MOF-ferrocene composite could filter oxygen from air

Materials World magazine
9 Mar 2016

Metal-organic frameworks (MOFs) are useful for pulling gases out of air or other mixed gas streams, but, unfortunately, not oxygen. But in results reported on 9 March in Advanced Materials, materials scientists at the US Department of Energy’s Pacific Northwest National Laboratory (PNNL) have developed a composite of a MOF and a helper molecule, which work in concert to separate oxygen from other gases.

Industry currently uses cryogenic distillation to separate oxygen from other gases, but it is costly and requires energy-intensive chilling of gases. MOFs, on the other hand, work by sucking gases into their pores much like a sponge sucks up water. However, only a few of the thousands of MOFs can absorb molecular oxygen, and even those MOFs form oxides, like rust, which make the material unusable.

To overcome this, Dr Paveen Thallapally and his colleagues at PNNL created a composite of the especially high-surface-area MOF, MIL-101, and an inexpensive iron-containing molecule, ferrocene, as a helper molecule.

They sent gases through the composite material, which they found bound up a large percentage of the oxygen, but almost none of the added nitrogen, argon or carbon dioxide – demonstrating that the composite could separate oxygen from other gases.

The composite could have applications in numerous industrial processes, such as making pure oxygen for fuel cells, removing oxygen from food packaging and making oxygen sensors.