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Synthesis, optimization and characterization of zeolite A and its ion-exchange properties

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Abstract

Zeolite A was synthesized from fumed silica and sodium aluminate precursors. The optimum conditions for synthesis of zeolite A were studied to obtain a high ion-exchange capacity and an affinity for heavy metal ions. The findings revealed that the optimum conditions for synthesis of zeolite A were SiO2:Al2O3:H2O:Na2O molar ratios = 1:0.83:150:1.15 at 110 °C with 4 days crystallization time. As synthesized, zeolite A had a specific surface area of 497 m2/g and pore volume of 0.16 cm3/g. SEM images demonstrated that the produced zeolites A are highly ordered cubic crystals. Significant data were obtained through studying the main parameters affecting the adsorption of heavy metals on the optimized zeolite A during the removal of Cu, Cr, Ni, and Cd. The findings indicate that the pH, zeolite dose and ion concentration are significant but the shaking time and reaction temperature are insignificant. Maximum removal of heavy metals ∼100% onto zeolite was achieved at pH 4. Heavy metal ion uptake decreased for non-zeolite crystalline material or the amorphous synthesis products and mixtures of amorphous material and zeolite 4A due to decreased specific surface area and pore volume that resulted in lower accessibility and possibly less sites for ion exchange. The larger pore size of zeolite A provides more facile intraparticle diffusion for metal ions and increases the ion-exchange rate.

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... Zeolites are one of the ion-exchanging materials which their charge balancing cations can easily be substituted by cations in an electrolyte solution. Both natural and synthetic form of zeolites was used for removal of heavy-metal ions [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. ...
... Furthermore, they compared the activity of zeolite 4A with non-zeolite crystalline materials and amorphous synthesis products in removal of heavy-metal ions. Zeolite 4A, Because of larger pore size, provided more facile intra-particle diffusion for metal ions and had the higher IER (ion-exchange ratio) [6]. ...
... Therefore, the effect of temperature variation on MIER is insignificant. This is in agreement with both experimental and simulation studies [6,26]. ...
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Molecular dynamics simulation of heavy metal particles by zeolite particles was studied. • The most of the particles had the highest affinity of ion exchanging with lead (II). • The most of the particles had the lowest affinity of ion exchanging with copper (II). • Maximum mean ion-exchange ratio belongs to ion with the highest ratio in single-ion system. • Temperature variations had no significant effect on the mean ion-exchange ratios. In present study, molecular dynamics simulation of Cadmium (II), Lead (II) and Copper (II) removal from aqueous electrolyte solutions using the ion-exchange process with the zeolite particles was done. The results showed that, most of the particles had the highest affinity of ion exchanging with Lead (II) and the lowest affinity with Copper (II). The calculated mean ion-exchange ratios showed that, except for the zeolites which their pore sizes are in the same range of heavy-metal ions' size, an inverse relationship exists between this ratios and pore size of the zeolites. Furthermore, the ion-exchanging of zeolites LTJ, ANA, SVR, BEC and MER with aqueous electrolyte mixtures containing equal amounts of Cadmium (II), Lead (II) and Copper (II) were simulated. The results demonstrated that in the competitive exchange of electrolyte mixtures, the maximum mean ion-exchange ratio belongs to the ion which has the highest ratio in the single-ion system. Moreover, ion-exchanging of zeolites LTJ, ANA, SVR, BEC and MER with an aqueous electrolyte solution containing Copper (II), in the temperature range of 300-345 K were simulated. The results revealed that, no significant change in the mean ion-exchange ratios were found as a result of temperature variations.
... A lower Si/Al ratio ensures more accommodation for an exchangeable extra-framework cation. This results in a higher cation exchange capacity [31][32][33][34]. During alkaline hydrothermal treatment, zeolite undergoes selective desilication of the framework. ...
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The treatment of chabazite (CHA), a natural zeolite, with the alkaline hydrothermal method to improve its ion-exchange capacity is a widely adopted route by environmental scientists for the purpose of better ammonium (NH4+) removal from wastewater. This work addresses a noteworthy trend in environmental science, where researchers, impressed by the increased ion-exchange capacity achieved through alkaline hydrothermal treatment, often bypass the thorough material characterization of treated CHA. The prevalent misconception attributes the improved features solely to the parent zeolitic framework, neglecting the fact that corrosive treatments like this can induce significant alterations in the framework and those must be identified with correct nomenclature. In this work, alkaline-mediated hydrothermally treated CHA has been characterized through X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), solid-state magic-angle spinning nuclear magnetic resonance (MAS-NMR), high-resolution transmission electron microscopy (HRTEM), and energy-dispersive X-ray spectroscopy (EDS) and it is concluded that the treated samples have been transformed into a desilicated, aluminum (Al)-dense framework of analcime (ANA) with a low silica–alumina ratio and with a strikingly different crystal shape than that of parent CHA. This treated sample is further examined for its NH4+ removal capacity from synthetic wastewater in a fixed-bed column arrangement. It achieved a maximum NH4+ removal efficiency of 4.19 meq/g (75.6 mg/g of NH4+), twice that of the parent CHA. Moreover, the regeneration of the exhausted column yielded a regenerant solution, with 94% reclaimed NH4+ in it, which could be used independently as a nitrogenous fertilizer. In this work, the meticulous compositional study of zeolitic materials, a well-established practice in the field of material science, is advocated for adoption by environmental chemists. By embracing this approach, environmental scientists can enhance their comprehension of the intricate changes induced by corrosive treatments, thereby contributing to a more nuanced understanding of zeolitic behavior in environmental contexts.
... Sodalite is usually formed in place of LTA zeolite when kaolin that did not complete the metakaolinization process is used [16]. The shape of the crystals are also affected by the Si/Al ratio for example, when a ratio of 1:5 Si:Al is used, crystals with beveled edges instead of very well defined edges are obtained [19]. ...
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The hydrothermal method of zeolite synthesis was used to obtain the Linde Type A (LTA) zeolites from kaolin found in Darazo. Characterization confirms the presence of alumina and silica which are the precursor materials for zeolite synthesis. The Fourier Transform Infrared Spectroscopy (FTIR) and X-ray diffraction (XRD) analyses indicate the presence of characteristic zeolite peaks while the scanning electron microscope (SEM) shows clearly defined cubic zeolite-A crystals. In addition, a water adsorption test on the synthesized LTA zeolites showed good water adsorption capacities of 27.96 and 28.01% for samples calcined at 700 and 900°C respectively. Such results enable these materials to be good candidates for water adsorption applications. These experiments show that LTA zeolites can successfully be synthesized from kaolin found in the Darazo area using the hydrothermal process of zeolite synthesis with similar results obtained for both LTA zeolites produced from Darazo kaolin calcined at 700 and 900°C. A comparison of the different calcination temperatures for the LTA zeolites shows that the materials calcined at 900°C give better adsorption properties.
... The remarkable properties of ordered nanoporous silica are responsible for the elimination of organic waste from water bodies owing to their larger surface area, confined pore size distribution, tunable pore diameters, considerable chemical and thermal stability with excellent selectivity towards organic pollutants, high possibility of adsorbent-adsorbate interaction and large pore volume (Lu et al. 2006). Apart from these, nanoporous silica has gained attention due to its potential applications in areas such as gas separation, catalysis, ion exchange, gas sensing, energy storage, biomedical, drug delivery, and adsorption (Nasrallah et al. 2018, Sun et al. 2016, Ismail et al. 2010, Lewinski et al. 2010, Wagner et al. 2013, Orellano et al. 2022, Zhang et al. 2022, Santos et al. 2012. ...
