Functionalized titanate nanotube-polyetherimide nanocomposite membrane for improved salt rejection under low pressure nanofiltration

Abstract

Functionalized titanate nanotubes were prepared using a facile and eco-friendly method. Nanofiltration membranes were fabricated via a simple phase inversion method. The neat and mixed matrix membrane (MMMs) was prepared using PEI as a polymeric material and nanomaterials such as TiO2 particles (TP), as-synthesized hydrogen trititanate nanotubes (pTNT), N-doped TiO2NT (N-TNT) and Cu-doped H2Ti3O7NT (Cu-TNT) served as additives. The crystal phase characterization revealed the anatase phase for TP, trititanate phase for pTNT, anatase-rutile mixed phase for N-TNT, Cu-TNT materials and similar observations were found with the MMMs. The morphology analysis of the neat PEI membrane exhibited a denser top layer and the beneath part of the membrane is tighter. Different from the neat PEI membrane nanocomposites of MMMs showed finger-like macrovoids towards the bottom of the membrane. The water uptake and hydrophilic character of the membranes are found in the following order: neat PEI > PEI/TP > PEI/pTNT > PEI/N-TNT > PEI/Cu-TNT. Interestingly, the salt rejection performance of monovalent (NaCl) and divalent (K2SO4 and CaCl2) ions in the single salt mixture were found to increase in the same order. The salt rejection performance of PEI/Cu-TNT was found in the decreasing order: K2SO4 (80%) < NaCl (75%) < CaCl2 (45%). The high performance of PEI/Cu-TNT in salt rejection and antifouling properties is ascribed to the tubular morphology, and the copper dopant results in the high hydrophilic character of the MMMs