Researchers design new metal-free porous framework materials

In a study published in the journal Nature, the research team used inexpensive and abundant non-metallic elements, such as chloride ions, to design non-metal organic porous frameworks (N-MOFs).

The new materials offer an alternative to metal-organic frameworks (MOFs), a class of porous, crystalline materials made up of metals connected by organic linker compounds.

More than 95,000 MOFs have so far been discovered with a broad range of applications in fields such as catalysis, gas separation and energy storage.

The new metal-free porous framework materials are yet to be fully explored but have already shown early promise for the capture of iodine, which is important in the nuclear industry.

Other applications areas could include proton conduction, catalysis, water capture and hydrogen storage.

The research team think that in the future, it should be possible to extend the strategy materials where organic linkers are connected by ions made up of other common non-metal elements such as nitrogen, oxygen and sulfur.

The research drew on complementary expertise in the discovery of new materials and robotics from the University of Liverpool alongside computational modelling expertise from the University of Southampton.

Professor Andrew Cooper from the University of Liverpool's Department of Chemistry and Materials Innovation Factory in Liverpool said: "This work opens up a range of possibilities. Our approach uses non-metal anions as nodes to build frameworks rather than metal cations in MOFs. There are more anions available than there are metals in the periodic table, so the space to search for new materials is huge."

However, there is a long-standing problem: metal nodes in MOFs direct the framework structure, rather like joints in a scaffold. These joints have a predictable geometry that allows MOFs to be designed for specific applications. This 'molecular Lego' approach does not work for non-metallic salts because the interactions are much less directional.

Professor Graeme Day from the University of Southampton's School of Chemistry said: "We guided the discovery of these materials using a computational method called crystal structure prediction. This allows us to predict which non-metal salts will form stable porous frameworks, which salts will not, and to anticipate the precise crystal structure in advance of experimental work. We don't have to assume a specific geometry for the joints in the framework, which is a fundamental principle in MOF chemistry."

The research forms part of a broader programme of research that aims to redefine the way that we discover new materials by combining emerging techniques in computational prediction, artificial intelligence, and robotics.

The project was funded by the European Research Council, the Leverhulme Trust and the Engineering and Physical Sciences Research Council.

The paper 'Porous isoreticular non-metal organic frameworks' is published in the journal Nature.

Professor Andrew Cooper FRS is Academic Director of the University of Liverpool's Materials Innovation Factory, an £81 million facility dedicated to the research and development of advanced materials and established in partnership with Unilever.

He is also Director of the Leverhulme Research Centre for Functional Materials Design and Co-Director of AIChemy, a national research hub for the use of artificial intelligence in chemistry. He is currently a Royal Society Research Professor.

Professor Graeme Day is Professor of Chemical Modelling in the School of Chemistry at the University of Southampton, leading a research group developing predictive computational methods for the organic solid state.