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In the current study, tetranuclear Ni complex [Ni4(LH)4]·CH3CN (1) (LH3=(E)-2-(hydroxymethyl)-6-(((2-hydroxyphenyl)imino)methyl)phenol) was prepared and incorporated in sulfonic acid functionalized MCM-48 material. This composite nanoporous material was investigated for the adsorption of toxic cationic water pollutant dyes like crystal violet (CV) and methylene blue (MB) from the water solution. Thorough characterization was carried out using a variety of techniques, including NMR, ICP, powder XRD, TGA, SEM, BET, and FT-IR, to verify the phase purity, existence of guest moiety, material morphology, and other crucial variables. The adsorption property was increased with the metal complex immobilization on the porous support. The effect of various parameters on the adsorption process was discussed, including adsorbent dosage, temperature, pH, NaCl concentration, and contact time. Maximum dye adsorption was found at 0.2 mg/ml adsorbent dosage, 10 ppm dye concentration, 6-7 pH, 25 °C temperature, and 15 minutes of contact time. The adsorption of MB (methylene blue) and CV (crystal violet) dyes by Ni complex integrated MCM-48 was effective, with over 99% adsorption achieved in 15 minutes. A recyclability test was also performed, and the material is reusable up to the third cycle, with no notable decline in adsorption found. From the previous literature survey, it is clear that very high adsorption efficiency was achieved using MCM-48-SO3-Ni in considerably short contact time which proves the novelty and effectiveness of the modified material. Graphical abstract Ni4 was prepared, characterized, and immobilized in sulfonic acid functionalized MCM-48, and this robust and reusable adsorbent was highly effective for the adsorption of methylene blue and crystal violet dyes with >99% adsorption efficiency in short duration.
... To some extent, the Si/Al ratio influences crystal shape. As a result, at a Si/Al ratio of 1.5, bevelled rather than sharp, well-defined edges are obtained [17]. ...
... For instance, the surface area of commercial zeolite Na-A reported by Katsuki et al. [25] was 8 m 2 /g. The zeolite Na-A produced by Ismail et al. [26] has the surface area in the range of 138.0-445.0 m 2 /g. ...
Conference Paper
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Spent bleaching clay (SBC), waste gathered from palm oil refinery, is normally discarded at landfills. In this study, water adsorbent was synthesized from regenerated SBC to dehydrate azeotrope ethanol-water mixture. The SBC was converted into water adsorbent using modified fusion technique at the best variables combinations i.e. temperature of fusion of 550 o C, temperature of aging of 80 o C, aging time of 3 days, water addition of 65% wt, added KOH of 56% wt and added alumina of 80 g/100 g material mass. The synthesized water adsorbent was characterized using XRD, FESEM-EDX and porosity analyzer. The synthesized water adsorbent was used to purify azeotrope mixture of ethanol-water in a simple adsorption apparatus to produce dehydrated ethanol. XRD analysis showed that the water adsorbent cannot be considered as zeolite A. It was believed that the porous water adsorbent consisted of several phases of zeolites such as zeolite A, MFI plus amorphous phase based on SEM images. In terms of breakthrough time, the water adsorbent performance was 66.0% of the commercial water adsorbent. Results showed that the Yoon & Nelson model can be used to simulate the experimental dehydration data. In conclusion, this study showed that low cost water adsorbent can be produced from spent bleaching clay using modified fusion technique and was able to produce dry ethanol (>99% weight) as alternative fuel in petrol driven engine and fuel cell.
... These varied utilizations have made zeolite-A an attractive material, drawing continuous interest for exploration of preparation techniques as well as the use of varied raw materials. Some workers have reported the synthesis of zeolite-A from different raw materials, such as sodium metasilicate and by-product from aluminum etching process [19], sodium silicate, and sodium aluminate [20], natural kaolin [21][22][23], fumed silica and sodium aluminate [24] and rice husk silica [25]. ...
Article
This study was conducted to evaluate the effect of crystallization time on the structure, microstructure, and catalytic activity of zeolite-A synthesized from rice husk silica and food-grade aluminium foil. Three samples were prepared with fixed crystallization temperature of 100 °C and crystallization times of 48, 72, and 96 h, followed by calcination at 550 °C for 6 h. The samples were characterized using XRD and SEM then used in pyrolysis of mixed solid cassava residue and palm oil. The bio-crude oil (BCO) produced was analyzed using the GC-MS technique. For comparison, a commercial zeolite-A was also characterized and used as the catalyst. Characterization using XRD revealed that zeolite-A has formed at a 48 h crystallization period, with sodalite as a minor component, and crystallization time of 72 h resulted in optimum growth of the zeolite-A. The results of SEM indicated the presence of cubic crystal, most evidently in the sample synthesized with crystallization time of 72 h. This particular sample is the most comparable to a commercial zeolite-A. Pyrolysis experiments produced BCO with hydrocarbons as the main components, with relative percentages of biogasoline fraction (C6–C12) in the range of 71.88–91.47% in the samples produced using synthesized zeolite and 97.52% using commercial zeolite.
... As evident, most of the zeolites exhibited slight diametric pore narrowing after formulation into binderless monoliths. As observed from Fig. 4, these effects could have been caused by slight malformation of the pore structure stimming from the interparticle bridging at high temperature [40]. Although this phenomenon did not yield any discernable changes in the bulk crystalline phases, as was evidenced by the XRD patterns, it did give rise to pronounced changes in micropore sizing. ...
Article
3D printing has emerged as an attractive way of formulating structured adsorbents, as it imparts lower manufacturing costs compared to hydraulic extrusion while also allowing for unprecedented geometric control. However, binderless structures have not been fabricated by 3D printing, as ink formulation has previously required clay binders which cannot be easily removed. In this study, we report the development of a facile approach to shape engineer binderless zeolites. 3D-printed inks comprised of 13X, 5A, ZSM-5, and experimental South African zeolites were prepared using gelatin and pectin as binding agents along with dropwise addition of various solvents. After printing, the dried monoliths were calcined to remove the biopolymers and form 100% pure zeolite structures. From N2 physisorption and CO2 adsorption measurements at 0 °C, all monoliths showed narrowing below 1 nm from their powders, which was attributed to pore malformation caused by intraparticle bridging during calcination. The various adsorption isotherms indicated that this narrowing led to varying degrees of enhanced adsorption capacities for all three gases, as the slightly smaller pores increased electrostatic binding between the sorbent walls and captured species. Analysis of CO2 adsorption performance revealed comparable diffusivities and adsorption capacities to the commercial bead analogues, implying that biopolymer/zeolite printing can produce contactors which are competitive to commercial benchmarks. The binderless monoliths also exhibited faster diffusivities compared to zeolite monoliths produced by conventional direct ink writing – on account of an enhancement in macroporosity – highlighting that this new method enhances the kinetic properties of 3D-printed scaffolds. As such, the sacrificial biopolymer technique is an effective and versatile approach for 3D printing binderless zeolite structures.
... Different crystalline shapes of synthesized EMRZ are caused by different types of zeolites. As demonstrated in the literature, typical shapes of synthesized zeolite are cubic and round, which matches zeolite A and zeolite P, respectively [27][28][29]. At initial Si/Al ratio of 1.5, zeolite A in its well-developed cubic shape as well as zeolite P in the shape of round crystals with a small amount of was presented (see Journal of Chemistry Figure 7(a)). ...
