Smart polymer desalination Down Under
There are many labs tackling the salty problem of finding fresh water, and one piece of research underway in Australia could use clever chemicals to sustainably grab the salt from seawater. Lucy Weaver, from CSIRO and runner up in Australia's FameLab competition this month, is looking at smart polymers...
Lucy - We've heard a lot about salt on the programme today and down in Australia we have a saltwater problem, and I don't just mean the fact that we're surrounded by it. Big industries, particularly the dairy and mining industries, produce a lot of salty wastewater that can't be reused very easily or cheaply. And water is a precious commodity in short supply across most of the country. So, as part of my work for the CSIRO, Australia's national research organisation, I'm investigating new ways to take the salt out of the salty wastewater so that the water can be reused rather than thrown away like some of it is as at the moment.
The way I'm trying to do this is by using molecules called smart polymers. To explain what smart polymers are, I want you to imagine that you're on stage in a theatre in front of a sellout crowd. If you look out over the audience, you'll see that they're all sitting in chairs in rows. Since you're all the way up on stage though, to you, those rows look a bit like chains of people. At the molecular level, polymers, also known as plastics,are also made up of chains. They are comprised of molecular building blocks, like the people in the audience, and these molecular links are held together by chemical bonds.
There are many different types of links that can be used to make different types of polymer chains and, depending on which links you use, you can give the polymers special properties. Some polymers can be made with links that allow them to respond to a stimulus and it's this ability to respond that makes some polymers smart.
Now, back in the theatre. Imagine that you bow and then the crowd applauds you. In this example, your bow was a stimulus and the response was applause. In the case of my smart polymers though, the stimulus is temperature and the response I'm trying to create is the binding and release of salt. I've made polymers that contain some links that respond to a change in temperature and other links that attract salt. All of these links are organic compounds in that they're made out of carbon, hydrogen, oxygen, and nitrogen atoms, and some of these links contain acidic and basic groups that are able to interact with the salt.
The way that I make these polymers is using a technique called raft polymerisation. Raft stands for reversible addition fragmentation transfer polymerisation, which is a fancy way of saying we can make polymer chains that are the right size and composition for our needs. So, if we add some room temperature, salty, wastewater to my smart polymers, the aim is to get them to latch onto, and soak up the salt leaving behind clean water which can be collected and used. But, rather than throwing the used, salt laden polymer away, if we increase the temperature just a little bit, perhaps with some help from the sun, this change in temperature makes the smart polymer shrink and coil up. This process could potentially squeeze out all of the salt which can then be removed. Then, if we cool things down again, the polymer chains uncoil and we're back to square one ready to bind more salt.
In real life, this heating-cooling process can happen again and again and the polymer chains, in theory, will never get tired. If my experiments are successful, this process of generating cleaner water could potentially cost much less than current methods and could use much less energy as the polymers are sensitive to very small changes in temperature. And so, I think you'll agree, the potential of smart polymers deserves a round of applause!