Honeycomb-like structure to trap dangerous gases

Researchers have developed a novel method that can trap potentially harmful gases emitted by coal factories, cars and trucks within honeycomb-like microscopic organo-metallic structures.
These metal organic frameworks, or MOFs, are made of different building blocks composed of metal ion centres and organic linker molecules, said researchers from The University of Texas at Dallas in the US.
Together they form a honeycomb-like structure that can trap gases within each comb, or pore.
The tiny nano-scale structures also have the potential to trap various emissions from things as immense as coal factories and as small as cars and trucks.
"These structures have the ability to store gases, but some gases are too weakly bound and cannot be trapped for any substantial length of time," said Dr Kui Tan, a research scientist at UT Dallas and lead author of the study.

After studying this problem, Tan decided to try to introduce a molecule that can cap the outer surface of each MOF crystal in the same way bees seal their honeycombs with wax to keep the honey from spilling out.

Tan introduced vapours of a molecule called ethylenediamine, or EDA, that created a monolayer, effectively sealing the MOF "honeycomb" and trapping gases such as carbon dioxide, sulphur dioxide and nitric oxide within.
This monolayer is less than one nanometre in thickness, or less than half the size of a single strand of DNA.
To quantify how much gas was trapped and remained in the EDA-capped MOF structures, the team used time-resolved, in-situ infrared spectroscopy, testing the efficiency of this molecular "cork" to trap weakly adsorbed gases.

The presence of the gas molecules adsorbed in the MOF was displayed on a nearby computer screen as inverted peaks, which revealed that EDA vapour was able to effectively retain the greenhouse gas carbon dioxide for up to a day.
"Potential applications of this finding could include storage and release of hydrogen or natural gas to run your car, or in industrial uses where the frameworks could trap and separate dangerous gases to keep them from entering the atmosphere," Tan said.
Tan also found that a mild exposure to water vapour would disrupt the monolayer, penetrate the framework and fully release the entrapped vapours at room temperature.

Such selectivity of the EDA membrane opens up new options for managing gas emissions, he said.
"The idea of using EDA as a cap came from Kui who proceeded to do an enormous amount of work to demonstrate this new concept, with critical theoretical input from our collaborators at Wake Forest University," said Yves Chabal, from Erik Jonsson School of Engineering and Computer Science.
The study was published in the journal Nature Communications.