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In this study, the cation exchange capacity (CEC); phosphate immobilization capacity (PIC); and chemical, mineralogical, and morphological characteristics of the synthesized electrolytic manganese residue (EMR) based zeolite (EMRZ) were systematically investigated during the synthesis process. By varying synthesis conditions, different zeolites with different purity were generated, and it was proven that a lower Si/Al ratio, relatively higher temperature, and relatively longer time favored the synthesis of zeolite. Besides, the decrease in Si/Al ratio and variation within a narrow range contributed to the forming of Al rich zeolite. Meanwhile, the discrepancy of CEC and PIC of EMRZ contributed to the case in which various elements in EMRZ do have an impact on CEC (Na2O element and type of zeolite) and PIC (calcium and iron components). Moreover, the synthesis conditions were optimized and evaluated in terms of their CEC, specific surface area (SSA), and crystallinity. According to the analyses using XRD, FE-SEM, and XRF and the SSA analysis, the EMRZ (mainly zeolite A, LTA) synthesized under the optimum conditions (initial Si/Al ratio of 1.5, at 100°C, for 1.5 h) was found to be mainly composed of highly ordered cubic zeolites A crystals with a Si/Al ratio of 1.02 and a CEC of 3.45 meq/g.
... The SEM image of the obtained zeolite is shown in Fig. 5a, in which a typical cubic crystal with homogeneous size distribution is observed. This is a characteristic morphology of zeolite A (Anuwattana and Khummongkol, 2009;Ayele et al., 2015Ayele et al., , 2016Ismail et al., 2010) sodium ions in the zeolite structure. Na + is the principal exchange cation to stabilize the structure of the Linde-type A zeolite, but the charge is balanced by the presence of K + . ...
Article
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A potential route to minimize the environmental impact of industrial activities is, among other approaches, the use of hazardous wastes as less-common raw materials for the preparation of other materials. Realistic technologies for waste management should include simple and low-cost processes as well as the nonproduction of new wastes. Thus, the total conversion of a type of hazardous aluminum waste into zeolite was achieved at the pilot-scale (200 l autoclave reactor) under mild hydrothermal operating conditions. In a one-step process, 3.2 tons of zeolite, 76.4 Nm3 of ammonia and 105.9 Nm3 of hydrogen can be produced per ton of aluminum waste. The process does not generate other wastes. The recycling of process effluents (mother liquor and rinse water), along with the process gases capture and its subsequent commercialization, would increase the environmental impact and the economic yield. The obtained Linde type-A zeolite, exhibited structural, textural and morphological characteristics similar to those of zeolites prepared from commercial reagents. A conceptual design for zero-waste process is proposed. The sustainable process developed can contribute to reduce the high environmental impact of aluminum industry waste, and contribute to the circular economy by converting a hazardous waste into a raw material.
... Meanwhile, the NH 3 desorption peak of V-H-ZSM-5-100 at 403°C (labeled as β) is ascribed to the strong acid sites. However, the strong acid sites decrease with the increment of vanadium content, and this result can be explained by the decrease of the relative crystallization of V-H-ZSM-5-n that leads to the decrease of the exchanging capacity of Na + -V-ZSM-5-100 [30]. Furthermore, we used the pyridine adsorption FTIR spectrum to investigate the acid type of V-H-ZSM-5-25 and V-ZSM-5-25 ( Fig. 6B.), thereinto, the band at 1443 cm −1 is typically due to Lewis acid sites including tetrahedral vanadium (V), VO x species and Al atom. ...
Article
Design and synthesis of low cost and efficacious industrial catalyst for the oxidation of styrene has been an important research project. Herein, ZSM-5 zeolite containing tetrahedral vanadium (V) and Brønsted acid sites (V-H-ZSM-5) was prepared, and identified by characterizations such as XRD, SEM, UV–vis, NH3-TPD, H2-TPR N2-adsorption/desorption and FTIR. V-H-ZSM-5 performed extremely enhanced catalytic activity for the oxidation of styrene with 30% H2O2 at 40 °C. Moreover, in-situ FTIR spectrum was used to investigate the catalytic mechanism. The results demonstrate that Brønsted acid site could not only increase the adsorption concentration of styrene in the micropores of V-H-ZSM-5 via the π complex interaction between double bond of styrene and Brønsted acid sites, but also increase the oxidation potential of H2O2. The synergetic action of tetrahedral vanadium (V) and Brønsted acid enhanced the catalytic activity for the oxidation of styrene with 30% H2O2. Impressively, V-H-ZSM-5 performed high reusability within five runs at a low reaction temperature (40 °C) for the first time.
... Aging time of 6 hours before crystallization can produce NaA zeolites with good crystallinity and stability 5 . Ismail et al. (2010) 16 proves that the temperature and time of crystallization play an important role in the quality of zeolite NaA produced. ...
Conference Paper
The synthesis of zeolite NaA from Bangka kaolin was started by activation step with calcination at temperature 650°C for 2 hours. This activation produced metakaolin, an amorphous phase as assigned by XRD pattern. Based on the result by XRF technique, metakaolin produced from thermal treatment was mostly composed of silicon and aluminum with SiO2/Al2O3 ratio=1.63, and other minor metal elements. This metakaolin was suitable to use as a source for zeolite NaA synthesis which had Si/Al ratio close to one. For the synthesis of zeolite NaA, metakaolin was mixed with NaOH solution, followed by crystallization at 100°C for 24 hrs. The solid product, zeolite NaA was separated by filtration. The resulted filtrate was reused for next zeolite NaA synthesis by the addition of metakaolin. The synthesis was performed by varying initial NaOH concentrations of 2, 3, 4, 5, and 6 M at a constant crystallization temperature at 100°C and constant crystallization time of 24 hours. The synthesis products were characterized by FTIR spectroscopy, X-ray diffraction, and scanning electron microscopy technique. The optimum results with the highest degree of purity and structural order were obtained from initial NaOH concentration 3M. Synthesis with NaOH concentration higher than 3M produced hydroxisodalite as another phase. The reused of filtrate in the synthesis showed the good product of zeolite NaA up to two times reused. Further reused of filtrate resulted significant decrease of purity and structural order. Further investigation indicates that another factor such as aging time for three days before synthesis could produce zeolite NaA at lower crystallization temperatures. While the amount of metakaolin in the initial mixture did not give a significantly better product. The production of zeolite NaA from Bangka kaolin using reused filtrate as partial nutrients could be an excellent way to minimize environmental impacts and decrease processing costs.
... Zeolite-A manifests Linde Type-A (LTA) structure, which has a 3D pore structure with pores that are perpendicular to one another. Zeolite has technological and scientific value due to its interacting ability with different molecules and ions in the inner pores as well as outer surfaces [34]. Elimination of phosphate from water can be done using various forms of iron, such as sponge iron, goethite, akaganeite, and iron ore. ...
Article
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Iron was incorporated into an LTA type zeolite using the sol-gel hydrothermal method to form Iron-zeolite-A (Iron-Z-A), and its phosphate adsorption-desorption efficiency were analyzed. Samples were characterized by EDS, SEM, XRD, EPR, FT-IR XPS, and Raman to ensure the apt synthesis of Iron-Z-A and to interpret the mechanism of adsorption-desorption of PO 4 3− in an aqueous solution. EPR and XPS analysis confirmed that the iron was doped as Fe3+ in the LTA structure. The XPS peak shift (Fe-2p), FT-IR band shift, and intensity change (-OH) confirmed the existence of the ligand exchange mechanism. In the adsorption phase at pH 5, the derivative of phosphate (H2PO 4 −) acts as a ligand and interacts with OH of Fe on the zeolite surface to form "Iron-zeolite (oxy) hydroxide bound phosphate". In the desorption phase at pH 10, phosphate ligand is detached and get mixed in the aqueous phase as HPO 4 2−. The EDS data, Si-O-Al band shift and intensity change in FT-IR and XPS peak intensity change proved the contribution of Al in the process of adsorption. The data of adsorption fitted well with the Langmuir's isotherm and pseudo-second-order kinetic model. The amount of PO 4 3− adsorbed was a function of adsorbent's surface area regardless of concentration. The amount of PO 4 3− being adsorbed by the metal ions was found to be 382.296 mg PO 4 3− /g Fe and 56.296 mg PO 4 3− /g Al.
