Exfoliation of 2D Metal-Organic Frameworks: toward Advanced Scalable Materials for Optical Sensing

Two-dimensional metal-organic frameworks (MOFs) occupy a special place among the large family of functional 2D materials. Even at a monolayer level, 2D MOFs exhibit unique sensing, separation, catalytic, electronic, and conductive properties due to the combination of porosity and organo-inorganic nature. However, lab-to-fab transfer for 2D MOF layers faces the challenge of their scalability, limited by weak interactions between the organic and inorganic building blocks. Here, comparing three top-down approaches to fabricate 2D MOF layers (sonication, freeze-thaw, and mechanical exfoliation), The technological criteria have established for creation of the layers of the thickness up to 1 nm with a record aspect ratio up to 2*10<^>4:1. The freezing-thaw and mechanical exfoliation are the most optimal approaches; wherein the rate and manufacturability of the mechanical exfoliation rivaling the greatest scalability of 2D MOF layers obtained by freezing-thaw (21300:1 vs 1330:1 aspect ratio), leaving the sonication approach behind (with a record 900:1 aspect ratio) have discovered. The high quality 2D MOF layers with a record aspect ratio demonstrate unique optical sensitivity to solvents of a varied polarity, which opens the way to fabricate scalable and freestanding 2D MOF-based atomically thin chemo-optical sensors by industry-oriented approach. High-quality 2D MOF membranes with a record aspect ratio of 21 300:1 have been created by freeze-thaw and mechanical exfoliation methods on arbitrary substrates for highly selective and sensitive optical sensing of chemicals.image

Automated summary

Two-dimensional metal-organic frameworks (MOFs) possess unique properties and exhibit high potential in various applications due to their porosity and organo-inorganic nature. However, the scalability of 2D MOF layers is limited by weak interactions between organic and inorganic building blocks. This study compared three top-down approaches and established technological criteria for creating 2D MOF layers with thickness up to 1 nm and a record aspect ratio of up to 2*10^4:1. The freezing-thaw and mechanical exfoliation methods showed the greatest scalability, surpassing the sonication approach, and high-quality 2D MOF layers with a record aspect ratio were achieved, enabling the fabrication of scalable and freestanding 2D MOF-based atomically thin chemo-optical sensors.