Improved performance of nanocomposite polyimide membranes for pervaporation fabricated by embedding spirobisindane structure-functionalized graphene oxide

Abstract

In this study, spirobisindane-functionalized graphene oxide (SFGO)/polyimide (Matrimid® 5218, i.e. M) solutions are spin-coated onto a polysulfone support to produce SFGO@M nanocomposite membranes for alcohol dehydration by pervaporation. Compounds 3,3,3′,3′-tetramethyl-1,1′-spirobisindane-6,6′-diol (TSD) and 4,4′-((3,3,3′,3′-tetramethyl-2,2′,3,3′-tetrahydro-1,1′-spirobi[indene]-6,6′-diyl)bis(oxy))dianiline (TTSD) are synthesized based on a conversion reaction from bisphenol A (BPA). Both TSD and TTSD contain spirobisindane structure, which is inspired by the structural unit from polymers of intrinsic microporosity. The fine structural characteristics of SFGO@M membranes are evaluated using positron annihilation lifetime spectroscopy. The membrane free volume increases in the following order: M < GO@M < BPA-GO@M < TSD-GO@M < TTSD-GO@M. These results reveal that SFGO affected the fine structural characteristics of membranes in a more significant manner when compared with GO@M and BPA-GO@M. Moreover, TSD-GO@M and TTSD-GO@M exhibit different levels of dehydration performance when tested on different alcohol feed solutions. After TTSD modification on GO, the membrane performance increased from 619.3 ± 124.0 g∙m-2h−1 for the pristine sample, to 915.5 ± 44.8 g∙m-2h−1 for TTSD-GO@M, and the water concentration in the permeate is maintained as high as 99 wt%. Furthermore, the modified membranes are stable under broad operating conditions with high potential for long-term use.