Gradient nanoporous phenolics filled in macroporous substrates for highly permeable ultrafiltration

Highly permeable and cost-affordable membranes are highly desired in separation processes. Herein, such membranes are produced by designing gradient phenolics inside the macropores of polyvinylidene fluoride (PVDF) substrates. Solutions consisting of resol, poly(ethylene oxide)/poly(propylene oxide) copolymer and ZnCl₂ are infiltrated into the macropores of PVDF. Phenolic nanoparticles and nanopores with increasing sizes are formed across the membrane thickness after fast solvent evaporation, ZnCl₂-facilitated resol polymerization and acid soaking. The prepared gradient phenolic@PVDF membranes exhibit a permeance up to 1315 L/(m² h bar), which is several times higher than that of other membranes with similar rejections to bovine serum albumin (91%) and lysozyme (71%). Moreover, the membranes are robust enough to withstand a pressure of at least 12.0 bar due to the interlaced structures of phenolics and PVDF. We demonstrate that thus-produced membranes can efficiently separate and concentrate gold nanoparticles with sizes down to 5 nm. This work suggests a new strategy for rational design of gradient porosities in macroporous substrates to produce robust membranes with high permeances and tight rejections.