Geopolymers can be regarded as the amorphous counterpart or precursor of crystalline zeolites. 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. The negatively charged aluminosilicate lattices, due to Al in IV fold coordination, need to be balanced by extra-framework cations (generally Na+, K+ and Ca2+), endowing both the materials with ion exchange properties. Geopolymer-zeolite composites were produced mixing different geopolymer metakaolinbased matrices with a synthetic commercial zeolite. A potassium or sodium silicate activating solution was used for the geopolymerization process and the commercial zeolite Na13X was used as filler. The microstructure of a metakaolin-based geopolymer consists of nano-particulates separated by micro- and mesopores [1,2] therefore, the main goal of the study was to combine this porosity with the peculiar and defined microporosity of zeolite. Since zeolite is partially reactive in alkaline medium [3], the production process and the synthesis parameters were investigated to limit the reaction of the zeolite. Moreover, the requirement of supporting or shaping powdery zeolites is important for industrial applications and often add complexity and cost to the final product, hence the geopolymer binder results extremely useful to consolidate the zeolite powder. The production of these geopolymer-zeolite composites result in the formation of 3-dimensionally interconnected structures with highly accessible and distributed open pores, particularly suitable for catalysts, filters and sorbents. The selected composites were deeply characterized in term of microstructure, mineralogical composition, porosity and specific surface area, together with the ability to adsorb CO2, in order to highlight one of the possible functional properties of the new material, since zeolites, and in particular zeolite X are largely used for the CO2 gas adsorption [4].
New Geopolymer-Zeolite Composites Materials
V Medri;E Papa;E Landi;M Mazzocchi;P Benito;A Vaccari
2017
Abstract
Geopolymers can be regarded as the amorphous counterpart or precursor of crystalline zeolites. 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. The negatively charged aluminosilicate lattices, due to Al in IV fold coordination, need to be balanced by extra-framework cations (generally Na+, K+ and Ca2+), endowing both the materials with ion exchange properties. Geopolymer-zeolite composites were produced mixing different geopolymer metakaolinbased matrices with a synthetic commercial zeolite. A potassium or sodium silicate activating solution was used for the geopolymerization process and the commercial zeolite Na13X was used as filler. The microstructure of a metakaolin-based geopolymer consists of nano-particulates separated by micro- and mesopores [1,2] therefore, the main goal of the study was to combine this porosity with the peculiar and defined microporosity of zeolite. Since zeolite is partially reactive in alkaline medium [3], the production process and the synthesis parameters were investigated to limit the reaction of the zeolite. Moreover, the requirement of supporting or shaping powdery zeolites is important for industrial applications and often add complexity and cost to the final product, hence the geopolymer binder results extremely useful to consolidate the zeolite powder. The production of these geopolymer-zeolite composites result in the formation of 3-dimensionally interconnected structures with highly accessible and distributed open pores, particularly suitable for catalysts, filters and sorbents. The selected composites were deeply characterized in term of microstructure, mineralogical composition, porosity and specific surface area, together with the ability to adsorb CO2, in order to highlight one of the possible functional properties of the new material, since zeolites, and in particular zeolite X are largely used for the CO2 gas adsorption [4].I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
