Sound waves summon new MOFs
Researchers have used sound waves to precisely manipulate atoms and molecules and produce breakthrough smart materials.
Metal-organic frameworks (MOFs) are incredibly versatile and super porous nanomaterials that can be used to store, separate, release or protect almost anything.
MOFs are gaining in popularity for sensing and trapping substances at minute concentrations, to purify water or air, and can also hold large amounts of energy, for making better batteries and energy storage devices.
Scientists around the world have designed more than 88,000 precisely-customised MOFs - with applications ranging from agriculture to pharmaceuticals.
However, the traditional process for creating them is environmentally unsustainable and can take several hours or even days.
Now, researchers from RMIT University have demonstrated a clean, green technique that can produce a customised MOF in minutes, harnessing the precision power of high-frequency sound waves.
Metal-organic frameworks are crystalline powders full of tiny, molecular-sized holes.
They have a unique structure - metals joined to each other by organic linkers - and are so porous that a gram of a MOF spread out would cover an area larger than a football pitch.
The new technique uses a microchip to produce high-frequency sound waves.
Co-author and acoustic expert Dr Amgad Rezk said these sound waves, which are not audible to humans, can be used for precision micro- and nano-manufacturing.
“At the nano-scale, sound waves are powerful tools for the meticulous ordering and manoeuvring of atoms and molecules,” Dr Rezk said.
The “ingredients” of a MOF - a metal precursor and a binding organic molecule - are exposed to the sound waves produced by the microchip.
Using the sound waves to arrange and link these elements together, the researchers were able to create a highly ordered and porous network, while simultaneously “activating” the MOF by pushing out the solvents from the holes.
The new method produces MOFs with empty holes and a high surface area, eliminating the need for post-synthesis “activation”.
“Existing techniques usually take a long time from synthesis to activation but our approach not only produces MOFs within a few minutes, they are already activated and ready for direct application,” said Professor Leslie Yeo, Director of the Micro/Nanophysics Research Laboratory at RMIT.
The researchers successfully tested the approach on copper and iron-based MOFs, with the technique able to be expanded to other MOFs and scaled out for efficient green production of these smart materials.