The effect of nanostructures on high pressure intrusion–extrusion of water and electrolyte solutions in hierarchical nanoboxes of silicalite-1

Abstract

This study of high pressure intrusion–extrusion of water and 20 M LiCl solution in silicalite-1 nanoboxes demonstrates how nanostructures can determine the properties of materials. The drastic effect of the presence of cavities on the intrusion–extrusion behavior and characteristics has been observed, particularly, in the case of LiCl aqueous solution. The nanoboxes demonstrate a combination of bumper and spring behavior in the first intrusion–extrusion cycle. The intrusion of 20 M LiCl solution is only partially reversible and takes place in two clearly marked steps, whereas only one intrusion step with a fully reversible spring behavior is observed for the micro- and nanocrystals. The first step, with an intruded volume of 0.07 mL g⁻¹ and an intruded pressure of 98 MPa, is irreversible and corresponds probably to the filling of mesoporous cavities, and the second one, with an intruded volume of 0.08 mL g⁻¹ and an intrusion pressure of 273 MPa, is fully reversible and related to the filling of the micropores of silicalite-1 walls. The filling of the nanocavities occurs probably through small mesoporous cracks in the nanobox walls. The characterization by structural and physicochemical methods shows that the dissolution–recrystallization process leads to the formation of a MFI structure with lower content of silanol defects in comparison with initial nanocrystals explaining the steeper slope of the intrusion step and the higher intrusion pressure observed for the “nanobox–H₂O” and “nanobox–20 M LiCl” systems.