolites from fly ash has become an increasingly promising remedy to the crisis of coal fly ash production and disposal in South Africa. In recent studies, South African fly ash was proven to be a suitable feedstock for the synthesis of essential industrially used zeolite A. However, the process involves a costly energy intensive step whereby fly ash is fused at high temperatures, which may make the process economically unattractive on a large scale. The aim of this study is to investigate the possibility of replacing high temperature fusion with less energy intensive sonochemical treatment for the synthesis of zeolite A. Sonochemical treatment was first thought possible due to the violent cavitation caused by high intensity sonication. The results of the study showed that fusion can be replaced by 10min of high intensity sonication. The incorporation of sonication also consequently reduced the crystallization temperature of the process making it possible to synthesize a pure phase zeolite A at lower temperatures and reduced times. This study effectively developed a novel process to replace the energy intensive fusion step with a short, easy and inexpensive treatment. Scale up of this synthesis approach may proffer a promising alternative option to the anticipated energy demand of the synthesis of fly ash-based zeolite with fusion method.

Facile synthesis of zeolite FAU molecular sieve membranes on bio-adhesive polydopamine modified Al2O3 tubes

A seeding-free synthesis strategy was developed for the preparation of dense and phase-pure zeolite FAU membranes through mussel-inspired polydopamine (PDA) modification of porous Al2O3 tubes. Zeolite FAU nutrients can be attracted and bound to the support surface via the formation of strong non-covalent and covalent chemical bonds, thus promoting the nucleation and growth of uniform, well-intergrown and phase-pure zeolite FAU membranes. The SEM and XRD characterizations demonstrate that a relative thin but dense and pure-phase zeolite FAU membrane with a thickness of about 2.3µm can be obtained on the PDA-modified Al2O3 tube after crystallization at 75°C for 24h, and no visible cracks, pinholes or other defects are observed on the membrane layer. The zeolite FAU membrane prepared at 75°C for 24h was evaluated in single gas permeation and mixed gas separation. For binary mixtures at 50°C and 1bar, the mixture separation factors of H2/CH4 and H2/C3H8 are 9.9 and 127.7, respectively, which are much higher than the corresponding Knudsen coefficients. And relative high H2 permeance of about 1.9×10−7molm−2s−1Pa−1 can be obtained through the FAU membrane due to the thin layer and the relative wide pore size of 0.74nm, demonstrating a viable direction for promising application of FAU membranes in hydrogen purification and separation.

Encapsulation of a fragrance molecule in zeolite X

Nanotechnological approach has recently been introduced into fragrance applications. One of these strategies involves encapsulation of fragrances in zeolites to tailor products with controlled release properties. In this study, encapsulation/release of a fragrance molecule, triplal, has been studied using zeolite X as a fragrance carrier. Two phase-pure zeolite X products with different average particle diameters 20 μm and 4 μm were synthesized hydrothermally. The desorption kinetics of triplal in these two different zeolite X products was investigated to determine the effect of the particle size on the desorption process. The first order three-stage kinetics model results indicated that larger crystals had slightly lower desorption rate constants.

Development of a hybrid membrane through coupling of high selectivity zeolite T on ZIF-8 intermediate layer and its performance in carbon dioxide and methane gas separation

This work demonstrated a novel hybrid membrane development through coupling of zeolite T membrane on ZIF-8 intermediate layer. ZIF-8 which acted as an intermediate layer was firstly grown on a macroporous α-alumina support via vacuum seeding. Pure phase zeolite T membrane was then synthesized on ZIF-8 which was pre-grown on the α-alumina support. Single gas permeation of standing free zeolite T membrane showed a CO2/CH4 selectivity of 68 with CO2 and CH4 gas permeances of 6.08×10−8 and 0.09×10−8mol/m2.s.Pa, respectively. On the other hand, the CO2/CH4 selectivity of the hybrid membrane was 3 folds as compared to standing free zeolite T membrane, giving the highest CO2/CH4 selectivity of 182 and the CO2 and CH4 gas permeances of 5.46×10−8 and 0.030×10−8mol/m2.s.Pa, respectively. Both gas permeances of CO2 and CH4 increased with increasing feed pressure from 1 to 4bar with a slight decrease in the selectivity observed at the feed pressure of 4bar. While for the effect under increasing temperature, CO2 showed an increasing trend of its gas permeability from 5.46×10−8 to 6.12×10−8mol/m2.s.Pa while CH4 gas permeability increased slightly from 0.03×10−8 to 0.042×10−8mol/m2.s.Pa due to greater mobility of gas molecules promoted by higher temperature.

