Swelling-controlled positioning of nanofillers through a polyamide layer in thin-film nanocomposite membranes for CO2 separation

Abstract

An effective and simple method named as Swelling-controlled Nanofiller Positioning (SNP) is proposed to construct unimpeded CO2 transport nanochannels through a polyamide (PA) layer of thin-film nanocomposite (TFN) membranes for CO2 separation. The SNP strategy can carefully pre-position the porous nanofiller (ZIF-8), providing gas transport channels, exactly at the support/solvent interface during interfacial polymerization (IP) process in order to keep ZIF-8 nanofillers through the selective layer after IP reaction. The pre-position was implemented via swelling the intermediate layer, polydimethylsiloxane (PDMS), in the organic solvent ahead of IP reaction. Swollen PDMS segments and the post-crosslinking reaction of unreacted PDMS oligomers in organic phase could restrain the mobility of ZIF-8 nanofillers and enhance the interfacial compatibility of nanofillers and PDMS. Then a PA layer with a tunable thickness was formed by IP reaction on the modified support with pre-positioned ZIF-8 nanoparticles. Additionally, we also investigated the deposition of ZIF-8 nanoparticles on swollen PDMS/PSf supports for further understanding the particle-size effects on the membrane structure and CO2 separation performance. High permselectivty is achieved for TFN membranes with unimpeded CO2 transport nanochannels in CO2/N2 mixed-gas tests.