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Microporous and Mesoporous Solids
Published in Elaine A. Moore, Lesley E. Smart, Solid State Chemistry, 2020
Elaine A. Moore, Lesley E. Smart
The channel system for mordenite (MOR) is shown in Figure 7.15. Mordenite has an orthorhombic structure and there are two types of channels, governed by 8-ring and 12-ring windows, respectively, all running parallel to each other and interconnected only by the smaller 5-ring and 6-ring systems. Interestingly, mordenite synthesised at low temperatures (<260°C) is found to have larger ports than natural mordenite or mordenite synthesised at higher temperatures, and this is due to crystal defects blocking some of the large pores. The channel structure of mordenite showing the larger channels running along the z direction.
Microporous and Mesoporous Molecular Sieves
Published in Rolando M.A. Roque-Malherbe, Adsorption and Diffusion in Nanoporous Materials, 2018
The HEU framework of clinoptilolite is a two-dimensional micropore channel system, where the 10-MR channel A and the 8-MR channel B run parallel to each other and to the c axis of the unit cell, whereas channel C (8-MR) is placed along the a axis intersecting both the A and B channels (Figure 8.3) [37]. The elliptical shaped 8-MR and 10-MR that make up the channel system are nonplanar, and consequently, cannot be simply dimensioned. The structure of mordenite (MOR framework type [37]) is characterized by the presence of a two-dimensional micropore channel system, one of the channels is the principal system because the other channel is normally blocked, which is a 12-MR channel running along the [001] axis with free access of 6.5 A × 7 A, the other channel is a 8-MR side pocket channel running along [010] with a window of access of 2.6 A × 5.7 A connecting the 12-MR channels [12,38].
Zeolite Composition and Structure
Published in Subhash Bhatia, Zeolite Catalysis: Principles and Applications, 2020
Mordenite crystal structure consists of five-membered rings with each Si or Al tetrahedron associated with at least one such ring. The rings are interconnected to form chains, and the chains are crosslinked to identical chains to form the crystal structure. The relatively high thermal and acid stability of mordenite among zeolites is thought to result from mordenites having the largest number of such five-membered rings; the mordenite chain consists of five membered silica rings, which form the backbone of the chain, and individual alumina tetrahedra. This structure is possible because the Si/Al ration is high, 5.1. The ideal unit cell formula is Na8(AlO2)8(SiO2)40·4H2O.
Influence of the chain length of surfactant in the modification of zeolites and clays. Removal of atrazine from water solutions
Published in Environmental Technology, 2018
Helen Paola Toledo-Jaldin, Alien Blanco-Flores, Víctor Sánchez-Mendieta, Osnieski Martín-Hernández
Bentonite is a clay mineral and maybe one of the most abundant clay rocks with exceptional adsorption properties. The main clay mineral present in bentonite is montmorillonite, which belongs to the smectite mineral group [18]. Structurally, in clay minerals the tetrahedral sheet is always combined with an octahedral sheet. A cation (Al3+, Mg2+, Fe2+) is surrounded by six neighbors (oxygens or hydroxyls). Throughout the mineral, there is a tetrahedral/octahedral (TO) layered structure with tight packing between the layers [19]. Mordenite is widely used zeolite used as adsorbent for water purification. It is abundant in nature as a mineral with high purity, though some sources contain admixtures of iron oxides, mordenite and quartz [20]. On the other hand, zeolites are crystalline aluminosilicates with open 3D framework structures built of SiO4 and AlO3 tetrahedra linked to each other by sharing all the oxygen atoms to form regular intra-crystalline cavities and channels of molecular dimensions [21].
