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Water Vapor Adsorption by Zeolites
Published in A. K. Haghi, Ana Cristina Faria Ribeiro, Lionello Pogliani, Devrim Balköse, Francisco Torrens, Omari V. Mukbaniani, Applied Chemistry and Chemical Engineering, 2017
Sefika Çağla Sayilgan, Semra Ülkü
Zeolites are classified into two groups according to the structural changes and continuity of dehydration curves. While zeolite A, X, Y, and chabazite, clinoptilolite which remain stable up to temperature range of 700-1000°C take place in the first group and natrolite, scolecite, and mesolite which transform into a metastable phase after dehydration are categorized in the second group. Although there are not any topographic changes in the framework structure of zeolites, the cation locations may change during reversible and continuous dehydration process.9, 14, 69, 75, 97 For instance, Na+ ions, which are located in the 8-ring and displaced about 1.2 Å from the center of dehydrated zeolite A, causes blocking of pores and affects the adsorption ability of zeolite A.
Inorganic Polymers
Published in Charles E. Carraher, Carraher's Polymer Chemistry, 2017
Zeolites are three-dimensional microporous crystalline solids. Zeolites include a whole group of aluminosilicates with an approximate formula of SiAlO4. With respect to the type of bonding, zeolites can be divided into three groups. The natrolite group (mesolite, thomsonite, edingtonite, natrolite) consists of structures that are built up from rings of four SiAlO4 tetrahedra linked together into chains with fewer linkages between the chains so that cleavage along the chain direction is preferred. These materials generally have a fibrous character. In the heulandite group (stilbite, epistilbite, and heulandite), the SiAlO4 tetrahedra form sheets of six-membered rings with few linkages between the sheets. These materials are mica-like in behavior. The third group, the so-called framework zeolites, has the density of bonding similar in all three directions. This group includes most of the zeolites mentioned below.
Natural Nanomaterials
Published in M. H. Fulekar, Bhawana Pathak, Environmental Nanotechnology, 2017
Zeolites are hydrated aluminosilicate minerals made of tetrahedral building blocks of AlO4 and SiO4 linked by rings. These units form a rigid, 3-D crystalline structure with a network of interconnected tunnels and cages. More than 40 naturally occurring zeolites are known. Natural zeolites are rock-forming, micro porous silicate minerals. An example is the mineral natrolite [Na2Al2Si3O10 ⋅ 2H2O]. In zeolite, the pore and channel sizes are nearly uniform, allowing the crystal to act as a nanoscale filter, or molecular sieve. Molecular sieves are materials that can be short molecules based on their size and chemical or electronic affinity. The size of the molecular or ionic species that can enter the pores of a zeolite is controlled by the diameters of the tunnels. The types of molecules that can pass through the pores are influenced by their electrical charges and chemical interaction with the sieve matrix. Due to the strong electron charge inside the pores and high surface energy, zeolites can act a catalyst. The nanoscale architecture of the silicate and alumina in zeolites gives them their remarkable properties. Because of their powerful properties as filters and catalysts, zeolites are invaluable scientific tools. Zeolites have an ‘open’ structure that can accommodate a wide variety of cations, such as Na+, K+, Ca2+, Mg2+ and others. These positive ions are rather loosely held and can readily be exchanged for others in a contact solution. Some of the more common mineral zeolites are analcime, chabazite, heulandite, natrolite, phillipsite and stilbite (Fuoco, 2012).
Study on the metakaolin-based geopolymer pervious concrete (MKGPC) and its removal capability of heavy metal ions
Published in International Journal of Pavement Engineering, 2021
Xiao Chen, Zidong Niu, Haoyu Zhang, Yuguang Guo, Min Liu, Mingkai Zhou
Some crystalline phases were also observed in sample M1 (SiO2/Al2O3 = 2.0). β-Al2O3 (JCPDS = 01-082-1399) was identified in M1. This may be due to the incomplete reaction of the β-Al2O3, which was incorporated in the sample to adjust the mole ratio of SiO2/Al2O3. Meanwhile, Natrolite (Na2Al2Si3O10•2H2O, JCPDS = 00-022-1224), a zeolite-type sodium aluminosilicate hydrate, was also present in sample M1. This finding is consistent with M.A.M. Ariffin et al. (2013) in a blended ash geopolymer concrete. It is known that the crystal structure of Natrolite is a Si-O–Al network structure and it is usually cubic, granular or dense (Meier et al. 1960, Barrer and Fender et al. 1961), which is also confirmed by the SEM of M1 as shown in Figure 12. M1-500 × and M1-5000 × . A number of studies have found that the Zeolite minerals including Natrolite have a significant adsorption abilityof heavy metal ions and thus they have been widely used in water purification (Hui et al. 2005, Nazdeem et al. 2014). Therefore, it can explain why the M1 has the strongest capability on removal of heavy metal ions from solution, compared to M2 and M3, just as shown in Figure 10.