Compressibility behavior and pressure-induced over-hydration of zeolite K AlSi-L

Lara Gigli,Rossella Arletti,Simona Quartieri,Giovanna Vezzalini

doi:10.1016/j.micromeso.2018.09.031

Abstract

Abstract This paper reports a study, performed by in-situ synchrotron X-ray powder diffraction, of the high-pressure behavior of zeolite L. The experiments were performed using both penetrating (methanol: ethanol: water mixture, m.e.w.) and non-penetrating (silicon oil, s.o.) pressure transmitting media (PTM) to study the compressibility and the possible pressure-induced hydration (PIH) of this synthetic zeolite, technologically relevant as host-guest system exploited in numerous application fields. The experiments were performed from Pamb to 6.2 and 6.3 GPa in s.o. and m.e.w., respectively. The crystal structure refinements were performed up to 6.3 GPa and 3.1 GPa for the patterns collected in m.e.w. and s.o., respectively, while the unit cell parameters were determined in the whole pressure range for both media. A strong PIH effect is evident when zeolite L is compressed in m.e.w. and the over-hydration is essentially ascribable to the filling of most the H2O sites, to the appearance of a new H2O site and to the partially filling of the K sites. The over-hydration starts at a very low pressure (0.5 GPa) and the maximum H2O content can be estimated in 31.1 H2O molecules, against the original value of 18. The PIH is completely reversible upon P release. The main difference between the compression behavior of zeolite L in the two media is the higher compressibility in the non-penetrating one, evidenced by ΔV = − 6.3% and −9.9% in m.e.w. and s.o, respectively. Our data are consistent with the general behavior of zeolites compressed with penetrating media, when the intrusion of H2O molecules hinders the effects of the applied pressure. The results of this work are compared with those obtained on a K-gallosilicate with LTL topology, where PIH induces the formation of H2O nanotubes inside the zeolite channel.

Highlights

The regular pore systems of the framework make zeolites ideal host matrices for achieving supramolecular organization of different molecules such as photo-active species, leading to versatile building blocks for the production of multifunctional composite materials [1,2]
Notwithstanding, several studies have dealt with the incorporation of dyes into zeolites [10,11,12,13,14,15], only a work [16] until now exploited the behavior of these systems under high pressure trying to establish whether compression could favor a different distribution of the dye molecules and lead to an improvement of the optical properties of the materials under investigation
The overall results here reported underline the high baric stability of LTL framework and confirm the results found by Ref. [16] for zeolite L-fluorenone hybrid material

Summary

Introduction

The regular pore systems of the framework make zeolites ideal host matrices for achieving supramolecular organization of different molecules such as photo-active species, leading to versatile building blocks for the production of multifunctional composite materials [1,2]. Since the nanometric diameter channels of zeolites may induce an anisotropic arrangement of photoactive molecules, the resulting hybrid materials show outstanding energy transfer capabilities, mimicking the functionalities of the antenna systems of living plants [3,4,5] and can be exploited for several advanced applications [6,7,8,9]. The properties of these materials depend on the packing of molecules inside the channels, which in turn controls the intermolecular interactions. A pressure-induced strengthening of the interaction between the fluorenone carbonyl group and the potassium cations of the zeolite was observed.These results are clearly related to the stiffness of the host zeolite framework, unravel that the P-induced deformations of the pristine host framework is of fundamental importance to understand the driving forces involved in the hybrid structural modifications

Methods

Results

Conclusion