(709b) Membranes with Non-Stick Surface to Mitigate Fouling for Water Purification

The conventional approach to mitigate fouling is to increase membrane surface hydrophilicity or surface energy to be as close to water (72 mJ/m²) as possible. On the other hand, surfaces with low energy (≈20 mJ/m²) such as Teflon and silicon rubber have demonstrated excellent antifouling properties due to their non-stick nature. In this work, we demonstrate two facile methods to reduce the surface energy of UF membranes by (1) direct coating of “non-stick” Teflon AF1600 (an amorphous glassy perfluoropolymer), and (2) two-step coating of polydopamine (PDA) followed by an amine-functionalized tetramethyldisiloxane (Si-NH₂). The surface modification significantly decreases the surface energy and adhesion of a model foulant of bovine serum albumin (BSA). For example, as the Teflon AF1600 coating layer thickness increased from 0 to 7.0 nm, the surface energy decrease from 42 to 15 mJ/m². Consistently, the BSA adsorption decreased from 14 µg/cm² to 2.5 µg/cm². The effect of the coating on the membrane MWCO, pure water permeance, and antifouling properties was systematically investigated. In dead-end filtration systems, the UF membranes coated with ≈5 nm Teflon AF1600 exhibit a 35% reduction in water permeance, less than the unmodified one (50% reduction) for obtaining the same amount of permeated water. Using a constant-flux crossflow system, the Teflon AF1600-coated membranes exhibit a much lower rate of transmembrane pressure (TMP) increase (i.e., lower fouling rate) than the unmodified ones. For instance, the membrane coated with ≈5 nm Teflon AF1600 showed a dTMP/dt value of 0.42 bar/h at a water flux of 70 LMH, much lower than that of the pristine membrane (1.0 bar/h). Similar behaviors have also been observed for the membranes modified with Si-NH₂. Specifically, the Si-modified membranes exhibit dTMP/dt values of ≈20% lower than the pristine ones. In contrast to the conventional approach of increasing surface hydrophilicity, this work demonstrates a new facile method of achieving non-stick surface to enhance membrane antifouling properties for water purification.