Abstract: The present invention provides a nanocomposite coating comprising: a two-dimensional material; and a polymer, wherein the nanocomposite coating is semi-permeable and is for providing on porous material to improve selectivity towards one phase over others thereby enabling separation of that phase by mass transfer. There is also provided a phase transformation and mass transfer unit comprising porous material coated with the nanocomposite coating, and a low temperature liquid phase separation method comprising flowing liquid mixture through a phase transformation and mass transfer unit comprising porous material coated with the nanocomposite coating.