Relying on an electrochemical process, a team of researchers at Massachusetts Institute for Technology (MIT) have developed a new method to remove very dilute concentrations of pollutants and even extremely low levels of unwanted compounds from water. Separation methods that existed before tend to consume a lot of energy and chemicals. The new method is credited to MIT postdoc Xiao Su, Ralph Landau Professor of Chemical Engineering T. Alan Hatton, and five others at MIT and at the Technical University of Darmstadt in Germany. The study, titled “Asymmetric Faradaic systems for selective electrochemical separations,” was first published in the Royal Society of Chemistry’s journal Energy and Environmental Science.
The method selectively removes every organic contaminant, such as pesticides, chemical waste products, and pharmaceuticals, even those present in very fine and small – yet toxic – concentrations. The new method also tackles the significant limitations of old school separation methods, such as acidity fluctuations and losses in performance that often happens as a result of competing surface reactions.
The methods and systems that are being used in current water treatment plants and labs include membrane filtration, which, despite its high cost, has limited effectiveness at low concentrations, electrodialysis and capacitive deionization, which often require high voltages that tend to produce side reactions. Adding to their shortcomings, these processes are hampered by excess background salts.
In the new electrochemical method, the water flows between chemically treated surfaces that serve as positive and negative electrodes. These electrode surfaces are coated with Faradaic materials, which can undergo reactions to become positively or negatively charged. These active groups can be tuned to bind strongly with a specific type of pollutant molecule, as the team demonstrated using ibuprofen and various pesticides.
Su argues that the same selective process should also be applied to the recovery of high-value compounds in a chemical or pharmaceutical production plant, where compounds might otherwise be wasted. “The system could be used for environmental remediation, for toxic organic chemical removal, or in a chemical plant to recover value-added products, as they would all rely on the same principle to pull out the minority ion from a complex multi-ion system,” he elaborates.
Matthew Suss, Assistant Professor of Mechanical Engineering at Technion Institute of Technology in Israel, who was not involved in this work, finds this technique as highly significant. “It extends the capabilities of electrochemical systems from basically nonselective toward highly selective removal of key pollutants. As with many emerging water purification techniques, it must still must be tested under real-world conditions and for long periods to check durability. However, the prototype system achieved over 500 cycles, which is a highly promising result,” Suss argues.