(Nanowerk News) Researchers at Oregon State University College of Science have demonstrated the potential of inexpensive nanomaterials to remove carbon dioxide from industrial emissions.
The findings, published in Cells Reporting Physics (“TOGETHER2 catchment of wet flue gas using a water-stable and cost-effective metal-organic framework”), is important because improving methods of carbon capture are key to tackling climate change, says OSU’s Kyriakos Stylianou, who led the research.
Carbon dioxide, a greenhouse gas, is produced from burning fossil fuels and is one of the main causes of climate warming.
Facilities that filter carbon from the air are starting to appear around the world – the world’s largest opened in 2021 in Iceland – but they are not yet ready to reduce the emissions problem worldwide, Stylianou noted. In a year, Icelandic factories can emit an amount of carbon dioxide equivalent to the annual emissions of about 800 cars.
However, technologies for reducing carbon dioxide at points of entry into the atmosphere, such as factories, are well developed. One such technology involves nanomaterials known as metal organic frameworks, or MOFs, which can intercept carbon dioxide molecules through adsorption as exhaust gases enter through a chimney.
“Capturing carbon dioxide is critical to meeting net-zero emissions targets,” said Stylianou, an assistant professor of chemistry. “MOFs have shown a lot of promise for carbon capture because of their porosity and structural versatility, but synthesizing them often means using both economically and environmentally expensive reagents, such as heavy metal salts and toxic solvents.”
In addition, dealing with the water portion of flue gas greatly complicates carbon dioxide removal, he said. Many MOFs that have demonstrated carbon capture potential lose their effectiveness in humid conditions. The flue gas can be dewatered, says Stylianou, but that adds significant cost to the carbon dioxide removal process, enough to render it unusable for industrial applications.
“So we attempted to create MOFs to overcome the various limitations of materials currently used in carbon capture: high cost, poor carbon dioxide selectivity, low stability in humid conditions, and low CO.2 absorption,” he said.
MOFs are crystalline, porous materials consisting of positively charged metal ions surrounded by organic “connecting” molecules known as ligands. Metal ions create knots that tie the connecting arms together to form a repeating structure that looks like a cage; its structure has nano-sized pores that absorb gas, similar to a sponge.
MOFs can be designed with various components, which determine the nature of MOFs, and there are millions of possible MOFs, says Stylianou. Nearly 100,000 of them have been synthesized by chemical researchers, and half a million other properties have been predicted.
“In this study we introduced a MOF consisting of aluminum and the available ligand, benzene-1,2,4,5-tetracarboxylic acid,” said Stylianou. “MOF synthesis occurs underwater and only takes a few hours. And MOF has pores of comparable size to CO2 molecule, meaning that there is limited space to imprison carbon dioxide.”
MOF works well in humid conditions and also prefers carbon dioxide to nitrogen, which is important because nitrogen oxides are an ingredient in exhaust gases. Without that selectivity, MOF has the potential to bind to the wrong molecules.
“This MOF is an excellent candidate for wet post-combustion carbon capture applications,” says Stylianou. “It is cost effective with excellent separation performance and can be regenerated and reused at least three times with comparable absorption capacities.”