Scientists Use Sunlight To Turn Plastics Into Vinegar Researchers at the University of Waterloo have found a way to use sunlight, and a specially designed catalyst, to turn plastics in water into acetic acid. Dr. Yimin Wu, a professor of mechanical and mechatronics engineering and the Tang Family Chair in New Energy Materials and Sustainability, is the lead author in a study published in the journal Advanced Energy Materials. The study was led by Waterloo PhD student Wei Wei under the guidance of Wu, and co-authored by Roy Brouwer, executive director of the Water Institute. Traditional recycling methods involve melting plastics back into raw forms. This method is inefficient and produces harmful gasses. Instead, the research team developed a method where plastic particles, suspended in water and exposed to sunlight, are broken down into acetic acid with the use of a catalyst. Scientists believe that this approach to plastic waste management is more efficient. More importantly, this new method breaks down microplastics at the chemical level, unlike the incineration process. “Both from a business and societal perspective, the financial and economic benefits associated with this innovation seem promising,” said Brouwer. “This method allows abundant and free solar energy to break down plastic pollution without adding extra carbon dioxide to the atmosphere,” added Wu. “Our goal was to solve the plastic pollution challenge by converting microplastic waste into high-value products using sunlight.” "The inspiration for our research came from nature. The white rot fungus (Phanerochaete chrysosporium) is famous for its ability to break down lignin, one of the toughest polymers found in wood. It does this using enzymes that generate highly reactive chemicals that are capable of dismantling complex carbon structures." "The catalyst we designed is iron-doped carbon nitride, a semiconductor that absorbs visible light. We then anchored individual iron atoms, creating what scientists call a single-atom catalyst." Rather than forming nanoparticles, each iron atom is isolated and embedded within the carbon nitride structure, referred to as Fe@C₃N₄ SAC. This atomic precision is crucial. Each iron atom behaves like an active site in a natural enzyme, maximizing efficiency while maintaining stability. The system works through a cascade of light-driven reactions. Under sunlight and in the presence of hydrogen peroxide, the iron sites activate the peroxide to generate highly reactive hydroxyl radicals. A radical is an atom, molecule or ion that has at least one unpaired electron. This makes them highly chemically reactive. These radicals attack the long carbon chains that make up plastics. The polymers are progressively oxidized and broken down into smaller molecules, eventually forming carbon dioxide (CO₂). Rather than allowing this CO₂ to escape, the same catalyst then performs a second job: it uses sunlight to reduce the CO₂ into acetic acid. In other words, the carbon in plastic waste is first oxidized and then re-assembled into a new, valuable molecule. Acetic acid is best known as the sour component of vinegar, but it is also a major industrial compound. It is used to produce adhesives, coatings, solvents, synthetic fibers and pharmaceuticals. Global demand runs into the millions of tons each year, representing a multi billion dollar market. Currently, most acetic acid is produced through an energy intensive process called methanol carbonylation, whereby methanol is reacted with carbon monoxide at high temperatures. The dispersed atomic structure of the catalyst maximizes active sites for reactions, maintains stability under repeated use, and controls how the chemical transformation proceeds. In lab tests, the catalyst efficiently converted plastic waste into acetic acid over multiple cycles without losing activity, which is a key factor for potential large scale applications. By turning a pollutant into a commodity chemical, the process creates both environmental and economic incentives. Additionally, the use of iron makes the system more scalable and sustainable than methods relying on rare or precious metals. Producing acetic acid directly from waste provides an economic incentive, where plastics are transformed rather than discarded. Unlike conventional chemical recycling, this approach doesn’t rely on high temperatures, harsh solvents, or added energy from fossil fuels. The reactions occur in water under ambient conditions. Researchers found that it not only works on various forms of polymers, such as: polyvinyl chloride (PVC), polypropylene (PP), polyethylene (PE), and polyethylene terephthalate (PET), but that it also works with with mixed compositions of those polymers. Wu and colleagues envision a future where solar powered plastic conversion contributes to a circular economy, reducing environmental harm while generating commercially useful chemicals. The study was supported in part by the Waterloo Institute for Nanotechnology and the Water Institute. Research findings are available online in the journal Wiley Advanced.