Strategy to Chemically Decorate Nanopores of a Carbon Membrane for Filtrating Polyphenolics from Ethanol

Abstract

This study invents a post-pyrolysis modification approach to render the resulting carbon membrane (CM) competent for organic solvent nanofiltration (OSN). A bitumen coating on a porous stainless-steel disk (PSD) serves as the precursor for the intended carbon membrane (CM), which is attained through pyrolysis in Ar. The bitumen coating casts dual-pore networks in the CM because of the dominant asphaltene constituent in bitumen. The subsequent chemical decoration of CM was pursued through the following protocol: dopamine (DA) was deployed in the nanopores of CM via pressurized infiltration and followed by Tris buffer passes through to trigger in situ conversion of DA to polydopamine (PDA), which was affixed over the pore walls to furnish chemical affinity (termed as CMPDA). Additionally, the catechol moiety of PDA was arranged to chelate with the Zn2+ ion, aiming to trim the −OH anchor (termed as CMPDA–Zn) to probe the effect of chelate on separation. The three membranes (CM, CMPDA, and CMPDA–Zn) were thereafter assessed by the separation of ethanol or isopropanol from phenolics [tannic acid (TA)/tetracycline (TC)]. A significantly improved OSN performance [rejection (%) ↔ permeance (L/(m2·h·bar))] of CM vs CMPDA was observed: (i) for TA feed, 13% ↔ 85 L/(m2·h·bar) vs 83% ↔ 12 L/(m2·h·bar); and (ii) for TC feed, 20% ↔ 78 L/(m2·h·bar) vs 78% ↔ 12 L/(m2·h·bar). Compared to CMPDA, CMPDA–Zn further advances the rejection performance (∼89% for TA and ∼80% for TC) over 50 h separation. They are benchmarked by the latest literature results. The performance enhancements can be attributed to the spreading of PDA or PDA–Zn sites in the dual-pore networks, so that they are able to offer H-bonding and steric blocking roles, a chemicomechanical effect, to seize solute molecules over pore walls. It is this interfacial drag effect that sustains the solute rejection.