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.

During manufacturing, about a tenth of all dye products are discharged into the waste stream. Most of these dyes escape conventional wastewater-treatment processes and remain in the environment, often reaching lakes, rivers and holding ponds, and contaminating the water for the aquatic plants and animals that live there. Even just a little added color can block sunlight and prevent plant photosynthesis, which disrupts the entire aquatic ecosystem.

A team led by the 91̽�� has created an environmentally friendly way to remove color from dyes in water in a matter of seconds. The technique was described in a published online in June in the journal Applied Catalysis B: Environmental.

“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 , an assistant professor of bioresource science and engineering in the 91̽��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.

Instead of removing dye from water, the research team sought to change the color of the dyes to something that falls outside of what we can see in the visible spectrum. A chemical reaction can, for example, disrupt the color red and make it appear clear, or colorless. In the case of dye waste products that artificially color the water in lakes and prevent photosynthesis, changing the dye from red to clear should allow plants to grow normally again.

The chemical reduction of dyes using molecules called “reducing agents” can alter the dye structure and change its color from red or blue to clear. However, the reaction is not very efficient and can take weeks to occur. The UW’s material contains a catalyst that works with the reducing agent to speed this process up to almost instantaneous.

In the new paper, the researchers describe the simple and sustainable process they developed to make the color-removing material. The researchers combined cellulose molecules with palladium metal, heated the solution and mixed it in a blender. Then they purified and freeze-dried the material so it became a porous, reusable substance. The resulting sponge is more than 99 percent air — its large pores allow water to flow in and out, while the metal catalyst particles within the material work to remove any color present.

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.

Researchers hold a small piece of the sponge-like material in water containing blue dye. After about 10 seconds, the water in the beaker turns clear. Click on each image in the sequence to view it larger. Photos by Mark Stone/91̽��

Outside of lab tests, the researchers say that many small sponge-like materials could be released into a lake polluted with dye, along with the molecule to help reduce the color. Similar to swirling a tea bag round a mug, the sponges could be dragged around the lake until all of 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.”

First author is Jin Gu, a visiting scholar at the 91̽��and associate professor at South China Agricultural University, and other co-authors are Chuanshuang Hu and Weiwei Zhang of South China Agricultural University.

Funding for this work is from the Guangdong Provincial Department of Science and Technology, the U.S. Department of Agriculture’s National Institute of Food and Agriculture, and the Bureau of Guangdong Forestry.

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For more information, contact Dichiara at abdichia@uw.edu.

In cities and large-scale manufacturing plants, a water leak in a complicated network of pipes can take tremendous time and effort to detect, as technicians must disassemble many pieces to locate the problem. The indicates that nearly a quarter-million water line breaks occur each year in the U.S., costing public water utilities about $2.8 billion annually.

A 91̽�� team wants to simplify the process for discovering detrimental leaks by developing “smart” paper that can sense the presence of water. The paper, laced with conductive nanomaterials, can be employed as a switch, turning on or off an LED light or an alarm system indicating the absence or presence of water.

The researchers described their discovery in a appearing in the November issue of the Journal of Materials Chemistry A.

“Water sensing is very challenging to do due to the polar nature of water, and what is used now is very expensive and not practical to implement,” said lead author , a 91̽��assistant professor of bioresource science and engineering in the School of Environment and Forest Sciences. “That led to the reason to pursue this work.”

This slideshow shows the process of making “smart” paper. Hover above each photo to see the caption and click on each one to see the full image.

Along with Dichiara, a team of 91̽��undergraduate students in the Bioresource Science and Engineering program successfully embedded nanomaterials in paper that can conduct electricity and sense the presence of water. Starting with pulp, they manipulated the wood fibers and carefully mixed in nanomaterials using a standard process for papermaking, but never before used to make sensing papers.

Discovering that the paper could detect the presence of water came by way of a fortuitous accident. Water droplets fell onto the conductive paper the team had created, causing the LED light indicating conductivity to turn off. Though at first they thought they had ruined the paper, the researchers realized they had instead created a paper that was sensitive to water.

When water hits the paper, its fibrous cells swell to up to three times their original size. That expansion displaces conductive nanomaterials inside the paper, which in turn disrupts the electrical connections and causes the LED indicator light to turn off.

This process is fully reversible, and as the paper dries, the conductive network re-forms so the paper can be used multiple times.

The researchers envision an application in which a sheet of conductive paper with a battery could be placed around a pipe or under a complex network of intersecting pipes in a manufacturing plant. If a pipe leaks, the paper would sense the presence of water, then send an electrical signal wirelessly to a central control center so a technician could quickly locate and repair the leak.

In addition, the paper is so sensitive that it can also detect trace amounts of water in mixtures of various liquids. This ability to distinguish water from other molecules is particularly valuable for the petroleum and biofuel industries, where water is regarded as an impurity.

“I believe that for large-scale applications, this is definitely doable,” Dichiara said. “The price for nanomaterials is going to drop, and we’re already using an established papermaking process. You just add what we developed in the right place and time in the process.”

The nanomaterials added to the paper were engineered in such a way that they can be incorporated during conventional papermaking without having to modify the process. These materials are made of extremely conductive carbon. Because carbon is found in all living things, nearly any natural material can be burned to make charcoal, and then carbon atoms can be extracted to synthesize the materials. The team has experimented with making nanomaterials from banana peels, tree bark and even animal feces.

They also tried making nanomaterials from wood scraps to show that the entire papermaking process can be completed with cheap, natural materials.

“Now we have a sustainable process where everything is from pulp and paper, and we can make conductive materials from them,” Dichiara said.

The paper, stiff and smooth in texture, is a rich black color because of the nanomaterials (carbon from charcoal). The 8-inch disks made in the lab are prototypes; the team hopes to test the process on an industrial-sized papermaking machine next, which will require more nanomaterials and paper pulp.

Other co-authors are Sheila Goodman, a 91̽��graduate student, and Delong He and Jinbo Bai of Universite Paris-Saclay in France. 91̽��undergraduate students Jimeng Cui, Riley Fitzpatrick, Sydney Fry, Demi Lidorikiotis, Anna Song and Zoie Tisler completed additional lab work.

Funding for this research came from the U.S. Department of Agriculture’s National Institute of Food and Agriculture, McIntire Stennis project, and from the 91̽��School of Environmental and Forest Sciences.

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For more information, contact Dichiara at abdichia@uw.edu or 206-543-1581.

Photos and video are .