Preparation of polysulfone-based block copolymer ultrafiltration membranes by selective swelling and sacrificing nanofillers

Selective swelling of block copolymers of polysulfone-b-poly(ethylene glycol) is an emerging strategy to prepare new types of polysulfone ultrafiltration membranes. Herein, we prepared nanoporous polysulfone-b-poly(ethylene glycol) ultrafiltration membranes by selective swelling and further promoted their porosity and ultrafiltration performances by using CaCO₃ nanoparticles as the sacrificial nanofillers. Different contents of CaCO₃ nanoparticles were doped into the solution of polysulfone-b-poly(ethylene glycol), and thus obtained suspensions were used to prepare both self-supported and bi-layered composite structures. Selective swelling was performed on the obtained block copolymer structures in the solvent pair of ethanol/acetone, producing nanoporous membranes with poly(ethylene glycol) lined along pore walls. The CaCO₃ nanoparticles dispersed in polysulfone-b-poly(ethylene glycol) were subsequently etched away by hydrochloric acid and the spaces initially occupied by CaCO₃ provided extra pores to the block copolymer layers. The porosity of the membranes was increased with increasing CaCO₃ content up to 41%, but further increase in the CaCO₃ content led to partial collapse of the membrane. The sacrificial CaCO₃ particles provided extra pores and enhanced the connectivity between adjacent pores. Consequently, the membranes prepared under optimized conditions exhibited up to 80% increase in water permeance with slight decrease in rejection compared to neat membranes without the use of sacrificial CaCO₃ particles. [Figure not available: see fulltext.]