Schematic showing the desalination of inorganic solutions using tunnel manganese oxides as electrode materials. The ions are removed from the water and inserted into the tunnel manganese oxide crystal structures. Lower left image is a transmission electron microscope image showing the atomic scale tunnels in the materials. The high contrast dots are columns of manganese atoms.
With nearly 40% of the world’s population facing water scarcity, there is an urgent need to develop efficient methods for the production of fresh water based on low cost materials. Drexel Materials researchers in Anne Stevens Assistant Professor Ekaterina Pomerantseva’s Materials Electrochemistry Group have recently shown that a family of inexpensive and environmentally friendly manganese oxides are effective at removing a number of different salts from solution via a process called hybrid capacitive deionization.
In a report recently published in Nano Energy, the researchers synthesized manganese oxides built from different size and shape tunnels with atomic scale dimensions. The materials could be produced via simple, scalable hydrothermal methods that result in a high aspect ratio nanowire morphology ideal for water treatment applications. The structural tunnels within the nanowires provide ample storage sites for salt ions removed from water to insert into. Atomic resolution images of these tunnels, obtained through careful electron microscopy performed by collaborators at Oak Ridge National Laboratory, provide valuable insight into the size, shape, and arrangement of the tunnels within the nanowires.
Study of the performance of the manganese oxides revealed that the tunnel size has an important impact on the desalination capabilities. By increasing the size of the tunnels, the researchers were able to improve the ability of the nanowires to remove larger hydrated salt ions from solution. Such results contribute to understanding the fundamental behavior of manganese oxides in desalination applications and provide design guidelines to maximize the performance of future materials for removal of contaminants from water.