Researchers at the University of Cambridge have developed a system that can convert two waste streams into two chemical products simultaneously – a first in a solar reactor. The reactor converts carbon dioxide (CO₂) and transforms plastics into a variety of products that are useful in a number of industries. CO during tests₂ were converted to synthetic gas, which is an important building material for sustainable liquid fuels, and plastic bottles to glycolic acid, which is widely used in the cosmetics industry. The system can be easily adjusted to produce different products by changing the type of catalyst used in the reactor.

Converting plastic and greenhouse gases, two of the biggest threats to the natural world, into useful and valuable products with the help of solar energy is an important step in the transition to a more sustainable circular economy. The results were published in the journal Nature Synthesis.

“Turning waste into something useful with solar energy is the main goal of our research,” said Professor Erwin Reisner from the Department of Chemistry, Yusuf Hamid, senior author of the paper. “Plastic pollution is a huge problem around the world, and most of the plastic we usually put in recycling bins is either incinerated or ends up in the landfill.”

Reisner also chairs the Cambridge Circular Plastics Center (CirPlas), which aims to eliminate plastic waste by combining blue thinking with practical action. Other solar “recycling” technologies are promising for solving the problem of plastic pollution and reducing the amount of greenhouse gases in the atmosphere, but to date they have not been combined in a single process.

“Solar-based technology that can simultaneously combat plastic pollution and greenhouse gas emissions could change the rules of the game for the circular economy,” said Subhajit Bhattacharjee, one of the paper’s authors.

“We also need something that can be customized so that you can easily make changes to the end product you want,” said Motiar Rahaman.

The researchers developed an integrated reactor with two separate chambers: one for plastics and the other for greenhouse gases. The reactor uses a perovskite-based light absorber, a promising alternative to silicon for next-generation solar cells.

The team developed several catalysts integrated into the light absorber. By changing the catalyst, researchers can change the final product. Reactor tests under normal temperature and pressure conditions have shown that the reactor can efficiently convert PET plastic bottles and CO.₂ to various carbon-based fuels such as CO, syngas or formate in addition to glycolic acid. The reactor developed in Cambridge also produced these products at a much higher rate than conventional photocatalytic CO reduction processes._2.

“Overall, the conversion of CO2₂ it takes a lot of energy, but you shine a light on it with our system and it starts turning harmful products into something useful and sustainable,” Rahaman said. “Before this system, we had nothing that could produce valuable products selectively and efficiently.”

“What’s so special about this system is its versatility and tunability – we’re currently making fairly simple carbon-based molecules, but in the future we may be able to tune the system to make much more complex products by simply changing the catalyst,” said Bhattacharjee.

Over the next five years, the researchers hope to continue improving the reactor to produce more complex molecules. Similar techniques could one day be used to develop a processing plant that runs entirely on solar cells, the researchers say.

“Developing a circular economy where we do useful things instead of throwing waste into landfills is vital if we are to take the climate crisis seriously and protect the natural world,” Reisner said. “And powering these solutions with the sun means we’re doing it in a clean and sustainable way.”