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A simple liquid battery containing a methylene blue solution (left) and a colorless solution of colorless methylene blue (right). Photo Credit: Meredith Forrest Kulwicki / University of Buffalo
A sapphire dye called methylene blue is a common component in textile mill wastewater. But scientists at the University of Buffalo believe that this industrial pollutant may have a second life. In a new study, they found that the dye can store and release energy well when dissolved in water.
This makes this compound a promising candidate for redox flow batteries-flow batteries are a large rechargeable liquid battery that can enable future wind farms and solar power plants to store electricity on sunny or rainy days.
The research was published online in the journal ChemElectroChem in August.
Methylene blue is a widely used dye. Dr. Timothy Cook, assistant professor of chemistry and principal researcher at the UB School of Arts and Sciences, said that it may be harmful to health, so it is not something you want to dump into the environment without governance. Much work has been done on how to separate methylene blue from water, but the problem with many of these methods is that they are expensive and produce other kinds of waste.
But what if we can find a new method of recycling, not just purifying water? Anjula Kosswattaarachchi, a Ph.D. student in chemistry at the University of Buffalo, said that this is the real motivation for this project.
Methylene blue solution (picture from the Internet)
Upgrade to recycle methylene blue-and wastewater?
This study is only the first step in assessing how and whether methylene blue in industrial wastewater can be used in batteries.
In order to achieve this goal, Cook said, we need to avoid the expensive process of extracting dyes from water. What interests us is whether there is a way to directly reuse the wastewater itself.
In textile manufacturing, wastewater contains salt. Normally, in order for the redox flow battery to work, you must add salt as a supporting electrolyte, so salt in wastewater may be a built-in solution. Now this is all speculative: we do n’t know if it will work because we have n’t tested it yet.
What Cook and Kosswattaarachchi have demonstrated so far is that methylene blue excels in important tasks related to energy storage. In the experiment, the scientists built two simple batteries, using dyes—dissolved in salt water—to capture, store, and release electrons (all the key tasks in the battery's life cycle).
The first battery made by the researchers was nearly perfect when it was charged and discharged 50 times: most of the electrical energy charged by scientists was released.
However, over time, when methylene blue molecules are trapped on a membrane that is critical to the device's normal function, the battery's ability to store energy begins to decline.
In the scientist's second battery, a new membrane material was selected to solve this problem. The device maintains the near-perfect efficiency of the first model, with no significant energy storage capacity reduction during 12 charge and discharge cycles.
The results show that methylene blue is a viable material for flow batteries. With this, the team hopes to do further research by obtaining real wastewater from textile mills that use the dye.
Cook said that we hope to evaporate the wastewater into a more concentrated solution containing methylene blue and salt, which can then be tested directly in the battery.
Sri Lanka's textile industry and the personal connections of researchers
From a personal point of view, the project is very important for Kosswattaarachchi: before coming to UB, she worked in the textile industry and developed new fabric technology for Sri Lanka Nanotechnology Research Institute (SLINTEC).
The textile industry is one of the most important economic sectors in the country, and the industry has created many jobs. But pollution is a disadvantage, and wastewater can become an environmental issue.
Kosswattaarachchi said that we believe this work can lay the foundation for an alternative route for wastewater management and pave the way for green energy storage technologies.
(Originally from: Daily Science China New Energy Network Synthesis)
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