This new twist on the common approach of “sieving” gases with porous materials allows greater control towards a ‘clean’ product. The discovery is a potential pathway to more efficient and sustainable gas purification processes in the energy sector.
The removal of CO2 from gas mixtures is an important and widespread industrial process and separating gases is currently expensive and energy intensive. Separation is used to remove impurities and compounds from natural gas or biogas as well as separating CO2 from other gases for carbon capture and in the production of blue hydrogen. Once separated, these cleaner fuels are an important step away from traditional fossil fuels, reducing CO2 emissions and accelerating the transition towards renewable energy sources.
The materials that the team have created are crystalline compounds (a family of flexible silver coordination polymers, or AgCPs), but their CO2-capturing ability is unlike traditional porous materials. The crystals achieve separation using a method that mimics how CO2 dissolves in certain liquids, like fluoroalkanes often used in artificial blood products.
The AgCPs are lined with fluorine-coated molecular chains (like Teflon on non-stick surfaces). When CO2 gas reaches a certain pressure, it triggers movement of these entangled chains allowing the crystal structure to temporarily open very small spaces and capture the gas. This mimics the process of dissolving CO2 in certain liquids. At the same time the AgCPs reject methane (CH4) - the main component of natural gas – which is incompatible with the fluorine-coated environment, ensuring near perfect separation of methane from CO2 and a ‘cleaner’ gas.
The scientists can control the required pressure trigger for CO2 uptake by simply adjusting the length of the fluorine-coated chains and have used X-ray crystallography to “see” the captured CO2 molecules. This remarkable level of control, harnessing molecular interactions within the crystals, could lead to the development of less energy-intensive, cheaper and more efficient separation processes.
This is a curious process that allows CO2 gas to enter these crystalline solids, not a conventional approach to capturing gases, that we hope will inspire investigation of new directions in purifying gases for energy applications.
Professor Lee Brammer
Lead author
The work of the team redefines how scientists might view gas adsorption in non-porous crystals and has the potential to change gas separation processes. A broader context for this study comes with the recent announcement that decades of work on metal-organic frameworks (MOFs), which have applications in gas separation, has been recognised by award of the 2025 Nobel Prize in Chemistry.