Dynamic adsorption of dimethyl methyl Phosphonate and 2-chloroethyl ethyl sulfide on zeolite-MOR and its nanocomposites monitored by gas chromatography flame ionized detector (GC-FID)
Published in Journal of Dispersion Science and Technology, 2022
Neeraj Kumar, Arvind Parashar, Km. Meenu, Arti Sharma, Radha Tomar
Mordenite (MOR) has been considered as highly siliceous zeolite occurring in nature[1] which possesses remarkable molecular-sieve properties as investigated by Barrer[2] in 1958. The crystalline structure of mordenite was firstly determined by Meier (1961) and refined by Gramlich (1971).[3,4] The topological framework of the zeolite has been characterized by five membered tetrahedral rings which are linked by edge-sharing chains along one axis. These in turn are linked together by four rings to form a puckered sheet in which eight-ring holes are present. Four membered rings are cross-linked in one direction with sharing of oxygen atoms[5] in other direction to form mordenite (Figure 1). The mordenite crystal consists of a lot of straight-shaped pores.[3,6,7] This type of material naturally exists in solid state with bright crystalline texture and a density of 2.12–2.16 g/cm3. Mordenite resists up to very high temperature (∼ 800–900 °C) without losing its structural morphology and does not dissolve in acid at room temperature.[8] Zeolites with its framework structure and microporous/mesoporous cavities act as effective adsorbent for nanoparticles. Interaction of metal and metal oxides with zeolites has opened a new window of applications such as catalytic, sensors,[9] super capacitors, electronics and magnetic, sorption and adsorption.[10–13]
Cs+ decontamination properties of mordenites and composite materials synthesized from coal fly ash and rice husk ash
Published in Journal of Asian Ceramic Societies, 2018
Hiromichi Aono, Tafu Kunimoto, Ryuichiroh Takahashi, Yoshiteru Itagaki, Erni Johan, Naoto Matsue
Zeolites are useful porous mineral aluminosilicates and widely used commercial adsorbents as ion-exchange materials for water purification and catalysts in the petrochemical industry [3,4]. The most promising characteristic of the zeolite is its highly selective Cs+ adsorption ability coexisting with other ions in solution. There are various kinds of natural or artificial zeolites. In these zeolites, a Na-P1-type artificial zeolite (Na6Al6Si10O32•12H2O) synthesized from coal fly ash has a high Cs+ ion adsorption ability and a high cation exchange capacity (CEC) value [5–8]. We evaluated the conditions for the Na-P1-type zeolite preparation and synthesized the composite material (magnetic zeolite) of the Na-P1-type zeolite and nanosized magnetite for the magnetic collection of the zeolite after the Cs+ ion adsorption [9]. However, we found that the mordenite has the best Cs+ adsorption selectivity among other zeolites, such as Na-P1, zeolite A, zeolite X, and clinoptilolite [10–12]. Based on these results, we focused on the mordenite (Na8Al8Si40O96•24H2O) synthesis. The preparation of artificial mordenite is necessary in order to improve the Cs+ ion adsorption ability and to synthesize the composite material. In previous studies, the mordenite has been artificially synthesized from commercial chemical reagents or a natural raw material called diatomite [13–17]. In many cases, the mordenite has been prepared using a template agent, such as diethanolamine (DEA) and/or a seed powder of the same zeolite. Although the synthesis of mordenite has been reported by a hydrothermal method using the reagents of Na, Al, and Si sources without the template and the seed, the conditions for the preparation have not been established in detail [18,19]. We established the preparation method for the mordenite or the composite materials of mordenite and nanosized magnetite from the diatomite or chemical reagents [20,21]. The most suitable Al/Si ratio of the raw materials was determined for the preparation of the mordenite. In the case of the preparation from the chemical reagents, amorphous SiO2 powder was necessary for the reaction using an NaOH solution. Based on these results, we considered the preparation of the mordenite from natural resources having a suitable Al/Si ratio using the combination of coal fly ash (high Al/Si ratio) and rice husk ash (low Al/Si ratio) at a low cost. It is well known that coal fly ash and rice husk are abundant by-products generated from a thermal power station or a rice milling factory, respectively. Furthermore, the preservation method for the zeolite containing radioactive Cs+ is an important study [22]. We suggested the glass solidification method for the Cs+ adsorbed zeolite by heat-treatment, because the zeolite is a glass formable Na2O-Al2O3-SiO2 systems [23].