New catalyst transforms CO2 into methanol with light

An international team of researchers from Nottingham University's School of Chemistry, Birmingham University, University of Queensland and University of Ulm designed the material, which is made up of copper anchored on nanocrystalline carbon nitride.

According to the team, the copper atoms are nested within the nanocrystalline structure, which allows electrons to move from carbon nitride to CO₂, an essential step in the production of methanol from CO₂ under the influence of solar irradiation. The research has been published in Sustainable Energy & Fuels.

In photocatalysis, light is shone on a semiconductor material that excites electrons, enabling them to travel through the material to react with CO₂ and water, leading to a variety of useful products, including methanol. However, this process lacks efficiency and selectivity.

It is possible to convert CO₂ to useful products, but traditional thermal methods rely on hydrogen sourced from fossil fuels. Alternative methods based on photo- and electrocatalysis can make use of sustainable solar energy and abundant water.

In a statement, co-lead Dr Madasamy Thangamuthu, a research fellow in Nottingham’s School of Chemistry, said: “There is a large variety of different materials used in photocatalysis. It is important that the photocatalyst absorbs light and separates charge carriers with high efficiency. In our approach, we control the material at the nanoscale. We developed a new form of carbon nitride with crystalline nanoscale domains that allow efficient interaction with light as well as sufficient charge separation.”

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The researchers said they have devised a process of heating carbon nitride to the required degree of crystallinity, maximising the functional properties of this material for photocatalysis. Using magnetron sputtering, they deposited atomic copper in a solventless process, allowing intimate contact between the semiconductor and metal atoms.

Tara LeMercier, a PhD student who carried out the experimental work at Nottingham’s School of Chemistry, said: “We measured the current generated by light and used it as a criterion to judge the quality of the catalyst. Even without copper, the new form of carbon nitride is 44 times more active than traditional carbon nitride. However, to our surprise, the addition of only 1mg of copper per 1g of carbon nitride quadrupled this efficiency. Most importantly, the selectivity changed from methane, another greenhouse gas, to methanol, a valuable green fuel.”

“Carbon dioxide valorisation holds the key for achieving the net-zero ambition of the UK,” said Nottingham’s Professor Andrei Khlobystov. “It is vitally important to ensure the sustainability of our catalyst materials for this important reaction. A big advantage of the new catalyst is that it consists of sustainable elements – carbon, nitrogen and copper – all highly abundant on our planet.”

This work was funded by the EPSRC Programme Grant ‘Metal atoms on surfaces and interfaces (MASI) for sustainable future’.