Specific features of the absorption of divalent manganese ions from aqueous solutions by zeolites

Sorption properties of natural zeolites from various Russia’s deposits for the Mn²⁺ ion were studied in comparison with various industrial adsorbents and some minerals. It was demonstrated that the equilibrium sorption capacity of these materials can be raised by their Na⁺-modification. The natural zeolites are advantageous at low Mn²⁺ ion concentrations over synthetic cation exchangers and activated carbons. The sorption capacity of the natural zeolites grows with increasing temperature.     

The Compatibility of Compositional and Structural Features of Aluminous Large Pore Zeolites with Sorption Characteristics

The parent NaX and KL samples were prepared by hydrothermal crystallization and their corresponding K- and Na-exchanged forms were obtained by post-synthesis modification by conventional ion-exchange technique. NaX, NaKX, KL and NaKL samples were characterized by powder XRD, IR, low temperature nitrogen adsorption and chemical analyses. Their sorption uptake behaviour has been investigated by gravimetric method. The kinetics of sorption using different sorbate probe molecules such as water, benzene and n-hexane was measured at 298 K, at P/P ₀ = 0.5 for 90 minutes. All the results obtained were discussed in terms of the compositional and structural variations of the adsorbents. Lack of high dimensionality of the pore system, less openness in structure, low average framework oxygen charge and less number of accessible nonframework cations are some of the prominent factors which has resulted in reduced hydro- and organo-philicity in LTL type zeolites as compared to X-type. The size and concentration of the accessible nonframework cations were also found to influence the sorptive properties of these aluminous large pore zeolites. Among all the probe molecules, n-hexane was found to be as a promising probe for differentiating the structural peculiarities especially dimensionality of the pore system.     

Influence of pore dimension and sorption configuration on the heat of sorption of hexane on monodimensional siliceous zeolites

Sorption of n-hexane on monodimensional pure silica SSZ-35, CIT-5, ZSM-12, and ZSM-22 zeolites with different pore dimension and on recently synthesized ITQ-29 was studied by IR spectroscopic and computational chemistry methods. Heats of sorption of n-hexane on these zeolites was determined experimentally from the temperature dependence of the intensity of IR bands of sorbed hexane as well as from theoretical calculations. Calculations have shown the different orientations of sorbed hexane molecules inside zeolite channels, which depend on the type of zeolite and loading. At high loadings, ordering of hexane inside the channels is observed due to optimization of sorbate-sorbate and sorbate-zeolite interaction energies. Such ordering is responsible for the increase of the sorption energy. A decrease of the sorption energy upon increasing the pore dimension of zeolite was observed, in agreement with results previously published in the literature. Effects of pore diameter of zeolites and ordering of molecules inside zeolite channels on the sorption energy of hexane are discussed.     

Conjugate Conversion of Methanol and Lower Alkanes C3-C4 on Zeolite-Containing Catalysts

Simultaneous conversion of methanol and lower alkanes C₃-C₄ on high-silica zeolites of ZSM-5 type of various compositions (SiO₂/Al₂O₃ 30, 50, 90) was studied. The catalytic activity of zeolite catalysts and their physicochemical properties (acidity, sorption capacity, and pore structure) were evaluated.     

Preparation of organomodified aluminosilicates for purification of biological solutions

Organomodified aluminosilicates for purification of biological solutions were prepared from a natural zeolite. The synthesis was performed by chemical deposition of chitosan on the zeolite surface followed by successive treatment with a solution of copper sulfate and a solution of potassium ferricyanide. The composition of sorbents was determined by elemental analysis. The physicochemical properties of the starting and modified zeolites were studied by the positron annihilation spectroscopy, IR spectroscopy, powder X-ray diffraction, and scanning electron microscopy, while the adsorption properties were examined by sorption of brilliant green. The adsorption behavior of the zeolites toward endotoxins was assessed. The sorbent containing the ferricyanide-chitosan complex was found to have the highest sorption capacity for lipopolyssacharides (endotoxins).     

