From fossil fuels to bucky balls and CO2 to nanotubes, carbon is well established as a key element in our lives. Carbon has some surprising applications and the recent resurgence of carbon in materials research points to a bright future for this element. One of the key features of carbon is that the properties of the material can be tuned to a desired application. For example, activated carbons have a very high surface area that can adsorb pollutants from water or odours from air. Ordered ‘graphitic’ carbons, such as graphene or carbon nanotubes, can have remarkable electrical properties that make them desirable for devices such as batteries.
One of the big challenges for the future of carbon research is how to incorporate such complex properties into a sustainable material. If carbons are to address key challenges such as clean water and energy generation and storage, they must be sustainable.
A large area of our sustainable materials chemistry research is the use of biomass to produce useful materials. Biomass, particularly agricultural, industrial and food waste, is an attractive resource as it is often of zero or even negative value to the producer. For a materials chemist, it is a treasure trove of complex biological chemicals such as cellulose and lignin. In our research, we discover ways to convert these biological materials into materials for a wide range of potential applications, such as water treatment or batteries.
Our recently published work looks at making carbons from sawdust. In terms of the process, it is not so different from making charcoal. You take some woody biomass and heat it in an air-free environment. What makes our process special is that we add a solution of iron salts to the sawdust before heating it. The iron is dispersed over the woody fibres and during the heating process, the iron compounds break down to form nanoparticles of a material called iron carbide. This is perhaps more familiar as one of the components of steels.
The iron carbide nanoparticles ‘burrow’ into the biomass, a little like a rabbit burrowing through the ground. What is left behind is essentially a carbon nanotube and so the result of our process is a solid material that looks a lot like charcoal, but is full of very tiny hollow tubes, each one 1000 times smaller than a human hair. What is particularly important about the process is that we can control the average size of the tubes and so we can start to ‘design’ our sustainable carbons for different applications. It’s exciting because this simple manufacturing method may open up new areas for carbons with a highly specific structure.