Tailoring of the textural properties of geopolymer and zeolite- geopolymer materials: foaming and cold sintering process

The geopolymers are amorphous alumina-silicate materials characterised by intrinsic mesoporosity. However, the porosity of these materials could be easily customized, and thus specially designated, depending on their end use. In this work, geopolymer and geopolymer-zeolite materials with different porosity were synthetized with the aim of obtaining adsorbents for the removal of pollutants from gaseous streams and wastewater. In particular, two techniques were used to modify the textural properties of the materials: the Cold Sintering Process (CSP) and the foaming process. The latter was used to induce macroporosity in the samples in order to minimise the pressure drop. Specifically, the silicon metal (0.03 wt.%) and hydrogen peroxide as blowing agent were used. In this way, foams containing either only geopolymer (K-based with Si/Al=2) or also containing zeolite Na13X (22 wt.% and 50 wt.%) were synthetised. To obtain samples with porosity in the meso and micro range, however, the Cold Sintering Process was used in an innovative way. Indeed, the CSP was applied on zeolite-geopolymer powders: the zeolite provides the microporosity and higher adsorption capacities. Either NaA that nucleated in the geopolymer matrix (Na-based with Si/Al=1.2) or commercial Na13X powder that was added in varying percentages to a K-based geopolymer powder (Si/Al=2) was used as the zeolite source. Research activities are carried in the framework of the MUR PRIN 2022 Project GEA - GEopolymer based Adsorbents for effective adsorption and selective separation of CO2 and eutrophication pollutants, - Prot. 20229THRM2, funded by the European Union – Next Generation EU.