Interfacial Wettability Regulation Enables One-Step Upcycling of the End-of-Life Polymeric Microfiltration Membrane

Polymeric membranes, which are typically synthesized from fossil-based polymers, will reach their end of life (EOL) and then be replaced, due to the inevitable accumulation of membrane fouling even though the periodic cleaning is applied. The conventional disposal methods of the EOL membranes are landfilling and incineration, which will lead to additional carbon emission and fossil resource depletion. Herein, we proposed a surfactant-regulated interfacial polymerization strategy, by adding sodium dodecylbenzene sulfonate (SDBS) in the piperazine (PIP) aqueous solution, for the one-step upcycling of the EOL polymeric microfiltration membrane to obtain a thin-film composite polyamide (PA) nanofiltration (NF) membrane. Revealed by the quartz crystal microbalance with dissipation analysis and molecular dynamics simulation, the presence of SDBS reduced interfacial tension (IFT) and regulated interfacial wettability, thereby facilitating adequate and uniform uptake of PIP monomers. The resulting upcycled NF membrane with 4 critical micelle concentration (CMC) of SDBS addition exhibited a favorable pure water permeance (20.1 ± 0.6 L m^–2 h^–1 bar^–1) and a satisfactory Na₂SO₄ rejection of 98.6 ± 0.4% owing to the formation of a continuous PA layer with high cross-linking degree (89.3 ± 0.5%). The Na₂SO₄ permeability of the 4 CMC upcycled NF membrane was more than 1 magnitude lower than that of the upcycled NF membrane without SDBS addition. This study provides a facile, rapid, and cost-effective method for the one-step upcycling of EOL polymeric membranes, which thus improves the sustainability of membrane technology.