Geopolymers as adsorbents for CO2

Geopolymers are synthetic and amorphous alkali aluminosilicates. Since they can be considered the amorphous counterpart and precursor of zeolites, they can be potentially use as molecular sieves. Geopolymer matrices with Si/Al=2 show a quite good CO2 adsorption capacity at low temperature and selectivity up to 200 and 100 for CO2/N2 and CO2/CH4 separation, respectively [1]. The CO2 adsorption capacity can be further improved with the addition of fillers such zeolites [2] or hydrotalcites [3], the latter working both for low and intermediate temperature (200°C) [4]. At 35°C, the CO2 capacity was about 20% larger in Na-based geopolymer-zeolite composites, revealing a synergistic effect between the geopolymer matrix partially transformed into NaA zeolite and the added zeolite 13X. In the case of the addition of hydrotalcites a thermal treatment is needed to promote the loss of interlayered anions and water and the formation of a mixed oxide metaphase with great affinity for CO2.