In-situ synthesis of PA/PVDF composite hollow fiber membranes with an outer selective structure for efficient fractionation of low-molecular-weight dyes-salts

A polyamide/poly(vinylidene fluoride) composite hollow fiber membrane (HFM) was designed by in situ interfacial polymerization (IP) during the fiber spinning process. Using a piperazine aqueous solution as the bore fluid and a dual-bath coagulation, the PA outer layer was formed via IP of the PIP in the bore fluid and TMC in the second reactive bath during phase inversion process. Chemical structure, membrane morphology and surface property were characterized by using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscope (XPS), scanning electron microscope (SEM), and zeta potential. The effects of several parameters involved in the membrane fabrication (e.g., piperazine concentration, bore fluid flow rate, residence time and heat treatment temperature) on the morphology and performance of resultant composite HFMs were investigated. The composite HFM showed a performance that is comparable favorably with conventional nanofiltration membranes in terms of showed water permeability (10.2 L/m2·h·bar), high rejection to dyes (i.e., 100% for CR and EBT, 99.99% for RhB and MB, 98.3% for MO) and low salt rejections (NaCl 6.2%). Moreover, the newly developed composite HFM showed good stability and flux recovery with simple water rinsing for treatment of simulated textile wastewater. This work is expected to provide a new approach to designing composite HFMs for the treatment and reuse of textile wastewater.