Intrinsic and Extrinsic Responses of ZIF-8 under High Pressure: A Combined Raman and X-ray Diffraction Investigation

Abstract

ZIF-8 is a prototypical porous material in the family of zeolitic imidazolate frameworks, and its structural stability is of great significance for a wide range of practical applications. Here, the intrinsic and extrinsic structural and mechanical responses of nanosized ZIF-8 perturbed by high external pressure have been comparatively investigated based on our in situ Raman measurements in different pressure environments, accompanied by synchrotron X-ray diffraction measurements and results from previous reports. An improvement of both the chemical and crystallographic stability of ZIF-8, rather than an intrinsic quick deterioration, can be observed when penetrating guest molecules get into the pores. Spectral evidence demonstrates that the CC section of the imidazolate ring is an optimal interaction site for the penetrating methanol, water, and nitrogen molecules. We further find that water molecules can cleave Zn−N bonds to bring linker-associated defects to ZIF-8. When compressed in the nonpenetrating silicone oil as a pressure transmitting medium (PTM) or when no PTM is used, irreversibility is observed, while samples show a highly reversible transformation both in the short-range and long-range regions upon decompression from a partially or entirely amorphous state in penetrating PTM. Furthermore, the released samples transform to a dense bulk state in the absence of penetrating PTM instead of preserving the original nanosized particles when penetrating pressure transmitting fluids is present. Moreover, the compressible behavior of ZIF-8 varies and is found to be strongly influenced by the size and polarity of molecules in the pores. The present results indicate that the stability, compressibility, and reversibility of ZIF-8 under pressure are closely related to the pressure environments and the characteristics of the guest molecules in the PTM. Thus, this study sheds light on the available mechanical modifications and selectable applications of ZIF-8 as gas absorbents for the future.

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

“…We have demonstrated that the pressure‐induced total amorphization of ZIF‐8 in liquid nitrogen is postponed to a much higher pressure of 28 GPa, and most Raman bands of ZIF‐8 move to higher wavenumber with respect to those in alcohols and water in the combined Raman and XRD study on ZIF‐8. [ 35 ] These results suggest that the framework is in a strained state at all time as pressure increases, withstanding not only a strong supporting/squeezing effect from the inner nitrogen molecules but also a highly external compression applied by the pressure transmitting medium. The host framework and the guest molecules interact on each other mutually in the confinement systems.…”

“…It has been reported that the structure of ZIF‐8 transforms to a high‐pressure phase above 1 GPa, due to reorientation of the methyl imidazolate ring triggered by interactions from the guest molecules. [ 35,38 ] This new structure exhibits enlarged diameters of the 4MR and 6MR windows and can capture more guests (see Figure 2). Our recent study showed that ZIF‐8 behaved in different ways in the presence of nitrogen molecules as pressure‐transmitting medium (PTM) in comparison with those obtained when nonpenetrating silicone oil was used or no PTM was used.…”

“…Our recent study showed that ZIF‐8 behaved in different ways in the presence of nitrogen molecules as pressure‐transmitting medium (PTM) in comparison with those obtained when nonpenetrating silicone oil was used or no PTM was used. [ 35 ] Almost all the Raman bands of ZIF‐8 moved to high wavenumbers and the normalized unit cell volume of ZIF‐8 expanded by about 1.4% at 1.3 GPa, accompanied by a low compressibility at higher pressures. Upon decompression, the chemical and crystallographic stability of ZIF‐8 were completely preserved and the pressure‐induced changes were completely reversible, instead of Raman irreversibility and amorphized state when no PTM was used.…”

“…[ 34 ] The characterizations of the as‐synthesized ZIF‐8 by X‐ray diffraction (XRD), transmission electron microscopy (TEM), and Raman spectroscopy have been performed in our recent article. [ 35 ] Raman spectra were acquired using a Renishaw inVia spectrometer with the excitation wavelength of 633 nm. The spectrometer was equipped with a 50× microscope objective, and the laser spot size was about 5 μm.…”

DNA adsorption on nanoscale zeolitic imidazolate framework-8 enabling rational design of a DNA-based nanoprobe for gene detection and regulation in living cells

“…ZIF-8 showed a characteristic band at 176 cm À1 and weak band at 281 cm À1 , originated from the Zn-N vibrations in the ZnN 4 tetrahedrons. 35,36 The high-frequency bands at 686 cm À1 , 1148 cm À1 , and 1460 cm À1 were attributed to imidazolate ring puckering, C-N stretching and C-H bending in the methyl group, respectively.…”