Fabrication of Self-Supporting Geopolymer Membranes and Gas Permeation through the Membranes

Abstract

Self-supported porous membranes composed of geopolymer, inorganic polymers with amorphous aluminosilicates were fabricated. Geopolymer paste was prepared by mixing metakaolin, as a aluminosilicate source, with sodium hydroxide or potassium hydroxide and silica gel in water. The paste was then casted on a glass plate and sandwiched with another glass plate to control the thickness of the membrane. The cast geopolymer paste was solidified to form a membrane by the curing process under a controlled temperature oven. The molar ratio of Si, Al, K or Na and the solid/liquid in the geopolymer paste was changed and the self-supported membrane was successfully formed for solid-liquid ratio at 0.5 and the molar ratio of SiO₂ : Al₂O₃ : K₂O=65 : 22.5 : 12.5. The pore size distribution of the geopolymer membrane depended on the curing temperature: the peak of the pore size distribution was observed for 20–30 nm for the membranes cured at 75°C or 100°C, while two peaks at about 20–30 nm and about 9 nm were observed for the membrane cured at 25°C. The gas permeation rate though the geopolymer membranes were inversely proportional to the one-half power of the product of the molecular weight of the permeated gas, the mean pore diameter, and the porosity, suggesting the Knudsen diffusion mechanism is dominant.