Improvement of permeability and rejection of an acid resistant polysulfonamide thin-film composite nanofiltration membrane by a sulfonated poly(ether ether ketone) interlayer

Acid resistant nanofiltration membranes are highly demanded for waste acid management in various industries, such as mining, steel, electroplating etc. In this study, sulfonated poly(ether ether ketone) (SPEEK) was introduced as a new interlayer polymer for preparing an acid-stable polysulfonamide (PSA) thin-film composite (TFC) nanofiltration membrane by interfacial polymerization. Diethylenetriamine (DETA) and naphthalene-1,3,6-trisulfonylchloride (NTSC) were used as monomers in reaction. SPEEK mediated nanofiltration membranes showed significantly higher negative charges than the membrane with no interlayer. High rejection for bivalent anions was observed followed by low rejection to bivalent cations. Structural stability during a long time pressurized test and acid stability were observed for PSA NF membranes with SPEEK interlayer. Analysis by scanning electron microscopy, energy dispersive X-Ray spectroscopy, atomic force microscopy and spectroscopic ellipsometer indicated that a very thin and smooth PSA active layer was prepared after a very thin hydrophilic SPEEK coating. The performance and morphology change was attributed to the improvement in hydrophilicity, blockage of monomer in water phase DETA from penetration into the pores of PSF and improvement of the diffusion of monomers to the interface for interfacial polymerization. The PSA nanofiltration membranes with SPEEK interlayer showed a smooth thin active layer and water flux (17.4 L.m(-2).h(-1)) and a 1000 mg/L Na2SO4 rejection (99.7%) at 10 bar, which is significantly higher than the membrane without interlayer. The excellent performance of SPEEK in controlling the interfacial polymerization process adds a new candidate for preparing nanofiltration membranes with enhanced performance.