Polyoxometalate-modified halloysite nanotubes-based thin-film nanocomposite membrane for efficient organic solvent nanofiltration

Abstract

Polyoxometalate-modified halloysite nanotubes (POM@MHNTs) were synthesized and doped into the polyamide (PA) matrix by interfacial polymerization to prepare doped POM@MHNTs thin-film nanocomposite (TFN) membranes for organic solvent nanofiltration (OSN). Likewise, thin-film composite (TFC) and TFN membranes doped with HNTs were fabricated. It is worth noting that the methanol flux of the TFN can be efficiently enhanced by tuning the contents of POM@MHNTs. The as-synthesized optimal sample (TFN-0.10) exhibits superior methanol flux of TFN-0.10 membrane of 14.80 L m−2 h−1 bar−1 (1.76 times of that of undoped TFC membrane and 1.12 times of that of doped HNTs membrane (TFN-HNTs-0.10). These are mainly due to the tubular structure of POM@MHNTs providing additional solvent transfer channels and the ridge-valley morphology of the membrane surface increasing the contact area between the membrane and the solvent. Meanwhile, the POM@MHNTs nanohybrids are similarly electrostatically attracted by the amide groups on the polyamide chains produced by interfacial polymerization, improving the compatibility of POM@MHNTs with polyamide membranes. TFN-0.10 OSN membrane showed stable chemical properties in medium polar organic (methanol, ethanol, THF), acid polar organic (acetonitrile), and strong polar organic (DMF) solvents. Prepared TFN OSN membranes exhibited strong long-term operation capability and organic solvent resistance after 80 °C DMF immersion for 7 days with inconspicuous separation performance changes. This work offers the prospect of using organic-inorganic hybrid modified nanomaterials to improve OSN performance.