The Experts below are selected from a list of 282 Experts worldwide ranked by ideXlab platform
Stephen O Ekolu - One of the best experts on this subject based on the ideXlab platform.
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Enhancing the reactivity of Aluminosilicate materials toward geopolymer synthesis
Journal of Materials Science, 2018Co-Authors: L. N. Tchadjie, Stephen O EkoluAbstract:Geopolymers are alternative materials to portland cement, obtained by alkaline activation of Aluminosilicates. They exhibit excellent properties and a wide range of potential applications in the field of civil engineering. Several natural Aluminosilicates and industrial by-products can be used for geopolymer synthesis, but a lot of starting materials have the disadvantage of poor reactivity and low strength development. This paper presents a comprehensive review of the main methods used to alter the reactivity of Aluminosilicate materials for geopolymer synthesis, as reported recently in the literature. The methods consist of mechanical, thermal, physical separation and chemical activation, of which mechanical activation is the most commonly employed technique. The reactivity of the activated Aluminosilicate materials is mainly related to the activation method and the treatment parameters. Chemical activation by alkaline fusion is a promising method allowing preparation of one-part geopolymer materials, an alternative class of geopolymeric binders. However, the resulting alkaline-fused geopolymer products are vulnerable to attack by excessive alkalis.
Jing Bin Ding - One of the best experts on this subject based on the ideXlab platform.
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Hierarchically porous Aluminosilicates as the water vapor adsorbents for dehumidification
Chemical Engineering Journal, 2013Co-Authors: Weilong Wang, Hongyin Chen, Jing Xiao, Li Zhang, Jing Bin DingAbstract:Hierarchically porous Aluminosilicates with large surface area (930–1010 m2/g) and ordered hexagonal structures were synthesized as the water vapor adsorbents for dehumidification in this work. Compared to the commercial microporous zeolite 3A (low Si/Al ratio), and mesoporous SILICA GEL (high Si/Al ratio), the synthesized Aluminosilicates showed higher adsorption capacity of water vapor at both high and low humidity ranges. Different from zeolite 3A (type I) and silica gel (type III), the adsorption isotherms of Aluminosilicates followed type IV isotherms. The Aluminosilicate materials showed low desorption activation energy of water vapor (
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hierarchically porous Aluminosilicates as the water vapor adsorbents for dehumidification
Chemical Engineering Journal, 2013Co-Authors: Weilong Wang, Hongyin Chen, Jing Xiao, Li Zhang, Jing Bin DingAbstract:Hierarchically porous Aluminosilicates with large surface area (930–1010 m2/g) and ordered hexagonal structures were synthesized as the water vapor adsorbents for dehumidification in this work. Compared to the commercial microporous zeolite 3A (low Si/Al ratio), and mesoporous SILICA GEL (high Si/Al ratio), the synthesized Aluminosilicates showed higher adsorption capacity of water vapor at both high and low humidity ranges. Different from zeolite 3A (type I) and silica gel (type III), the adsorption isotherms of Aluminosilicates followed type IV isotherms. The Aluminosilicate materials showed low desorption activation energy of water vapor (<20 kJ/mol, close to the intermolecular H2O–H2O H-bonding interaction). The Aluminosilicates showed a low desorption temperature of 87 °C and a relatively fast desorption rate. Moreover, regenerability test in the multiple adsorption–desorption cycles suggested that the synthesized Aluminosilicates were regenerable. With the promising dehumidification characteristics, including high adsorption capacity of water vapor, fast adsorption and desorption rates, low regeneration temperature, as well as good regenerability, the synthesized hierarchically porous Aluminosilicates can be potential adsorbents for energy-efficient and cost-effective dehumidification process in practical applications, i.e. rotary desiccant dehumidifiers.
Maria De La Luz Mora - One of the best experts on this subject based on the ideXlab platform.
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studies of the surface charge of amorphous Aluminosilicates using surface complexation models
Journal of Colloid and Interface Science, 2005Co-Authors: Alejandra A. Jara, Sabine Goldberg, Maria De La Luz MoraAbstract:Synthetic noncrystalline Aluminosilicates with variable charge, similar to allophanes present naturally in volcanic soils, were studied. The surface charge behavior was determined by zero point charge (ZPC) measured by electrophoretic mobility (isoelectric points, IEP) and determined by potentiometric titration (point of zero salt effect, PZSE). The ZPC calculated by Parks model (ZPCc), compared with IEP values, showed that the Aluminosilicate (AlSi) surface was slightly enriched by AlOH (34% Al2O3 and 66% SiO2) compared with the bulk composition (29% Al2O3 and 71% SiO2). For Aluminosilicate coated with iron oxide (AlSiFe) the ZPCc (4.4) was lower than the IEP (8.46), showing that the surface composition is formed mainly from iron oxide. The PZSE values for AlSi and AlSiFe were 6.2 and 4.8, respectively. The differences between the IEP and PZSE are attributed to the formation of Si–O–Fe or Si–O–Al bonds; therefore, the reactivity of Fe and Al atoms was modified on the surface. Two mechanistic models, the constant capacitance model (CCM) and the triple layer model (TLM), using the program FITEQL 3.2 were able to describe the surface behavior of both synthetic Aluminosilicates. The acidity constants determined using both models for the Aluminosilicates showed differences with respect to pure oxide, mainly attributed to the presence of SiOH sites on the internal surfaces. The ionic strength showed a good relation with the parameters obtained using the CCM (pK int a1 ,p K int2 and capacitance values) and the TLM (pK int1 ,p K int a2 ,p K int Cl − ,p K int K + , and inner capacitance) for both Aluminosilicates. However, the TLM
