High flux and selectivity of poly(m-phenylene isophthalamide) loose nanofiltration membrane prepared by mussel-inspired co-deposition for dye/salt separation

Textile wastewater containing organic dyes and inorganic salts poses significant risks to the water security and human health. Herein, the development of an effective separation membrane for the treatment of dye wastewater is highly desired. In this work, the poly(m-phenylene isophthalamide) (PMIA)/polydopamine (PDA)-polyethyleneimine (PEI) loose nanofiltration (NF) membrane with highly dye wastewater separation efficiency was fabricated using a mussel-inspired co-deposition method with PMIA porous membrane as the substrate. The effect of PEI concentration in the mussel-inspired solution on the structure of PMIA/PDA-PEI membrane was studied by scanning electron microscopy (SEM), Fourier transform infrared spectrometry (FTIR), X-ray photoelectron spectroscopy (XPS), water contact angle, and Zeta potential analysis. The separation performance for dye and salt molecules of PMIA/PDA-PEI membrane with varied PEI concentration was also evaluated comprehensively. The results demonstrated that the content of PEI can be used to regulate the structure and performance of the PMIA/PDA-PEI loose NF membrane. When the PEI content was 0.25 g L⁻¹, the prepared PMIA/PDA-PEI loose NF membrane exhibited excellent dye rejection for Congo red and outstanding water flux, while the salt rejection was comparatively low. Meanwhile, the prepared PMIA/PDA-PEI loose NF membranes showed excellent stability under different testing conditions. These results indicated that PMIA/PDA-PEI loose NF membrane is promising in dye wastewater treatment and has potential for practical applications.