Modification of the adsorption and catalytic properties of micro- and mesoporous materials by reactions with organometallic complexes

This review describes the work of two laboratories in the field of the modification of micro- and mesoporous molecular sieves through reactions with organometallic complexes. The modification of zeolites can occur inside the pore channels or on the external surface, depending on the size of the organometallic complex. When the modification occurs on the external surface, it results in a decrease of the pore entrance, which will lead in turn to a modification of the sorption properties of the zeolite, by decreasing the rate of the adsorption (mainly by a kinetic control). Such a material can be also used in catalysis, because the external acid sites, which are responsible for side-reactions, have been removed upon grafting. When small organometallic complexes are used, they can fill the channels and cages of the zeolite and react with internal hydroxyl groups. Due to the high acidity of zeolites, the reaction occurs very easily (for example at ?100 °C on faujasite), in contrast to what is observed on the external surface, therefore leading to high metal loadings. In that case, the modification of the sorption properties will be mainly related to a thermodynamic control. The resulting materials can be useful in catalysis, by combining the activity of the organometallic complex and properties (for example shape-selectivity) of the zeolite. Modification of mesoporous molecular sieves occurs always in the pores and results in altering of the sorption properties of the solid, by changing the interaction type between the sorbent and the sorbate. For example the sorption isotherm of alkanes is changed from type II to type III according to the IUPAC nomenclature.     

Characterization of the products obtained from alkaline conversion of tuff and metakaolin

Currently, there has been a growing interest of zeolite materials for industrial and scientific purpose. Synthetic zeolites are more often used than natural ones due to its higher purity and more uniform particle sizes. Numerous investigations are conducted in searching of inexpensive raw materials suitable for zeolite synthesis. Moreover, the temperature, pressure, times and SiO₂/Al₂O₃ ratio are the most important parameters which play key roles in the synthesis processes. Due to such a large number of factors that affect the process, zeolite synthesis has been undergoing constant development. Nowadays, researchers focus on the methods of synthesizing zeolites at ambient temperature and pressure. Metakaolin and tuff are natural raw materials which can be turned into a brand new class of synthetic zeolites. However, each requires different method of synthesis in order to obtain a material with best physical properties. This paper discusses the process of alkaline activation of synthetic zeolites from natural raw materials: volcanic tuff excavated in Filipowice and metakaolin obtained from Rominco company. Two methods: fusion and low-temperature synthesis, were used in the presented research. Moreover, the physical properties of raw materials and zeolites obtained were shown. Based on the XRD analysis, it was verified that materials after the synthesis process contained zeolites A, Na-X and faujasite-Na. Furthermore, the dehydration and thermal decomposition phenomena of the tuff and metakaolin before and after the synthesis process were determined by coupled TG/MS techniques.     

Template method for the synthesis of a heterogeneous fenton catalyst based on the hierarchical zeolite FeZSM-5

Zeolite h-FeZSM-5 with a hierarchical micro/macropore system has been synthesized in the presence of a template based on the close-packed polystyrene (PS) spheres, and the conventional zeolite FeZSM-5 has been obtained in the absence of a PS template. The zeolites have been characterized by X-ray diffraction, scanning and high-resolution transmission electron microscopy, and N₂ sorption. The macropore walls of the hierarchical zeolite consist of ZSM-5 nanocrystals and amorphous globules of silica. Compared to the conventional zeolite, the hierarchical one has a high BET and external surface areas of 245 and 472 m²/g, respectively, and a high pore volume of 0.6 cm³/g. The catalytic properties of the Fe-containing zeolites were studied in the H₂O₂ decomposition reaction in the absence and in the presence of EDTA ligands and in the oxidation of low- and high-molecular-weight organic compounds by hydrogen peroxide at 25°C. Hierarchical zeolite h-FeZSM-5 is highly efficient in the oxidation of large molecules.     

