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This study investigates organic solvent nanofiltration (OSN) using the membranes composed of 2D Zn-TCPP(Fe) nanosheets. A group of organic dyes with different molecular weights, hydrophilic properties and functional groups was selected as probe solutes in ethanol, isopropanol and ethyl acetate, respectively, to examine their OSN characteristics through the Zn-TCPP(Fe) membrane. The intermolecular interactions of organic solvent, dye and Zn-TCPP(Fe) nanosheets profoundly influence the mass transfer in the nano channels of the lamellar membrane. Representatively, the isopropanol solution of Brilliant Blue G dye turns out to have a favorable OSN performance (>90 % rejection with an average permenance of 175 L ∙ m - 2 ∙ h - 1 ∙ b a r - 1 ) over 4 h, whereas replacement of isopropanol by ethanol results in incipient loss of rejection. However, for this ethanol solution feed, incorporating an optimal dose of ZIF-8 nanograins into the nanosheets via co-deposition, a particle-over-lamellae structure formed unveils a significant improvement on OSN. Such boost is attributed to a combinative effect, i.e., alleviating dye-nanosheet complexation so as to reduce disturbing the lamellar structure as well as to assist desolvation of the dye over the feed side. To comprehend how solvent-slolute-nanosheet interactions dominate OSN, besides the experimental characterizations, both visco-molar volume and Stokes-Einstein diameter that describe fluid dynamic properties of solute molecule in a solvent are employed to assist the analysis. Possessing hydrophilic characteristic, Zn-TCPP(Fe) nanosheet engages strong hydrophilic association with hydrophilic dye and solvent, leading to weak OSN performance. Fundamentally, there are mutual interactions among solvent, solute and nanosheets in this membrane system, in which the prevailed pair of them impacts OSN performance.

This work invents a composite membrane constituted by the granular NaY zeolite as the major phase (~ 74 vol%), which is integrated with carbonaceous (~ 23 vol%) and glass-fiber phases. The zeolite particles are intimately bonded by carbonaceous to constitute a dendritic distribution of zeolite-carbonaceous amalgam frames (ZCF) that enclose micron-scaled voids, thus resembling a solid foam. These copious voids act virtually as tiny separation cells so as to favor permeance. The membrane shows high rejection to traces of water-soluble dyes, namely Methylene Blue (MB), Rhodamine-B (RB) and Methyl Orange (MO). Rejection to the probe dye molecules relies on electrostatic-interactions between the molecules and ZCF along carbonaceous pores. The interactions are influenced by the pH of feed since it affects magnitude and sign of charge on both ZCF and the dyes. Sterically, since NaY allows only water to penetrate, the dye molecules could crossover the carbonaceous phase in the filtrate if there are no rejection mechanisms. Typically, the membrane manifests a stable rejection (99%) and permeance (88 L/h m2 bar) for the 10 ppm MB solution. Attaching a stable surfactant thin layer on the pore wall allows the membrane to handle higher MB concentrations.

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.