Water-Polyamide Chemical Interplay in Desalination Membranes explored by Ambient Pressure X-ray Photoelectron Spectroscopy
Sabrina Gericke, William D. Mulhearn, Dana E. Goodacre, Joseph Raso, Daniel J. Miller, Lauryn Carver, Slavomir Nemsak, Osman Karslioglu, Lena Trotochaud, Hendrik Bluhm, Christopher M. Stafford, Christin Buechner
Reverse osmosis using aromatic polyamide membranes is currently the most important technology for seawater desalination. The performance of reverse osmosis membranes is highly dependent on the interplay of their surface chemical groups with water and water contaminants. We study ultrathin polyamide films that chemically resemble reverse osmosis membranes, using ambient pressure X-ray photoelectron spectroscopy. This technique can identify the functional groups at the membrane-water interface and allows monitoring small shifts in the electron binding energy that indicate interaction with water. We observe deprotonation of free acid groups and formation of a water complex with nitrogen groups in the polymer upon exposure of the membrane to water vapor. The chemical changes are reversed when water is removed from the membrane. While the correlation between functional groups and water uptake is an established one, this experiment serves to understand the nature of their chemical interaction, opening possibilities for tailoring future materials to specific requirements.