... The Si/Al ratio also appears to have an effect on the shape of the crystals. For example, when the Si/Al ratio is 1.5, beveled edges as opposed to sharp well defined edges are obtained (Ismail et al., 2010). ...
Article
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This work investigates the hydrothermal synthesis and characterization of zeolite-4A from kaolin found in Ajebo, Nigeria calcined at 700 and 900 o C respectively. The synthesized zeolite-4A was further characterised using X-ray Fluorescence (XRF), Fourier Transform Infrared spectrometer (FTIR), Scanning Electron Microscopy (SEM), X-Ray diffraction (XRD), Brunauer-Emmet-Teller (BET) surface area analysis as well as Differential Thermal Analysis/Thermo-gravimetric (TG). Water adsorption capacity tests were also carried out on the synthesized zeolite-4A. The results from the XRF measurements indicated that the amount of Al 2 O 3 and SiO 2 in the studied kaolin was similar to the standard kaolin composition making it a perfect candidate for zeolite-4A synthesis. FTIR showed the characteristic zeolite peaks while XRD confirmed the crystalline nature of the synthesized zeolite-4A. TG studies showed that the zeolite-4A samples were stable up to temperatures of 700 o C. This stability as well as the surface area and pore size of 7 Å makes it potentially suitable for use in water treatment applications. The SEM showed cubic crystals which were typical of the morphology of zeolite-4A with water adsorption capacity of approximately 29%. These results indicate that zeolite-4A can be synthesized from kaolin found in Ajebo as an inexpensive alternative to traditionally sourced materials and also is suitable for use as adsorption agent.
... An amorphous phase formed at 75°C, however, literature pointed out 70°C is not adequate for the formation of a crystalline phase [14,19] indicating the importance of crystallization time for the process. Higher crystallization temperature (beyond 120°C) leads to phase transformation to hydroxysodalite because of water evaporation during hydrothermal treatment causes increasing of sodium concentration in the liquid phase [41]. Raising crystallization temperature to 125°C showed no impure phases formed during crystallization. ...
Article
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This paper sheds light on key factors controlling the growth of 4A zeolite crystals during a conventional hydrothermal synthesis. SiO2/Al2O3 ratio, Na2O/SiO2 ratio, H2O/Na2O ratio, crystallization time and crystallization temperature affecting zeolite growth during the hydrothermal synthesis were investigated. Optimizing the SiO2/Al2O3 ratio, Na2O/SiO2 ratio and H2O/Na2O ratio crucially controls the formation of pure zeolite. It was found that mild alkalinity favors crystallization of 4A zeolite. Also for a chosen gel formula, crystallization temperature and time significantly affect the morphology and crystal size of the final products. Conducting the crystallization at 100°C for 4 h produced crystals having cubic morphology with planar surfaces, well-defined and sharp edges. Rietveld refinement analysis was used to study the influence of crystallization temperature on the structure of 4A zeolite. The micro strain values for an amorphous sample significantly varied from those values for the well-crystallized samples. Also, the efficacy of the prepared 4A zeolite for heavy metal removal was examined with both nickel and lead ions. All 4A zeolite samples showed significant heavy metal uptakes due to obtaining a well-crystallized structure which offers sufficient surface area for ion-exchange. Removal of lead ion encompasses both ion-exchange and precipitation process simultaneously.
... Zeolite is a unique inorganic ion exchanger and is thus widely used in gas and water treatments [15]. Zeolite is a type of hydrated aluminosilicate of alkali and alkaline earth metals so, SiO 4 and AlO 4 are the primary building units, forming the framework [16]. The presence of aluminum results in a negatively charged framework, which is compensated for by cations, mostly sodium ions. ...
Article
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As development of industrialization grows constantly, the purification of hazardous solid particles and ions is one of the most important topics in environment and ecosystem. In this report, we designed and developed a novel and advanced type of filter media for the removal of both solid particles and hazardous ions, we choose Cs ⁺ and Ca ²⁺ here, by enclosing zeolite in wet-laid nonwoven media. The performance of the prepared filter media was evaluated by continuous sorption experiments, which were followed by solid particles and ion-removal efficiency studies. The prepared filter media showed excellent uniformity. The prepared filter media exhibited a solid removal efficiency rate which ranged from 80 to 82%, and the initial removal efficiency of ions exceeded 99%. These values are in effect as the main layer in the completed liquid filter media and for the next step to prepare the completed multi-layered liquid filter units. The results here suggest that this novel filter media can be used in high-efficiency and multi-functional liquid filter units for residential and industrial engineering.
... Conventional removal methods of heavy metals from water and wastewater are reverse osmosis [2], ion exchange [3], chemical precipitation [4], electrochemical treatment [5], membrane filtration [6], ion imprinted polymers [7,8], adsorption [9,10], and floatation [11]. Among the mentioned techniques, adsorption is the most efficient, economic and easy-to-control technique for heavy metal removal. ...
Article
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Wholly heterocycles-based polyamide-sulfide (PAS) containing pyridine and thiazole rings with thioether linkage was synthesized and used as a novel adsorbent for lead ion removal from water. The polymer adsorbent was fully characterized via FTIR, NMR and scanning electron microscopy (SEM). The thermal properties of the synthesized polyamide were also studied by thermogravimetric analysis and the outcome showed that the polymer has a good to moderate thermal stability. The SEM was used to investigate the morphology of the wholly heterocycles-based polyamide and the outcomes displayed a porous and globular-like morphology, which guarantee effective metal adsorption. Pb(II) ion removal capacity of the synthesized polymer was studied by varying the contact time and the adsorbent concentration. The maximum removal of Pb(II) was obtained as 99%. Equilibrium behavior and kinetic of the adsorption were also investigated using prevalent isotherm and kinetic models. The adsorption capacity was obtained to be around 714 mg g⁻¹. The Langmuir isotherm and the pseudo-second order kinetic model suggested superior agreement with the equilibrium and kinetic adsorption data, respectively. Generally, the results of this research demonstrated that the synthesized polymer is a super-adsorbent for heavy metal removal from water.
... According to Ismail et al., when the Si/Al ratio is 1.5, beveled as opposed to sharp well defined edges are obtained [50]. ...
... Scarcely any changes are observed in XRD patterns when Na 2 O/SiO 2 is more than 1.0. These results indicate that the value of Na 2 O/SiO 2 of 1.0 is adequate for synthesis of 4A zeolite crystals with high crystallinity, in accordance with the results of a published report (Ismail et al., 2010). Regarding 4A zeolite samples at different crystallization temperatures, the XRD patterns are presented in Figure 3(c). ...
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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.
... Zeolites can be synthesized to have distinct characteristics by modifying experimental parameters, such as Si:Al ratio, Na 2 O/SiO 2 mole ratio, H 2 O/SiO 2 mole ratio, crystallisation temperature and time, etc. For example, by changing the Si:Al ratio on zeolite A from 1 to 2, Cd uptake in zeolite increased from 17.8% to 94% (Ismail et al., 2010). Wibowo et al. (2017b) also found an increased temperature from 100 C to 225 C led to disposal of organic substances that clog the channels and increased dealumination, consequently it helped to reduce the salinity in seawater, whereas a further temperature increase from 225 C to 600 C resulted in decreased efficiency possibly due to zeolite solidification. ...