Thermochemical study of sorption of pyridine derivates by copper forms of synthetic and natural zeolites

Sorption of hazardous pyridine derivates by copper forms of synthetic zeolite ZSM5 and natural zeolite of the clinoptilolite type (CT) has been investigated. Sorption of 2-chloropyridine (clpy) and 2-ethylpyridine (ethylpy) from liquid and gas phase by copper forms of zeolites (Cu-ZSM5 and Cu-CT) has been studied by CHN analysis, thermal (TG, DTG and DTA) analysis, FTIR spectroscopy, X-ray powder diffractometry and determination of the surface areas and the pore volumes by low-temperature adsorption of nitrogen. The results of thermal analyses of Cu-ZSM5, Cu-(clpy) _x -ZSM5, Cu-(ethylpy) _x -ZSM5, Cu-CT, Cu-(clpy) _x -CT and Cu-(ethylpy) _x -CT zeolitic products with different composition (x depends on the experimental conditions of sorption of pyridine derivates) clearly confirmed their different thermal properties and the sorption of pyridine derivates. The main part of the decomposition process of zeolitic samples containing pyridine derivates occurs at considerably higher temperatures than the boiling point of pyridine derivates proving strong bond and irreversibility of clpy- and/or ethylpy–zeolite interaction. FTIR spectra showed well-resolved bands for pyridine derivates in the Cu-(clpy) _x -zeolite and Cu-(ethylpy) _x -zeolite. Surface area and pore volumes of the samples Cu-clpy-ZSM5, Cu-ethylpy-ZSM5, Cu-clpy-CT and Cu-ethylpy-CT in comparison with Cu-ZSM5 and Cu-CT decreased due to the adsorption of pyridine derivates.     

Adsorption of molecular hydrogen on aluminophosphate zeolites at 77 K

The H₂ sorption properties of the aluminophosphate zeolites AlPO-5, AlPO-31, AlPO-11, AlPO-36, and AlPO-8 at 77 K have been investigated. A series of H₂ adsorption isotherms has been obtained for cylindrical micropore channels in the aluminophosphate zeolites. The absolute values of the amount adsorbed α(P) for the mesoporous aluminophosphate materials and the effective density of adsorbed H₂ in the micropore space β*(P, d) have been determined. It has been demonstrated experimentally that the sorbate density depends on the size of the micropore channel of the zeolite d. Hydrogen sorption isotherms have been calculated from experimental isotherms. A procedure allowing β*(P, d) to be estimated for intermediate d values is presented.     

Arsenic sorption by modified clinoptilolite–heulandite rich tuffs

Recent works show that modified natural zeolites improve the remotion of anionic or non-polar organic pollutants from water. In this work the arsenic sorption from aqueous solutions onto clinoptilolite–heulandite rich tuffs modified with lanthanum, hexadecyltrimethylammonium or iron was investigated considering the arsenic chemical species and the pH of the arsenic solutions. Clinoptilolite–heulandite rich tuffs were characterized by scanning electron microscopy and X-ray diffraction analysis. The elemental composition of the zeolitic samples was also determined. According to the Langmuir isotherm model the arsenic (V) sorption capacity of the zeolites was 75.4 μg As/g at pH 3, 3.9 μg As/g at pH 5 and 53.6 μg As/g at pH 6, for the lanthanum, HDTMA and iron modified clinoptilolite–heulandite rich tuff from Chihuahua (México), respectively. In general, the results suggested that the arsenic retention depends on the precedence of zeolitic material, the nature of arsenic chemical species, pH as well as the characteristics of modified natural zeolites. In this work the arsenic adsorption mechanisms are also discussed.     

Sorption and diffusion of VOCs in DAY zeolite and silicalite-filled PDMS membranes