Synthesis of Zeolite A from Natural Ca-Bentonite Using a Direct Alkali Hydrothermal Approach

Ca-bentonite can be converted into zeolite A via hydrothermal alkaline treatment by varying the synthetic parameters. This paper focuses on the effects of SiO2/Al2O3 molar ratio, Na2O/SiO2 molar ratio, reaction temperature, reaction time on the synthesis of zeolite A. Phase-pure zeolite A was synthesised under optimum conditions of 3Na2O:0.25Al2O3:1SiO2:150H2O by heated at 90°C for 12 h, whose shape and average crystal sizes are the cube of 1∼3 μm by the SEM micrograph. Compared with chemical synthesis method, one-step alkali fusion method has the advantages of low cost, simple operation, short time etc, which are worthy of further consideration in industrialization.

Iso-butanol dehydration by pervaporation using zeolite LTA membranes prepared on 3-aminopropyltriethoxysilane-modified alumina tubes

Dense and phase-pure zeolite LTA membranes were hydrothermally synthesized on 3-aminopropyltriethoxysilane (APTES)-modified macroporous Al2O3 tubes without seeding. Pervaporation experiments were conducted for the separation of liquid water/iso-butanol and water/ethanol mixtures to evaluate the separation performances of the zeolite LTA membranes. A water flux of 4.5kg/m2h is obtained at 100°C for the separation of a 95.0wt% iso-butanol/5.0wt% water mixture, and the separation factors of water/iso-butanol are found to be about 3000 for all temperatures and concentrations studied.

Covalent synthesis of dense zeolite LTA membranes on various 3-chloropropyltrimethoxysilane functionalized supports

A seeding-free synthesis strategy was developed for the preparation of dense and phase-pure zeolite LTA membranes on 3-chloropropyltrimethoxysilane (CPTMS) functionalized supports. Through the functionalization of supports by using CPTMS, the nucleation and growth of a thin, well intergrown zeolite LTA membrane could be promoted on various porous supports such as Al2O3 disks and tubes, and TiO2 disks, as well as on dense supports such as stainless steel, PTFE, and glass disks. The SEM and XRD characterizations indicate that a relative thin but dense and phase-pure zeolite LTA membrane with a thickness of about 3.0μm can be formed on the porous Al2O3 and TiO2 disks by crystallization at 60°C for 24h, and no cracks, pinholes or other defects were observed in the membrane layer. The zeolite LTA membranes prepared on CPTMS-functionalized Al2O3 disks were evaluated in single gas permeation and mixed gas separation. It is found that the zeolite LTA membranes prepared on CPTMS-modified Al2O3 disks show molecular sieving in gas separation. For binary mixtures at 20°C and 1bar, the mixed gas separation factors of H2/CO2, H2/N2, H2/CH4, H2/C3H8 and H2/C3H6, are found to be 7.4, 6.8, 5.2, 15.3 and 36.8, which are higher than the corresponding Knudsen coefficients.

Synthesis and Properties of Zeolites from Autoclaved Aerated Concrete (AAC) Waste

AbstractSyntheses routes for the conversion of autoclaved aerated concrete (AAC) waste into aluminosilicate zeolites like LTA and related phases were developed. The procedures always started with leaching steps of the pure AAC waste by combinations of strong alkaline (NaOH) and mild acid (citric acid) treatments, before the real crystallization process was performed separately under addition of sodium aluminate. All products were characterized by X‐ray powder diffraction (XRD), scanning electron microscopy (SEM) combined with energy dispersive X‐ray analysis (EDX‐analysis) and Fourier‐transform infrared spectroscopy (FTIR). Zeolites LTA and related phases basic sodalite (SOD), hydrosodalite (SOD), cancrinite (CAN) and an intermediate phase between SOD and CAN were observed. Depending on the preparation route tailor made synthesis of pure phase zeolite LTA with crystal sizes up to 5 μm was worked out. In addition to syntheses procedures important properties of the zeolites were discussed with respect to the treatment procedure of AAC. It is shown, that the special synthesis pathway is not only responsible for the product composition and formation of a certain structure type but also exhibits a strong influence on the crystallinity, crystal size, and morphology. The water sorption capacity and the hydrothermal stability of the products were selected for those further investigations. Whereas adequate water sorption capacity up to 272 mg·g–1 were measured for zeolites LTA obtained from two different reaction routes, limited hydrothermal stabilities were revealed for other products. Under the conditions of strong hydrothermal treatment at a temperature of 473 K for 72 h, a more or less extended phase transformation into ANA‐Type zeolites occurred. This process was least extensive for pure phase zeolite LTA obtained from the alkaline solution of AAC leaching.