Manufacturing strategies and emerging directions of mixed-matrix membranes based on natural Halloysite nanotubes

Mixed-matrix membranes (MMMs) have overcome the technical limitations of single organic or inorganic materials, thereby presenting promising application prospects. As a natural clay mineral with anisotropic surfaces and tubular morphology, halloysite nanotubes (HNTs) are extensively used in emerging directions of MMMs. Herein, the characteristics and advantages of fabrication strategies for HNT-based MMMs are compared, including casting, coating, nonsolvent induced phase separation, electrospinning, electrophoretic deposition, and vacuum filtration. Furthermore, this study provides a detailed discussion of recent representative applications of HNT-based MMMs in gas separation, organic solvent recovery, water purification, flexible electronics, smart response systems, protection, and bioapplications. Suitable fabrication strategies for HNT-based MMMs make it possible to accurately control the structures and considerably enhance the performance of membranes. However, numerous challenges and unresolved problems, including interfacial compatibility, understanding the mass transfer mechanism, and ensuring practical expandability, still need to be solved and deserve attention and further exploration. This progress report may offer meaningful guidance for designing and optimizing HNT-based MMMs, thereby accelerating the practical applications and successful implementation of membrane materials.