One direction trumps

6 December 2016

Published in Nature: An international team of scientists led by the CSIRO has found a way to harness the full potential of the most porous materials on the planet, designer crystals known as Metallic Organic Frameworks (MOFs)

Made of metals joined to each other by organic linkers, MOFs - shown in right image - are crystalline powders full of holes. These molecular-sized holes can store, separate, release or protect just about anything. Images: CSIRO

Discovered in 1999, MOFs are already in use in a range of fields, including pharmaceutics, electronics and horticulture.

MOFs grow in a crystal form and are extremely flexible, especially when combined with nanoparticles that can add functional benefits.

Their main appeal lies in the great surface area they display due to the many holes present in the powdry material.

The storage and separation of gases, the protection of biomolecules in harsh conditions, the sensing and capture of substances at very low concentrations, and the removal of heavy metals, oil or toxins from water are among the potential applications.

However, their erratic structure has so far limited their use.

But the new research, which also involved Monash University and the University of Adelaide, has now discovered a way to control that the pores in MOFs are all aligned in one direction.

It is a critical step toward their application to advanced technologies such as optics, microelectronics, microfluidics and sensing, the researchers write.

For example, aligned MOF films conduct currents far better, which makes them more usable in implantable medical devices.

The structural control will also improve their potential use in storing, separating, releasing and protecting valuable compounds.

CSIRO already develops MOFs as molecular shells that can protect and deliver vaccines and drugs. MOFs may also act as a 'solar sponge' for the capture and release of carbon dioxide emissions, or be used for the development of plastic material that gets better with age.

The researchers achieved the structural control in a one-step method that employs copper hydroxide as substrate for the growth of the MOF crystals.

They then demonstrated the alignment by placing a polarisable fluorescent dye in the MOFs. This produced a film in which the fluorescent molecules lit up along one axis - and by simply rotating the film the light could then be switched on or off.

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