Immobilization of sulfonated polysulfone via 2D LDH nanosheets during phase-inversion: A novel strategy towards greener membrane synthesis and enhanced desalination performance

Abstract

Sulfonated polysulfone (sPSf) is a commonly used hydrophilic additive to polysulfone (PSf) substrates for preparing polyamide membranes with enhancement desalination performance. However, severe leaching of water-soluble sPSf into the coagulation water bath during substrate formation can lead to weakened mechanical strength of the substrate, loss of the expensive sPSf polymer, and potential environmental pollution. In this study, we report a novel and efficient strategy to “anchor” sPSf in the PSf matrix by using 2D layered double hydroxide (LDH) nanosheets. LDH nanosheets effectively immobilized sPSf due to their electrostatic interaction, resulting in greener membrane synthesis. Substrates modified with LDH anchored sPSf (PSf/sPSf5-LDHx) exhibited enhanced mechanical strength and water permeability compared to the pristine PSf substrate as well as the sPSf-blended substrates (sPSf/sPSf5). Interfacial polymerization on the PSf/sPSf5-LDHx substrate resulted in a polyamide rejection film containing more extensive nanovoids and thus greater effective filtration area, which enhanced water permeability without major loss of salt rejection. In forward osmosis tests, this novel membrane enjoyed an additional advantage of less severe internal concentration polarization, as reflected by its significantly reduced structural parameter.