Anthropogenic climate change is no longer a matter for debate. The US National Oceanic and Atmospheric Administration, US recently reported that atmospheric CO2 levels have risen to 400 parts per million for the first time in three million years. The culprits are also clear: increasing concentrations of carbon dioxide and other greenhouse gases from burning fossil fuels. Despite global agreements to reduce emissions, current efforts may prove inadequate without more effective – and more affordable – carbon control technologies. However, a recent breakthrough means next generation carbon scrubbers may soon be at hand.
Researchers at the University of South Florida, US, and King Abdullah University of Science and Technology, Saudi Arabia, have developed a series of metal-organic materials (MOMs) that capture carbon dioxide from pre- and post-energy production – and have tremendous potential for reducing global warming and removing impurities from gases. (Possibilities include clean coal technologies and purified methane in natural gas wells.) Known collectively as SIFSIX-1-Cu, these materials have atoms that form porous, lattice-like structures, making them highly effective at carbon capture and separation.
SIFSIX-1-Cu is not only more efficient, but also less expensive and more reusable than existing carbon scrubbing materials. (Currently, the energy costs of carbon control amount to nearly 15% of global energy production.) In fact, the researchers optimize SIFSIX-1-Cu for precise control over pore size and functionality, engineering linked metal nodes that form three-dimensional nets with maximized surface area. Moreover, these materials maintain their abilities in the presence of water vapor – which impedes carbon capture in other materials – and allow molecules in air to pass.
“The new materials show very selective carbon dioxide capture,” notes Brian Space, professor of chemistry at the University of South Florida. “Indeed, carbon dioxide fits like a glove; nothing else fits as well.”
As the researchers report in a letter published in Nature, variants of SIFSIX-1-Cu exhibit some of the highest reported carbon dioxide uptakes for MOMs. By gaining a clearer sense of the interactions between gases and structures, Brian Space's team can predict which variants will attract which gases. “We work with the experimental groups in a back-and-forth process,” explains Space. “We try to explain their data, and our results give them hints on how to change the way the material works.”
Producing exact simulations of even small numbers of gas molecules (and their interactions with each other and the MOMs) requires intricate quantum mechanical modeling. Because this process is so memory-intensive, Pittsburgh Supercomputing Center's Blacklight supercomputer and MOLPRO system were called into action. Using the results obtained, Space's team is then able to perform further calculations (to simulate larger scale interactions) on several resources within the National Science Foundation's XSEDE network – including Texas Advanced Computing Center's Ranger, San Diego Supercomputing Center's Trestles, and Georgia Tech's Keeneland. “These energy models were not even possible a few years ago,” says Space. “We can now explain the experiments at an unprecedented level of accuracy.”
With better explanations of the properties of each variant, the research team is simulating new structures in an attempt to improve carbon capture and separation – and taking advantage of the material's moisture stability, the breakthrough that led to their publication in Nature. While next steps include collaborating with engineers on manufacturing and implementation, the demonstrated accuracy of the simulations has created a clear sense of excitement in the field: cleaner energy and more efficient power plants (meaning more power in the grid) are attainable.
The researchers predict that demand for industrial commodities will triple by 2050. SIFSIX-1-Cu offers significant advances in carbon separation and purification, and its small energy footprint and low regeneration costs are attractive to industry. Ultimately, the material could prevent the release of large amounts of carbon dioxide into the atmosphere from industrial fossil fuel use, reducing global warming and ocean acidification – and it may just lead to alternative energy sources, by purifying natural gas, biogas (natural gas produced from plant materials), and syngas (the main source of hydrogen in refineries).