Shaping materials at the atomic scale

An introduction to membrane nanoscience

by Peifu Cheng, postdoctoral scholar, Chemical and Biomolecular Engineering

Membrane research has significantly benefited from nanotechnology, and many sectors of the global ecosystem have benefited from membrane research. Water treatment or desalination is one example. Membranes with nanoscale pores also are used to separate gases for carbon capture and storage to alleviate climate change. Dialysis tubing made of semi-permeable membrane with pores of 1 to 10 nanometers is used in artificial kidney research, with the goal of improving the lives of millions of people.

Peifu Cheng

Membranes with different sieving sizes have made a tremendous impact on food processing, from dairy products to juice filtration and sugar purification. Membranes play an important role in energy fields, such hydrogen fuel cell cars and energy generation from the mixing of rivers into the sea.

Challenges remain. An ideal membrane has minimal thickness and a high density of uniform nanoscale pores for ultrafast transport and precise ionic/molecular sieving. However, scalable fabrication of such membranes remains difficult, and a single large nanopore can compromise membrane performance.

One big goal—and big challenge—is fine-tuning membranes on atomic scale, and Vanderbilt engineers are at the forefront of such research. The following two pages contain more detailed examples of recent breakthroughs.Shihong Lin, assistant professor of civil and environmental engineering, and his collaborators changed the conventional membrane fabrication process itself and made nanofiltration membranes with sub-Angstrom precision that can successfully separate two ions with extremely small size differences (p 15). Piran Kidambi, assistant professor of chemical and biomolecular engineering, and his team developed atomically thin graphene membranes with trillions of controlled holes in the range of 0.3 to 0.6 nanometers over a square centimeter. These membranes allow for ultrahigh water permeance, about 23 times higher than commercially available membranes, with excellent rejection of salt ions and small organic molecules (p 16).

Using nanotechnology, we can make materials stronger, lighter, more durable, more reactive, more sieve-like, or better electrical conductors, among many other traits.