New technique produces tunable, nanoporous materials

October 27, 2017 by Jacqueline Carey, University of Illinois at Chicago
New technique produces tunable, nanoporous materials
Left and center: Magnetite- and gold-based nanoparticles self-assemble into lattice-like structures. Right: Individual gold and magnetite based nanoparticles. Credit: Petr Kral

A collaborative group of researchers including Petr Kral, professor of chemistry at the University of Illinois at Chicago, describe a new technique for creating novel nanoporous materials with unique properties that can be used to filter molecules or light. They describe their research in the journal Science.

Nanoparticles are made up of a central solid core to which molecules called ligands are often attached. Nanoparticles can self-assemble into lattice-like formations that have unique optical, magnetic, electronic and catalytic properties.

Experimentalists led by Rafal Klajn, professor of chemistry at the Weizmann Institute of Science in Israel and corresponding author on the paper, produced thin lattice structures made up of two kinds of nanoparticles: one with a magnetite core and another with a gold core.

In order to form these thin, lattice-like structures, nanoparticles self-assembled within a layer of drying solvent floating on another liquid in which the particles are insoluble.

"The self-assembly mechanisms in the thin solvent layer differ from those at work when nanoparticles are allowed to self-assemble in bulk solvents," Kral explained.

The experimentalists also developed a technique for chemically etching out one of the two types of nanoparticles from the self-assembled lattice-like structures. The resulting material had tiny, regularly spaced holes.

The experimentalists then turned to Kral's theoretical chemistry group, which included Lela Vukovic, assistant professor of at the University of Texas at El Paso, to help them understand how these lattices formed.

Kral and Vukovic used atomistic molecular dynamics simulations to model exactly how the two different nanoparticles self-assembled into the thin, lattice-like structures. They found that depending on the type of liquids used in this process, nanoparticles self-assemble into different structures.

"Based on the known properties of the nanoparticles and the different liquid surfaces they were placed onto, we were able to predict how and why different lattices formed," said Kral, whose group has extensively studied how nanoparticles interact to form complex superstructures.

By changing the composition of the nanoparticles and the liquids on which they self-assemble, Kral said chemists can create a huge number and variety of new . Different sized would, when etched out, create different pore sizes.

Explore further: Magnetic nanocubes self-assemble into helical superstructures

More information: Thumu Udayabhaskararao et al. Tunable porous nanoallotropes prepared by post-assembly etching of binary nanoparticle superlattices, Science (2017). DOI: 10.1126/science.aan6046

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