Graphene oxide sifts out CO2

An intensive worldwide effort to find new and more efficient ways to separate carbon dioxide (CO₂) from gas streams is being driven by growing concerns about climate change.

KAUST professor Klaus-Viktor Peinemann, who has been at the forefront of this field for many years, and his research colleagues at the University have now prepared an advanced hybrid membrane that can achieve highly selective separation of CO₂ with several advantages over existing CO₂ capture methods.

Peinemann explained that selectively permeable membranes that either permit or restrict the passage of specific gas molecules are ideal candidate materials for use in large-scale industrial separation applications. Nine years ago, he began adapting a commercially available polymer called PolyActive^TM for gas separation procedures. PolyActive^TM contains bound polyethylene glycol groups that encourage water and CO₂ to permeate a membrane while most other molecules are held back. 

“In our current work at KAUST, we are improving the performance of PolyActive^TM membranes by adding small amounts of graphene oxide,” Peinemann said.

Graphene is a celebrated nano-material that is composed of a flat network of carbon atoms in hexagonal rings. It is renowned for being prepared in sheets that can be as little as one atom thick. Graphene itself is impermeable to gas molecules, but combining it with varying amounts of oxygen creates graphene oxides with selective permeabilities.

Pure graphene oxide membranes are brittle, but combining them with PolyActive^TM produces flexible membranes with permeability that can be fine-tuned by varying the size and proportions of the polymer and graphene oxide components¹.

The hybrid membranes are easily prepared from dispersions of the components in water. Evaporation of excess water is the simplest of several methods available to actually form the membrane. The selective permeability of even the best membranes is not perfect, as they allow a small proportion of nitrogen to pass through, in addition to CO₂. However, they are very effective for applications such as removing CO₂ from industrial flue gas streams.

The simple and inexpensive method of preparation, physical flexibility and adjustable permeability of the membranes makes them ideal for further exploration of commercial possibilities.

“We will now develop our own PolyActive^TM-like polymer for preparing the membranes, and we will then seek patent protection and commercial partners,” Peinemann said.

As well as the use of the membranes for CO₂ removal from flue gases, he sees potential for their use in natural gas treatment and the humidification of dry gas streams or in routine air-conditioning due to the high permeability of the membranes to water vapor. 

References

1. Karunakaran, M., Shevate, R., Kumar, M. & Peinemann, K-V. CO₂-selective PEO-PBT (PolyActive^TM)/graphene oxide composite membranes. Chemical Communications 51, 14187–14190 (2015). | article