Organic Dye Solution Nanofiltration by 2D Zn-TCPP(Fe) Membrane – leverage of chemical and fluid dynamic effects

Abstract

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∙bar-1) over 4h, whereas replacement of isopropanol by ethanol results in incipient loss of rejection. However, for this ethanol solution feed, incorporating an optimal dose of ZIF-8nanograins 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.