A Simple Step toward Enhancing Hydrothermal Stability of ZIF-8.

Shunsuke Tanaka,Yasuhito Tanaka

doi:10.1021/acsomega.9b02812

Abstract

ZIF-8 is a flexible zeolitic imidazole-based metal–organic framework and has been extensively studied because of its high structural stability. However, ZIF-8 is hydrolyzed in water at higher temperature, resulting in degradation of its crystalline and porous structure. In order to prevent ZIF-8 from structural collapse due to the hydrolysis reaction of the metal–ligand bond and/or ligand substitution reaction, it is effective to shield the metal–ligand bond from the attack of water molecules. This work reports on the thermal and hydrothermal stability of mechanochemically synthesized ZIF-8 and presents an incredibly simple step to modify the outermost surface of ZIF-8, improving the hydrothermal stability. The partial carbonization resulting in the formation of a carbon-rich outermost layer endowed ZIF-8 with not only high hydrothermal stability but also a high adsorption rate on liquid phase adsorption.

Highlights

Metal−organic frameworks (MOFs) are a unique type of crystalline microporous and inorganic−organic hybrid materials, which can be self-assembled from metal ions/ clusters and organic ligands.[1−6] MOFs offer many interesting opportunities in adsorption and separation technology because of their chemical and structural tunabilities
According to our previous report,[32−34] the pristine ZIF-8 was prepared by mechanochemical synthesis using zinc oxide, zinc acetate dihydrate, and 2-methylimidazole
Several of the literature shows that ZIF-8 undergoes hydrolysis under hydrothermal conditions

Summary

■ INTRODUCTION

Metal−organic frameworks (MOFs) are a unique type of crystalline microporous and inorganic−organic hybrid materials, which can be self-assembled from metal ions/ clusters and organic ligands.[1−6] MOFs offer many interesting opportunities in adsorption and separation technology because of their chemical and structural tunabilities. The pristine ZIF-8 preserved its crystalline structure after immersing in water at room temperature for one week, which is in good agreement with an earlier report by Yaghi et al.[25] In addition, no changes were observed in nitrogen adsorption isotherms and surface areas, as shown in Figures 4 and 5. The fact that ZIF/550 and ZIF/650 are dispersed in water is attributed to the high relative content of N on the surface (Figure S5) This result is in reasonable agreement with the chemical structure including physically adsorbed water estimated by FTIR. The enhancement in the adsorption rate suggests that the surface resistance on diffusion of hydroquinone is reduced by pore size enlargement of the outermost surface due to the disappearance of Zn in the carbon-rich layer

■ CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES