By taking advantage of thermodynamic Pourbaix diagrams, scientists can squeeze catalysts inside host materials, like a ship in a bottle. Image: Jingwei Hou.
By taking advantage of thermodynamic Pourbaix diagrams, scientists can squeeze catalysts inside host materials, like a ship in a bottle. Image: Jingwei Hou.

Scientists at Queen Mary University of London in the UK have found a way to place catalysts inside the tiniest pores of different host materials, a bit like fitting a model ship inside a bottle. When materials are confined like this on such a small scale, and without breaking the host, they behave differently from their bulk form, a change that scientists call the confinement effect.

In the case of catalysts, which are materials that speed up chemical reactions, confinement may lead to higher activity by keeping particles well separated, which is key to preventing loss of function in catalysis and preserving their highly reactive surface. Similarly, when a material is squeezed in a small space, its electrons are not free to move as far as usual and the material's light emission color could change – an effect that could be used in micro lasers.

This strategy also opens up the possibility of multifunctional materials in which either the guest and host do different things separately or, because the guest is confined, the interactions between the host and guest produce novel properties.

To illustrate the approach, the researchers used porous nanomaterials, which are like sponges but with 1nm pockets inside where other molecules can fit. However, loading reactive catalysts inside a nanoporous host is challenging because often the reaction conditions can destroy the host.

In a paper in Nature Communications, the researchers describe using thermodynamics to overcome these issues, after realizing they could estimate the stability of the host under various reaction conditions. The research was carried out with colleagues at the University of Cambridge in the UK, the Dalian Institute of Chemical Physics in China, the National University of Singapore and The University of New South Wales in Australia.

"We had some ideas that confinement could change properties, as such changes have been seen in other systems," explained principal investigator Stoyan Smoukov from Queen Mary University of London. "The question was – was there a general way in which we could try and guide researchers so they could synthesize all kinds of large guests with various functions – like metals, metal oxides, sulfides, nitrides – without destroying the hosts?"

Using thermodynamic diagrams, the researchers developed a concept called Pourbaix-enabled guest synthesis (PEGS), where conditions and precursor compounds can be chosen not to destroy the hosts. They also produced a tutorial system that demonstrates how to make a large variety of new guest/host combination compounds.

"From a practical perspective, the PEGS approach links the materials chemistry with the design of functional materials for applications such as heterogeneous catalysis," said co-corresponding author Qiang Fu from Dalian Institute of Chemical Physics. "The confined oxide nanostructures obtained by the PEGS method in this work can present enhanced catalytic performance, which is of great significance for design of advanced oxide catalysts."

"The upcoming impact can be enormous," added Tiesheng Wang from the University of Cambridge, who was one of the lead authors. "Since quantum theory describes nature at atomic-to-subatomic scales, the work that helps to achieve new confined states at small scales may contribute to the foundation to explore the quantum world experimentally."

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