Dyes are widely used in industries such as textiles, cosmetics, food processing, papermaking and plastics. Globally, we produce about 700,000 metric tons — the weight of two Empire State Buildings — of dye each year to color our clothing, eye shadow, toys and vending machine candy.
Sponge it up!
A team led by the University of Washington has created an environmentally friendly way to remove color from dyes in water in a matter of seconds. “A small amount of dye can pollute a large volume of water, so we needed to find a way to very quickly and efficiently remove the color,” said senior author Anthony Dichiara, an assistant professor of bioresource science and engineering in the UW School of Environmental and Forest Sciences. “We were pretty impressed with what we were able to achieve.”
The research team developed a method that removes color from water using a sponge-like material they created from wood pulp and small bits of metal. Cellulose, the main structure in plant cell walls and the most abundant natural material on Earth, provides the backbone of the material, which is decorated with tiny pieces of palladium. This metal serves as a catalyst to help remove color quickly.
Fast and easy
Just like a real sponge, the material can be squeezed of its water and reused multiple times without losing the ability to remove color from water. The researchers say it is difficult to make such a lightweight material that is flawless after many rounds of squeezing and filtering, especially when the sponge must maintain its Swiss cheese-like structure fused with color-reducing particles.
The researchers tested their sponge in the lab using blue and red dyes commonly found in the textile industry. They poured the colored water — already mixed with the existing molecule that helps reduce color — over the sponge. As the liquid passed through the material, the resulting water was clear. In another test, they swirled the sponge material inside a jar containing blue-dyed water, and after about 10 seconds the color disappeared.
“Just a little amount of dye can change the color of a lake dramatically,” Dichiara said. “This method could work well when you have low concentrations of dye in water that you need to take care of really quickly.”