Computational Design of 2D Covalent-Organic Framework Membranes for Organic Solvent Nanofiltration

Abstract

Covalent-organic frameworks (COFs) are ordered crystalline materials covalently formed by building blocks of light elements. There has been increasing interest in the development of COF membranes for chemical separation. In this study, seven two-dimensional (2D) COF membranes are computationally designed with different functional groups and aperture sizes. By 245 sets of molecular simulations, the seven ultrathin COF membranes are investigated for organic solvent nanofiltration (OSN) of seven solvents (acetonitrile, acetone, methanol, ethanol, isopropyl alcohol, methyl ethyl ketone, and n-hexane) and four solutes (2,5-furandiamine, paracetamol, α-methylstyrene dimer, and Nile red). The solvent fluxes through the COF membranes are revealed to be governed by the aperture size and membrane functionality, as well as solvent properties. In general, the larger the aperture size, the higher is the flux. For membranes with comparable aperture size, the hydrophobic one exhibits higher fluxes than the hydrophilic counterpart for all the solvents except n-hexane. To elucidate this trend, solvent structures near the membranes are analyzed and the potentials of mean force for solvent permeation are evaluated. The solvent permeances through hydrophobic and hydrophilic membranes are correlated respectively with two different combinations of solvent properties. The solute rejection is found to depend on a complex interplay among solute size and polarity, solvent viscosity, solute–solvent interaction, aperture size and membrane functionality. In the presence of solutes, solvent permeances are reduced by approximately 10%. From the bottom-up, this comprehensive computational study provides quantitative insights into solvent permeation and solute rejection in the COF membranes, unravels the key governing factors, and would facilitate the development of new membranes for high-performance OSN.

Emerging Functional Porous Polymeric and Carbonaceous Materials for Environmental Treatment and Energy Storage

“…COFs with rich secondary amine groups have also been synthesized by interfacial polymerization to improve the ethanol permeance . A computational study was also used to unravel the key governing factors of solvent permeation and solute rejection in COF membranes . The solvent permeances were correlated with different combinations of solvent properties in the hydrophilic and hydrophobic membranes; the rejection was governed by the complex interplay of membrane functionality, solute size and polarity, solvent viscosity, solute–solvent interaction, and pore size.…”

Pore engineering of ultrathin covalent organic framework membranes for organic solvent nanofiltration and molecular sieving

“…[14][15][16] Recent simulation studies have revealed that the COF nanopores offer fast transport pathways. [17][18][19] Considerable research progress has been devoted to the synthesis of COF membranes recently. Banerjee et al reported a group of b-ketoenamine based COF structures that have shown unpredictable chemical stability not only in organic solvents but also in aqueous, acidic and basic media.…”

Covalent Organic Framework Membranes for Efficient Chemicals Separation

“…A simulation work has been conducted to guide the selection of COF materials for OSN and explore the factors affecting the OSN performance of COF membrane. [204] Seven types of singlelayered TpPa-X membranes with different apertures (5.2-7.6 Å) and hydrophilicity were computationally designed by introducing different functional groups. The permeances of some solvents, such as acetonitrile, methanol, ethanol, acetone, isopropanol (IPA), and methyl ethyl ketone (MEK), are regulated by the pore size and membrane functionality, while the flux of n-hexane is determined merely by the aperture because of the relatively weak interaction between the membrane and the solvent (Figure 27a).…”