Hybrid NF and UF membranes tailored using quaternized polydopamine for enhanced removal of salts and organic pollutants from water

In this work, a quaternized polydopamine (QSiPD) nanohybrid was synthesized via condensation reaction between the silicon hydroxyl moieties of the hydrolyzed QSiP and hydroxyl moieties of polydopamine (PDA) and applied for the first time as a single additive to Poly(ether sulfone) (PES) ultrafiltration (UF) and loose nanofiltration (NF) membranes made via non-solvent induced phase separation (NIPS). QSiPD was added at a maximum loading of 8 and 20 wt% in UF and NF membranes, respectively. The nanohybrid material and membranes were thoroughly characterized. The hydrophilicity, surface charge, and pore structures of the hybrid membranes were progressively tuned with the increase of the QSiPD loading. The UF membrane water permeability of the membrane with 2 wt% QSiPD was as high as ~559 L m⁻² h⁻¹ bar⁻¹. The hybrid UF membranes also exhibited superior antifouling activity with a BSA rejection rate of ~99 % uncompromised by the high membrane flux. The hybrid NF membranes showed significant rejection (45–67 %) of several monovalent (NaCl) and divalent (CaCl₂, MgSO₄, Na₂SO₄) salt solutions and an outstanding rejection of Congo red dye (>99.9 %). Furthermore, both hybrid UF and NF membranes showed a strong antibacterial activity against E. coli.