One-step template-free hydrothermal synthesis of partially Sr-incorporated hierarchical K-CHA zeolite microspheres

Abstract

Abstract Partially Sr-incorporated hierarchical K-CHA zeolite microsphere of primary truncated bi-pyramidal crystallites was hydrothermally synthesized by one-step template-free hydrothermal process and the formation mechanism was investigated in detail. Its crystallization was accelerated by addition of strontium, and it was formed by three distinct steps: formation and aggregation of amorphous hollow nanospheres, collapse of agglomerated hollow nanospheres to multilayered disc, and rotational intergrowth into thread ball shape microsphere. The hollow nanosphere was formed by thermal expansion of Sr-coated solid silica nanoparticle, and the multilayered disc, by collapse of spherically aggregated hollow nanospheres. The collapse took place to minimize total surface energy by flattening sticky hollow spheres and oriented attachment of crystallites nucleated in the shell of hollow spheres. The multilayered disc grew finally to be thread ball shape microspheres. K-CHA zeolite microspheres displayed hierarchical character and showed excellent 298 K adsorptions for water (316 cm3 g−1), and CO2 (167.0 mg g−1 at 10 bar). The CO2/N2 adsorption selectivity was 10 due to incorporated potassium ions. Evidently, partially Sr-incorporated K-CHA zeolite microsphere was a good adsorbent for solvent dehydration and carbon capture.