The two-dimensional silicon dioxide layer – not visible to the naked eye – is deposited on a gold surface. Photo by Ruhr-Universität Bochum, KramerA multi-disciplinary team from Bielefeld, Bochum and Yale universities have collaborated to develop a layer of two-dimensional (2D) silicon dioxide with natural pores that can be used as a sieve for both molecules and ions. Their breakthrough could find uses in desalinating seawater and also in new types of fuel cells.
It is known that if 2D materials are punctured in a highly precise way, they can be used to filter out specific ions and molecules. Many studies have attempted to perforate the 2D carbon atoms of graphene for just this reason, but the pores needed to be inserted artificially as the material has no natural pores. However, it is not straightforward to produce holes of a specific size in graphene without damaging the material since this reduces its mechanical stability.
An alternative was therefore required and, as reported in Nano Letters [Naberezhnyi et al. Nano Lett. (2022) DOI: 10.1021/acs.nanolett.1c04535], here a fabrication process of bilayer silicates was described that benefits from the crystal lattice of 2D silicon dioxide as it naturally contains pores, demonstrating that these pores can be used to separate some gases from each other.
As researcher Petr Dementyev said, “This is very exciting because 2D silicon dioxide has a very high density of tiny pores by nature that is simply not possible to be created in artificial membranes. Unlike in perforated graphene, the pores are all almost the same size. And there’s such an incredible number of them that the material behaves like a fine-mesh sieve for molecules.”
2D silica, which was first made in 2010, is very expensive to make, and can only be achieved at a small scale. Here, a new material fabrication process was developed based on atomic layer deposition, which was used to deposit a single layer of silicon dioxide onto a gold surface. A high-pressure process then transferred the layer into its 2D form before it was characterised in detail using spectroscopy and microscopy.
The gas flow through the 2D membrane in a vacuum chamber was then assessed, with vaporous water and alcohol being shown to penetrate the silica layer, while nitrogen and oxygen were not able to pass through. Materials with such selective permeability are increasingly being sought for their industrial applications.
As researcher Anjana Devi said, “Such 2D membranes could be at the forefront of aiding sustainable development, for example in the field of energy conversion or storage”. However, before the 2D silica can be used in real-world scenarios, it is key to assess how many different molecules can attach to the surface of the material or how they can penetrate it.
“This is very exciting because 2D silicon dioxide has a very high density of tiny pores by nature that is simply not possible to be created in artificial membranes. Unlike in perforated graphene, the pores are all almost the same size. And there’s such an incredible number of them that the material behaves like a fine-mesh sieve for molecules.”Petr Dementyev