Our life occurs in voids; for example, rooms in buildings are nothing but voids and these rooms and the furniture in them consist of materials full of voids. Porous materials are omnipresent – both in nature and in technology. Even the bodies of our cars become increasingly porous – in this case to reduce weight and to save fuel. Voids are extremely powerful, determining and changing the character of substances. Making a material porous by inflating it with air can change it into a detergent, trapping dirt in its voids. “The chemical composition of a material does not change by making it porous. Its modified architecture, however, completely changes its properties and, thus, its fields of application,” attests Christian Slugovc from the Institute for Chemistry and Technology of Materials, stressing the enormous relevance of voids. Many applications rely entirely on the porosity of a material. This applies, for example, to catalytic converters, which are mostly based on highly porous ceramics filled with catalysts.
When crystals start to grow in the reaction vessel, joy breaks out in the lab.
Tiny pores, huge reservoir
At TU Graz, a multidisciplinary consortium consisting of 14 scientists from the areas of materials science, chemistry, physics, electrical engineering and biotechnology is concerned with a special type of porosity relying on pore sizes in the nanometer range. An important role in this context is played by microporous crystals, in which metal ions are connected by organic linkers (so-called metal-organic frameworks or MOFs). Due to their high porosity they make up a huge internal surface area providing them with an enormous potential for a variety of applications. A few cubic centimeters of these metal-organic scaffolds, for example, contain the surface area of a soccer field. The tiny pores can accommodate a variety of substances ranging from dirt to medicines.
Crystals of GUT-2. For the choice of the name of a metal-organic framework, in many cases the acronym of the research institution is chosen followed by a consecutive number.
Using funding to the amount of 1.5m euros from the interdisciplinary large-scale project, the scientists don’t want to focus solely on MOFs, but also other important porous materials, such as nanoporous metals and paper. “Our goal is to control the properties of the pores in a precise manner, manipulating their size, distribution and also the ratio between pores and dense material,” stresses Paolo Falcaro who, together with Christian Slugovc and Egbert Zojer of the Institute of Solid State Physics, leads the Porous Materials@Work project. “These characteristics of porosity have a decisive impact on the quality of a material.” As soon as one can control the growth of MOFs, materials for a variety of applications can be “designed”. “Depending on the arrangement and texture of the crystals the same material can exhibit different properties,” stresses the Professor for Biobased Materials Technology at TU Graz.
Depiction of the molecular structure of GUT-2.
Focused TU Graz expertise
For years, a number of scientists at TU Graz have been concerned with a variety of aspects of porous materials, as they are needed in many areas for numerous applications. A goal of the lead project is to focus this scattered expertise. Moreover, by hiring Paolo Falcaro at the Faculty of Technical Chemistry, Chemical and Process Engineering, Biotechnology two years ago, an internationally established expert and scientific pioneer in the area of porous materials, TU Graz has significantly strengthened its knowledge base and reputation in this seminal field. For his research on microporous materials, he has recently been awarded approx. 2m euros of funding through a Consolidator Grant from the European Research Council (ERC).
So far, apart from TU Graz there is no other institution in Austria that explicitly focuses its research on porous materials. Even worldwide, there are only few centers concentrating on this crucial interdisciplinary topic. The ambitious goal of the TU Graz scientists is to “eventually become one of the top three research centers for porous materials”, as Paolo Falcaro has stated. A big advantage in this context is that at TU Graz it is not necessary to start from scratch, rather the focus has to be on joining existing knowhow and combining different views to generate new insights and a comprehensive understanding of porous materials. “Interdisciplinarity will be the key to success,” states Paolo Falcaro. “Therefore, even at this stage the project comprises scientists from four faculties.” The expertise on porous materials at TU Graz, however, reaches out far beyond the people already involved in the lead project: “For this reason it is one of our key goals to attract an even greater pool of scientists in this way laying the foundation for a sustainable development,” stresses solid-state physicist Egbert Zojer, one of the coinitiators of the project. The scientists are unanimously convinced that “fundamental discoveries will allow us to optimize porous materials to a degree that will make possible not only improved but also entirely new applications. At TU Graz we are definitely ready to enter into yet unexplored terrain.”
The intensive link between basic research and experience in applications will trigger innovations, for example, in the area of environmental engineering and the fabrication of photovoltaic cells or the realization of energy storage applications. Also in the areas of medical and pharmaceutical engineering, the envisioned research activities will have a profound impact. For example, many drugs currently need to be stored at low temperatures, which increases costs and complicates their transport These problems can be avoided, provided that a porous “packing material” becomes available. “We are working on the encapsulation of enzymes, proteins and DNA in the pores of MOFs to make them insensitive to temperature variations,” Paolo Falcaro explains. “The crystalline structure around the “guest” in the pore protects it like a tough coat.”
In nature the internal architecture of porous materials is often quite chaotic. In contrast, in artificial materials the quest is usually for strict order regarding size, orientation and arrangement of the pores. “In many technical applications porosity only creates real benefits when pores are not strongly disordered,” explains Christian Slugovc, as a motivation for the scientists search for perfect order. “Typically, pores fulfill their tasks best, when they are strictly aligned like soldiers.” The degree of order can be controlled by crystal growth. “With Paolo Falcaro we have a clear competitive edge in this context,” the chemist states enthusiastically. Another goal of the research in Porous Materials@Work is the realization of material with a perfect horizontal arrangement of the pores to bring about high electrical conductivities. Combined with ionic conductivity achieved by filling the pores with an electrolyte, such materials will be highly attractive for many applications, including batteries, light-emitting devices and solar cells. “The controlled fabrication of crystals will boost our possibilities for developing such materials,” Christian Slugovc explains. A further advantage of the interdisciplinary consortium is also that it will allow ideas developed in basic research to be tested and transferred to a broad field of applications. There will be many exciting possibilities ahead on this voyage of discovery into the smallest voids of matter.