High-porosity geopolymer foams with tailored porosity for thermal insulation and wastewater treatment

High-porosity metakaolin-based geopolymer foams (GFs) were fabricated by a gelcasting technique using hydrogen peroxide (foaming agent) in combination with Tween 80 (surfactant). Slurries processed in optimized conditions enabled to fabricate potassium based GFs with a total porosity in the range of similar to 67 to similar to 86 vol% (similar to 62 to similar to 84 vol% open), thermal conductivity from similar to 0.289 to; 0.091 W/mK, and possessing a compressive strength from similar to 0.3 to similar to 9.4 MPa. Moreover, factors that influence the compressive strength, the porosity, the thermal conductivity, and the cell size distribution were investigated. The results showed that the cell size and size distribution can be controlled by adding different content of surfactant and foaming agent. The foamed geopolymer can also be used as adsorbents for the removal of copper and ammonium ions from wastewater. The foams, due to their low thermal conductivity, could also be used for thermal insulation. It was also possible to produce geopolymer formulations that could be printed using additive manufacturing technology (Direct Ink writing), which enabled to produce components with nonstochastic porosity.