Halloysite as main nanostructural filler in multifunctional mixed matrix membranes – review of applications and new possibilities

Innovative, composite mixed matrix membrane (MMM) structures with specific naturally occurring halloysite nanotubes (HNTs) provide new possibilities in gaseous and liquid mixtures separation. Halloysite filler, introduced into the polymer phase, can find itself useful both as natural clay mineral with adsorption/catalytic properties, as well as the convenient support for other, targeted and highly specialised nanoparticles. Numerous laboratory studies indicate that hydrophilicity of the resulting membrane is advantageously improved, providing higher pure water flux than obtained in the one-phase membrane. Optimised structures of the halloysite-based nano-fillers can find them useful in various technological applications, for example, separation of dyes or/and oils from post-processed wastewaters, the concentration of salts in solutions, inhibition of bacterial population growth, as well as separation of gaseous mixtures components. The research done so far and reported in the literature in respect to MMMs with halloysite, applied as a natural mineral and with targeted functionalisations, was systematized and presented. Particular attention was paid to the natural, unique halloysite nanoplates (HNPs), which potential use in technological applications is still not fully discovered and exploited.