Synthesis and Characterization of Polyether-Ether Ketone Supported TpPa-1 Covalent Organic Framework Membrane for Organic Solvent Nanofiltration

Abstract

There is a lot of potential for energy-efficient separation in membranes made up of covalent organic frameworks (COF). It has been reported that COFs are able to separate dyes, salts, bacteria, and nanoparticles based on size-selective transport through ordered pore structure. They have recently emerged as promising membranes for separations involving organic liquids. In the last decade, organic solvent nanofiltration (OSN) has received a lot of attention since it is an energy- and waste-efficient method for separating mixtures down to the molecular level. Although the number of OSN publications has increased in recent years, there is a need to search for new membrane materials with a combination of excellent solvent stability and adequate separation performances. In this work, continuous TpPa-1 COF membranes were synthesized on polyether ether ketone (PEEK) supports via the interfacial polymerization (IP) method, in a similar way to the standard IP process used for the synthesis of polyamide (PA) membranes. A conformal TpPa-1 COF membrane was formed on the porous substrate within a minute owing to the fast reaction between amine and aldehyde monomers, which were dissolved in the aqueous and organic solutions, respectively. The separation performances of the TpPa-1 membranes were evaluated in water and organic solvent systems with ethanol as the polar organic solvent and with dye molecules as the model solutes. Anionic dyes such as methyl blue and fast green (FG) dye molecules were rejected at a rate of 95% with a permeance of 229.88 L〖 m〗^(-2) hr^(-1) bar^(-1) and 86.55% with a permeance of 48 L〖 m〗^(-2) hr^(-1) bar^(-1) for aqueous system. The molecular weight cut off (MWCO) of the membranes for OSN in the ethanol system was ~780 g⋅mol^(-1). The rejection mechanism of TpPa-1 COF membrane in the polar solvent has also been discussed. Moreover, solvothermal synthesis was used to synthesize TpPa-1 COF powder, and their structural stability was examined using polar and nonpolar solvents. Covalent organic framework materials along with highly stable polyether ether ketone substrate appear to have great potential for OSN applications.