Japan turns plastic waste into super water-filtering materials using sunlight

Scientists are increasingly interested in the idea of harnessing solar energy as a powerful ally in cleaning up polluted water sources.

Photocatalyst technology allows sunlight to decompose toxic substances in water, while photothermal evaporation uses this energy to heat and evaporate dirty water, then condenses it into pure, drinkable water.

However, both methods often require expensive or difficult-to-manufacture materials, limiting their large-scale deployment. So researchers around the world are looking to create a single, cheap, efficient material that can perform a variety of water-purification tasks — and ideally, one made from readily available waste.

Japan turns plastic waste into super water-filtering materials using sunlight Picture 1

Turning plastic waste into a versatile catalyst

In a breakthrough, a research team at the Nagoya Institute of Technology (NITech), Japan, led by Associate Professor Takashi Shirai, along with colleagues Kunihiko Kato, Yunzi Xin and Yuping Xu, has found a way to turn common plastic waste into a new material that can filter and desalinate water using sunlight.

To create the material, the team used a planetary ball mill and carefully refined the grinding process. They started with a mixture of molybdenum trioxide (MoO₃) and polypropylene (PP), a plastic commonly found in packaging and household items.

Using precise mechanical mechanisms, this waste mixture is transformed into composite particles containing hydrogen molybdenum bronze (HxMoO₃–y), molybdenum dioxide (MoO₂) and activated carbon – three components that work together to absorb sunlight and promote various water purification reactions.

' The mechanochemical process we propose outperforms existing methods in both energy efficiency and cost, ' Dr. Shirai emphasized.

One material – many amazing possibilities

Through a series of tests, the research team discovered that this composite material absorbs a wide spectrum of light – from near infrared (NIR), visible light to ultraviolet (UV), helping to effectively decompose toxic organic substances in water.

Remarkably, even in the absence of light, the particles act as Brønsted acid catalysts, continuing to remove pollutants from the water.

In addition, the material also exhibits a plasmonic effect that helps absorb and convert sunlight into heat extremely quickly, creating a photothermal effect that helps evaporate dirty water with outstanding high efficiency.

The oxygen-containing carbon particles left over from the grinding process can also adsorb and remove heavy metal ions from wastewater – adding a natural cleaning mechanism.

The team is now continuing to refine the ball milling process to create similar 'all-in-one' catalysts for water treatment and other environmental applications.

' Our technology can be applied to a wide range of oxides and plastics. We believe it will help upgrade existing materials, recycle plastic waste and ensure safe drinking water for communities, ' Dr Shirai said.