Sunlight powers chemical recycling of polyethylene terephthalate

Catalytic processes to chemically break down polyethylene terephthalate (PET) typically require high temperatures that consume a lot of energy. Researchers have now designed a system that uses sunlight to drive the catalytic breakdown of this common plastic into valuable monomers (Matter 2022, DOI: 10.1016/j.matt.2022.02.002). The solar method should save 3.7 gigajoules of energy and 0.4 metric ton of carbon emissions for each ton of recycled PET compared with conventional catalytic methods, Soochow University chemist Jinxing Chen says. For their solar-driven upcycling method, Chen and his colleagues relied on two photothermal materials—carbon nanotubes and polydopamine—which absorb sunlight to produce heat locally. The researchers coated the nanotubes with polydopamine, then suspended them in ethylene glycol along with an ionic liquid catalyst. They added flakes of PET to this mix and placed it in the sun, which caused the photothermal composite to heat up to 150 °C. This heat and the catalyst triggered the ethylene glycol to break ester linkages in PET, producing high-purity bis(2-hydroxyethyl) terephthalate (BHET) powder. Higher light intensity and exposure time boosted yields. The researchers repolymerized the monomers into PET. This process can break down PET that has been dyed or blended with another polymer.