Tunable alkali-aluminosilicates geopolymers and composites as solid adsorbents for CO2 capture applications

Novel geopolymeric formulations have been developed to fabricate materials and composites to be used as solid adsorbents for the removal of CO2 from gaseous streams, e.g. for carbon capture. The geopolymer stoichiometry, phase composition and combination with other aluminosilicates such as zeolites have been considered in order to tune the resulting adsorptive performances, for targeted application. In particular, the Si/Al ratio has been varied from 1 to 2, using either K+ or Na+ silicates, and combined to different zeolites (including Na13X and NaA type). The results obtained indicated that Na+-based geopolymers present a superior CO2 capacity than those based on K+, , while a CO2/N2 selectivity results larger for the latter system. Interestingly, the addition of a zeolite fillers further enhances the CO2 capacity, often revealing a synergistic interplay among the phases; the effect is due to positive interactions obtained by efficient chemical mixing and the geopolymerization reaction, with the formation of a crystalline phase (NaA-type). When combined to zeolite Na4A, the obtained CO2 capacity reaches values comparable to those of benchmark adsorbents, identifying an optimal Si/Al ratio equal to 1.2.