A “micro-explosion” strategy for preparing membranes with high porosity, permeability, and dye/salt separation efficiency

[Display omitted] •A high porosity separation membrane was prepared using in-situ foaming technology.•The preparation of separation membrane by in-situ foaming technology has not been reported.•The membrane exhibited high permeability and good separation performance for dye/salt mixtures.•The in-situ foaming technology is universal for different types of separation membranes. In this study, inspired by “micro-explosion” strategies, a separation membrane with high porosity and permeability, and highly efficient separation performance was prepared. With the use of polyvinylidene fluoride (Solvay6015) as membrane material, azodicarbonamide (AC) as an “explosion center point” to the casting membrane solution, and NaOH as an “external stimulus” in the coagulation bath, the two chemicals undergo in-situ foaming reaction to form a loose nanofiltration membrane. FTIR, XPS, and TGA results demonstrated that the decomposition of AC was complete, which produced gases that increased the porosity of the membrane. The optimized membrane has a higher flux (101.72 L m−2 h−1 at 0.3 Mpa), higher negative surface charge, and better mechanical properties under the premise of separating CR/NaCl. In the separation of pollutants with different molecular weights, the permeation flux of the optimized membrane increased by more than double. This foaming technology was also applied to another membrane material, ethylene vinyl alcohol, from which we found that the membrane also had higher porosity and better permeability. Together, this paper presents an in-situ foaming method for preparing separation membranes and lays the foundation for solving the trade-off between membrane permeability and rejection in dye/salt separation.