This illustration shows how CO2-selective polymeric chains anchored on graphene effectively pull CO2 from a flue gas mixture. Image: KV Agrawal (EPFL).The carbon dioxide (CO2) produced by burning fossil fuels is still mostly released into the atmosphere, adding to the burden of global warming. One way to cut down on this release is through carbon capture: a chemical technique that removes CO2 from emissions (‘postcombustion’), preventing it from entering the atmosphere. The captured CO2 can then either be recycled or stored away in gas or liquid form, a process known as sequestration.
Carbon capture can be performed using so-called ‘high-performance membranes’, which are polymer filters that can specifically pick out CO2 from a mix of gases, such as those coming out of a factory's flue. These membranes are environmentally friendly, don't generate waste, can intensify chemical processes and can be used in a decentralized fashion. In fact, they are now considered to be one of the most energy-efficient routes for reducing CO2 emissions.
Scientists led by Kumar Varoon Agrawal at EPFL (Ecole Polytechnique Fédérale de Lausanne) Valais Wallis in Switzerland have now developed a new class of high-performance membranes that exceeds post-combustion capture targets by a significant margin. The membranes are based on graphene, an atom-thick sheet of carbon, with a selective layer thinner than 20nm. They are highly tunable in terms of chemistry, meaning they can pave the way for next-generation high-performance membranes for several critical separations. The scientists describe the new membranes in a paper in Energy & Environmental Science.
Current membranes for carbon capture are required to exceed 1000 gas permeation units (GPUs) and have a ‘CO2/N2 separation factor’ – a measure of their carbon-capturing specificity – above 20. The membranes that the EPFL scientists developed show a six-fold higher CO2 permeance, at 6180 GPUs, with a separation factor of 22.5. The GPUs shot up even further, to 11,790, when the scientists optimized the graphene’s porosity, pore size and functional groups (the chemical groups that actually react with CO2), while other membranes they made showed separation factors up to 57.2.
"Functionalizing CO2-selective polymeric chains on nanoporous graphene allows us to fabricate nanometer-thick, yet CO2-selective, membranes," says Agrawal. "This two-dimensional nature of the membrane drastically increases the CO2 permeance, making membranes even more attractive for carbon capture. The concept is highly generic, and a number of high-performance gas separations are possible in this way."
This story is adapted from material from EPFL, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.