Abstract
The foamed alkali-activated zeolite materials have been studied primarily in terms of mechanical and structural properties as potential substitutes for concrete and other building materials. However, they also have interesting textural and acid properties that make them much more useful, especially in the chemical industry. The aim of the study is to map in detail the influence of post-synthesis modifications of alkali-activated natural zeolite foams on their chemical, mechanical, and textural properties for possible use in catalytic and adsorption applications. Alkali-activated natural zeolite foam pellets were prepared by activation with mixed potassium hydroxide and sodium silicate activator and foamed using H2O2 solution. The foam pellets were post-synthetic modified by leaching with mineral and organic acids and calcination. The properties of the modified materials were characterised on the basis of XRF, XRD, N2 physisorption, DRIFT, SEM, NH3-TPD analyses, and the strength measurements. Our data showed that the basic clinoptilolite structure remains unchanged in the material which is stable up to 600 °C after acid leaching. In two-step leaching, the specific surface area increases to 350 m2/g and the leaching process allows the acid properties of the materials to be varied.
Highlights
Alkali-activated foamed zeolites represent a new group of materials potentially useful in the chemical industry, especially in the field of catalysis and sorption
The alkaline activation of natural zeolites with the mixed KOH activator and Na—water glass and subsequent foaming of the alkaline activated mixture resulted in the formation of inorganic materials which are structurally similar to geopolymers
The zeolite foams prepared by alkaline activation of the natural zeolite represent the heat resistant materials in which further post-synthesis treatments can be performed to improve their properties
Summary
Alkali-activated foamed zeolites represent a new group of materials potentially useful in the chemical industry, especially in the field of catalysis and sorption. In the case of alkaline activation of metakaolin (geopolymerization), the original layered structure is completely dissolved, and a new amorphous network is formed. The amorphous network is formed by an N(K)–A–S–H matrix exhibiting zeolite-like properties. Alkaline activation of natural zeolites containing predominantly clinoptilolite produces a composite material composed of the original structure and the binder N(K)–A–S–H matrix from the original zeolite (clinoptilolite). The N(K)–A–S–H matrix is formed by dissolving the surface of the individual grains and the accompanying minerals which in the case of natural zeolites are other aluminosilicate minerals such as feldspars, mica, and clays [3]
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