The sorption and diffusion properties of ethanol, 1,1,1-trichloroethane (TCA) and trichloroethylene (TCE) were determined in silicalite-filled and dealuminized-Y-zeolite (DAY)-filled poly[dimethylsiloxane] (PDMS) membranes at 25, 100 and 150°C. Zeolite filling results in increased solubility coefficients (S) for polar solvents like ethanol over pure PDMS. No significant increase in S is observed in case of TCA and TCE which act as good solvents for PDMS. However, at higher temperatures, the sorption is higher in zeolite-filled membranes even for the good solvents. The VOC diffusivity decreases with increasing degree of zeolite filling because of higher characteristic diffusion time in zeolites (for ethanol) and increasing tortuosity of the diffusion path (for TCA). Due to the presence of carbon=carbon double bond, TCE exhibits marginal diffusivity drop in zeolite-filled membranes. The specific zeolite-polymer interactions, that is, tendency of zeolite pore blocking by polymer chains or the formation of voids on zeolite-polymer interface are influenced by the zeolite pore size and type of VOC permeating through the composite membrane. The variation in experimentally observed ethanol permeability due to zeolite filling could be qualitatively estimated from the sorption-diffusion data.     

PIGE and PIXE analyses of pentasil type boroaluminosilicates

The elemental composition of various synthetic crystalline sodium-boroaluminosilicates, especially the Al content and the silicon to aluminium bulk ratio, were determined by means of the combination of PIGE (Proton-Induced Gamma-Ray Emission Spectrometry) and PIXE (Proton-Induced X-Ray Emission Spectrometry). Light elements (B, O, Na, Al) were determined by means of gamma-ray emission. Proton-induced X-ray emission provided information on heavy elements present down to impurities. The Si/Al ratios, which mainly determine the catalytic and adsorptive properties of the zeolites, are compared with those obtained with other methods (EPMA, H₂O sorption capacity) and show good agreement.     

苯在酸碱处理多级孔Y分子筛上的吸附及传质行为

利用H_4EDTA-NaOH共处理的方法制备了具有不同孔径分布的多级微-介孔NaY分子筛。运用XRD、N_2吸附、SEM、TEM对其结构进行了表征。采用频率响应(FR)和智能重量分析仪(IGA)技术研究了苯在改性后的多级孔NaY分子筛及微孔NaY分子筛上的吸附和传质性能。结果表明,适当的酸碱处理不会改变分子筛的晶体结构,但可调变NaY分子筛的精细结构;介孔的引入降低了分子在孔道中的扩散阻力,较大的孔径和较好的孔道贯通性有利于扩散和吸附中心的可接近性;对于微孔NaY分子筛,苯在分子筛上的吸附过程为其传质过程的速控步骤,对于酸碱处理的多级孔NaY分子筛,分子筛颗粒中微/介孔内的扩散过程及分子筛微-介孔孔道间的分子交换过程是传质过程的速控步骤。     

Effect of the acidic treatment on the adsorption and structural properties of the natural mineral sorbent M45C20

Adsorption and structural properties of the initial natural mineral sorbent M₄₅C₂₀ and the sorbent treated with 2.33 M H₂SO₄ were studied. The sorbent mainly consists of montmorillonite and clinoptilolite. Aluminum, calcium, magnesium, sodium, and potassium ions are removed from the structure under the action of the acid. The specific surface, porosity of the sorbent, and pore size increase during this process. The sorption of ammonium ions in the natural samples predominantly follows the ion-exchange mechanism (exchange to calcium, magnesium, sodium, and potassium ions). The acid treatment changes the composition of the cation-exchange complex and results in an increase in the sorption capacity to ammonium ions by a factor of ??1.3.     

Porous structure of natural and modified clinoptilolites

The evaluation of the pore-size distribution (PSD) of natural and modified mesoporous zeolites, i.e., clinoptilolites is presented. We demonstrate the SEM results showing that the pores of fracture-type from 25-50 nm to 100 nm in size between clinoptilolite grains, as well as pores between crystal aggregates up to 500 nm in size are present in the studied material. The detailed distribution of pore sizes and tortuosity factor of the above-mentioned materials are determined from the adsorption-desorption isotherms of nitrogen measured volumetrically at 77 K. To obtain the reliable pore size distribution (PSD) of the above-mentioned materials both adsorption and desorption branches of the experimental hysteresis loop are described simultaneously by recently developed corrugated pore structure model (CPSM) of Androutsopoulos and Salmas. Evaluated pore size distributions are characterized by well-defined smooth peaks placed in the region of the mesoporosity. Moreover, the mean pore diameter calculated from the classical static measurement of nitrogen adsorption at 77 K correspond very well to the pore diameters from SEM, showing the applicability of the CPSM for characterization of the porosity of natural zeolites. We conclude that classical static adsorption measurements combined with the proper modeling of the capillary condensation/evaporation phenomena are a powerful method which can be applied for pore structure characterization of natural and modified clinoptilolites.     

