A guest/host material of LiCl/H-STI (stilbite) zeoliteassembly: preparation, characterization and humidity-sensitive properties

Abstract

The novel zeolite guest/host material, LiCl/H-STI (stilbite) assembly was synthesized by a thermal dispersion method, and characterized in detail by powder XRD, ⁷Li MAS NMR, SEM/EDX, DTA and FT-IR. The loading threshold of LiCl was confirmed by XRD to be 0.14 g/g. The ⁷Li MAS NMR spectra were measured for a solution of LiCl, LiCl crystallites, LiCl/H-STI assembly, Li⁺ ion-exchanged STI (Li-STI) as well as LiCl dispersed on supports of zeolite ZSM-39, zeolite ZSM-5, silica gel and quartz. According to the chemical shifts, the states of Li⁺ can be identified as Li⁺ ions in solution, LiCl isolated in zeolite channels, Li⁺ cations balancing the framework charges and LiCl as a crystalline phase or cluster. Characterization results proved the LiCl guest was highly dispersed into the channels of the host at the threshold assembly loading. The interactions of LiCl with the zeolite framework and H₂O are also discussed. The threshold loading LiCl/H-STI material was found to possess optimum humidity-sensitive performance with a linear change of 4 orders of magnitude in electrical conductivity over the whole range of relative humidity. In addition, it also shows satisfactory reversibility and fast responses to environmental moisture changes.