(569g) Molecular Drilling and Bonding for Highly Permeable and Fouling-Resistant Reverse Osmosis

Higher permeability and lower fouling propensity have been the persistent pursuit for reverse osmosis (RO) membranes over the past decades. Though it is argued that the benefits in energy saving for seawater desalination brought by further increment in the permeability of current RO membranes is only marginal, recent research found that membranes with a three-times-higher permeability can reduce the energy consumption by 46% in brackish water desalination. In addition, fouling is one of the major concerns in the membrane desalination process. Attachment of inorganic and organic foulants from the feed solution onto the membrane surface can cause significant flux decline, which leads to increased operating pressure and frequent physical/chemical cleaning. To reduce the operational cost and increase energy efficiency of the current system, proper antifouling strategies are critical. Existing methods reported in literature to modify reverse osmosis (RO) membranes for enhanced anti-fouling properties usually involve two or more complicated reactions on membrane surface and toxic chemicals, which are difficult to scale up. One-step and environmentally friendly approaches are strategically important for the upsize and commercialization of any new types of antifouling RO membranes.

This paper reports a fast, cost-effective and environmental-friendly method to engineer the 3D membrane structure, and simultaneously enhance the permeance and fouling resistance in RO. By free radical polymerization in water, copolymers containing fouling-resistant zwitterionic and anchoring groups are synthesized and quickly bonded to the polyamide membrane surface. The copolymer also functions as the molecular engine to reduce the thickness of the polyamide layer and drill nanopores, thereby re-shaping its 3D structure for higher permeability. It is revealed that by design of the size and functionality of the copolymer, the water permeability and salt rejection may be simultaneously increased. Our hollow fiber membrane demonstrates a pure water permeability of 10.5 ± 0.5 L m^-2 h^-1 bar^-1 which outperforms currently available membranes by 2 to 3 times, NaCl rejection of 98.1 ± 0.2 %, and superior fouling resistance towards various foulants and realistic feed from the local RO plants. This paper provides a new perspective for the development of highly permeable, fouling-resistance membranes not only for RO, but also nanofiltration.