Highly Porous Geopolymers Through Templating and Surface Interactions

The natural porosity of geopolymers and the simplicity of geopolymer synthesis make them a potential candidate for the formation of highly porous ceramics. Here, the synthesis of highly porous (≈70 vol% or more) metakaolin geopolymer is demonstrated using a novel emulsion preparation with one-pot curing and hydrophobization of the interior pores with alkylalkoxysilanes. Using mercury intrusion porosimetry, tailoring of the characteristic percolation pore size is demonstrated over a range of ≈200 nm to 10 μm. Using powder X-ray diffraction, reactivity was shown to be decreased versus typical geopolymers, but substantial geopolymerization still occurred and the samples formed cohesive monoliths. Optional calcination under inert conditions allowed for formation of a glassy ceramic with a notable SiC phase, as well as further increasing the porosity by removing the hydrophobic pore coatings.