Preparation of ultrafiltration membranes based on carbon dioxide adsorption-desorption assisted NIPS phase transition

CO 2 bubble-assisted nonsolvent-induced phase inversion separation (NIPS) technique has demonstrated remarkable advantages in fabricating ultrafiltration (UF) membranes with high porosity and narrow pore size distribution. In this study, an improved CO 2 bubble-assisted NIPS was developed by incorporating polyethyleneimine (PEI) into the casting solution to form a homogeneous single-phase system, thereby avoiding the aggregation issues commonly associated with using CaCO 3 as the CO 2 foaming source. The freshly cast nascent membrane was exposed to a CO 2 atmosphere, allowing rapid CO 2 adsorption by the surface PEI layer, followed by immersion in an acidic coagulation bath to trigger prompt CO 2 desorption. By tuning the CO 2 adsorption and desorption conditions, the phase separation dynamics and membrane pore morphology were effectively regulated. The resulting membrane exhibited a surface porosity of 14.7%, a narrow pore size distribution, and an average pore diameter of approximately 10.5 nm. The influence of factors such as the casting solution solvent type and temperature, CO 2 adsorption time, and coagulation bath pH on the membrane structure was investigated. The membrane formation mechanism was analyzed based on SEM surface morphology with XPS. The fabricated membrane exhibited excellent performance, with a pure water permeance of 653.1 L·m −2 ·h −1 ·bar −1 and a high rejection rate of 98.5% toward bovine serum albumin. This work provides an effective strategy for fabricating UF membranes with high porosity and narrow pore size distribution.