Exfoliation of metal-organic framework nanosheets using surface acoustic waves

Xia Liu; Qinxiang Jia; Yongqing Fu; Tengfei Zheng

doi:10.1016/j.ultsonch.2022.105943

Exfoliation of metal-organic framework nanosheets using surface acoustic waves

Ultrason Sonochem. 2022 Feb:83:105943. doi: 10.1016/j.ultsonch.2022.105943. Epub 2022 Feb 2.

Authors

Xia Liu¹, Qinxiang Jia², Yongqing Fu³, Tengfei Zheng⁴

Affiliations

¹ State Key Laboratory for Manufacturing Systems Engineering Xi'an Jiaotong University, Xi'an 710049, People's Republic of China; Shaanxi Key Lab of Intelligent Robots, Xi'an Jiaotong University, Xi'an 710049, People's Republic of China.
² Department of Chemistry, Xi'an Key Laboratory of Sustainable Energy Materials Chemistry, Xi'an Jiaotong University, Xi'an 710049, People's Republic of China.
³ Faculty of Engineering & Environment, Northumbria University, Newcastle upon Tyne NE1 8ST, UK.
⁴ State Key Laboratory for Manufacturing Systems Engineering Xi'an Jiaotong University, Xi'an 710049, People's Republic of China; Shaanxi Key Lab of Intelligent Robots, Xi'an Jiaotong University, Xi'an 710049, People's Republic of China. Electronic address: tengfz@xjtu.edu.cn.

Abstract

Two-dimensional (2D) metal-organic framework (MOF) nanosheets have recently received extensive attention due to their ultra-thin thickness, large specific surface area, chemical and functional designability. In this study, an unconventional method using surface acoustic wave (SAW) technology is proposed to exfoliate large quantities and uniform layers of 2D MOF-Zn₂(bim)₄ nanosheets in a microfluidic system. We successfully demonstrated that the thickness of 2D MOF is effectively and accurately controlled by optimizing the SAW parameters. The mechanisms for the efficient exfoliation of 2D MOF nanosheets is attributed to both the electric and acoustic fields generated by the SAWs in the liquid. The electric field ionizes the methanol to produce H⁺ ions, which intercalate Zn₂(bim)₄ sheets and weaken the interlayer bonding, and the strong shear force generated by SAWs separates the MOF sheets. A yield of 66% for monolayer MOFs with a maximum size of 3.5 μm is achieved under the combined effect of electric and acoustic fields. This fast, low-energy exfoliation platform has the potential to provide a simple and scalable microfluidic exfoliation method for production of large-area and quantities of 2D MOFs.

Keywords: Electric field; Metal–organic framework (MOF- Zn(2)(bim)(4)) nanosheets; Surface acoustic wave(SAW).