L. N. Tchadjie - One of the best experts on this subject based on the ideXlab platform.
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Enhancing the reactivity of Aluminosilicate materials toward geopolymer synthesis
Journal of Materials Science, 2018Co-Authors: L. N. Tchadjie, Stephen O EkoluAbstract:Geopolymers are alternative materials to portland cement, obtained by alkaline activation of Aluminosilicates. They exhibit excellent properties and a wide range of potential applications in the field of civil engineering. Several natural Aluminosilicates and industrial by-products can be used for geopolymer synthesis, but a lot of starting materials have the disadvantage of poor reactivity and low strength development. This paper presents a comprehensive review of the main methods used to alter the reactivity of Aluminosilicate materials for geopolymer synthesis, as reported recently in the literature. The methods consist of mechanical, thermal, physical separation and chemical activation, of which mechanical activation is the most commonly employed technique. The reactivity of the activated Aluminosilicate materials is mainly related to the activation method and the treatment parameters. Chemical activation by alkaline fusion is a promising method allowing preparation of one-part geopolymer materials, an alternative class of geopolymeric binders. However, the resulting alkaline-fused geopolymer products are vulnerable to attack by excessive alkalis.
Fengshou Xiao - One of the best experts on this subject based on the ideXlab platform.
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hydrothermally stable ordered hexagonal mesoporous Aluminosilicates assembled from a triblock copolymer and preformed Aluminosilicate precursors in strongly acidic media
Chemistry of Materials, 2002Co-Authors: Shuo Wu, Fengshou Xiao, Dongsheng Li, Xiaozong ZhangAbstract:Mesoporous Aluminosilicates (MAS-9) with ordered hexagonal struture have been prepared by assembly of preformed Aluminosilicate precursors with a triblock copolymer in strongly acidic media by a two-step procedure. MAS-9 exhibits extraordinarily good hydrothermal stability and high catalytic activities for the cracking of both cumene and 1,3,5-tri-isopropylbenzene. Even after treatment in boiling water for 120 h, MAS-9 continues to show a large surface area (680 m2/g) and high catalytic activities. Furthermore, this two-step strategy could be used as a new general method for the preparation of mesoporous Aluminosilicate materials under strongly acidic conditions.
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mesoporous Aluminosilicates with ordered hexagonal structure strong acidity and extraordinary hydrothermal stability at high temperatures
Journal of the American Chemical Society, 2001Co-Authors: Zongtao Zhang, Runwei Wang, Yiqian Wang, Fengshou Xiao, Yi Yu, Ze Zhang, Dongyuan ZhaoAbstract:Highly ordered hexagonal mesoporous Aluminosilicates (MAS-5) with uniform pore sizes have been successfully synthesized from assembly of preformed aluminosilcate precursors with cetyltrimethylammonium bromide (CTAB) surfactant. The Aluminosilicate precursors were obtained by heating, at 100−140 °C for 2−10 h, aluminasilica gels at the Al2O3/SiO2/TEAOH/H2O molar ratios of 1.0/7.0−350/10.0−33.0/500−2000. Mesoporous MAS-5 shows extraordinary stability both in boiling water (over 300 h) and in steam (800 °C for 2 h). Temperature-programmed desorption of ammonia shows that the acidic strength of MAS-5 is much higher than that of MCM-41 and is comparable to that of microporous Beta zeolite. In catalytic cracking of 1,3,5-triisopropylbenzene and alkylation of isobutane with butene, MAS-5 exhibits greater catalytic activity and selectivity, as compared with MCM-41 and HZSM-5. The MAS-5 samples were characterized with infrared, UV−Raman, and NMR spectroscopy and numerous other techniques. The results suggest that ...
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strongly acidic and high temperature hydrothermally stable mesoporous Aluminosilicates with ordered hexagonal structure
Angewandte Chemie, 2001Co-Authors: Zongtao Zhang, Runwei Wang, Dongyuan Zhao, Yi Yu, Fengshou XiaoAbstract:Publisher Summary This chapter discusses strong acidic and high-temperature hydrothermally stable mesoporous Aluminosilicates with well-ordered hexagonal structure. These mesoporous Aluminosilicates have been successfully synthesized from the assembly of preformed Aluminosilicate precursors with cetyltrimethylammonium bromide (CTAB) surfactant. The MAS-5 shows extraordinary stability both in boiling water and in steam. Temperature-programmed desorption of ammonia (NH 3 ) shows that the acidic strength of MAS-5 is much higher than that of MCM-41.