... Due to ingestion of these metals, various diseases occurs such as serious seminal and neurological issue that can cause even death. Currently, the most widely recognized techniques to expel substantial metals from water and wastewater are particle exchange [25][26][27], reverse osmosis [28, 29], compound precipitation [30], electrochemical treatment [31][32][33], layer filtration [34], floatation [35], and adsorption. The adsorption is most important method to remove these metals from water samples. ...
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Clean, secure, and adequate water is basic to the endurance of every individual living life frame. Environmental pollutants pose serious threats to freshwater supply, living organisms, and public health, despite their occurrence at low concentration ranges. Thus, treatment of waste water required around the creation. So, nanotechnology is an innovative technique for the treatment of water and wastewater to improve water quality and to improve water supply through safe usage of clean water source. Therefore, in past various techniques utilized for wastewater treatment, for example, adsorption, compound precipitation, sol-gel, solvo-thermal response, and so on, for the incorporation of nanoadsorbents, which can be viably utilized for groundwater treatment. This chapter concentrates on the removal of pollutants from water using a variety of adsorbents such as nanotubes, nano wires, and nanoadsorbents by using adsorption technology, which has turned out to be one of the best technologies for wastewater treatment. The survey will aid the readers to select suitable nanomaterials and to get up further research required for pollutant removal using nanoadsorbents, depending on the characteristics of effluents to be processed, industrial applicability, release standards, cost- effectiveness, regulatory demands, and durable ecological impacts.
... According to Ismail et al., when the Si/Al ratio is 1.5, beveled as opposed to sharp well defined edges are obtained [50]. ...
... Kaolin is a cheap clay mineral whose deposits are found vastly around mining areas in Zimbabwe. Many researchers have reported the synthesis of zeolites from kaolin under different conditions [6][7][8][9][10][11]. Kaolin is not stable under severe alkaline conditions and as such it is desirable to convert it into a more reactive form (metakaolin) by calcination at elevated temperatures. ...
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... This can be explained by considering the difference in ionic charge of contaminants and the pH zpc of 4A-molecular sieve, as well as the difference in adsorption mechanism. The ammonium has been likely removed from solution through electrostatic attraction and ion-exchange, 29 which can be explained by variation of equivalent concentrations of cations in the solution before and aer reaction in the 4Amolecular sieve-solution system given in Fig. 5. As shown in Fig. 5, the equivalent concentration of Na + in the solution increased aer adsorption and the ion exchange amount of Na + and NH 4 + accounted for more than 90% of the total ion exchange amount. ...
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... Zeolites are crystalline aluminosilicates with a distinctive pore structure in the microporous range (Ismail et al. 2010). They are characterized by a large selectivity and the ability to separate substances based on the variation in sizes and shapes of separated molecules. ...
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Chapter
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As a scarce natural resource, the preservation of water quality is of fundamental importance to guarantee its availability for future generations. Due to the increasing industrial activity, effluents are generated with a series of chemical compounds, such as nitrogenous, phosphoric, and organic compounds, heavy metals, and dyes which, if improperly disposed of, contribute to contamination, followed by significant environmental impacts, in addition to the damage to human health. The adsorption technique is an effective approach for removing contaminants from effluents, showing high versatility, due to the use of various materials as adsorbents. Belonging to a wide variety of materials, zeolites reveal to be a promising adsorbent. Zeolites are minerals found in nature or which can be synthesized from industrial residues, standing out in the treatment of contaminated effluents. Zeolite removal efficiency depends on the contaminant to be removed and can reach up to 96% for heavy metals, 90% for phosphoric compounds, 96% for dyes, 80% for nitrogen compounds, and 89% for organics. Aiming at the identification of the more relevant findings and research gaps to advance the use of zeolites in the large-scale treatment of industrial effluents, a review on the recent application of zeolites is needed. This paper presents a global view of zeolites, and a review is conducted on several recent studies using zeolites as adsorbents for the contaminants considered, indicating the main characteristics of the various adsorption systems, demonstrating the particularities of each process, and aiming to reveal useful information to provide future research, in addition to identifying points that need further investigation.
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The adsorption capacity of synthetic NaX zeolite for Pb2+, Cd2+, Cu2+ and Zn2+ in single and multi-component systems were investigated. The effects of electronegativity and hydration energy on the selective adsorption, as well as potential selective adsorption mechanism of the NaX zeolite for Pb2+, Cd2+, Cu2+ and Zn2+ were also discussed. The maximum adsorption capacity order of the heavy metals in the single system was Pb2+ > Cd2+ > Cu2+ > Zn2+, and this could be related to their hydration energy and electronegativity. The values of the separation factors (α) and affinity constant (KEL) in different binary systems indicated that Pb2+ was preferentially adsorbed, and Zn2+ presented the lowest affinity for NaX zeolite. The selective adsorption capacities of the metals were in the order, Pb2+ > Cd2+ ≈ Cu2+ > Zn2+. The trend for the selective adsorption of NaX zeolite in ternary and quaternary systems was consistent with that in the binary systems. Pb2+ and Cu2+ reduced the stability of the Si-O-Al bonds and the double six-membered rings in the NaX framework, due to the high electronegativity of Pb2+ and Cu2+ than that of Al3+. The selective adsorption mechanism of NaX zeolite for the high electronegative metal ions could mainly result from the negatively charged O in the Si-O-Al structure of the NaX zeolite, hence heavy metal ions with high electronegativity display a strong affinity for the electron cloud of the oxygen atoms in the Si-O-Al. This study could evaluate the application and efficiency of zeolite in separating and recovering certain metal ions from industrial wastewater.
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In this study, a novel magnetic NiFe 2 O 4 photocatalyst was produced from electroplating wastewater and pickling waste liquor via microwave hydrothermal method. It was shown that 99% of heavy metal ions (Fe 3+ and Ni 2+) in the wastewater could be effectively removed through precipitation. And physi-cochemical properties of the material were characterized by several techniques, such as X-ray diffrac-tion, scanning electronic microscopy and vibrating sample magnetometer. The values of saturation magnetization of magnetic NiFe 2 O 4 was about 13.28 emu/g. In addition, photocatalytic degradation of methylene blue (MB) was studied using NiFe 2 O 4 with H 2 O 2 under visible light. The main influence factors (pH, the dosage of NiFe 2 O 4 and concentration of MB) were investigated, which showed that the maximum MB removal efficiency could reach 99%. Degradation kinetics data followed the pseudo-first-order model. And there was a synergistic effect between NiFe 2 O 4 and H 2 O 2 in the visible light photocatalytic advanced oxidation process. H 2 O 2 was activated by NiFe 2 O 4 and generated hydroxyl radicals (⋅OH). Meanwhile, the mechanism of the reaction was also discussed in this paper.
