Development of hydrogen bonding stabilized conjugated carbonaceous polyaryl organic solvent nanofiltration membranes for molecular sieving

Abstract

Organic solvent nanofiltration (OSN) has enormous potential for transforming the way organic solvents are purified and recovered in the chemical industry. Apart from conventional thin film composite (TFC) nanofiltration membrane fabrication methods, a greener, simpler, and more efficient approach has been utilized to fabricate OSN membranes. Oxidative polymerization of an aqueous solution of a pyrrole monomer on a hydrolyzed/crosslinked polyacrylonitrile (H-PAN/C-PAN) support yielded a dense polypyrrole (PPy) skin layer consisting of a conjugated carbonaceous polyaryl network. The presence of multiple amino groups (>NH) in the PPy chain develops extensive hydrogen bonding with the –COOH and –NH groups present in the H-PAN/C-PAN support. The shift in the ATR-FTIR peaks of PPy upon deposition on the H-PAN/C-PAN support confirmed the interaction between PPy and the H-PAN/C-PAN support. When the OSN performance of the fabricated membranes was studied, the PPy@C-PAN/PETP membrane showed a better performance in terms of rejection of model solutes including charged and neutral molecules compared to the PPy@H-PAN/PETP membrane. Both membranes rejected >99% of Rose Bengal, Congo red, and Eriochrome black T used as model solutes in the current study. For the neutral molecules, PPy@H-PAN@PETP was able to reject 44% of triphenylbenzene (TPB) and >99% of hexaphenylbenzene (HPB), whereas PPy@C-PAN@PETP rejected 72% of TPB and >99% of HPB. In the case of methylene blue, a rejection of 48% was found for PPy@H-PAN/PETP while a rejection of 82% was recorded for PPy@C-PAN/PETP. Moreover, the permeance of n-hexane was found to be 9.3 L m⁻² h⁻¹ bar⁻¹ for PPy@H-PAN/PETP and 3.3 L m⁻² h⁻¹ bar⁻¹ for the PPy@C-PAN/PETP membrane.