Highly efficient MnO2-modified antifouling loose nanofiltration membrane for dye/salt separation

Loose nanofiltration (NF) membranes are promising in textile wastewater treatment due to their selective separation capabilities for dyes and salts. However, their widespread applications are hindered by complex manufacturing processes and membrane fouling. This work focuses on fabricating antifouling loose NF membranes using a facile method. Thereinto, amine-functionalized loose NF matrixes were first prepared using polyelectrolyte-complex induced phase inversion, where polyethyleneimine (PEI) in a coagulation bath as an inducer triggered an instantaneous phase inversion via electrostatic interactions with sulfonated polysulfone (SPSF) in dope solution. The acquired NF matrix has a dense skin layer with a mean pore size of 0.72 nm, endowing it with excellent dye retention. Consequently, the Fenton catalyst, MnO₂, was in situ grown on the membrane via the interaction between amine and Mn²⁺ followed by a one-step mineralization reaction. The MnO₂-loaded loose NF membrane could achieve 99.7 % CR rejection while allowing only 1.67 % rejection of Na₂SO₄ in a mixed solution of 60 mg/L Congo Red (CR) and 20 g/L Na₂SO₄ at the permeability of 51.6 L m⁻² h⁻¹·bar⁻¹. After cleaning with H₂O₂, the flux recovery rate of the membrane remains above 97 %, attributed to the catalytic effect of MnO₂ on the membrane surface. Additionally, the membrane displayed similar performance in dealing with real wastewater, underscoring its potential for practical applications in textile wastewater treatment.