Geopolymers are produced by reacting an aluminosilicate powder (metakaolins, blast furnace slags, fly ashes, pozzolana etc.) with an aqueous alkali hydroxide and/or alkali silicate solution [1], through an environmental friendly low temperature process. Furthermore, geopolymers can be regarded as the amorphous counterpart or precursor of crystalline zeolites [1]. Indeed, the final geopolymer structure consists of an amorphous network of SiO4 and AlO4- tetrahedral units connected by oxygens and charge-balanced by hydrated alkali cations, while zeolites are crystalline hydrated aluminosilicates with 3-dimensional structures. Both the materials have ion exchange properties, due to the presence of extra-framework cations (generally Na+, K+ and Ca2+) that balance the negatively charged aluminosilicate lattices caused by Al in IV fold coordination. Zeolites are extensively used as ion-exchangers, catalysts, molecular sieves and adsorbents thanks to the possibility to encapsulate a wide range of molecules in their structures formed by channels. Geopolymers, thanks to the mentioned similarities with zeolites, can be extended to a range of potential applications, similar to those of zeolites. This study reports the production and characterization of novel geopolymer-zeolite materials obtained adding a commercial synthetic zeolite X as filler to a metakaolin-based geopolymer matrix. Since the microstructure of a metakaolin-based geopolymer consists of nano-particulates separated by micro- and mesopores [1,2], the main goal was to combine the defined microporosity of zeolite with the mesoporosity of the geopolymer matrix, together with the possibility to consolidate the zeolite powder. In fact, the shaping of zeolite powders is important for industrial applications and often increases the complexity and the cost of the final product. The presence of a geopolymer binder results extremely useful to consolidate and form the zeolites also in complex and large shapes. 3-dimensionally structures with interconnected, distributed and highly accessible open pores were obtained and, because of zeolites, and in particular zeolite X, are largely used for the CO2 gas adsorption [3], the produced composites were tested in term of CO2 uptake, to highlight possible uses of the composites in adsorption or gas separation applications.
Development of geopolymer-zeolite composites for CO2 adsorption
E Papa;V Medri;E Landi;M Mazzocchi;P Benito;A Vaccari
2017
Abstract
Geopolymers are produced by reacting an aluminosilicate powder (metakaolins, blast furnace slags, fly ashes, pozzolana etc.) with an aqueous alkali hydroxide and/or alkali silicate solution [1], through an environmental friendly low temperature process. Furthermore, geopolymers can be regarded as the amorphous counterpart or precursor of crystalline zeolites [1]. Indeed, the final geopolymer structure consists of an amorphous network of SiO4 and AlO4- tetrahedral units connected by oxygens and charge-balanced by hydrated alkali cations, while zeolites are crystalline hydrated aluminosilicates with 3-dimensional structures. Both the materials have ion exchange properties, due to the presence of extra-framework cations (generally Na+, K+ and Ca2+) that balance the negatively charged aluminosilicate lattices caused by Al in IV fold coordination. Zeolites are extensively used as ion-exchangers, catalysts, molecular sieves and adsorbents thanks to the possibility to encapsulate a wide range of molecules in their structures formed by channels. Geopolymers, thanks to the mentioned similarities with zeolites, can be extended to a range of potential applications, similar to those of zeolites. This study reports the production and characterization of novel geopolymer-zeolite materials obtained adding a commercial synthetic zeolite X as filler to a metakaolin-based geopolymer matrix. Since the microstructure of a metakaolin-based geopolymer consists of nano-particulates separated by micro- and mesopores [1,2], the main goal was to combine the defined microporosity of zeolite with the mesoporosity of the geopolymer matrix, together with the possibility to consolidate the zeolite powder. In fact, the shaping of zeolite powders is important for industrial applications and often increases the complexity and the cost of the final product. The presence of a geopolymer binder results extremely useful to consolidate and form the zeolites also in complex and large shapes. 3-dimensionally structures with interconnected, distributed and highly accessible open pores were obtained and, because of zeolites, and in particular zeolite X, are largely used for the CO2 gas adsorption [3], the produced composites were tested in term of CO2 uptake, to highlight possible uses of the composites in adsorption or gas separation applications.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
