Electrified membrane and molecule combo transforms nitrate into ammonia

The electrochemical conversion of the nitrate found in contaminated ammonia water offers a potentially environmentally friendly solution for water treatment and the development of fertilizer without fossil and carbon -free fuel. However, finding an effective and inexpensive way to do so was not easy. Yale researchers, however, may have found the solution. The results are published in Chemical genius of nature.

Nitrate, a pollutant found in wastewater, can be converted into ammonia which can then be transformed into fertilizers, carbon -free fuel and other useful products. The main challenges to do so, however, imply what researchers in the field call selectivity and activity. In other words, you want to convert nitrate to ammonia while creating the least by-products, and you want to do it quickly, explained Lea Winter, who led the study and is a professor of chemical and environmental engineering.

One way in which researchers are reporting to these challenges is to focus on the innovations of electrocatalysis that triggers conversion reactions. “By manipulating the properties of materials, you can make the catalyst more active and more selective,” said Winter. But it can be expensive.

“When you use expensive materials and complicated synthetic techniques to make these refined nanostructured materials, you add a lot of cost,” said Winter. “And if we end up with something high costly because of these expensive metals, then it becomes prohibitive. This is particularly true when you try to mitigate nitrate in wastewater through this method.”

The solution

The winter research group has adopted a two -component approach. On the one hand, they added to their system an ionophore, a molecule attracted by certain ions – in this case, nitrite. This is useful because when you convert the nitrate to ammonia, nitrite is a sub-product that forms along the way. Sometimes it escapes in water before it is entirely converted to ammonia.

“So, our trick here was to incorporate the ionophore, which is good to keep the nitrite nearby, which allows it to convert to ammonia before it is released into the water. And it is our key to obtain the very high selectivity of ammonia.”

For the second part of their technology, they incorporated an electrified membrane based on copper and carbon nanotubes, an electrochemical conversion platform in which the winter laboratory specializes. This is what allows the system to convert ammonia to nitrate so quickly.

“Part of the challenge is that because the membrane works so quickly, you end up getting a lot of nitrite,” said Winter. “But when we combine the electrified membrane with the ionophore, we obtain both very high activity as well as the high selectivity of ammonia without having to compromise one or the other.”

Compared to other systems that focus on selectivity and activity, winter takes place from afar. While other systems operate on a scale of hours, the winter method passes from nitrate through the membrane and converted into ammonia in just six seconds. In addition, 92% of the nitrate is transformed into ammonia.

To test their system in a real world application, the researchers used it on the water of a lake near the Yale campus and a wastewater treatment plant at the University of Connecticut. In both cases, they found that their system passed a crucial test to remain stable for several hours. In addition, because the membranes are very flexible, Winter said that there are opportunities to go back to the level of conventional water treatment processes.