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In this research, the molecular dynamics simulation of separating metal ions from water at 298 K using LAMMPS software for LTA, FAU, LTN, THO, NAT and EDI zeolites and electrolyte solutions containing Cu ²⁺ , Cd ²⁺ and Pb ²⁺ individually and in pairs of ions have been studied. Among the single ions, the lowest ion exchange rate was Pb ²⁺ and the highest was Cd ²⁺ , as well as the adsorption rate and ion exchange, which was directly related to the size of zeolite cavities. The FAU zeolite with the largest cavity diameter had the fastest adsorption rate. The LTA structure with the adsorption of 69% of cadmium and FAU with 46% adsorption had the highest and lowest ion exchange rate. Furthermore, the highest ion displacement in different types of zeolites was related to copper ion due to its low weight. In two cations electrolytes solutions, all the structures tended to adsorb cadmium ion EDI structures with 100% cadmium adsorption and 85% copper, FAU with 78% cadmium adsorption and 40% copper have been shown the highest and lowest selectivity and uptake of cadmium relative to copper, respectively. In addition, for electrolyte containing cadmium and lead, EDI structure with 100% cadmium adsorption against 60% lead and THO structure with 70% cadmium adsorption versus 38% lead had the highest and lowest selectivity for cadmium. In copper-leaded electrolytes, copper was superior to selected. EDI adsorbed 100% copper versus 60% lead, and FAU had a 40% copper uptake, compared to 65% lead.
Chapter
This work reports the investigation of Zeolite 3A layers obtained by spin coating process at low temperature for registration alcohol vapor. Phase composition of Zeolite 3A layers was studied with the help of X-ray diffraction (XRD). Optical polarization properties and sensorics application of Zeolite 3A layers deposited onto different substrates were investigated by modulation polarimetry. Optical polarization properties were observed by measuring of angular characteristics of V-component of Stokes Vector. The influence of substrate materials for Zeolite 3A on amplitude parameter of angular characteristics of V-component of Stokes Vector was studied. The dielectric and conductor materials as Glass slide, Indium Tin Oxide nanofilm and Gold nanofilm were used. The highest amplitude value of V-component of Stokes Vector corresponds to the Zeolite layer on gold nanofilm. The response to ethanol vapor was registered for the Zeolite layer on gold nanofilm. © 2018, Springer Science+Business Media B.V., part of Springer Nature.
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The synthesis of novel mobile composite adsorbents dedicated to the efficient removal of heavy metal ions from aqueous solutions is presented. The acidic condensation of resorcinol and 2-thiophenecarboxaldehyde in the presence of carbon-encapsulated iron nanoparticles results in a monolithic solid composite which has superior adsorption properties. The magnetic properties of the composite can be tuned by changing the content of the magnetic filler. The adsorption performance of the composite has been evaluated in the removal of Fe(III) Cu(II) ions from aqueous solutions. The composites obtained have also been subjected to post-synthesis sulfonation to further improve their adsorption properties. The composite adsorbents obtained have better adsorption performance than the commercially available cation exchange resin.
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Modified nanosized MFI (ZSM-5 and silicalite-1) zeolites were successfully synthesized by a hydrothermal method using aluminum isopropoxide and tetraethylorthosilicate as the raw materials. The synthetic zeolites were characterized by X-ray diffraction, energy dispersion spectroscopy, and scanning electron microscopy. The ZSM-5 and silicalite-1 zeolites exhibited ellipse-like and cubic columns, respectively. The K⁺ ion-exchange equilibrium and ion-exchange capacity of the synthetic zeolites in seawater were investigated. The K⁺ ion-exchange of synthetic zeolites was rapid and reached an ion-exchange balance in approximately 20 min. The K⁺ ion-exchange capacity of ZSM-5 and silicalite-1 in seawater was 56.7 and 48.7 mg/g, respectively. The synthetic zeolites have high selectivity toward K⁺, and therefore, they can be used to selectively extract potassium from seawater.
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The aim of this study was to synthesize and characterize zeolite-based magnetic polymer composites (m-ZPC) for Cu(II) and Cr(III) removal from aqueous solutions. Synthetic zeolite NaA and magnetic iron oxide nanoparticles were immobilized into blended polymer hydrogels composed of poly(vinylidene fluoride) (PVDF) and poly(vinyl alcohol) (PVA) in order to prepare m-ZPC (average particle diameter = 2.97 ± 0.18 mm). Stability tests for m-ZPC against acidic and alkaline solutions indicate that it was stable between solution pHs of 2.0 and 9.0. Batch experiments demonstrate that the maximum adsorption capacities for Cu(II) and Cr(III) were 3.90 and 2.04 mg/g, respectively. The removal of Cu(II) and Cr(III) increased as the pH increased from 2.0 to 5.0. The removal of Cu(II) and Cr(III) was enhanced with a rise of temperature from 15°C to 45°C. In addition, m-ZPC could be reused for Cu(II) removal after regeneration with 5 M NaCl solution. Thermodynamic analyses indicate that the removal of Cu(II) and Cr(III) was endothermic and spontaneous sorption processes (Cu(II): ΔH° = 115.0 kJ/mol; ΔG° = -5.13 to -17.64 kJ/mol, and Cr(III): ΔH° = 73.0 kJ/mol; ΔG° = -2.50 to -10.36 kJ/mol). This study demonstrates that m-ZPC can be used as a magnetic adsorbent for heavy metal removal in combination with magnetic separation.
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A robust hydrothermal preparation of nanozeolite LTA has been made. It is the first report of zeolite NaA synthesis with smallest crystal sizes, highest surface area and a hierarchical structure as micron-sized spheres formed by nanocrystallites assemblies in a short time. The effects of time, temperature of crystallization and seeding on the final products properties have been studied. The prepared samples have been characterized using various techniques. Moreover, the synthesis procedure has been fulfilled using the initial natural precursors supplied from the mines in Iran. The results ascertain the successful synthesis of the high-qualified products with potential adsorptive and catalytic applications.
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In this study, the effects of parameters such as crystallization time and temperature on the phase and morphology of NaA zeolite prepared by hydrothermal method were investigated. The textural properties of the synthesized zeolites were characterized using XRD, SEM, FTIR and BET analyses. The findings revealed that the optimum time and temperature of NaA preparation to be 20 h and 363 K, respectively. The adsorption experiments of CO2 and CH4 by synthesized and commercial NaA zeolites were carried out at three temperatures (277, 290 and 310 K) for pressures up to 10 bar. The experimental data were analyzed using Langmuir and Sips equations, and the Sips model better described the experimental data. It was found that the synthesized NaA had BET specific surface area of 222.8 m² g⁻¹ and pore volume of 0.096 cm³ g⁻¹. Also, the adsorption capacities of 5.2 and 2.6 mmolg⁻¹ were obtained for CO2 and CH4 by the synthesized samples, respectively. Comparing with commercial sample, the synthesized zeolite showed higher adsorption capacities for CO2 and CH4 under the same condition. The heat of adsorption at zero coverage of CO2 and CH4 on the synthesized NaA zeolite were found to be 48.5 and 24.4 kJ mol⁻¹, respectively. The ideal CO2/CH4 selectivity of the synthesized and commercial zeolites were 7.1 and 6.4, respectively, at atmospheric pressure and 290 K. The dynamic adsorption experiments of CO2/CH4 gas mixture confirmed that the synthesized NaA zeolite had more promising performance for the separation of CO2/CH4 compared to the commercial zeolite.
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The design, synthesis and some optical properties of hybrid organic-inorganic nanocomposites materials are presented. The properties that can be expected for such materials depend on the chemical nature of their components, but they also depend on the synergy of these components. Thus, the interface in these nanocomposites is of paramount significance and one key point of their synthesis is the control of this interface. These nanocomposites can be obtained by hydrolysis and condensation reactions of organically functionalized alkoxide precursors. Striking examples of hybrids made from modified silicon, tin and transition metal alkoxides are presented. Some optical properties (photochromic, luminescence, NLO) of siloxane based hybrids are also discussed.
