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Graphene Enables Tunable Ion Filter

Graphene Enables Tunable Ion Filter

Researchers from National Institute of Standards and Technology (NIST) conducted simulations that suggest modification of graphene for a tunable filter

Simulations performed by a team of researchers from National Institute of Standards and Technology (NIST) suggested that graphene can be modified with special pores. The modification enables the use of graphene as a tunable filter or strainer for ions in a liquid. Moreover, the approach also works with other membrane materials and can be used in nano-scale mechanical sensors, drug delivery, water purification, and others. The research was published in the journal Nature Materials on November 26, 2018.

According to Alex Smolyanitsky, project leader, production of such graphene sieve can facilitate the first artificial ion channel that offers an exponential increase in ion flow when stretched. This in turn facilitates new possibilities for fast ion separations or pumps or precise salinity control. Graphene is a two dimensional material with layer of carbon atoms arranged in hexagons. Graphene is an excellent conductor of electricity. The simulations focused on a graphene sheet 5.5 by 6.4 nanometers (nm) in size that contained small holes lined with oxygen atoms. These pores are crown ethers, an electrically neutral circular molecules that trap metal ions. In a previous simulation research, the team showed that this type of graphene membrane can be used for nano-fluidic computing.

The simulations included suspension of graphene in water that contained potassium chloride. The crown ether pores are capable of trapping potassium ions. The trapping and release rates can be controlled with the help of electricity. The team applied electric field of various strengths to drive the ion current flowing through the membrane. The tugging on the membrane was simulated with various degrees of force to stretch and dilate the pores. This led to significant increase in the flow of potassium ions through the membrane. The team found that significant increase in ion flow was attributed to a subtle interplay of a number of factors such as thinness of graphene, interactions between ions and the surrounding liquid, and the ion-pore interactions.