Pressure‐induced insertion and transformation of N₂ in the cavities of zeolitic imidazolate framework‐8: A Raman study

Abstract

We have investigated the pressure‐induced behaviors of nitrogen confined in the zero‐dimensional cavities of zeolitic imidazolate framework (ZIF)‐8 using Raman spectroscopy. Pressure forces the nitrogen molecules in the pressure‐transmitting medium (PTM) to enter the inner pores of ZIF‐8, and two Raman bands attributed to the nitrogen molecules interacting with the framework of ZIF‐8 and those approximately in the central part of the cavities surrounded by the former are observed. The confined nitrogen species transform in a different way under high pressure from those of the bulk nitrogen and the confined nitrogen in the one‐dimensional inorganic channels. Both the intermolecular interaction and the host–guest interaction jointly contribute to the transformation and a highly disordered and densely compressed state of the confined nitrogen is formed at 20 GPa. A hysteresis is found when comparing the Raman spectra at low and industrially accessible pressures after a compression and decompression cycle, suggesting that the ability of ZIF‐8 to storage nitrogen molecules increases. This study opens a new path toward understanding new behaviors of nitrogen in the nanostate and applications of ZIF‐8 for gas storage and capture.

ZIF-75 under Pressure: Negative Linear Compressibility and Pressure-Induced Instability

“…These characteristics mean that these materials are appropriate for a large series of technological and industrial applications, such as gas and compound adsorption [6][7][8][9][10][11], separation [4,7,[12][13][14][15], and storage [10,16,17]; catalysis [4,7,[18][19][20][21][22]; drug delivery [23]; and sensor and device development [24][25][26][27][28]. Furthermore, these compounds are highly flexible and sensitive to the action of pressure [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45]. These properties make them appropriate for a large spectrum of additional applications [23,[46][47]…”

“…However, for the evaluation of the suitability of these compounds for practical, specific applications, the behavior of their structures under the effect of pressure must be investigated. The study of the mechanical properties of microporous compounds has been the subject of a large amount of research in recent decades [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45]. The first principles solid-state methodology have been satisfactorily applied for this purpose and have enhanced our knowledge of the mechanical properties of these materials since they give access to the full tensorial elasticity of these materials [34][35][36][37][67][68][69][70][81][82][83]86,87,[99][100][101][102][103][104][105][106][107][108].…”