Carbonization of gradient phenolics filled in macroporous substrates for high-flux tight membranes: Toward ultrafiltration of polypeptides

Tight ultrafiltration (UF) membranes with high permeances have gained growing attention in the separation of biomacromolecules. Herein, we report the preparation of gradient carbonaceous structures filled in macroporous polyvinylidene fluoride (PVDF) substrates and their efficient separation of polypeptides. Gradient phenolics composed of nanoparticles with sizes increasing from top side to bottom side are firstly synthesized inside PVDF substrates. When soaked in concentrated H₂SO₄, phenolic nanoparticles are partially carbonized and foamed to form micropores while the PVDF substrate maintains intact. Thus-produced carbonaceous membranes are mechanical robust and exhibit narrowed pore sizes and enhanced hydrophilicity. Their permselectivity can be adjusted simply by changing the dosages of phenolic precursors filling into the PVDF substrates. Low dosages lead to remarkably high water permeances up to 1721 L/(m²·h·bar). At higher dosages, the membrane is tightened to show a molecular-weight-cut-off (MWCO) down to 3.7 kg/mol and high permeances several times larger than other membranes with similar MWCOs. We demonstrate that such a tight UF membrane efficiently separates polypeptides with molecular weights of only a few kg/mol (angiotensin Ⅱ and thymosin β4). Our work opens a new avenue for the synthesis of high-flux tight UF membranes with narrowed pores, enabling the precise separation and fractionation of biomacromolecules.