New synthesis method aligns MOFs to novel applications

The porous crystals known as metal-organic frameworks (MOFs) consist of metallic intersections connected by organic molecules. Thanks to their high porosity, MOFs have an extremely large surface area: a teaspoonful of MOF has the same surface area as a football pitch. The large number of pores situated in an extremely small space offer room for ‘guests’, allowing MOFS to be used for gas storage or as a ‘molecular gate’ for separating chemicals.

But MOFs have a much greater potential, and this is what Paolo Falcaro from the Institute of Physical and Theoretical Chemistry (PTC) at the Graz University of Technology (TU Graz) in Austria wants to unlock. “MOFs are prepared by self-organization,” Falcaro explains. “We don’t have to do anything other than mix the components, and the crystals will grow by themselves. However, crystals grow with random orientation and position, and thus their pores. Now, we can control this growth, and new properties of MOFs will be explored for multifunctional use in microelectronics, optics, sensors and biotechnology.”

In a paper in Nature Materials, Falcaro and his team report a method for growing MOFs on a comparatively large surface area of 1cm² that offers an unprecedented level of control over the orientation and alignment of the crystals. Other members of the team include Masahide Takahashi from Osaka Prefecture University in Japan and researchers from the University of Adelaide, Monash University and the Commonwealth Scientific and Industrial Research Organisation (CSIRO), all in Australia.

Incorporating functional materials into these precisely-oriented crystals allows the creation of anisotropic materials, which are materials with directionally-dependent properties. In the paper, the research team describes incorporating fluorescent molecules into a precisely-oriented MOF. Just by rotating the film, the fluorescent signal can be turned ‘on’ or ‘off’, producing an optically-active switch.

“This has many conceivable applications and we’re going to try many of them with a variety of different functionalities,” says Falcaro. “One and the same material can show different properties through different orientations and alignments. Intentional growth of MOFs on this scale opens up a whole range of promising applications which we’re going to explore step by step.”

A major aim of Falcaro and his team at TU Graz is developing MOFs for biotechnological applications. “We are trying to encapsulate enzymes, proteins and even DNA in MOFs and to immunize their activity against fluctuations in temperature,” he says. “The crystalline structure surrounding the ‘guest’ in the pore has a protective effect, like a tough jacket. We want to check out the possibilities more accurately.”

This story is adapted from material from TU Graz, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.