Risen Interest in the Use of Graphene in Desalination Systems

Over the last few years, interest has risen in the use of graphene in desalination systems. Its conductive properties have led to interest as an electrode material in capacitive deionization systems and its ability to be made in sheets that are only one atom thick is of interest to membrane scientists.

Scientists at China’s Nanjing University of Aeronautics and Astronautics have now announced that graphyne, an allotrope of graphene, is a promising desalination alternative that “could filter salt from seawater at rates several orders of magnitude faster than conventional desalination techniques.”

According to Wanlin Guo, a professor of mechanics and nanoscience, graphyne is a two-dimensional sheet of carbon atoms, which are connected together in a geometry that is similar to graphene. However, an altered structure, which results from replacing certain double bonds with triple bond acetylenic linkages, creates many nanopores between the atoms that are large enough to pass water molecules, while excluding salts.

Dr Guo explained that graphyne membranes accomplish ion separation via a sieving effect, which still requires that the feed solution’s osmotic pressure be overcome to accomplish desalination, adding, “It is noteworthy that the most attractive advantage of the graphyne desalination device, is high throughput as well as the complete rejection of ions and other pollutants.”

An apparent advantage of graphyne over graphene is that the pores in a graphyne sheet are part of the material’s structure and are all the same size, whereas a graphene sheet would likely require perforations to be introduced by ion beam drilling or some other method.

“In our graphyne desalination system, very high energy recovery may be achieved, as much energy is retained in the desalinated water due to the low energy barrier for water permeation—which has yielded the high water flux. A high energy recovery will certainly save energy during desalination,” he said.

As interesting as their conclusions are, it should be noted that the graphyne sheets described have not yet been synthesized; all of the work done thus far, has been done using molecular dynamics (MD) simulations and first principles modeling.