Development of an advanced reverse osmosis membrane based on detailed nanostructure analysis

Due to an increase in the number and severity of water shortages worldwide, reverse osmosis (RO) membrane technologies are widely used for seawater desalination and wastewater reclamation. There are increasing demands for enhancing the water production rate and solute rejection rate to obtain higher quality water by consuming less energy. Therefore, it is necessary to understand the nanoscale structure and permeation mechanism of RO membranes. Typical RO membranes have a composite structure, with an ultrathin separation functional layer of cross-linked fully aromatic polyamide. The functional layer has sub-μm sized protuberance structures and sub-nm sized water channels. The protuberance structures were quantitatively examined by advanced TEM techniques. The relationship between the membrane performance and morphological parameters of protuberance structures was revealed. Hydrated structures are formed by the complex intermolecular interactions between polymers and water molecules. The structure was investigated by neutron scattering measurements and molecular dynamics simulations. In the water-rich polyamide/water system, water molecules are well connected to each other to form water channels. Based on the above results, innovative RO membranes are being developed through the precise control of nanostructures.