And natural sunlight has a lot to do with the process.
In collaboration with researchers in the Departments of Chemical Engineering and Mechanical Engineering, Seshadri Ramkumar, a professor in the Texas Tech Department of Environmental Toxicology, and doctoral candidate Lihua Lou have found a way to decay the dye by filtering the water through special nanofiber webs and exposing it to visible light–a process called “photodegradation.”
When fabrics are dyed, one of the final stages is the washing process, which helps to set the dye in the fabric and remove any excess. After the dyeing process, however, the water is contaminated with leftover synthetic dyes and pigments–up to 200,000 tons each year, by some estimates, the researchers noted.
Most of the dyes stay in the environment dues to inefficient and non-environmentally friendly conventional wastewater treatment processes, since the dyes are designed to hold up to light, temperature and detergents. Previously, the process of decaying the dye has used predominantly ultraviolet (UV) rays, but Ramkumar said there are several reasons using visible light is better.
“It is green, renewable and environmentally friendly,” Ramkumar 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.”
The textile industry has long been considered one of the worst contributors to water pollution and waste. The sustainability movement involving recycled, reused and renewable materials has made environmental strides, and while vegetable and less harmful chemical dyes have come into use, this process could go a long way into solving the problem of waste from dyestuffs.
For the study, Lou added nanoparticles into a polymer solution that was then electrospun into nanofibers. When the composite nanoparticle or nanofiber webs were immersed in water containing a reddish dye, a chemical reaction occurred. Researchers found that 80 percent of the red dye, known as RhB, was degraded within six hours, and the remaining 20 percent degraded slowly, completely disappearing after 49 days.
Removing the color compounds is one of the most difficult tasks wastewater treatment plants face because the dyes and pigments do not easily biodegrade, Lou noted. It’s also one of the most important tasks, since these dyes can pose threat to the human ecosystem.
“Some dyes are highly mutagenic and toxic,” Lou said. “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 wastewater.”
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.
“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.” It can also be less expensive than traditional methods, the researchers said.