Cambridge University scientists have developed a new method for creating nanoporous materials.
In order to produce a porous material, it is necessary to have multiple components. When the minor component is removed, small pores are left in its place. Until now, creating nanoporous materials has been limited because the minor component had to be connected throughout the structure, as well as to the outside, in order for it to be removed.
The new research, published in the journal Nature Materials, has demonstrated a more effective, flexible method for creating porous structures called Collective Osmotic Shock (COS).
The scientists have shown that by using osmotic forces even structures with minor components entirely encapsulated in a matrix can be made porous (or nanoporous).
Dr Easan Sivaniah, lead author from Cambridge University’s Cavendish Laboratory, told The Engineer: ‘We broke down the polymers on the inside into small molecules using a bit of heat, sunshine and some vinegar. The molecules have a high solubility, so if you introduce a solvent it will dissolve as many of them as possible and this induces a large osmotic pressure.’
According to Sivaniah, the osmotic pressure forces the spherical molecules to expand and deform the matrix around it, thus creating a porous material.
He believes the most obvious application for nanoporous materials lies in filtration. Sivaniah added that the Cambridge team is looking at filtration on the nanoscale to filter out dyes from colourants.
The team is also looking at developing the technique so that it could be used for desalination and the removal of salts from seawater.
Furthermore, Sivaniah said: ‘The process generates this layered, self-supported material that has some potentially interesting applications, which go beyond just having a nanoporous high-surface-area material.
‘If you have layers of a material that are separated by layers of another material, then these can potentially be used as diffraction gratings or wave guides in optical communications. In order for that to work, the layers need to have a different density or refractive index,’ he said.
Multi-layered materials already exist but they have to be manufactured sequentially, which can be both time consuming and costly. ‘Also, the densities tend to be the same so the contrast is low, which means lots of layers are needed to get diffraction to occur,’ added Sivaniah.
‘In our case, we can put down a single material and introduce as many layers as we want, almost instantaneously,’ he said.