Effect of zeolite pore morphology on solvent-less alkylation of benzene with 1-hexene

In an attempt to convert the carcinogenic benzene which is almost restricted for its use in gasoline, alkylation reaction with olefin 1-hexene has been conducted on various zeolites. Four zeolites having different pore topology and pore size have been applied as solid acid catalysts for effective production of alkylate in a liquid phase, solvent-less low temperature reaction. The textural properties of all the four zeolites (ZSM-5, MOR, BEA, HY) have been characterized for crystal morphology by TEM, crystal structure by XRD and FTIR, BET for surface area, N₂ sorption for porosity and TPD for acidity. Among the zeolite, BEA possessed high surface area (600.61 m²/g) and enhanced meso pores volume (0.3956 cm³/g) as compared to other zeolite samples. The performance of BEA was also observed to be superior in the liquid phase alkylation of benzene with 1-hexene in a batch reactor under autogenous pressure without using any solvent. At the optimum reaction conditions, the benzene conversion was 86.6 wt% and 3-Phenylhexane, 2-Phenylhexane yield were about 47.9 wt% and 38.7 wt% respectively on this catalyst. The BEA also exhibited longer time-on-stream and reusability performance, thus offers an attractive route for converting benzene into valuable (3-Phenylhexane, 2-Phenylhexane) alkylate product useful for the manufacturing of fine chemicals, dyestuff, detergents and scents.     

Dihydrogen adsorption isotherms (77 K) on carbon nanomaterials

Dihydrogen adsorption at 77 K on a number of fine-particle carbon materials, activated carbons, and carbon nanotubes has been investigated. The micropore structure parameters of these materials have been determined using a volumetric comparative method and nonlocal density functional theory (NLDFT). These data processing methods lead to different values of textural parameters. This difference is attributed to the presence of specific sorption sites on the surface of real carbon materials. The pore size range in which the NLDFT method is applicable to the C-H₂ system has been determined. A comparison between the hydrogen sorption properties of different carbon nanotubes is presented.     

Photoluminescence properties of Ag2S semiconductor clusters synthesized in micropores and mesopores

Silver sulfide (Ag₂S) clusters were synthesized in microporous zeolites and mesoporous AlMCM-41 by the sulfurization of Ag⁺ ions exchanged within the pores of the host. Characterization was performed by means of XRD, UV-Vis Ag K-edge XAFS and photoluminescence. The pore size of the host has great effects on the photoluminescence properties. Ag₂S/AlMCM-41 showed photoluminescence at the longer wavelengths than Ag₂S/zeolites. The photoluminescence band of Ag₂S in the zeolite with 1-dimensional channels was narrow in comparison to the Ag₂S in zeolites with 2- or 3-dimensional channels.     

Properties of polyamide 6 and thermoplastic polyurethane blends containing modified montmorillonites

In this paper are reported some experimental data related to the influence of preparation regimes and characteristics of exfoliated graphite based sorbents produced by thermal expansion of H₂SO₄-graphite intercalation compounds (H₂SO₄-GICs) on their sorption properties. Investigations involving X-ray diffraction analyses, surface area, bulk density and oil sorption capacity measurements, have been performed. Sorption capacity was discussed as a function of bulk density, total pore volume and surface area. Some empirical correlation between studied characteristics of exfoliated graphite have been found. The differences among the obtained samples, as a consequence of synthesis conditions, were also put in evidence by thermal analysis (TG, DTG and DTA) performed after their exposure to oil sorption.It was found that thermal analysis method could provide information about the exfoliated graphite pore system related to the sorbed oil oxidation rate. The capacity for oil uptake was also discussed in the case of graphite oxide soot.