Researchers in Japan have proposed a simple, energy-efficient method to convert carbon dioxide into metal-organic frameworks, reducing greenhouse gases and global warming.
According to the 2021 Global Energy Review, energy-related carbon dioxide emissions are projected to rise by 1.5 billion tons this year, the second-largest increase in history and the largest annual rise since the 2010 recovery from the global financial crisis. This stark rise in greenhouse gases is expected to reverse most of last year’s decline, which occurred due to the COVID-19 pandemic. To reduce carbon emissions or better yet, achieve a carbon-neutral society, scientists have innovated green technologies, turned to renewable energy, and explored ways to reduce emissions.
One emerging field of study is the conversion of carbon dioxide into functional materials like highly designable and porous metal-organic frameworks that can be used for gas storage, biomedical imaging, and luminescent materials among many others. However, because carbon dioxide is chemically inert, scientists have yet to find a way to convert it into more useful chemicals. Additionally, synthesising metal-organic frameworks from carbon dioxide require high energy reactants and harsh conditions.
Fortunately, researchers at the Institute for Integrated Cell-Material Sciences of Kyoto University have developed a new, energy-efficient way to convert carbon dioxide into metal-organic frameworks. The team specifically targeted metal-organic frameworks because they can be used in a variety of ways from biosensors to catalysts. Because these structures are porous and can hold large amounts of gas, they are also promising candidates as storage devices for sustainable hydrogen fuel.
“Taking the [carbon dioxide] released from fossil fuel combustion and converting the gas into valuable chemicals and materials is a promising approach to protect the environment. But because [carbon dioxide] is a very inert and stable molecule, it is difficult to get it to react using conventional conversion processes,” said Satoshi Horike, who led the study. “Our work demonstrates an easier approach that can be run at a much lower temperature and pressure. This should make reactions that use [carbon dioxide] easier to produce and more popular.”
To run the reaction, the researchers bubbled carbon dioxide at a temperature of 25 degrees Celsius and a pressure of 0.1 MPa through a solution containing piperazine, an organic molecule, in what is known as a “one-pot” procedure. The metal-organic frameworks quickly formed as a white microcrystalline powder that the scientists collected and dried. Upon analysing the structure using X-ray and nuclear magnetic resonance spectroscopy, the team confirmed that they were able to convert carbon dioxide into their desired product as planned. The metal-organic frameworks also had a high surface area even though they were made from more than 30 per cent carbon dioxide by weight, thus making them highly suitable as functional materials.
Motivated by these positive results, the team is currently planning to examine how they can use the reaction to directly convert carbon dioxide from industrial fumes, like those released by coal and gas-fired power stations, into useful materials.
“Direct utilisation of [carbon dioxide] is challenging, but it will potentially save a lot of energy that is required for the capture and separation of the gas,” said Horike. “The emission of [carbon dioxide] by fossil fuel combustion must be reduced and regulated to protect the environment. Our method here is a potential clue to help solve some important environmental problems.”
Source: Kadota et al. (2021). One-Pot, Room-Temperature Conversion of CO2 into Porous Metal–Organic Frameworks. Journal of the American Chemical Society.