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Visible light can remove toxic dyes

EcoNote | September 9, 2019 | By:

A team of Texas Tech University (TTU) researchers working in advanced textiles has found a new way to remove toxic dye pollutants from wastewater, and their approach is safer, cheaper and easier than traditional methods, a recent release from TTU says.  

Water contaminated with leftover synthetic dyes and pigments, a result of washing the textiles at the end of the dyeing process, totals up to 200,000 tons each year, by some estimates. Most of the dyes persist in the environment. Conventional wastewater treatment processes are inefficient and non-environmentally friendly. Furthermore, the dyes are designed to hold up to light, temperature and detergents—the very things that might be used to clean them, the scientists said.  

Often, the process of decaying the dye has used predominantly ultraviolet (UV) rays. In collaboration with researchers in the departments of chemical engineering and mechanical engineering, Seshadri Ramkumar, professor in Texas Tech’s Dept. of Environmental Toxicology, and doctoral candidate Lihua Lou have found a way to decay the dye by filtering the water through nanofiber webs and exposing it to visible light—a process called photodegradation.

Ramkumar says there are several reasons using visible light is superior to using UV rays. “It is green, renewable and environmentally friendly,” he said. “Using visible light for photodegradation is not harmful, and it’s cost-effective and easy to operate. It makes the color removal in the industry economical.”

For this study, Lou added nanoparticles into a polymer solution, which was then electrospun into nanofibers. When the composite nanoparticle/nanofiber webs were immersed in water containing a reddish dye called Rhodamine B (RhB), a chemical reaction occurred.

The researchers found that 80 percent of RhB was degraded within six hours, and the remaining 20 percent degraded slowly, completely disappearing after 49 days.

“Our research is multidisciplinary and addresses an important problem for the global textile sector,” Ramkumar said. “After finishing the photodegradation process, the composite can be easily removed from water without leaving much harmful residue.”

Based on their success with RhB, the team’s next step is to try the same method with other types of synthetic and natural dyes, including methyl orange, methylene blue and reactive blue 19.

“Some dyes are highly mutagenic and toxic,” Lou explained. “RhB is a highly water‐soluble chemical compound and widely used colorant in textiles. However, the wastewater with RhB may cause irritation to the skin, eyes and respiratory tracts of human beings and animals. Moreover, several health issues, such as neurotoxicity, carcinogenicity, reproductive toxicity and developmental toxicity, arise due to RhB [in] wastewater.”

Support for the research was provided by the Texas Tech Graduate School and the American Association of Textile Chemists and Colorists.

The study’s results are described in the journal Particle & Particle Systems Characterization.

The Nonwovens and Advanced Materials Laboratory, TTU,has been carrying out research with nanofibers and advanced fibrous materials for two decades.

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