ZIF-8: A comparison of synthesis methods

doi:10.1016/j.cej.2015.02.094

Chemical Engineering Journal

Volume 271, 1 July 2015, Pages 276-280

https://doi.org/10.1016/j.cej.2015.02.094 Get rights and content

Highlights

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ZIF-8 was prepared by 7 different synthesis methods.
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Physicochemical properties of the samples were compared.
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ZIF-8 with smaller particle size showed better activity in condensation reaction.
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Fe₃O₄ nanoparticles entrapped in ZIF-8 enabled effective separation in liquid.

Abstract

A zeolitic imidazolate framework, ZIF-8, was prepared via a variety of synthesis routes: solvothermal, microwave-assisted, sonochemical, mechanochemical, dry-gel, and microfluidic methods. Their textural properties and morphology were examined by surface area measurements and scanning electron microscopy, and compared with those of commercial ZIF-8. Although the BET surface areas fell within a range of 1250–1600 m² g⁻¹, the particle size of the samples prepared by dry-gel and sonochemical routes were significantly smaller than the others, which led to superior performance in the Knoevenagel condensation reaction. The effective incorporation of magnetic Fe₃O₄ nanoparticles into the ZIF-8 structure for easy particle separation in the liquid phase was feasible using solvothermal, dry-gel and mechanochemical synthesis methods. Dry-gel and mechanochemical synthesis produced a higher ZIF-8 yield.

Introduction

Zeolitic imidazolate frameworks (ZIFs) are porous hybrid materials with structures analogous to zeolites that are built upon 4-connected nets of tetrahedral units, wherein metal ions, such as Zn²⁺ or Co²⁺, are linked through N atoms in ditopic imidazolate anions [1], [2]. ZIFs have emerged as a potential material for H₂ storage [3], CO₂ adsorption [4], alkane/alkene separation [5], and heterogeneous catalysis [6] owing to their structural flexibility, which allows rational design of the pore sizes and surface functionality, and their relatively high chemical and thermal stability [7]. Among the ZIFs, ZIF-8 (Zn(mIM)₂, mIM = 2-methylimidazolate) exhibits a sod topology comprised of 1.16 nm cages connected through six-membered windows, 0.34 nm in size (Fig. 1), and is currently the most widely investigated ZIF material for a range of applications [8], [9], [10].

ZIF-8 can be prepared in high purity through several different synthesis routes [1], [2], [11], [12], [13], [14], [15], [16]. Synthesis in an environmental-friendly manner under facile conditions is desirable, and particular emphasis has been placed upon size-controlled ZIF-8 synthesis [17], [18], [19] and the easy separation of nano- to submicron-sized ZIF-8 by incorporating a magnetic Fe₃O₄ guest into the ZIF-8 particle [11], [16], [20].

In the present study, ZIF-8 was synthesized using 7 different synthesis methods (conventional solvothermal in different organic solvents of dimethylformamide (DMF) and methanol (MeOH); microwave-assisted; sonochemical; mechanochemical; dry-gel; microfluidic), and their physicochemical properties were compared with those of commercial ZIF-8 prepared using an electrochemical method. The differences in the physicochemical properties among the ZIF-8 samples were manifested in the probe catalytic reaction of the Knoevenagel condensation of benzaldehyde with malononitrile. The feasibility of incorporating Fe₃O₄ nanoparticles into ZIF-8 produced via the different synthesis routes was also examined.

Section snippets

Synthesis

The detailed synthesis steps of ZIF-8 via solvothermal (in DMF and MeOH), microwave-assisted, sonochemical, mechanochemical, dry-gel, and microfluidic routes (Fig. S1) are reported in Supporting information.

Characterization

The X-ray diffraction (XRD) patterns of the ZIF-8 samples were obtained on a Rigaku diffractometer using Cu Kα (λ = 1.54 Å) radiation. The N₂ adsorption and desorption isotherms were obtained on an ASAP-2020 (Micromeritics, USA) sorptometer at a liquid nitrogen temperature. Prior to the

Various synthesis of ZIF-8

The XRD patterns for all the ZIF-8 samples [(a)–(g)] synthesized in this work and that of commercial ZIF-8(h) (Fig. S2) were all in good agreement with the simulated pattern of the ZIF-8 structure. All the ZIF-8 samples showed type-I N₂ adsorption isotherms at 77 K with no hysteresis (Fig. S3). Table 1 lists the summary of synthesis conditions and textural properties (BET surface area, total pore volume, and external surface area) and Table 2 shows the SEM images and particle size of the

Conclusions

ZIF-8 was prepared using several methods: solvothermal (DMF, MeOH), microwave-assisted, sonochemical, mechanochemical, dry-gel, and microfluidic method. Few differences in textural properties were detected, but the dry-gel and sonochemical techniques produced significantly smaller particles, which resulted in faster reaction rates in the Knoevenagel condensation reaction of benzaldehyde with malononitrile. The encapsulation of Fe₃O₄ nanoparticles within ZIF-8 was feasible using solvothermal as

Acknowledgement

This study was supported by a National Research Foundation of Korea (NRF) grant funded by the Korean Government (MEST) (No. 2013005862).

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Short communicationZIF-8: A comparison of synthesis methods

Highlights

Abstract

Introduction

Section snippets

Synthesis

Characterization

Various synthesis of ZIF-8

Conclusions

Acknowledgement

J. Mol. Catal. A: Chem.

Catal. Today

Microporous Mesoporous Mater.

Chem. Eng. J.

Chem. Eng. J.

J. Colloid Interface Sci.

High-throughput synthesis of zeolitic imidazolate frameworks and application to CO2 capture

Science

Exceptional chemical and thermal stability of zeolitic imidazolate frameworks

Proc. Natl. Acad. Sci.

Molecular sieve membrane: supported metal-organic framework with high hydrogen selectivity

Angew. Chem. Int. Ed.

A combined experimental–computational investigation of carbon dioxide capture in a series of isoreticular zeolitic imidazolate frameworks

J. Am. Chem. Soc.