Multifunctional polysulfone composite membranes via constructing electrically conductive gradient and magnetic-core/electric-shell dual-gradient microstructures: A strategy to tackle multiple hazards

The rapid advancement of industries and technologies leads to the emergence of new pollutants such as dyeing wastewater and electromagnetic interference (EMI), and their efficient treatment poses great challenges for traditional materials and methods. Herein, a novel electrically conductive membrane (ECM) was fabricated on a large scale through the electric field-assisted membrane formation. Carbon nanotubes (CNTs) and carbon black (CB) were uniformly dispersed in dope solution by strong hydrogen bonding with suitable polyvinylpyrrolidone (PVP) molecules. They moved towards the coating layer upper surface under an electric field, forming electrically conductive gradient microstructures. Subsequently, a stable electrically conductive skin layer was generated due to the excellent film-forming ability of PVP, which hindered the loss of CNTs and CB into coagulating bath. The optimized membrane possessed a high electrical conductivity of 34.3 ± 0.7 S/m, and exhibited superior permeate fluxes (>515.6 L/m² h·bar), dye rejections (>87.1 %) and flux recovery ratios (>91.5 %) in the electric-assisted filtration. Moreover, magnetic Fe₃O₄ nanoparticles were incorporated on the bottom surface and inside the pores by vacuum filtration, yielding an innovative magnetic-core/electric-shell dual-gradient microstructure. Electromagnetic wave went through an “absorption-multiple reflection/absorption-strong reflection-reabsorption/multiple reflection” process within the membrane, and then was consumed through the superposition of magnetic loss, polarization loss and conducting loss. Accordingly, the membrane displayed an EMI shielding efficiency of 23.6 ± 0.5 dB with a thickness of 0.2 mm at a low CB-CNTs loading of 20 wt%. This work provides a strategic framework for designing adaptable multifunctional membranes, bridging critical applications from wastewater remediation to next-generation electronic shielding technologies.