Nanostructured membranes with interconnected pores via a combination of phase inversion and solvent crystallisation approach

Polyethersulfone (PES) is an important membrane material in wastewater and medical applications due to its outstanding thermal and mechanical properties. However, when processing the PES into the asymmetric membranes through nonsolvent-induced phase separation (NIPS) method, the emergence of macro voids and discrete porosities has hampered its permeation performance. In this study, we present a novel phase inversion and solvent crystallisation approach that combines NIPS with the combined crystallisation and diffusion (CCD) technique, named as (NIPS-CCD) to significantly improve PES ultrafiltration membrane permeation without use of any additives. The NIPS-CCD method is simple and requires only a change in casting plate material and water bath temperature. The resultant membrane features a typical NIPS-like skin layer and elongated finger like structure, which are integrally connected to aligned microchannels formed through the CCD technique. With the enhanced pore connectivity, a 50-fold increase in water permeation up to 771 LMH bar-1 was obtained from the NIPS-CCD membrane with the pore size of 6-7 nm. This approach can be easily adapted to industrial production for other high-performance membrane materials with a minimal process modification, making it a promising strategy for improving the permeation properties of membranes used in various applications.