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Well-ordered cubic zeolites 4A were synthesised using sol–gel process in the presence of different silica and aluminum sources. The aluminum and silica sources determined whether or not zeolites were formed at precise silica/alumina mole ratio. Zeolites were formed only when the aluminum source was sodium aluminate, the silica source was fumed silica, colloidal silica or sodium metasilicate. Our findings indicated that the type of zeolite invariably obtained was 4A and SEM images indicated that the produced zeolites are cubic shaped crystals with planar surfaces and well-defined edges and sharp crystals. In turn, synthesis parameters are seen to have a significant effect in maximizing heavy metals uptake (for example Cu2+, Cr3+, Cd2+ and Ni2+) by synthesized zeolites. Zeolite 4A gave better heavy metal uptakes than amorphous or non-zeolite crystalline materials. This was attributed to higher ion-exchange capacity and higher BET specific surface area 445 m2/g and pore volume 0.141 cm3/g. The latter attribute possibly translates to greater accessibility of ion-exchange sites and selectivity towards metal type by this zeolite followed the sequence: Cu2+ > Cr3+ ≥ Cd2+ > Ni2+.
Chapter
The aim of this paper is to give an impression of the work of the recently disbanded IUPAC Sub-Committee on the Characterization of Porous Solids. It provides a brief description of the development, content and philosophy of the Recommendations of the Sub-Committee, to be published in Pure and Applied Chemistry. An outline is given of the terminology required to define a porous solid and of the proposed general guidelines for the selection of the most appropriate methods of characterization.
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This review focuses on some aspects of the chemistry involved in the preparation of oxides by sol-gel methods. This field is opening interesting possibilities for molecular chemistry and among those presented herein are: 1) the use of precursors containing functional groups for the preparation of solids with specific chemical reactivity; 2) the nonhydrolytic gelation (NHG) route, a new general method for the synthesis of oxides that allows the use of oxygen donors (ethers, alcohols, alkoxides) other than water; the mechanism is based on oxygen-carbon bond cleavage; 3) organic-inorganic hybrid solids containing covalent bonds for which the chemical reactivity is used to demonstrate the presence of substructure in the globally amorphous solid; the substructure greatly depends on the geometry of the organic moiety.
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This review focuses on some aspects of the chemistry involved in the preparation of oxides by sol–gel methods. This field is opening interesting possibilities for molecular chemistry and among those presented herein are: (1) the use of precursors containing functional groups for the preparation of solids with specific chemical reactivity; (2) the non-hydrolytic gelation (NHG) route, a new general method for the synthesis of oxides that allows the use of oxygen donors (ethers, alcohols, alkoxides) other than water; the mechanism is based on oxygen–carbon bond cleavage; (3) organic–inorganic hybrid solids containing covalent bonds for which the chemical reactivity is used to demonstrate the presence of substructure in the globally amorphous solid; the substructure greatly depends on the geometry of the organic moiety.
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The sol–gel process, with its associated mild conditions, offers a new approach to the synthesis of composite materials with domain sizes approaching the molecular level. Transparent organic–inorganic composites can be prepared by dissolving preformed polymers into sot–gel precursor solutions, and then allowing the tetraalkyl orthosilicates to hydrolyze and condense to form glassy SiO2 phases of different morphological structures. Alternatively, both the organic and inorganic phases can be simultaneously formed through the synchronous polymerization of the organic monomer and the sol–gel precursors. Depending upon such factors as the structures of the organic and inorganic components, the phase morphology, the degree of interpenetration, and the presence of covalent bonds between the phases, the properties of these composites can vary greatly and range from elastomeric rubbers to high–modulus materials.
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Porous texture characterisation of LTA, FAU and MFI type zeolites has been carried out by N2 adsoption at 77K and CO2 and CO2 adsorption at 273K. These results have been compared to the data obtained from crystallographic estimations. In this way, the micropore volumes obtained by CO2 adsorption at 273K are, in all the cases, similar to the expected from the crystal framework of the zeolite. However, the micropore volumes obtained by N2 adsorption at 77K are significantly smaller. These results confirm the limitations of the N2 adsorption at 77K in measuring narrow microporosity and make evident usefulness of CO2 adsorption at 273K to characterise porous solids with narrow microporosity.
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The crystal structures of hydrated (a = 12.32 Å) and vacuum-dehydrated (a = 12.17 Å) thallium-exchanged zeolite A have been determined by single crystal X-ray techniques. Tl(I) ions are distributed among three equipoints in each structure: two such sites are on the threefold axis on either side of the six-oxygen ring and the third is near the center of the eight-oxygen ring. Small changes in cation positions and in the zeolite frame-work are observed upon dehydration. The shortest Tl(I)-O approaches are 2.75 (2), 2.81 (2), and 2.86 (3) Å in the hydrated crystal and 2.64 (1), 2.60 (3), and 2.82 (3) Å, respectively, for the dehydrated form. Changes in framework angles of +14, -17, and -6° at the three nonequivalent oxygen atoms, corresponding to rotations of aluminosilicate tetrahedra, are observed upon dehydration.
Article
The crystal structure of vacuum-dehydrated (activated) zeolite A of apparent composition Na12-Al12Si12O48 has been determined by single-crystal X-ray diffraction techniques. Least-square refinement in the space group Pm3m (a = 12.263 Å) has led to a conventional R index of 0.069. Sodium ions are distributed among three equipoints in the structure: eight of the twelve ions occupy threefold axis positions 0.20 Å from the plane of three nearest neighbors in the six-oxygen ring; three more lie in the planes of the eight-oxygen rings, displaced from the center by 1.23 Å along a diagonal mirror line; and the twelfth ion is found on a twofold axis opposite a four-oxygen window in the large cavity. The shortest approach distances to framework oxygen atoms are 2.32, 2.4, and 2.5 Å respectively. Small changes in cation positions and in the zeolite framework are observed upon dehydration. The changes due to dehydration in framework angles at the three nonequivalent oxygen atoms, corresponding to rotations of aluminosilioate tetrahedra, are much less than those observed for the Tl-exchanged form of zeolite A. An attempt to sorb C2Cl4, although unsuccessful, yielded a structure in which the twelfth sodium ion is about 1.1 Å further from its nearest neighbors in the zeolite framework, presumably because an impurity or decomposition product which associates with that sodium ion was sorbed to a small extent.
Article
A modified fusion process was studied to synthesize zeolites A and X from fly ash. It was found that the addition of aluminum hydroxide to the fused fly ash solution followed by hydrothermal treatment at 60 °C produced single-phase zeolite A or a mixture of zeolites A and X depending on the source of the as-received fly ash. The result confirms that the quantity of dissolved Al species is critical for the type of zeolite formed in precursor solutions prepared from fused fly ashes. The ion-exchange behaviors of treated fly ashes containing zeolites A and X were tested with Co2+ ions. It was found that the ion-exchange capability (IEC) of treated fly ash with Co2+ ions was much larger than that with Cs+ ions. In addition, the Co2+ ion-exchange rate of zeolite X was faster than that of zeolite A. This is probably related to the bigger pore channels in zeolite X. The Co2+ IEC of treated fly ash containing zeolite A reached 67.6% of commercial zeolite A and that containing zeolite X 83.1% of commercial zeolite X. Our study demonstrated that fly ashes can be converted to zeolites A and X, and these treated fly ashes have great potential for removing heavy metals.
Article
Metal alkoxides of the type (R'O)(n)E-X-A, where A represents a functional organic group, and X is a hydrolytically stable spacer linking A and the metal alkoxide moiety E(OR')(n), are interesting precursors for the preparation of novel materials composed of both inorganic and organic entities. The basic chemistry behind the preparation and the sol-gel processing of these compounds is reviewed. The manifold options for chemical modification of both the inorganic and the organic groups allow the deliberate preparation of materials with special properties, Selected materials syntheses are discussed to demonstrate the scope of possible applications.
