Unprecedented water permeation in nanostructured PVDF membranes prepared by unidirectional freezing and surface melting method

Phase inversion has played a vital role in membrane technology by offering the economic viability for producing polymeric membrane in quantity, and it allows for the development of wastewater treatment technologies with the membrane as a promising energy-saving separator. However, most existing phase inversion membranes suffer from low permeance, thus diminishing their advantages in the quest for more efficient and sustainable separation processes. Here, based on unidirectional freezing approach, we showcase a hierarchical porous membrane that outperforms the permeance of the phase inversion membranes without compromising the membranes’ separation capabilities. An unprecedented surface melting atop a frozen membrane cast film promotes the phase inversion in the water phase, which in turn constructs an additional separating layer on membrane surface. These membranes exhibit tuneable pores in the range between 9 and 50 nm and pure water permeation which is 16–25 times higher than that of an equivalent industry standard. Moreover, the synergy between freezing and melting enables a separate design of pore sizes from membrane both surfaces, leading to a dual-skin polymeric membrane showing enhanced functionality throughout its cross-section. With the enhanced efficiencies, these membranes have potential to positively contribute to the current water-energy nexus, by considerably improving the economic and technological viability of many water-treatment and filtration-based separation systems.