Zeolitic imidazole Framework-8 (ZIF-8) fibers by gas-phase conversion of electroblown zinc oxide and aluminum doped zinc oxide fibers

Jani Holopainen,Mikko J Heikkilä,Leo D Salmi,Kaisu Ainassaari,Mikko Ritala

doi:10.1016/j.micromeso.2018.04.003

Jani Holopainen, Mikko J Heikkilä + Show 3 more

Open Access

https://doi.org/10.1016/j.micromeso.2018.04.003

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Abstract

Electroblowing was used to prepare ZnO and aluminum doped zinc oxide (AZO, 1–3 cation-% of Al) fibers. The as-blown fibers were calcined at 500 °C to obtain the target material. The average fiber diameters ranged from 240 ± 60 nm for ZnO fibers to 330 ± 80 nm for AZO with 3% Al. Smaller crystallite size was measured with x-ray diffraction for the Al doped fibers. Electroblowing was found out be an effective method to increase the fiber productivity over electrospinning and other methods reported in literature to prepare AZO fibers as a high production rate of 0.32 g/h was achieved. The ZnO and AZO fibers could be converted to zeolitic imidazole framework-8 [ZIF-8, zinc(2-methylimidazolate)2] by a solvent free thermal treatment in an autoclave under 2-methylimidazole (HmIM) vapor at 150 and 200 °C while preserving the fibrous structure. The conversion process to ZIF-8 occurred faster at higher temperatures and on fibers with smaller crystallite size. Depending on the conversion treatment time either ZnO/ZIF-8 and AZO/ZIF-8 core/shell fibers or ZIF-8 fibers could be obtained. At best the prepared ZIF-8 fibers had a very high BET specific surface area of 1340 m2/g.

Highlights

Metal organic frameworks (MOFs) are hybrid materials consisting of metal ions or clusters connected by organic linker molecules
The electroblowing of ZnO nanofibers was done using poly(vinyl pyrrolidone) (PVP) as the carrier polymer and zinc nitrate as the zinc source that were selected based on initial screening tests
ZnO and aluminum doped zinc oxide (AZO, 1–3 cation-% of Al) fibers were prepared for the first time by electroblowing

Summary

Introduction

Metal organic frameworks (MOFs) are hybrid materials consisting of metal ions or clusters connected by organic linker molecules. Methylimidazole (HmIM) vapor [8,9] This gas phase conversion enables the preparation of conformal ZIF-8 coatings with a uniform thickness, controlled at a much more accurate level compared to the more commonly used solvothermal preparation methods. The excellent controllability of fiber properties and the wide range of attainable materials have made electrospinning the most popular nanofiber preparation method, its industrial applicability is limited due to its modest production rate [46]. Solution blow spinning has recently emerged as a new straightforward method for improving fiber productivity [53,54,55] It relies on a high velocity gas flow to draw a polymer solution into fibers. This is to the best of our knowledge the first report on the preparation of bare ZIF-8 or any other kind of metal-organic framework fibers

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