Article
This paper characterizes two natural zeolites, chabazite and clinoptilolite, and investigates the effects of treatment and conditioning on the removal of Pb and Cd from effluent wastewaters. The results demonstrated that the as-received zeolites contained a complement of exchangeable K, Ca, and Na ions but exposing them to concentrated NaCl solutions converts them to a homoionic state in the Na form, which improves significantly their exchange capacity. Particle size was found to have no effect on the exchange, suggesting that the mechanism is not surface controlled. Pb and Cd removal results using as-received, conditioned, and treated zeolites showed that conditioning and treatment improved both the exchange capacity and the removal efficiency when operating at metal concentrations greater than 250 mg/L. NaOH-treated chabazite and clinoptilolite performed best with optimum Pd and Cd exchange capacities exceeding 200 mg/g. The chabazite exchange capacity performance was superior to the clinoptilolite's for both Pd and Cd. This result was expected as chabazite characterization showed that it had a higher Al substitution of Si, which in turn will produce a negative framework favorable to higher cation exchange capability. Overall, metal removal efficiencies exceeding 99 % were achieved, revealing the natural zeolites potential in treating effluent contaminated with high levels of Pb and Cd.
Article
This contribution reviews a new family of inorganic-organic hybrid materials that are assembled by sol-gel polymerization of polyfunctional molecular building blocks. These bridged polysilsesquioxanes are three-dimensional network materials that are distinguished by incorporation of an organic fragment as an integral component of the network. The intimate association of the organic and inorganic phase, a true molecular composite, coupled with the variability of the organic component, permits engineering of both chemical and physical properties of the material. The paper reviews bridged polysilsesquioxanes, arylene-bridged polysilsesquioxanes, alkylene-bridged polysilsesquioxanes; and their applications.
Article
This article describes hybrid materials and systems in which the core integrity of inorganic nanobuilding blocks (NBBs) is preserved and reviews the main synthetic procedures presented in the literature. The relation between the NBB and the resulting hybrid networks is discussed for several striking examples:? silicon and tin oxo clusters, polyoxometalates, and transition metal?oxo-based clusters. This approach is extended to nanoparticule-based hybrids. The chemical strategies offered by the coupling of soft chemistry processes and this approach based on functional NBBs allows, through an intelligent and tuned coding, to develop a new vectorial chemistry that is able to direct the assembly of a large variety of structurally well-defined clusters or nanoparticles into complex architectures.
Article
Two samples of fly ash were treated for 2-48 h in 3.5 M NaOH at 100 degrees C. Powder XRD patterns of resulting products were obtained, and their CEC was determined. Zeolite P and/or hydroxysodalite formed during the treatment from the glassy part of fly ash, while quartz gradually dissolved and mullite remained stable. Approximately 50% of fly ash could be converted to zeolites with the CEC of resulting products reaching 2.5-3 mequiv/g. Concentrations of extractable B, Mo, and Se in fly ash considerably decreased upon treatment. Adsorption isotherms of lead on treated fly ash suggested that at low initial lead concentrations and at pH lower than 6 precipitation of lead compounds is not likely. A desorption experiment indicated ii incomplete reversibility at higher concentrations, suggesting that part of the adsorption may not have been cation exchange related. Treated fly ash displayed high selectivity for Pb2+ > Sr2+ > CU2+ > Cd2+ > Zn2+ > Cs+ in competition with Na+, especially at low concentrations of these cations, and was effective in removing Pb and Zn from industrial wastewaters. It was not selective for Ni2+ and UO22+. In a column test, 160 bed vols of NH4+-contaminated fish-pond water was filtered through treated fly ash until NH4+ breakthrough occurred.
Article
The possibility of using zeolites to reduce the levels of heavy metals present in motorway stormwater has been investigated. Currently, the primary pollutant removal mechanism used in treating stormwater is retaining the large volume of stormwater in detention ponds to allow time for the contaminants (mainly those associated with particulate matter) to separate out. There is also a need to reduce the levels of heavy metals in the dissolved phase, possibly by introducing some kind of ion exchange material into the treatment facility. Batch experiments have been conducted on two zeolites (synthetic MAP and natural mordenite) to test their ability to remove dissolved heavy metals from simulated and spiked motorway stormwater. Synthetic zeolite MAP showed almost complete removal (>91%) of the studied heavy metals (Zn, Cu, Pb, Cd) from both solutions. However, the use of such synthetic zeolites could have serious environmental implications as it was found to increase sodium levels to 295 mg/l, remove calcium and increase the pH of the spiked motorway stormwater to 8.5. Mordenite was less effective at reducing the levels of heavy metals (42-89% in synthetic solution, 6-44% in motorway stormwater) and exhibited a preference for Pb>Cu>Zn approximately Cd. It is proposed that the uptake of heavy metals is partially inhibited by the other dissolved contaminants present in motorway stormwater.
Article
In the present paper a study is conducted in order to distinguish the several types of capacity used in the literature on zeolite ion-exchange systems, to verify the use of each capacity type, and to analyze the several experimental methods used for capacity determination. Although the study is focused on zeolite clinoptilolite as a characteristic paradigm, its theoretical approaches and experimental findings and methods could also apply to other zeolites.
Article
The potential value of zeolitic materials (ZM) obtained from a hazardous waste, such as coal fly ash, for the retention of NH(4)(+) present in liquid effluents from a Sewage Treatment Plant (STP) is studied. A wastewater sample was taken from an STP in Zaragoza (Spain) after conventional treatment at the Plant. The water was treated with different amounts of three ZM: NaP1 zeolite, K-F zeolite and K-Chabazite/K-Phillipsite zeolites all of them in powdered and granulated state. The wastewater was treated by two kinds of processes: continuous stirring batch experiments with powdered ZM, and fixed packed bed of granulated ZM in a column. The powdered materials reduced about 80% of NH(4)(+) from wastewater, even in the presence of Ca(2+), which competes with NH(4)(+) for the cation exchange sites in zeolites. Around 70% of NH(4)(+) reduction was achieved with granulated materials. In both cases, moderate ZM/wastewater ratios had to be used to achieve those results, with K-zeolites slightly less effective in NH(4)(+) retention.
Article
The uptake capacity of Fe(III) and Zn(II) ions in NaY zeolite was investigated. Experiments were carried out in a fixed bed column at 30 degrees C, pH 3.5 and 4.5 for Fe(III) and Zn(II), respectively, and an average particle size of 0.180 mm. In order to minimize the diffusional resistances the influence of flow rate on the breakthrough curves at feed concentrations of 1.56 meq/L for Fe(III) and 0.844 meq/L for Zn(II) was investigated. Flow rate of the minimal resistance in the bed according to mass transfer parameter were 2.0 mL/min for iron and 8.0 mL/min for zinc ions. Freundlich and Langmuir isotherm models have been used to represent the column equilibrium data. The iron dynamic isotherm was successfully modeled by the Langmuir equation and this mathematical model described well the experimental breakthrough curves for feed concentrations from 0.1 up to 3.5 meq/L. The zinc dynamic isotherm was successfully modeled by the Freundlich equation. This equilibrium model was applied to mathematical model. Experimental breakthrough curves could be predicted. Experiments were also carried out in a batch reactor to investigate the kinetics adsorption of the ions Fe(III) and Zn(II). Langmuir kinetic model fit well both experimental data.
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