Effect of altering linker ratio on nano-ZIF-8 polymorphisms in water-based and modulator-free synthesis

Abstract

A transition between a micron-leaf-like structure (ZIF-L) at room temperature to the nano-zeolitic imidazolate framework-8 (n-ZIF-8) was produced by using a water-based synthesis without modulating agents. Polymorphisms of ZIF structures were produced in an hour by mixing varying molar ratios of 2-methylimidazole and zinc nitrate hexahydrate (8:1, 21:1, and 35:1). The polymorphic phase transition of the ZIFs was identified using powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), thermal gravimetric analysis (TGA), and surface and pore characteristics from a nitrogen adsorption analyzer. The sizes of the particles range from micron to nano (ZIF-L = 2 µm, n₂₁ZIF-8 = 400 nm, and n₃₅ZIF-8 = 100 nm). The n₃₅-ZIF-8 has amongst the highest surface area of any ZIF-8 currently reported, with approximately 1776 m²g⁻¹ and is thermally stable up to 400 °C. Meanwhile, n₂₁ZIF-8 demonstrated the greatest CO₂ absorption capacity by absorbing up to 22.71 mmolg⁻¹ of CO₂ at 273 K.

Graphical Abstract

Keywords:

• Zeolitic imidazolate frameworks
• water-based
• modulator free
• nanomaterial

Additional information

Funding

This work was sponsored by the Research Management Centre, Universiti Putra Malaysia, under the Geran Putra Berimpak (9570200). We would like to express our gratitude and appreciation to Kyle E. Cordova (Royal Scientific Society, Amman, Jordan) for his contribution as an advisor on this project. N.F.H also would like to thank UPM for a Graduate Research Fellowship award for her study.