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Solar reactor converts both CO2 and plastic waste into useful products

Jun 28, 2023

Greenhouse gases and plastic waste are two of the biggest environmental problems the world faces today. A new reactor from Cambridge is designed to tackle both at once, converting CO2 and used plastic bottles into useful materials, powered entirely by sunlight.

Atmospheric carbon dioxide is at its highest levels in millennia, leading to devastating climate consequences. Meanwhile, our reliance on plastic is causing a huge buildup of the stuff in rivers, oceans and everywhere from pole to pole. Research in both of these fields has led to scientists designing reactors that convert either captured CO2 or plastic waste into oils, fuels and other useful chemicals and materials.

But now, scientists at Cambridge have designed the first reactor that can deal with both pollutants at once. The device is made up of two separate compartments – one for plastic and one for CO2 – as well as a unit in each compartment that absorbs energy from light and uses it to trigger a catalyst that converts the feedstock into something more useful. The light absorber is perovskite, which is emerging as a promising material for solar cells, while the catalyst can be changed depending on the desired final product.

"Generally, CO2 conversion requires a lot of energy, but with our system, basically you just shine a light at it, and it starts converting harmful products into something useful and sustainable," said Dr Motiar Rahaman, co-first author of the study. "Prior to this system, we didn't have anything that could make high-value products selectively and efficiently."

In tests, the team demonstrated that the reactor could work efficiently under normal temperature and pressure conditions, using only sunlight for energy. A copper-palladium alloy catalyst was able to convert PET plastic bottles into glycolic acid, a chemical used in the cosmetics industry. Carbon dioxide was converted into carbon monoxide using a cobalt compound, syngas using a copper-indium alloy, and formate using a specific enzyme.

Better yet, the reactor works very efficiently. The team says that its production rate is up to 100 times more efficient than devices using other solar-powered catalysts. The next steps are to develop the reactor further over the next five years to produce more complex molecules.

"What's so special about this system is the versatility and tuneability – we’re making fairly simple carbon-based molecules right now, but in future, we could be able to tune the system to make far more complex products, just by changing the catalyst," said Subhajit Bhattacharjee, co-first author of the study.

The research was published in the journal Nature Synthesis.

Source: University of Cambridge