Cellulose Sponge Removes Color from Harmful Dye Pollution

A team at the University of Washington has developed a wood-based material that can remove color from dyes instantaneously to reduce pollution in lakes and rivers.

Commercially used dyes are often discarded in lakes and rivers during the manufacturing process—posing harm to the natural environment in a number of ways, including through their color. To solve this problem, a team led by researchers at the University of Washington has created an environmentally friendly way to remove color from dyes in water in mere seconds. They are using a wood-based biomaterial that acts similar to a sponge.

Experts estimate that about 10 percent of the dyes used in industries like textiles, cosmetics, and food processing—to name a few—is discharged into the normal stream of waste. However, unlike other waste, these dyes typically bypass wastewater treatment and remain in the environment to pollute lakes, rivers, and other bodies of water.

dye removal material
A sponge-like material developed by researchers at the University of Washington (UW), left, is made from wood pulp, or cellulose, and small bits of palladium metal that can remove color from dyes in water within seconds. (Image source: Mark Stone/UW)

Blocking Light

The key problem with the color in the dyes is that even just a small amount can block sunlight, which can prevent plant photosynthesis. This can have a ripple effect through an entire aquatic ecosystem, said Anthony Dichiara, an assistant professor of bioresource science and engineering in the UW School of Environmental and Forest Sciences, in a university press release.

“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,” he said in the release. “We were pretty impressed with what we were able to achieve.” 

That achievement was to create a material from wood pulp—or cellulose, the main structure in plant cell walls and Earth’s most abundant natural material—and small bits of the metal palladium that can remove color quickly.

Color Change

Though the material is sponge-like, it doesn’t actually absorb the color, researchers said. Instead of removing the dye, it changes the color of the dyes to something that falls outside of what can be seen in the visible spectrum. For instance, the material can change something that’s red and make it appear as if it has no color or is clear. This can allow photosynthesis in lakes and rivers to grow as they normally do, removing the negative effect of the dye, researchers said.

While there are reducing agents that can chemically reduce dyes, most of them currently take weeks to create the reaction needed to do this. The material from the UW team, on the other hand, contains a catalyst that can cause this reaction almost instantaneously, Dichiara said. How the team developed the material was to combine cellulose molecules with palladium metal. They then heated the solution and mixed it in a blender. After this process, the material was purified and freeze-dried to become porous and reusable.

The resulting sponge-like material is composed of more than 99 percent air, with large pores that allow water to flow in and out. The palladium catalyst particles within the material in effect remove the color from the water. Just like a real sponge, users can squeeze the water from the material and reuse it several times without it losing its effectiveness, researchers said.

The researchers tested their sponge in the lab using blue and red dyes commonly found in the textile industry and found that it can remove the dyes and turn water clear in about 10 seconds. For real-world use, the team envisions that a number of sponges made from their material could be released into a lake polluted with dye along with the reduction agent. It would then be swirled around like a tea bag in a cup until all the color disappears.

“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.”

The team published a paper on its work in the journal Applied Catalysis B: Environmental.

Elizabeth Montalbano is a freelance writer who has written about technology and culture for 20 years. She has lived and worked as a professional journalist in Phoenix, San Francisco, and New York City. In her free time, she enjoys surfing, traveling, music, yoga, and cooking. She currently resides in a village on the southwest coast of Portugal.

 

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