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Many desalination plants around the world rely on membrane distillation to extract drinkable water from seawater. However, membrane distillation is also used to treat industrial wastewater prior to discharging it into the environment. Industrial wastewater poses a difficulty for desalination plants due to its high concentrations of oils and greases. Oils frequently wet and foul traditional hydrophobic membranes used for desalination, disrupting operations. Oil removal requires an oleophobic (hydrophilic) membrane, whereas salt removal requires a hydrophobic membrane. To perform these processes simultaneously during membrane distillation, a two-sided Janus membrane is used. Untreated water first flows along the hydrophilic/antifouling side of the membrane before exiting at the hydrophobic side in the form of water vapor. This vapor condenses and is carried away as treated (desalinized) water.
Despite the Janus membrane’s importance, its usage is currently limited by existing fabrication methods. Current methods create a Janus membrane from zwitterionic and other polymers which have varying degrees of adhesion to different substrates. This is problematic because some water treatment applications require inorganic substrates whereas others require polymeric substrates. Poor adhesion of a membrane to a substrate can cause premature failure.
To overcome this challenge, Kalam et al. developed a substrate-independent fabrication technique for Janus membranes. After coating their substrates with polydopamine (PDA), which adheres to almost any substrate or polymer, Kalam used Harrick Plasma’s Expanded Plasma Cleaner (PDC-001) to polymerize the PDA and immobilize Br initiators on the surface. Next, a zwitterionic polymer (PSBMA) brush layer was grafted to the PDA by atom transfer radical polymerization (ATRP). The intermediate PDA layer allows numerous membrane-substrate combinations without sacrificing adhesion. This substrate-independent method allows Janus membranes to be fabricated for a variety of water treatment needs.
Membrane Distillation Articles
Kalam, S., Dutta, A., Du, X., Li, X., Tong, T., & Lee, J. (2024). “A non-substrate-specific technique of antifouling and antiwetting Janus membrane fabrication for membrane distillation.” Desalination, (2024) 573:117195 doi.org/10.1016/j.desal.2023.117195