Climate change and energy security may be big global problems, but the solutions can often occur at a molecular level. How we deal with a range of gases, whether it is capturing and storing carbon dioxide, or turning hydrogen into a clean energy source to replace fossil fuels, will be essential to solving these problems.
A New Zealand local, who completed his doctorate at Oxford University and post doc in Vancouver before landing at the ANU in 2015, Dr Nick White is working at this molecular level to make his contribution to these solutions.
“We work in an area called supramolecular chemistry and that literally means chemistry beyond molecules,” White explains. “So we look at how molecules interact with each other, either designing one molecule to associate with another molecule or designing molecules that can assemble themselves into a larger kind of construct.”
Through supramolecular chemistry, researchers have been working to develop 3D porous materials that can capture or store particular gases. The most obvious example of this is to store captured carbon dioxide, but the process is also valuable in the development of new clean fuels, such as hydrogen.
“You can store more hydrogen in a tank filled with porous materials than in an empty tank,” White explains. “This seems to make no sense but it's because you can basically organise. If you just put hydrogen in a tank, the hydrogen is not going to be very close together. If you fill it with these ordered 3D materials you can actually order the hydrogen molecules and get them much closer together. So you can fit far more hydrogen. So people are looking at this as part of the hydrogen economy. To use hydrogen as a fuel for, cars for example.”
While many chemists are investigating the best ways to store and order gases in this way, White and his team are focused on developing new ways to create these porous materials in the first place.
“A lot of people make these porous materials based on metals. So they will take metals and bind them to ligand molecules, and use that to make these 3D materials.
“Whereas we are using hydrogen bonding to do that, so we don't have any metals. The interactions we are using are weaker, so potentially they won't be as stable. However, what we’ve found is that the materials have actually turned out to be pretty stable, and because of these weak interactions, when you make them, you can do that in a more controlled way.”
Making these materials without metals brings a range of benefits. In particular, White explains, structures with metal all have similar characteristics, binding to certain molecules very well, but not doing as well with others. By creating these structures without metals, White is able to develop structures with different characteristics.
“We use a completely different approach so things have quite different character. So for example most metal organic frameworks are really unstable to water. They can't tolerate it and they just fall apart.
“Our materials however are completely fine in water. A lot of people think that hydrogen bonds won't really survive in water because water itself is very good at hydrogen bonding. So they think hydrogen bonded materials will just fall apart. But actually we make ours in water and they do tolerate water. It seems like we can make surprisingly stable materials using this approach.”
While White acknowledges that the application of many of these structures is “way beyond my own level of understanding”, his team is working with colleagues in Adelaide to find effective applications to the new structures they are developing.
In turn White has become a sort of chemical construction worker, a position he is quite happy with.
“Certainly we are looking at the gas binding but we are looking at new ways to make these things, rather than getting really into the applications,” White explains. “We’re trying to do something different and see what happens.”
As we continue to face the challenges of climate change and energy security, this try-and-see approach is likely to be essential to finding solutions.