Janus membranes are an emerging class of materials having opposing properties at an interface. This structure results in selective and often novel transport characteristics. In this Minireview, a definition of the Janus membrane, beyond merely asymmetric materials, is introduced and common fabrication strategies are outlined. Also presented are current and potential applications in directional transport, switchable permeation, and performance optimization with detailed mechanisms.

Mussel-inspired polydopamine (PDA) deposition offers a promising route to fabricate multifunctional coatings for various materials. However, PDA deposition is generally a time-consuming process, and PDA coatings are unstable in acidic and alkaline media, as well as in polar organic solvents. We report a strategy to realize the rapid deposition of PDA by using CuSO4/H2O2 as a trigger. Compared to the conventional processes, our strategy shows the fastest deposition rate reported to date, and the PDA coatings exhibit high uniformity and enhanced stability. Furthermore, the PDA-coated porous membranes have excellent hydrophilicity, anti-oxidant properties, and antibacterial performance. This work demonstrates a useful method for the environmentally friendly, cost-effective, and time-saving fabrication of PDA coatings.

Ultrathin metal/covalent–organic framework (MOF/COF) membranes have attracted increasing research interest and have been considered as state-of-the-art platforms applied in various environment- and energy-related separation/transportation processes.

Mussel-inspired chemistry has attracted widespread interest in membrane science and technology. Demonstrating the rapid growth of this field over the past several years, substantial progress has been achieved in both mussel-inspired chemistry and membrane surface engineering based on musselinspired coatings. At this stage, it is valuable to summarize the most recent and distinctive developments, as well as to frame the challenges and opportunities remaining in this field. In this review, we present recent advances in rapid and controllable deposition of mussel-inspired coatings, dopamine-assisted co-deposition technology and photo-initiated grafting directly on mussel-inspired coatings. Some of these technologies have not yet been employed directly in membrane science. Beyond discussing advances in conventional membrane processes, we discuss emerging applications of mussel-inspired coatings in membranes, including as a skin layer in nanofiltration, interlayer in metalorganic framework based membranes, hydrophilic layer in Janus membranes and protective layer in catalytic membranes. Finally, we raise some critical unsolved challenges in this field and propose some potential pathways to address them.

Nanofiltration membranes are of great interest in brackish water desalination and drinking water purification.