Cross-linked mixed matrix membranes (MMMs) consisting of amine-functionalized multi-walled carbon nanotubes and P84 polyimide for organic solvent nanofiltration (OSN) with enhanced flux

Abstract

High-flux mixed matrix membranes (MMMs) for organic solvent nanofiltration (OSN) were designed using amine-functionalized multi-walled carbon nanotubes (NH2-MWCNTs) and P84 polyimide with the aid of 1,6-hexanediamine (HDA) as a cross-linker and thermal annealing to tighten the pore size. The embedding of hydrophilic NH2-MWCNTs into the P84 matrix not only enhanced membrane's porosity, sorption capacity, and liquid transport but also resulted in an amidation reaction between them. The resultant MMMs had higher water, ethanol, and isopropanol permeances than the pristine P84 one. However, a higher loading of NH2-MWCNTs diminished the rejection due to visible agglomeration among them. The cross-linked MMMs consisting of 2mg/g of NH2-MWCNTs/P84 showed a rejection of > 98% to eosin Y (MW of 648g/mol) while pure water, ethanol, and IPA permeances were 16.4, 3.3, and 1.4 LMH/bar at 20bar, respectively. Moreover, they showed a superlative rejection of 92.1% to tetracycline, a smaller drug solute with a MW of 444g/mol, in IPA solutions after thermal annealing at 120°C for 40min. Interestingly, the annealed MMMs still possessed a higher ethanol flux and solute rejections than the pristine P84 membrane. Besides, they also showed promising OSN performance in 72-h continuous tests.